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The functional organization of the plant nuclear envelope is gaining increasing attention through new connections made between nuclear envelope-associated proteins and important plant biological processes. Animal nuclear envelope proteins play roles in nuclear morphology, nuclear anchoring and movement, chromatin tethering and mechanical signaling. However, how these roles translate to functionality in a broader biological context is often not well understood. A surprising number of plant nuclear envelope-associated proteins are plant-unique, suggesting that separate functionalities evolved after the split of Opisthokonta and Streptophyta. Significant progress has now been made in discovering broader biological roles of plant nuclear envelope proteins, increasing the number of known plant nuclear envelope proteins, and connecting known proteins to chromatin organization, gene expression, and the regulation of nuclear calcium. The interaction of viruses with the plant nuclear envelope is another emerging theme. Here, we survey the recent developments in this still relatively new, yet rapidly advancing field.

Dynamic nuclear positioning requires the formation of robust connections between the cytoskeleton and components of the LINC complex, a protein assembly that spans the nuclear envelope. A new study by Lim et al. (2021) reveals the mechanism of association between the LINC complex proteins Nesprin-1/2 Giant and the cytoplasmic formin FHOD1.

The function of the nucleus depends on the integrity of the nuclear lamina, an intermediate filament network associated with the linker of nucleoskeleton and cytoskeleton (LINC) complex. The LINC complex spans the nuclear envelope and mediates nuclear mechanotransduction, the process by which mechanical signals and forces are transmitted across the nuclear envelope. In turn, the AAA+ ATPase torsinA is thought to regulate force transmission from the cytoskeleton to the nucleus. In humans, mutations affecting nuclear envelope-associated proteins cause laminopathies, including progeria, myopathy, and dystonia, though the extent to which endogenous mechanical stresses contribute to these pathologies is unclear. Here, we use the Caenorhabditis elegans germline as a model to investigate mechanisms that maintain nuclear integrity as germ cell nuclei progress through meiotic development and migrate for gametogenesis-processes that require LINC complex function. We report that decreasing the function of the C. elegans torsinA homolog, OOC-5, rescues the sterility and premature aging caused by a null mutation in the single worm lamin homolog. We show that decreasing OOC-5/torsinA activity prevents nuclear collapse in lamin mutants by disrupting the function of the LINC complex. At a mechanistic level, OOC-5/torsinA promotes the assembly or maintenance of the lamin-associated LINC complex and this activity is also important for interphase nuclear pore complex insertion into growing germline nuclei. These results demonstrate that LINC complex-transmitted forces damage nuclei with a compromised nuclear lamina. Thus, the torsinA-LINC complex nexus might comprise a therapeutic target for certain laminopathies by preventing damage from endogenous cellular forces.

Actomyosin networks are organized in space, direction, size, and connectivity to produce coordinated contractions across cells. We use the C. elegans spermatheca, a tube composed of contractile myoepithelial cells, to study how actomyosin structures are organized. FLN-1/filamin is required for the formation and stabilization of a regular array of parallel, contractile, actomyosin fibers in this tissue. Loss of fln-1 results in the detachment of actin fibers from the basal surface, which then accumulate along the cell junctions and are stabilized by spectrin. In addition, actin and myosin are captured at the nucleus by the linker of nucleoskeleton and cytoskeleton complex (LINC) complex, where they form large foci. Nuclear positioning and morphology, distribution of the endoplasmic reticulum and the mitochondrial network are also disrupted. These results demonstrate that filamin is required to prevent large actin bundle formation and detachment, to prevent excess nuclear localization of actin and myosin, and to ensure correct positioning of organelles.

Despite its size and rigidity, the cell nucleus can be moved or reorganized by cytoskeletal filaments under various conditions (for example, during viral infection)1-11. Moreover, whereas chromatin organizes into non-random domains12, extensive heterogeneity at the single-cell level13 means that precisely how and why nuclei reorganize remains an area of intense investigation. Here we describe convolutional neural network-based automated cell classification and analysis pipelines, which revealed the extent to which human cytomegalovirus generates nuclear polarity through a virus-assembled microtubule-organizing centre. Acetylation of tubulin enables microtubules emanating from this centre to rotate the nucleus by engaging cytoplasmically exposed dynein-binding domains in the outer nuclear membrane protein nesprin-2G, which polarizes the inner nuclear membrane protein SUN1. This in turn creates intranuclear polarity in emerin, and thereby controls nuclear actin filaments that spatially segregate viral DNA from inactive histones and host DNA, maximizing virus replication. Our findings demonstrate the extent to which viruses can control the nucleus from the cytoplasm.

The canonical function of Bcl-2 family proteins is to regulate mitochondrial membrane integrity. In response to apoptotic signals the multi-domain pro-apoptotic proteins Bax and Bak are activated and perforate the mitochondrial outer membrane by a mechanism which is inhibited by their interaction with pro-survival members of the family. However, other studies have shown that Bax and Bak may have additional, non-canonical functions, which include stress-induced nuclear envelope rupture and discharge of nuclear proteins into the cytosol. We show here that the apoptotic stimuli cisplatin and staurosporine induce a Bax/Bak-dependent degradation and subcellular redistribution of nesprin-1 and nesprin-2 but not nesprin-3, of the linker of nucleoskeleton and cytoskeleton (LINC) complex. The degradation and redistribution were caspase-independent and did not occur in Bax/Bak double knockout (DKO) mouse embryo fibroblasts (MEFs). Re-expression of Bax in Bax/Bak DKO MEFs restored stress-induced redistribution of nesprin-2 by a mechanism which requires Bax membrane localization and integrity of the α helices 5/6, and the Bcl-2 homology 3 (BH3) domain. We found that nesprin-2 interacts with Bax in close proximity to perinuclear mitochondria in mouse and human cells. This interaction requires the mitochondrial targeting and N-terminal region but not the BH3 domain of Bax. Our results identify nesprin-2 as a Bax binding partner and also a new function of Bax in impairing the integrity of the LINC complex.

Nuclear movement and positioning play a role in developmental processes throughout life. Nuclear movement and positioning are mediated primarily by linker of nucleoskeleton and cytoskeleton (LINC) complexes. LINC complexes are comprised of the inner nuclear membrane SUN proteins and the outer nuclear membrane (ONM) KASH proteins. In Arabidopsis pollen tubes, the vegetative nucleus (VN) maintains a fixed distance from the pollen tube tip during growth, and the VN precedes the sperm cells (SCs). In pollen tubes of wit12 and wifi, mutants deficient in the ONM component of a plant LINC complex, the SCs precede the VN during pollen tube growth and the fixed VN distance from the tip is lost. Subsequently, pollen tubes frequently fail to burst upon reception. In this study, we sought to determine if the pollen tube reception defect observed in wit12 and wifi is due to decreased sensitivity to reactive oxygen species (ROS). Here, we show that wit12 and wifi are hyposensitive to exogenous H2O2, and that this hyposensitivity is correlated with decreased proximity of the VN to the pollen tube tip. Additionally, we report the first instance of nuclear Ca2+ peaks in growing pollen tubes, which are disrupted in the wit12 mutant. In the wit12 mutant, nuclear Ca2+ peaks are reduced in response to exogenous ROS, but these peaks are not correlated with pollen tube burst. This study finds that VN proximity to the pollen tube tip is required for both response to exogenous ROS, as well as internal nuclear Ca2+ fluctuations.

The positioning of nuclei within the cell is a dynamic process that depends on the cell’s fate and developmental stage and that is adjusted for optimal cell function. This is especially true in skeletal muscle cells, which contain hundreds of myonuclei distributed evenly along the periphery of the muscle cell. Mispositioned myonuclei are often associated with muscle dysfunction and disease. Different mechanisms governing myonuclear positioning are now emerging, with several of the new genes implicated in nuclear movement linked to human muscle disease. Here we discuss the recent advances in myonuclear positioning and its implications for muscle size and function from the view of Drosophila. Additionally, we highlight similarities and differences to mammalian systems and provide connections to human muscle disease.

In this review, we explore recent advances in knowledge of the structure and dynamics of the plant nuclear envelope. As a paradigm, we focused our attention on the Linker of Nucleoskeleton and Cytoskeleton (LINC) complex, a structurally conserved bridging complex comprising SUN domain proteins in the inner nuclear membrane and KASH domain proteins in the outer nuclear membrane. Studies have revealed that this bridging complex has multiple functions with structural roles in positioning the nucleus within the cell, conveying signals across the membrane and organizing chromatin in the 3D nuclear space with impact on gene transcription. We also provide an up-to-date survey in nuclear dynamics research achieved so far in the model plant Arabidopsis thaliana that highlights its potential impact on several key plant functions such as growth, seed maturation and germination, reproduction and response to biotic and abiotic stress. Finally, we bring evidences that most of the constituents of the LINC Complex and associated components are, with some specificities, conserved in monocot and dicot crop species and are displaying very similar functions to those described for Arabidopsis. This leads us to suggest that a better knowledge of this system and a better account of its potential applications will in the future enhance the resilience and productivity of crop plants.

In S. cerevisiae prophase meiotic chromosomes move by forces generated in the cytoplasm and transduced to the telomere via a protein complex located in the nuclear membrane. We know that chromosome movements require actin cytoskeleton [13,31] and the proteins Ndj1, Mps3, and Csm4. Until recently, the identity of the protein connecting Ndj1-Mps3 with the cytoskeleton components was missing. It was also not known the identity of a cytoplasmic motor responsible for interacting with the actin cytoskeleton and a protein at the outer nuclear envelope. Our recent work [36] identified Mps2 as the protein connecting Ndj1-Mps3 with cytoskeleton components; Myo2 as the cytoplasmic motor that interacts with Mps2; and Cms4 as a regulator of Mps2 and Myo2 interaction and activities (Figure 1). Below we present a model for how Mps2, Csm4, and Myo2 promote chromosome movements by providing the primary connections joining telomeres to the actin cytoskeleton through the LINC complex. Fil: Lee, C. Y.. Oklahoma Medical Research Foundation; Estados Unidos Fil: Bisig, Carlos Gaston. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Química Biológica de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Centro de Investigaciones en Química Biológica de Córdoba; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Química Biológica; Argentina Fil: Conrad, M. N.. Oklahoma Medical Research Foundation; Estados Unidos Fil: Ditamo, Yanina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Química Biológica de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Centro de Investigaciones en Química Biológica de Córdoba; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Química Biológica; Argentina Fil: Almeida, L. Previato de. Oklahoma Medical Research Foundation; Estados Unidos Fil: Dresser, M.E.. Oklahoma Medical Research Foundation; Estados Unidos Fil: Pezza, Roberto. Oklahoma Medical Research Foundation; Estados Unidos

The heart continually senses and responds to mechanical stimuli that balance cardiac structure and activity. Tensile forces, compressive forces, and shear stress are sensed by the different cardiac cell types and converted into signals instructing proper heart morphogenesis, postnatal growth, and function. Defects in mechanotransduction, the ability of cells to convert mechanical stimuli into biochemical signals, are implicated in cardiovascular disease development and progression. In this review, we summarize the current knowledge on how mechanical forces are transduced to chromatin through the tensed actomyosin cytoskeleton, the linker of nucleoskeleton and cytoskeleton (LINC) complex and the nuclear lamina. We also discuss the functional significance of the LINC complex in cardiovascular disease.

Skeletal muscle demonstrates a high degree of adaptability in response to changes in mechanical input. The phenotypic transformation in response to mechanical cues includes changes in muscle mass and force generating capabilities, yet the molecular pathways that govern skeletal muscle adaptation are still incompletely understood. While there is strong evidence that mechanotransduction pathways that stimulate protein synthesis play a key role in regulation of muscle mass, there are likely additional mechano-sensitive mechanisms important for controlling functional muscle adaptation. There is emerging evidence that the cell nucleus can directly respond to mechanical signals (i.e., nuclear mechanotransduction), providing a potential additional level of cellular regulation for controlling skeletal muscle mass. The importance of nuclear mechanotransduction in cellular function is evident by the various genetic diseases that arise from mutations in proteins crucial to the transmission of force between the cytoskeleton and the nucleus. Intriguingly, these diseases preferentially affect cardiac and skeletal muscle, suggesting that nuclear mechanotransduction is critically important for striated muscle homeostasis. Here we discuss our current understanding for how the nucleus acts as a mechanosensor, describe the main cytoskeletal and nuclear proteins involved in the process, and propose how similar mechanoresponsive mechanisms could occur in the unique cellular environment of a myofiber. In addition, we examine how nuclear mechanotransduction fits into our current framework for how mechanical stimuli regulates skeletal muscle mass.

Acephalic spermatozoa syndrome is a rare genetic and reproductive disease. Recent studies have shown that approximately 33–47% of patients with acephalic spermatozoa syndrome have SUN5 mutations, but the molecular mechanism underlying this phenomenon has not been elucidated. In this study, we generated Sun5 knockout mice and found that the head-to-tail linkage was broken in Sun5–/– mice, which was similar to human acephalic spermatozoa syndrome. Furthermore, ultrastructural imaging revealed that the head-tail coupling apparatus (HTCA) and the centrosome were distant from the nucleus at steps 9–10 during spermatid elongation. With the manchette disappearing at steps 13–14, the head and the tail segregated. To explore the molecular mechanism underlying this process, bioinformatic analysis was performed and showed that Sun5 may interact with Nesprin3. Further coimmunoprecipitation (Co-IP) and immunofluorescence assays confirmed that Sun5 and Nesprin3 were indeed bona fide interaction partners that formed the linker of the nucleoskeleton and cytoskeleton (LINC) complex participating in the connection of the head and tail of spermatozoa. Nesprin3 was located posterior and anterior to the nucleus during spermiogenesis in wild-type mice, whereas it lost its localization at the implantation fossa of the posterior region in Sun5–/– mice. Without correct localization of Nesprin3 at the nuclear membrane, the centrosome, which is the originator of the flagellum, was distant from the nucleus, which led to the separation of the head and tail. In addition, isobaric tag for relative and absolute quantitation results showed that 47 proteins were upregulated, and 56 proteins were downregulated, in the testis in Sun5–/– mice, and the downregulation of spermatogenesis-related proteins (Odf1 and Odf2) may also contribute to the damage to the spermatozoa head-to-tail linkage. Our findings suggested that Sun5 is essential for the localization of Nesprin3 at the posterior nuclear membrane, which plays an essential role in the sperm head-tail connection.

During cell migration, the movement of the nucleus must be coordinated with the cytoskeletal dynamics that influence the efficiency of cell migration. Our previous study demonstrated that osteopontin (OPN) significantly promotes the migration of bone-marrow-derived mesenchymal stem cells (BMSCs). However, the mechanism that regulates nuclear mechanics of the cytoskeleton during OPN-promoted BMSC migration remains unclear. In this study, we investigated how the actin cytoskeleton influences nuclear mechanics in BMSCs. We assessed the morphology and mechanics of the nuclei in the OPN-treated BMSCs subjected to disruption or polymerization of the actin cytoskeleton. We found that disruption of actin organization by cytochalasin D (Cyto D) resulted in a decrease in the nuclear projected area and nuclear stiffness. Stabilizing the actin assembly with jasplakinolide (JASP) resulted in an increase in the nuclear projected area and nuclear stiffness. SUN1 (Sad-1/UNC-84 1) is a component of the LINC (linker of nucleoskeleton and cytoskeleton) complex involved in the connections between the nucleus and the cytoskeleton. We found that SUN1 depletion by RNAi decreased the nuclear stiffness and OPN-promoted BMSC migration. Thus, the F-actin cytoskeleton plays an important role in determining the morphology and mechanical properties of the nucleus. We suggest that the cytoskeletal–nuclear interconnectivity through SUN1 proteins plays an important role in OPN-promoted BMSC migration.

The linker of the nucleoskeleton and cytoskeleton (LINC) complex is formed by the conserved interactions between Sad-1 and UNC-84 (SUN) and Klarsicht, ANC-1, SYNE homology (KASH) domain proteins, providing a physical coupling between the nucleoskeleton and cytoskeleton that mediates the transfer of physical forces across the nuclear envelope. The LINC complex can perform distinct cellular functions by pairing various KASH domain proteins with the same SUN domain protein. For example, in Caenorhabditis elegans, SUN protein UNC-84 binds to two KASH proteins UNC-83 and ANC-1 to mediate nuclear migration and anchorage, respectively. In addition to distinct cytoplasmic domains, the luminal KASH domain also varies among KASH domain proteins of distinct functions. In this study, we combined in vivo C. elegans genetics and in silico molecular dynamics simulations to understand the relation between the length and amino acid composition of the luminal KASH domain, and the function of the SUN–KASH complex. We show that longer KASH domains can withstand and transfer higher forces and interact with the membrane through a conserved membrane proximal EEDY domain that is unique to longer KASH domains. In agreement with our models, our in vivo results show that swapping the KASH domains of ANC-1 and UNC-83, or shortening the KASH domain of ANC-1, both result in a nuclear anchorage defect in C. elegans.

The cardiomyocyte cytoskeleton, including the sarcomeric contractile apparatus, forms a cohesive network with cellular adhesions at the plasma membrane and nuclear-cytoskeletal linkages (LINC complexes) at the nuclear envelope. Human cardiomyopathies are genetically linked to the LINC complex and A-type lamins, but an full understanding of disease etiology in these patients is lacking. Here we show SUN2-null mice display cardiac hypertrophy coincident with enhanced AKT/MAPK signaling, as has been described previously for mice lacking A-type lamins. Surprisingly, in contrast to lamin A/C-null mice, SUN2-null mice fail to show coincident fibrosis or upregulation of pathological hypertrophy markers. Thus, cardiac hypertrophy is uncoupled from pro-fibrotic signaling in this mouse model, which we tie to a requirement for the LINC complex in productive TGFβ signaling. In the absence of SUN2, we detect elevated levels of the integral inner nuclear membrane protein MAN1, an established negative regulator of TGFβ signaling, at the nuclear envelope. We suggest that A-type lamins and SUN2 play antagonistic roles in the modulation of pro-fibrotic signaling through opposite effects on MAN1 levels at the nuclear lamina, suggesting a new perspective on disease etiology.

Cellular behavior is continuously affected by microenvironmental forces through the process of mechanotransduction, in which mechanical stimuli are rapidly converted to biochemical responses. Mounting evidence suggests that the nucleus itself is a mechanoresponsive element, reacting to cytoskeletal forces and mediating downstream biochemical responses. The nucleus responds through a host of mechanisms, including partial unfolding, conformational changes, and phosphorylation of nuclear envelope proteins; modulation of nuclear import/export; and altered chromatin organization, resulting in transcriptional changes. It is unclear which of these events present direct mechanotransduction processes and which are downstream of other mechanotransduction pathways. We critically review and discuss the current evidence for nuclear mechanotransduction, particularly in the context of stem cell fate, a largely unexplored topic, and in disease, where an improved understanding of nuclear mechanotransduction is beginning to open new treatment avenues. Finally, we discuss innovative technological developments that will allow outstanding questions in the rapidly growing field of nuclear mechanotransduction to be answered.

Mesenchymal stem cells (MSC) rely on their ability to integrate physical and spatial signals at load bearing sites to replace and renew musculoskeletal tissues. Designed to mimic unloading experienced during spaceflight, preclinical unloading and simulated microgravity models show that alteration of gravitational loading limits proliferative activity of stem cells. Emerging evidence indicates that this loss of proliferation may be linked to loss of cellular cytoskeleton and contractility. Low intensity vibration (LIV) is an exercise mimetic that promotes proliferation and differentiation of MSCs by enhancing cell structure. Here, we asked whether application of LIV could restore the reduced proliferative capacity seen in MSCs that are subjected to simulated microgravity. We found that simulated microgravity (sMG) decreased cell proliferation and simultaneously compromised cell structure. These changes included increased nuclear height, disorganized apical F-actin structure, reduced expression, and protein levels of nuclear lamina elements LaminA/C LaminB1 as well as linker of nucleoskeleton and cytoskeleton (LINC) complex elements Sun-2 and Nesprin-2. Application of LIV restored cell proliferation and nuclear proteins LaminA/C and Sun-2. An intact LINC function was required for LIV effect; disabling LINC functionality via co-depletion of Sun-1, and Sun-2 prevented rescue of cell proliferation by LIV. Our findings show that sMG alters nuclear structure and leads to decreased cell proliferation, but does not diminish LINC complex mediated mechanosensitivity, suggesting LIV as a potential candidate to combat sMG-induced proliferation loss.

The rigid skeleton formed by networks of A- and B-type lamins is responsible for maintaining the nucleus shape. Moreover, the change in the ratio of lamin proteins in its composition, apparently, is a key factor determining mechanical properties of the cell nucleus, in particular plasticity. In this paper, the effect of the component composition of the nuclear lamina on the resistance of cells to mechanical stress and on the cell motility was considered. Expression of mutant forms of lamin A is accompanied by changes in the distance between microdomains of lamins within the nuclear membrane, and its increased bubbling relative to wild-type cells and cells overexpressing lamin A is observed. An increased number of deformed nuclei are noted when exposed to osmotic shock. The assessment of the effect of a change in the molecular composition of the nuclear lamina due to an increase (decrease) in expression of lamin A, as well as the introduction of progerin in an experimental wound model, showed that there are no differences under conditions of unlimited space.

SUMMARY Structural heterogeneity is a hallmark of living cells that drives local mechanical properties and dynamic cellular responses. However, the robust quantification of intracellular mechanics is lacking from conventional methods. Here, we describe the development of deformation microscopy, which leverages conventional imaging and an automated hyperelastic warping algorithm to investigate strain history, deformation dynamics, and changes in structural heterogeneity within the interior of cells and cell nuclei. Using deformation microscopy, we found that partial or complete disruption of LINC complexes in cardiomyocytes in vitro and lamin A/C deficiency in myocytes in vivo abrogate dominant tensile loading in the nuclear interior. We also found that cells cultured on stiff substrates or in hyperosmotic conditions displayed abnormal strain burden and asymmetries at interchromatin regions, which are associated with active transcription. Deformation microscopy represents a foundational approach toward intracellular elastography, with the potential utility to provide mechanistic and quantitative insights in diverse mechanobiological applications., Graphical Abstract, In Brief Ghosh et al. show that deformation microscopy, a technique based on image analysis and mechanics, reveals deformation dynamics and structural heterogeneity changes for several applications and at multiple scales, including tissues, cells, and nuclei. They reveal how the disruption of nuclear proteins and pathological conditions abrogate mechanical strain in the nuclear interior.

How the nuclear envelope is remodeled to facilitate insertion of large protein complexes is poorly understood. Chen et al. use superresolution imaging with bimolecular fluorescence complementation to show that a novel noncanonical linker of nucleoskeleton and cytoskeleton (LINC) complex forms at sites of nuclear envelope fenestration in yeast., Bipolar spindle formation in yeast requires insertion of centrosomes (known as spindle pole bodies [SPBs]) into fenestrated regions of the nuclear envelope (NE). Using structured illumination microscopy and bimolecular fluorescence complementation, we map protein distribution at SPB fenestrae and interrogate protein–protein interactions with high spatial resolution. We find that the Sad1-UNC-84 (SUN) protein Mps3 forms a ring-like structure around the SPB, similar to toroids seen for components of the SPB insertion network (SPIN). Mps3 and the SPIN component Mps2 (a Klarsicht-ANC-1-Syne-1 domain [KASH]–like protein) form a novel noncanonical linker of nucleoskeleton and cytoskeleton (LINC) complex that is connected in both luminal and extraluminal domains at the site of SPB insertion. The LINC complex also controls the distribution of a soluble SPIN component Bbp1. Taken together, our work shows that Mps3 is a fifth SPIN component and suggests both direct and indirect roles for the LINC complex in NE remodeling.

Matrix proteolysis mediated by MT1-MMP facilitates the invasive migration of tumor cells in dense tissues, which otherwise get trapped in the matrix because of limited nuclear deformability. A digest-on-demand response has been identified, which requires nucleus-microtubule linkage through the LINC complex and triggers MT1-MMP surface-exposure to facilitate nucleus movement.

During meiosis, homologous chromosomes undergo a dramatic movement in order to correctly align. This is a critical meiotic event but the molecular properties of this ‘chromosomal dance’ still remainunclear. We identified DEB-1 – an orthologue of mammalian vinculin – as a new component of the mechanistic modules responsible for attaching the chromosomes to the nuclear envelope as apart of the LINC complex. In early meiotic nuclei of C. elegans, DEB-1 is localized to the nuclear periphery and alongside the synaptonemal complex of paired homologues. Upon DEB-1 depletion, chromosomes attached to SUN-1 foci remain highly motile until late pachytene. Although the initiation of homologue pairing started normally, irregularities in the formation of the synaptonemal complex occur, and these results in meiotic defects such as increased number of univalents at diakinesis and high embryonic lethality. Our data identify DEB-1 as a new player regulating chromosome dynamics and pairing during meiotic prophase I.

Proper organ development often requires nuclei to move to a specific position within the cell. To determine how nuclear positioning affects left-right (LR) development in the Drosophila anterior midgut (AMG), we developed a surface-modeling method to measure and describe nuclear behavior at stages 13-14, captured in three-dimensional time-lapse movies. We describe the distinctive positioning and a novel collective nuclear behavior by which nuclei align LR symmetrically along the anterior-posterior axis in the visceral muscles that overlie the midgut and are responsible for the LR-asymmetric development of this organ. Wnt4 signaling is crucial for the collective behavior and proper positioning of the nuclei, as are myosin II and the LINC complex, without which the nuclei fail to align LR symmetrically. The LR-symmetric positioning of the nuclei is important for the subsequent LR-asymmetric development of the AMG. We propose that the bilaterally symmetrical positioning of these nuclei may be mechanically coupled with subsequent LR-asymmetric morphogenesis., Summary: The distinctive positioning and a novel collective nuclear behavior by which nuclei align left-right (LR) symmetrically in the Drosophila anterior midgut are responsible for the LR-asymmetric development of this organ.

International audience; Nuclear architecture undergoes an extensive remodeling during spermatogenesis, especially at levels of spermatocytes (SPC) and spermatids (SPT). Interestingly, typical events of spermiogenesis, such as nuclear elongation, acrosome biogenesis, and flagellum formation, need a functional cooperation between proteins of the nuclear envelope and acroplaxome/manchette structures. In addition, nuclear envelope plays a key role in chromosome distribution. In this scenario, special attention has been focused on the LINC (linker of nucleoskeleton and cytoskeleton) complex, a nuclear envelope-bridge structure involved in the connection of the nucleoskeleton to the cytoskeleton, governing mechanotransduction. It includes two integral proteins: KASH- and SUN-domain proteins, on the outer (ONM) and inner (INM) nuclear membrane, respectively. The LINC complex is involved in several functions fundamental to the correct development of sperm cells such as head formation and head to tail connection, and, therefore, it seems to be important in determining male fertility. This review provides a global overview of the main LINC complex components, with a special attention to their subcellular localization in sperm cells, their roles in the regulation of sperm morphological maturation, and, lastly, LINC complex alterations associated to male infertility.

Summary Cells actively position their nuclei within the cytoplasm for multiple cellular and physiological functions.1, 2, 3 Consequently, nuclear mispositioning is usually associated with cell dysfunction and disease, from muscular disorders to cancer metastasis.4, 5, 6, 7 Different cell types position their nuclei away from the leading edge during cell migration.8, 9, 10, 11 In migrating fibroblasts, nuclear positioning is driven by an actin retrograde flow originated at the leading edge that drives dorsal actin cables away from the leading edge. The dorsal actin cables connect to the nuclear envelope by the linker of nucleoskeleton and cytoskeleton (LINC) complex on transmembrane actin-associated nuclear (TAN) lines.12, 13, 14 Dorsal actin cables are required for the formation of TAN lines. How dorsal actin cables are organized to promote TAN lines formation is unknown. Here, we report a role for Ctdnep1/Dullard, a nuclear envelope phosphatase,15, 16, 17, 18, 19, 20, 21, 22 and the actin regulator Eps8L223, 24, 25 on nuclear positioning and cell migration. We demonstrate that Ctdnep1 and Eps8L2 directly interact, and this interaction is important for nuclear positioning and cell migration. We also show that Ctdnep1 and Eps8L2 are involved in the formation and thickness of dorsal actin cables required for TAN lines engagement during nuclear movement. We propose that Ctdnep1-Eps8L2 interaction regulates dorsal actin cables for nuclear movement during cell migration., Graphical abstract, Highlights • Ctdnep1 and Eps8L2 are required for nuclear positioning and TAN lines formation • Ctdnep1 directly interacts with Eps8L2 for nuclear movement and cell migration • Ctdnep1-Eps8L2 interaction regulates dorsal actin organization, Nucleo-cytoskeletal connections are crucial for nuclear positioning. Calero-Cuenca et al. show that Ctdnep1 and Eps8L2 interact to regulate perinuclear actin cables organization promoting transmembrane actin-associated nuclear (TAN) lines formation. Ctdnep1-Eps8L2 interaction is required for nuclear positioning and proper cell migration.

© 2017 American Chemical Society. Signal modulation has been developed in living cells throughout evolution to promote utilizing the same machinery for multiple cellular functions. Chemical and mechanical modules of signal transmission and transduction are interconnected and necessary for organ development and growth. However, due to the high complexity of the intercommunication of physical intracellular connections with biochemical pathways, there are many missing details in our overall understanding of mechanotransduction processes, i.e., the process by which mechanical signals are converted to biochemical cascades. Cell-matrix adhesions are mechanically coupled to the nucleus through the cytoskeleton. This modulated and tightly integrated network mediates the transmission of mechanochemical signals from the extracellular matrix to the nucleus. Various experimental and computational techniques have been utilized to understand the basic mechanisms of mechanotransduction, yet many aspects have remained elusive. Recently, in silico experiments have made important contributions to the field of mechanobiology. Herein, computational modeling efforts devoted to understanding integrin-mediated mechanotransduction pathways are reviewed, and an outlook is presented for future directions toward using suitable computational approaches and developing novel techniques for addressing important questions in the field of mechanotransduction.

The eukaryotic genome inside the nucleus is enveloped by two membranes, the Outer Nuclear Membrane (ONM) and the Inner Nuclear Membrane (INM). Tethered to the INM is the nuclear lamina, a fibrillar network composed of lamins-the nuclear intermediate filaments, and membrane associated proteins. The nuclear lamina interacts with several nuclear structures, including chromatin. As most nuclear functions, including regulation of gene expression, chromosome segregation and duplication as well as nuclear structure, are highly conserved in metazoans, the Caenorhabditis elegans nematode serves as a powerful model organism to study nuclear processes and architecture. This translucent organism can easily be observed under a microscope as a live embryo, larvae and even adult. Here we will review the data on nuclear lamina composition and functions gathered from studies using C. elegans model organisms: We will discuss genome spatial organization and its contribution to gene expression. We will review both the interaction between the cytoplasm and the nucleus and mechanotransduction mechanism. Finally, we will discuss disease causing mutation in nuclear lamins, including the use of this animal model in diseases research.

The H2A.Z histone variant is deposited into the chromatin by the SWR1 complex, affecting multiple aspects of meiosis. We describe here a SWR1-independent localization of H2A.Z at meiotic telomeres and the centrosome. We demonstrate that H2A.Z colocalizes and interacts with Mps3, the SUN component of the linker of nucleoskeleton, and cytoskeleton (LINC) complex that spans the nuclear envelope and links meiotic telomeres to the cytoskeleton, promoting meiotic chromosome movement. H2A.Z also interacts with the meiosis-specific Ndj1 protein that anchors telomeres to the nuclear periphery via Mps3. Telomeric localization of H2A.Z depends on Ndj1 and the N-terminal domain of Mps3. Although telomeric attachment to the nuclear envelope is maintained in the absence of H2A.Z, the distribution of Mps3 is altered. The velocity of chromosome movement during the meiotic prophase is reduced in the htz1¿ mutant lacking H2A.Z, but it is unaffected in swr1¿ cells. We reveal that H2A.Z is an additional LINC-associated factor that contributes to promote telomere-driven chromosome motion critical for error-free gametogenesis., This work was supported by grant BFU2015-65417-R from the Ministry of Economy and Competitiveness (MINECO) of Spain to PS-S, grant RTI2018-099055-B-I00 from the Ministry of Science, Innovation and Universities (MCIU/AEI/FEDER, UE) of Spain to PS-S and JC, the Stowers Institute for Medical Research to SJ, grant R01GM121443 from the National Institute of General Medical Sciences of the National Institutes of Health to SJ, and NIH grants GM111715 and GM123035 to AH. SG-A was partially supported by the Unidad de Excelencia de Biología Funcional y Genómica Ref. 2019/X002/05 from the University of Salamanca. The IBFG was supported in part by an institutional grant from the Junta de Castilla y León, Ref. CLU-2017-03 co-funded by the P.O. FEDER de Castilla y León 14-20. This manuscript has been released as a preprint at bioRxiv (GonzálezArranz et al., 2020). Open Access publication fee is partially supported by the CSIC.

Background Spectrin repeat containing nuclear envelope family member 3 (SYNE3) encodes an essential component of the linker of the cytoskeleton and nucleoskeleton (LINC) complex, namely nesprin-3. In a tumor, invasiveness and metastasis rely on the integrity of the LINC complex, while the role of SYNE3/nesprin-3 in cancer is rarely studied. Methods Here, we explored the expression pattern, prognostic value, and related mechanisms of SYNE3 through both experimental and bioinformatic methods. We first detected SYNE3 in BALB/c mice, normal human tissues, and the paired tumor tissues, then used bioinformatics databases to verify our results. We further analyzed the prognostic value of SYNE3. Next, we predicted miRNA targeting SYNE3 and built a competing endogenous RNA (ceRNA) network and a transcriptional network by analyzing data from the cancer genome atlas (TCGA) database. Interacting genes of SYNE3 were predicted, and we further performed GO and KEGG enrichment analysis on these genes. Besides, the relationship between SYNE3 and immune infiltration was also investigated. Results SYNE3 exhibited various expressions in different tissues, mainly located on nuclear and in cytoplasm sometimes. SYNE3 expression level had prognostic value in tumors, possibly by stabilizing nucleus, promoting tumor cells apoptosis, and altering tumor microenvironment. Additionally, we constructed a RP11-2B6.2-miR-149-5p-/RP11-67L2.2-miR-330-3p-SYNE3 ceRNA network and a SATB1-miR-149-5p-SYNE3 transcriptional network in lung adenocarcinoma to support the tumor-suppressing role of SYNE3. Conclusions Our study explored novel anti-tumor functions and mechanisms of SYNE3, which might be useful for future cancer therapy.

The canonical LINC complex is composed of two different transmembrane proteins; this work reveals the heterotrimeric composition of the telomere-associated LINC complex in budding yeast., The linker of the nucleoskeleton and cytoskeleton (LINC) complex is composed of two transmembrane proteins: the KASH domain protein localized to the outer nuclear membrane and the SUN domain protein to the inner nuclear membrane. In budding yeast, the sole SUN domain protein, Mps3, is thought to pair with either Csm4 or Mps2, two KASH-like proteins, to form two separate LINC complexes. Here, we show that Mps2 mediates the interaction between Csm4 and Mps3 to form a heterotrimeric telomere-associated LINC (t-LINC) complex in budding yeast meiosis. Mps2 binds to Csm4 and Mps3, and all three are localized to the telomere. Telomeric localization of Csm4 depends on both Mps2 and Mps3; in contrast, Mps2’s localization depends on Mps3 but not Csm4. Mps2-mediated t-LINC complex regulates telomere movement and meiotic recombination. By ectopically expressing CSM4 in vegetative yeast cells, we reconstitute the heterotrimeric t-LINC complex and demonstrate its ability to tether telomeres. Our findings therefore reveal the heterotrimeric composition of the t-LINC complex in budding yeast and have implications for understanding variant LINC complex formation.

Gottardi and Luxton preview work from the Borghi laboratory implicating LINC complex proteins as mechanotransducers that fine-tune Wnt/β-catenin signaling during epithelial–mesenchymal transition., How LINC complexes mediate nuclear mechanotransduction remains unclear. In this issue, Déjardin, Carollo, et al. (2020. J. Cell Biol. https://doi.org/10.1083/jcb.201908036) show that the LINC complex protein nesprin-2G is a mechanosensor of epithelial–mesenchymal transitions (EMTs), recruiting α-catenin to the nucleus to attenuate Wnt/β-catenin signaling.

The regulation of genomic function is in part mediated through the physical organization and architecture of the nucleus. Disruption to nuclear organization and architecture is increasingly being recognized by its contribution to many diseases. The LINC complexes - protein structures traversing the nuclear envelope, that physically connect the nuclear interior, and hence the genome, to cytoplasmic cytoskeletal networks are an important component in the physical organization of the genome and its function. This connection, potentially allows for the constant detection of environmental mechanical stimuli, resulting in altered regulation of nuclear architecture and genome function, either directly or via the process of mechanotransduction. Here, we review the influences LINC complexes exert on genome functions and their impact on cellular/organismal health.

© 2020 Déjardin et al. This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms/). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 4.0 International license, as described at https://creativecommons.org/licenses/by-nc-sa/4.0/)., LINC complexes are transmembrane protein assemblies that physically connect the nucleoskeleton and cytoskeleton through the nuclear envelope. Dysfunctions of LINC complexes are associated with pathologies such as cancer and muscular disorders. The mechanical roles of LINC complexes are poorly understood. To address this, we used genetically encoded FRET biosensors of molecular tension in a nesprin protein of the LINC complex of fibroblastic and epithelial cells in culture. We exposed cells to mechanical, genetic, and pharmacological perturbations, mimicking a range of physiological and pathological situations. We show that nesprin experiences tension generated by the cytoskeleton and acts as a mechanical sensor of cell packing. Moreover, nesprin discriminates between inductions of partial and complete epithelial-mesenchymal transitions. We identify the implicated mechanisms, which involve α-catenin capture at the nuclear envelope by nesprin upon its relaxation, thereby regulating β-catenin transcription. Our data thus implicate LINC complex proteins as mechanotransducers that fine-tune β-catenin signaling in a manner dependent on the epithelial-mesenchymal transition program., This material is based on work supported by the Centre national de la recherche scientifique (CNRS), Agence nationale de la recherche (ANR; grants ANR-13-JSV5-0007 and ANR-14-CE09-0006), France BioImaging (ANR-10-INBS-04), la Ligue contre le Cancer (REMX17751 to P.M. Davidson), and the Fondation ARC pour la Recherche sur le Cancer (PDF20161205227 to P.M. Davidson). P.S. Carollo has received funding from the European Union’s Horizon 2020 Framework Programme for Research and Innovation (Marie Skłodowska-Curie grant agreement 665850-INSPIRE) and acknowledges the Ecole Doctorale Frontières de l'Innovation en Recherche et Éducation (FIRE) Programme Bettencourt. E.R. Gomes was supported by a European Research Council consolidator grant (617676).

The nucleolar structure is highly dynamic and strictly regulated in response to internal cues, such as metabolic rates, and to external cues, such as mechanical forces applied to cells. Although the multilayered nucleolar structure is largely determined by the liquid-like properties of RNA and proteins, the mechanisms regulating the morphology and number of nucleoli remain elusive. The linker of the nucleoskeleton and cytoskeleton (LINC) complex comprises inner nuclear membrane Sad1/UNC-84 (SUN) proteins and outer nuclear membrane-localized nesprins. We previously showed that the depletion of SUN1 proteins affects nucleolar morphologies. This study focuses on the function of SUN1 splicing variants in determining nucleolar morphology. An RNA interference strategy showed that the predominantly expressed variants, SUN1_888 and SUN1_916, were crucial for nucleolar morphology but functionally distinct. In addition, the depletion of either SUN1_888 or SUN1_916 altered the chromatin structure and affected the distribution of histone modifications. Based on these results, we propose a model in which the LINC complex plays a role in modulating nucleolar morphology and numbers via chromatin.

The nuclear position in eukaryotic cells is controlled by a nucleo-cytoskeletal network, with important roles in cell differentiation, division and movement. Forces are transmitted through conserved linker of nucleoskeleton and cytoskeleton (LINC) complexes that traverse the nuclear envelope and engage on either side of the membrane with diverse binding partners. Nesprin-2 giant (Nes2G), a LINC element in the outer nuclear membrane, connects to the actin network directly as well as through FHOD1, a formin whose major activity is bundling actin. Much of the molecular details of this process remain poorly understood. Here, we report the crystal structure of Nes2G bound to FHOD1. We show that the G-binding domain of FHOD1 is rather a spectrin repeat binding enhancer for the neighboring FH3 domain, possibly establishing a common binding mode among this subclass of formins. The FHOD1-Nes2G complex structure suggests that spectrin repeat binding by FHOD1 is likely not regulated by the DAD helix of FHOD1. Finally, we establish that Nes1G also has one FHOD1 binding spectrin repeat, indicating that these abundant, giant Nesprins have overlapping functions in actin-bundle recruitment for nuclear movement.

The nuclei of cone photoreceptors are located on the apical side of the outer nuclear layer (ONL) in vertebrate retinas. However, the functional role of this evolutionarily conserved localization of cone nuclei is unknown. We previously showed that Linkers of the Nucleoskeleton to the Cytoskeleton (LINC complexes) are essential for the apical migration of cone nuclei during development. Here, we developed an efficient genetic strategy to disrupt cone LINC complexes in mice. Experiments with animals from both sexes revealed that disrupting cone LINC complexes resulted in mislocalization of cone nuclei to the basal side of ONL in mouse retina. This, in turn, disrupted cone pedicle morphology, and appeared to reduce the efficiency of synaptic transmission from cones to bipolar cells. Although we did not observe other developmental or phototransduction defects in cones with mislocalized nuclei, their dark adaptation was impaired, consistent with a deficiency in chromophore recycling. These findings demonstrate that the apical localization of cone nuclei in the ONL is required for the timely dark adaptation and efficient synaptic transmission in cone photoreceptors.

Summary Centrosome separation in late G2/ early prophase requires precise spatial coordination that is determined by a balance of forces promoting and antagonizing separation. The major effector of centrosome separation is the kinesin Eg5. However, the identity and regulation of Eg5-antagonizing forces is less well characterized. By manipulating candidate components, we find that centrosome separation is reversible and that separated centrosomes congress toward a central position underneath the flat nucleus. This positioning mechanism requires microtubule polymerization, as well as actin polymerization. We identify perinuclear actin structures that form in late G2/early prophase and interact with microtubules emanating from the centrosomes. Disrupting these structures by breaking the interactions of the linker of nucleoskeleton and cytoskeleton (LINC) complex with perinuclear actin filaments abrogates this centrosome positioning mechanism and causes an increase in subsequent chromosome segregation errors. Our results demonstrate how geometrical cues from the cell nucleus coordinate the orientation of the emanating spindle poles before nuclear envelope breakdown., Graphical Abstract, Highlights • Dynein and the actin/MT network coordinate centrosome positioning and separation • The MT/actin network antagonizes Eg5-dependent separation • LINC-complex-dependent perinuclear actin is critical for this mechanism • Disrupting the LINC/actin interaction results in centrosome mis-positioning, Stiff et al. describe how prophase-specific perinuclear actin in connection with polymerizing microtubules regulates the positioning of centrosome separation before nuclear envelope breakdown. This depends on the interaction of the LINC complex with actin. Breaking this link results in centrosome mispositioning and an increase in sister chromatid segregation errors.

The nuclear envelope delineates the eukaryotic cell nucleus. The membrane system of the nuclear envelope consists of an outer nuclear membrane and an inner nuclear membrane separated by a perinuclear space. It serves as more than just a static barrier, since it regulates the communication between the nucleoplasm and the cytoplasm and provides the anchoring points where chromatin is attached. Fewer nuclear envelope proteins have been identified in plants in comparison with animals and yeasts. Here, we review the current state of knowledge of the nuclear envelope in plants, focusing on its role as a chromatin organizer and regulator of gene expression, as well as on the modifications that it undergoes to be efficiently disassembled and reassembled with each cell division. Advances in knowledge concerning the mitotic role of some nuclear envelope constituents are also presented. In addition, we summarize recent progress on the contribution of the nuclear envelope elements to telomere tethering and chromosome dynamics during the meiotic division in different plant species.

Chromatin of the eukaryotic cell nucleus comprises of microscopically dense heterochromatin and loosely packed euchromatin domains, each with distinct transcriptional ability and roles in cellular mechanotransduction. While recent methods have been developed to characterize the nucleus, measurement of intranuclear mechanics remains largely unknown. Here, we describe the development of nuclear elastography, which combines microscopic imaging and computational modeling to quantify the relative elasticity of the heterochromatin and euchromatin domains. Using contracting murine embryonic cardiomyocytes, nuclear elastography reveals that the heterochromatin is almost four times stiffer than the euchromatin at peak deformation. The relative elasticity between the two domains changes rapidly during the active deformation of the cardiomyocyte in the normal physiological condition but progresses more slowly in cells cultured in a mechanically stiff environment, although the relative stiffness at peak deformation does not change. Further, we found that the disruption of the LINC complex in cardiomyocytes compromises the intranuclear elasticity distribution resulting in elastically similar heterochromatin and euchromatin. These results provide insight into the elastography dynamics of heterochromatin and euchromatin domains, and provide a non-invasive framework to further investigate the mechanobiological function of subcellular and subnuclear domains limited only by the spatiotemporal resolution of the image acquisition method.

DNA endoreplication has been implicated as a cell strategy for cell growth and in tissue injury. Here, we demonstrate that barrier-to-autointegration factor (BAF) represses endoreplication in Drosophila myofibers. We show that BAF localization at the nuclear envelope is eliminated in flies with mutations of the linker of nucleoskeleton and cytoskeleton (LINC) complex in which the LEM-domain protein Otefin is excluded, or after disruption of the nucleus-sarcomere connections. Furthermore, BAF localization at the nuclear envelope requires the activity of the BAF kinase VRK1/Ball, and, consistently, non-phosphorylatable BAF-GFP is excluded from the nuclear envelope. Importantly, removal of BAF from the nuclear envelope correlates with increased DNA content in the myonuclei. E2F1, a key regulator of endoreplication, overlaps BAF localization at the myonuclear envelope, and BAF removal from the nuclear envelope results in increased E2F1 levels in the nucleoplasm and subsequent elevated DNA content. We suggest that LINC-dependent and phosphosensitive attachment of BAF to the nuclear envelope, through its binding to Otefin, tethers E2F1 to the nuclear envelope thus inhibiting its accumulation in the nucleoplasm., Summary: Localization of BAF at the nuclear envelope of myonuclei depends on a functional LINC complex and on nucleus-sarcomere connections, and is shown to restrict E2F1 levels in the nucleoplasm.

The Linker of Nucleoskeleton and Cytoskeleton (LINC) complex mechanically couples cytoskeletal and nuclear components across the nuclear envelope to fulfil a myriad of cellular functions, including nuclear shape and positioning, hearing, and meiotic chromosome movements. The canonical model is that 3:3 interactions between SUN and KASH proteins underlie the nucleocytoskeletal linkages provided by the LINC complex. Here, we provide crystallographic and biophysical evidence that SUN-KASH is a constitutive 6:6 complex in which two constituent 3:3 complexes interact head-to-head. A common SUN-KASH topology is achieved through structurally diverse 6:6 interaction mechanisms by distinct KASH proteins, including zinc-coordination by Nesprin-4. The SUN-KASH 6:6 interface provides a molecular mechanism for the establishment of integrative and distributive connections between 3:3 structures within a branched LINC complex network. In this model, SUN-KASH 6:6 complexes act as nodes for force distribution and integration between adjacent SUN and KASH molecules, enabling the coordinated transduction of large forces across the nuclear envelope.

Telomere-led rapid chromosome movements or rapid prophase movements direct fundamental meiotic processes required for successful haploidization of the genome. Critical components of the machinery that generates rapid prophase movements are unknown, and the mechanism underlying rapid prophase movements remains poorly understood. We identified S. cerevisiae Mps2 as the outer nuclear membrane protein that connects the LINC complex with the cytoskeleton. We also demonstrate that the motor Myo2 works together with Mps2 to couple the telomeres to the actin cytoskeleton. Further, we show that Csm4 interacts with Mps2 and is required for perinuclear localization of Myo2, implicating Csm4 as a regulator of the Mps2-Myo2 interaction. We propose a model in which the newly identified functions of Mps2 and Myo2 cooperate with Csm4 to drive chromosome movements in meiotic prophase by coupling telomeres to the actin cytoskeleton. Fil: Lee, Chih Ying. Oklahoma Medical Research Foundation; Estados Unidos Fil: Bisig, Carlos Gaston. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Química Biológica de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Centro de Investigaciones en Química Biológica de Córdoba; Argentina Fil: Conrad, Michael M.. Oklahoma Medical Research Foundation; Estados Unidos Fil: Ditamo, Yanina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Química Biológica de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Centro de Investigaciones en Química Biológica de Córdoba; Argentina Fil: Previato de Almeida, Luciana. Oklahoma Medical Research Foundation; Estados Unidos Fil: Dresser, Michael E.. Oklahoma Medical Research Foundation; Estados Unidos Fil: Pezza, Roberto J.. Oklahoma Medical Research Foundation; Estados Unidos

© 2020 Colón-Bolea et al., RHO GTPases are key regulators of the cytoskeletal architecture, which impact a broad range of biological processes in malignant cells including motility, invasion, and metastasis, thereby affecting tumor progression. One of the constraints during cell migration is the diameter of the pores through which cells pass. In this respect, the size and shape of the nucleus pose a major limitation. Therefore, enhanced nuclear plasticity can promote cell migration. Nuclear morphology is determined in part through the cytoskeleton, which connects to the nucleoskeleton through the Linker of Nucleoskeleton and Cytoskeleton (LINC) complex. Here, we unravel the role of RAC1 as an orchestrator of nuclear morphology in melanoma cells. We demonstrate that activated RAC1 promotes nuclear alterations through its effector PAK1 and the tubulin cytoskeleton, thereby enhancing migration and intravasation of melanoma cells. Disruption of the LINC complex prevented RAC1-induced nuclear alterations and the invasive properties of melanoma cells. Thus, RAC1 induces nuclear morphology alterations through microtubules and the LINC complex to promote an invasive phenotype in melanoma cells., B.C.’s laboratory is supported by a Retos Jóvenes Investigadores grant SAF2015-73364-JIN Ministerio de Ciencia, Innovación y Universidades (MICIU/AEI/FEDER, UE), a PIE grant from Consejo Superior de Investigaciones Científicas (CSIC)—MCIU, and the Ramón y Cajal Research Program (MICIU, RYC2018-024004-I). P.C is supported by grant SAF-2015 63638R (MINECO/FEDER, UE); by Red Temática de Investigación Cooperativa sobre el Cáncer (RTICC), RD/12/0036/0033, and by Asociación Española Contra el Cáncer (AECC) grant GCB141423113. X.R.B. is supported by grants from the Castilla-León Government (BIO/SA01/15, CSI049U16), MINECO (SAF2015-64556-R, RD12/0036/0002), Worldwide Cancer Research (14-1248), Ramón Areces Foundation, and AECC (GC16173472GARC). Spanish funding to B.C., P.C., and X.R.B. is partially supported by the European Regional Development Fund.

© 2020 Elsevier Ltd. All rights reserved., Mechanical forces are known to influence cellular processes with consequences at the cellular and physiological level. The cell nucleus is the largest and stiffest organelle, and it is connected to the cytoskeleton for proper cellular function. The connection between the nucleus and the cytoskeleton is in most cases mediated by the linker of nucleoskeleton and cytoskeleton (LINC) complex. Not surprisingly, the nucleus and the associated cytoskeleton are implicated in multiple mechanotransduction pathways important for cellular activities. Herein, we review recent advances describing how the LINC complex, the nuclear lamina, and nuclear pore complexes are involved in nuclear mechanotransduction. We will also discuss how the perinuclear actin cytoskeleton is important for the regulation of nuclear mechanotransduction. Additionally, we discuss the relevance of nuclear mechanotransduction for cell migration, development, and how nuclear mechanotransduction impairment leads to multiple disorders.

The positioning and movement of the nucleus has recently emerged as an important aspect of cell migration. Understanding of nuclear positioning and movement has reached an apogee in studies of fibroblast migration. Specific nuclear positioning and movements have been described in the polarization of fibroblast for cell migration and in active migration in 2D and 3D environments. Here, we review recent studies that have uncovered novel molecular mechanisms that contribute to these events in fibroblasts. Many of these involve a connection between the nucleus and the cytoskeleton through the LINC complex composed of outer nuclear membrane nesprins and inner nuclear membrane SUN proteins. We consider evidence that appropriate nuclear positioning contributes to efficient fibroblast polarization and migration and the possible mechanism through which the nucleus affects cell migration.

Cell migration is a highly orchestrated cellular event that involves physical interactions of diverse subcellular components. The nucleus as the largest and stiffest organelle in the cell not only maintains genetic functionality, but also actively changes its morphology and translocates through dynamic formation of nucleus-bound contractile stress fibers. Nuclear motion is an active and essential process for successful cell migration and nucleus self-repairs in response to compression and extension forces in complex cell microenvironment. This review recapitulates molecular regulators that are crucial for nuclear motility during cell migration and highlights recent advances in nuclear deformation-mediated rupture and repair processes in a migrating cell.

Emery-Dreifuss muscular dystrophy (EDMD) is a rare genetic disorder characterised by the early development of muscle contractures, progressive muscle weakness, and heart abnormalities. The latter may result in serious complications, or in severe cases, sudden death. Currently, there are very few effective treatment options available for EDMD and so there is a high clinical need for new therapies. Various genetic mutations have been identified in the development and causation of EDMD, each encoding proteins that are components of the Linker of Nucleoskeleton and Cytoskeleton (LINC) complex, which spans the nuclear envelope and serves to connect the nuclear lamina to the cytoskeleton. Within this review, we examine how mutations in the genes encoding these proteins, including lamins A/C, emerin, nesprins 1/2, FHL1, and SUN1/2 lead to muscle cell differentiation and development pathway defects. Further work to identify conserved molecular pathways downstream of these defective proteins may reveal potential targets for therapy design.

Sperm head shaping is a key event in spermiogenesis and is tightly controlled via the acrosome–manchette network. Linker of nucleoskeleton and cytoskeleton (LINC) complexes consist of Sad1 and UNC84 domain–containing (SUN) and Klarsicht/ANC-1/Syne-1 homology (KASH) domain proteins and form conserved nuclear envelope bridges implicated in transducing mechanical forces from the manchette to sculpt sperm nuclei into a hook-like shape. However, the role of LINC complexes in sperm head shaping is still poorly understood. Here we assessed the role of SUN3, a testis-specific LINC component harboring a conserved SUN domain, in spermiogenesis. We show that CRISPR/Cas9-generated Sun3 knockout male mice are infertile, displaying drastically reduced sperm counts and a globozoospermia-like phenotype, including a missing, mislocalized, or fragmented acrosome, as well as multiple defects in sperm flagella. Further examination revealed that the sperm head abnormalities are apparent at step 9 and that the sperm nuclei fail to elongate because of the absence of manchette microtubules and perinuclear rings. These observations indicate that Sun3 deletion likely impairs the ability of the LINC complex to transduce the cytoskeletal force to the nuclear envelope, required for sperm head elongation. We also found that SUN3 interacts with SUN4 in mouse testes and that the level of SUN4 proteins is drastically reduced in Sun3-null mice. Altogether, our results indicate that SUN3 is essential for sperm head shaping and male fertility, providing molecular clues regarding the underlying pathology of the globozoospermia-like phenotype.

Linkers of the nucleoskeleton and cytoskeleton are key molecular complexes that span the nuclear envelope (NE) and provide a direct linkage between the nucleoskeleton and cytoskeleton. Two major components of these complexes are members of the SUN and KASH protein families that interact in the perinuclear space to allow the transmission of mechanochemical signals across the NE. Structural details of the mammalian SUN domain protein SUN2 have established that SUN2 must form a trimer to bind to KASH, and that this trimerization is mediated through two predicted coiled-coil regions of the protein, CC1 and CC2, which precede the SUN domain. Recent crystallographic data suggest that CC2-SUN formed an unexpected autoinhibited monomer unable to bind to KASH. These structural insights raise the question of how full-length SUN2 transitions from a monomer to a trimer inside the NE. In this study we used a computational approach to model a fragment of SUN2 containing CC1, CC2, and the SUN domain. We observed the dynamics of these modeled structures using ∼1 μs molecular dynamics simulations and showed that the interplay between CC1 and CC2 may be sufficient for the release of CC2-SUN2 from its autoinhibited state. Additionally, using our models and gel filtration analysis, we show the involvement of an E452 residue on CC1 in the monomer–­trimer transition of SUN2. Intriguingly, mutations in this residue have been seen in muscular dystrophy–associated SUN2 variants. Finally, we propose a Ca2+-dependent monomer–trimer transition of SUN2.