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Diaphanous-related formin 1 (DIAPH1) is a formin homology F-actin elongating protein encoded by DIAPH1. Homozygous recessive variants resulting in the loss of DIAPH1 function cause seizures, cortical blindness, and microcephaly syndrome (SCBMS), but hearing loss has not been reported. In contrast, dominant variants of human DIAPH1 are associated with DFNA1 non-syndromic sensorineural hearing loss. The deafness phenotype is due partly to abnormal F-actin elongation activity caused by disruption of the DIAPH1 autoinhibitory mechanism. We report an elderly female heterozygous for the c.3145C>T: p.R1049X variant who showed late-onset sensorineural hearing loss in her fifth decade. p.R1049X lacks F-actin elongation activity because this variant truncates one-third of the FH2 domain, which is vital for DIAPH1 dimerization and processive F-actin elongation activity. Concordantly, no increase of F-actin or processive F-actin elongation activity was observed after overexpression of p.R1049X DIAPH1 in HeLa cells or by single-molecule microscopy using Xenopus XTC cells. However, overexpression of the p.R1049X variant impairs formation of cell-cell junctions and mitosis. We speculate that late-onset hearing loss is a long-term consequence of heterozygosity for the recessive p.R1049X variant, a phenotype that may have been overlooked among carriers of other recessive alleles of DIAPH1.

For the protist parasite Entamoeba histolytica, endocytic processes, such as phagocytosis, are essential for its survival in the human gut. The actin cytoskeleton is involved in the formation of pseudopods and phagosomal vesicles by incorporating a number of actin-binding and modulating proteins along with actin in a temporal manner. The actin dynamics, which comprises polymerization, branching, and depolymerization is very tightly regulated and takes place directionally at the sites of initiation of phagocytosis. Formin and profilin are two actin-binding proteins that are known to regulate actin cytoskeleton dynamics and thereby, endocytic processes. In this article, we report the participation of formin and profilin in E. histolytica phagocytosis and propose that these two proteins interact with each other and their sequential recruitment at the site is required for the successful completion of phagocytosis. The evidence is based on detailed microscopic, live imaging, interaction studies, and expression downregulation. The cells downregulated for expression of formin show absence of profilin at the site of phagocytosis, whereas downregulation of profilin does not affect formin localization.

Genetic mutations in actin regulators have been emerging as a cause of cardiomyopathy, although the functional link between actin dynamics and cardiac contraction remains largely unknown. To obtain insight into this issue, we examined the effects of pharmacological inhibition of formins, a major class of actin-assembling proteins. The formin inhibitor SMIFH2 significantly enhanced the cardiac contractility of isolated frog hearts, thereby augmenting cardiac performance. SMIFH2 treatment had no significant effects on the Ca2+ sensitivity of frog muscle fibers. Instead, it unexpectedly increased Ca2+ concentrations of isolated frog cardiomyocytes, suggesting that the inotropic effect is due to enhanced Ca2+ transients. In contrast to frog hearts, the contractility of mouse cardiomyocytes was attenuated by SMIFH2 treatment with decreasing Ca2+ transients. Thus, SMIFH2 has opposing effects on the Ca2+ transient and contractility between frog and mouse cardiomyocytes. We further found that SMIFH2 suppressed Ca2+ -release via type 2 ryanodine receptor (RyR2); this inhibitory effect may explain the species differences, since RyR2 is critical for Ca2+ transients in mouse myocardium but absent in frog myocardium. Although the mechanisms underlying the enhancement of Ca2+ transients in frog cardiomyocytes remain unclear, SMIFH2 differentially affects the cardiac contraction of amphibian and mammalian by differentially modulating their Ca2+ handling.

Background information In many cellular processes including cell division, the synergistic dynamics of actin filaments and microtubules play vital roles. However, the regulatory mechanisms of these synergistic dynamics are not fully understood. Proteins such as formins are involved in actin filament-microtubule interactions and Arabidopsis thaliana formin 14 (AtFH14) may function as a crosslinker between actin filaments and microtubules in cell division, but the molecular mechanism underlying such crosslinking remains unclear. Results Without microtubules, formin homology (FH) 1/FH2 of AtFH14 nucleated actin polymerization from actin monomers and capped the barbed end of actin filaments. However, in the presence of microtubules, quantitative analysis showed that the binding affinity of AtFH14 FH1FH2 to microtubules was higher than that to actin filaments. Moreover, microtubule-bound AtFH14 FH1FH2 neither nucleated actin polymerization nor inhibited barbed end elongation. In contrast, tubulin did not affect AtFH14 FH1FH2 to nucleate actin polymerization and inhibit barbed end elongation. Nevertheless, microtubule-bound AtFH14 FH1FH2 bound actin filaments and the bound actin filaments slid and elongated along the microtubules or elongated away from the microtubules, which induced bundling or crosslinking of actin filaments and microtubules. Pharmacological analyses indicated that AtFH14 FH1FH2 promoted crosslinking of actin filaments and microtubules in vivo. Additionally, cosedimentation and fluorescent dye-labeling experiments of AtFH14 FH2-truncated proteins in vitro revealed the essential motifs of bundling actin filaments or microtubules, which were 63-92 aa and 42-62 aa in the AtFH14 FH2 N-terminal, respectively, and 42-62 aa was the essential motif to crosslink actin filaments and microtubules. Conclusions and significance Our results aid in explaining how AtFH14 functions as a crosslinker between actin filaments and microtubules to regulate their dynamics via different manners during cell division. They also facilitate further understanding of the molecular mechanisms of the interactions between actin filaments and microtubules. This article is protected by copyright. All rights reserved.

Epithelial collective cell migration requires the intrinsic locomotor activity of cells to be coordinated across populations. This coordination is governed by the presence of cell-cell adhesions as well as the cooperative behaviour of cells within the monolayer. Here, we report a role for Caveolin-1 (CAV1) in epithelial collective cell migration. CAV1 depletion reduced the migratory behaviour of AML12 liver epithelial cells when grown as monolayers, but not as individual cells. This suggested that CAV1 is a component of the process by which multicellular collectivity regulates epithelial motility. The correlation length for migration velocity was increased by CAV1 RNAi, a possible sign of epithelial jamming. However, CAV1 RNAi reduced migration, even when monolayers were allowed to migrate into unconfined spaces. The migratory defect was ameliorated by simultaneous depletion of the FMNL2 formin, whose cortical recruitment is increased in CAV1 RNAi cells. We therefore suggest that CAV1 modulates intraepithelial motility by controlling the cortical availability of FMNL2. Although epithelial collective cell migration has been observed in multiple contexts both in vivo and in vitro, the inherent coupling and coordination of activity between cells within the monolayer remain incompletely understood. Our study highlights a role for CAV1 in regulating intraepithelial motility, an effect that involves the formin FMNL2.

T-complex 11 like 2 (TCP11L2) is a protein containing a serine-rich region in its N-terminal region. However, the function of TCP11L2 is unclear. Here, we showed that TCP11L2 expression gradually increased during muscle-derived satellite cell (MDSC) differentiation in vitro, reaching a peak on Day 3, which is the migration and fusion stage of MDSCs. Using CRISPR/dCas9 gene-editing technology to elevate or repress the expression of TCP11L2, we also showed that TCP11L2 promoted MDSC differentiation. Moreover, wound-healing assays showed that TCP11L2 promoted the migration of MDSCs during differentiation. Additionally, immunofluorescence analyses showed that TCP11L2 was mainly distributed around the microfilament and microtubules. Furthermore, the expression of TCP11L2 affected the expression of actin-related protein 2/3 (ARP2/3) complex. Co-immunoprecipitation assays and immunofluorescence analysis showed that TCP11L2 interacted with formin-like 2 (FMNL2). This protein promoted migration of bovine MDSCs by affecting the expression of ARP2/3. Finally, the activities of TCP11L2 during MDSC differentiation and migration were blocked when FMNL2 was inhibited. Taken together, our data established that TCP11L2 interacted with FMNL2 to promote MDSC migration and differentiation.

Actin networks are highly dynamic cytoskeletal structures that continuously undergo structural remodeling. One prominent way to probe these processes is via Fluorescence Recovery After Photobleaching (FRAP), which can be used to estimate the rate of turnover for filamentous actin monomers. It is thought that head-to-tail treadmilling and de novo filament nucleation constitute two primary mechanisms underlying turnover kinetics. More generally, these self-assembly activities are responsible for many important cellular functions such as force generation, cellular shape dynamics, and cellular motility. In what relative proportions filament treadmilling and de novo filament nucleation contribute to actin network turnover is still not fully understood. We used an advanced stochastic reaction-diffusion model in three dimensions, MEDYAN, to study turnover dynamics of actin networks containing Arp2/3, formin and capping protein at experimentally meaningful length- and time-scales. Our results reveal that, most commonly, treadmilling of older filaments is the main contributor to actin network turnover. On the other hand, although turnover and treadmilling are often used interchangeably, we show clear instances where this assumption would not be justified, for example, finding that rapid turnover is accompanied by slow treadmilling in highly dendritic Arp2/3 networks.

BACKGROUND The aim of this study was to ascertain the expression and role of FMNL3 in tongue squamous cell carcinoma (TSCC) tissues. MATERIALS AND METHODS Immunohistochemistry, qRT-PCR, and western blot were used to study the expression of FMNL3 in TSCC tissues and its adjacent normal tissues. The relationship between FMNL3 overexpression and various clinicopathological parameters and patients' survival were further assessed. Next, we applied SCC25 and UM1 cell lines to study the effect of FMNL3 on tumor cell proliferation, migration, and invasion by silencing FMNL3. RESULTS In this study, we demonstrated that FMNL3 expression was notably upregulated in TSCC tissues and associated with poor prognosis. The Cox regression survival analyses identified FMNL3 as an important independent predictor for patients' overall survival. We found that FMNL3 silencing by siRNA inhibited SCC25 and UM1 cell migration an invasion. CONCLUSION FMNL3 overexpression is related to the metastasis of TSCC and poor prognosis. High expression of FMNL3 may become a new potential prognostic biomarker for patients with TSCC.

Epithelial cell-cell junctions have dual roles of accommodating morphological changes in an epithelium, while maintaining cohesion during those changes. An abundance of junction proteins have been identified, but many details on how intercellular junctions respond to morphological changes remain unclear. In Caenorhabditis elegans, the spermatheca is an epithelial sac that repeatedly dilates and constricts to allow ovulation. It is thought that the junctions between spermatheca epithelial cells undergo reversible partial unzipping to allow rapid dilation. Previously, we found that EXC-6, a C. elegans protein homolog of the human disease-associated formin INF2, is expressed in the spermatheca and promotes oocyte entry. We show here that EXC-6 localizes toward the apical aspect of the spermatheca epithelial junctions, and that the EXC-6-labeled junction domains “unzip” and dramatically flatten with oocyte entry into the spermatheca. We demonstrate that the C-terminal tail of EXC-6 is necessary and sufficient for junction localization. Moreover, expression of the tail alone worsens ovulation defects, suggesting this region not only mediates EXC-6 localization, but also interacts with other components important for junction remodeling.

The formin family proteins have the ability to regulate actin filament assembly, thereby functioning in diverse cytoskeletal processes. Fhod3, a cardiac member of the family, plays a crucial role in development and functional maintenance of the heart. Although Fhod1, a protein closely-related to Fhod3, has been reported to be expressed in cardiomyocytes, the role of Fhod1 in the heart has still remained elusive. To know the physiological role of Fhod1 in the heart, we disrupted the Fhod1 gene in mice by replacement of exon 1 with a lacZ reporter gene. Histological lacZ staining unexpectedly revealed no detectable expression of Fhod1 in the heart, in contrast to intensive staining in the lung, a Fhod1-containing organ. Consistent with this, expression level of the Fhod1 protein in the heart was below the lower limit of detection of the present immunoblot analysis with three independent anti-Fhod1 antibodies. Homozygous Fhod1-null mice did not show any defects in gross and histological appearance of the heart or upregulate fetal cardiac genes that are induced under stress conditions. Furthermore, Fhod1 ablation did not elicit compensatory increase in expression of other formins. Thus, Fhod1 appears to be dispensable for normal development and function of the mouse heart, even if a marginal amount of Fhod1 is expressed in the heart.

The nuclear transcription factor-κB (NF-κB) plays a pivotal role in controlling both innate and adaptive immunity and regulates the expressions of many immunological mediators. Abundant evidences have showed the importance of NF-κB pathway in the host immune responses against Mycobacterium leprae in the development of leprosy. However, no particular association study between leprosy and NF-κB pathway-related gene polymorphisms was reported. Here, we performed a large-scale and two-stage candidate association study to investigate the association between 94 NF-κB pathway-related genes and leprosy. Our results showed that rs58744688 was significantly associated with leprosy (P = 7.57 × 10-7 , OR = 1.12) by combining the previous genomewide association data sets and four independent validation sample series, consisting of a total of 4631 leprosy cases and 6413 healthy controls. This founding implicated that MAP3K14 and FMNL1 were susceptibility genes for leprosy, which suggested the involvement of macrophage targeting and NF-κB pathway in the development of leprosy.

Formins are a family of regulators of actin and microtubule dynamics that are present in almost all eukaryotes. These proteins are involved in many cellular processes, including cytokinesis, stress fiber formation, and cell polarization. Here we review one sub-family of formins, the inverted formins. Inverted formins as a group break several formin stereotypes, having atypical biochemical properties and domain organization, and they have been linked to kidney disease and neuropathy in humans. In this review, we will explore recent research on members of the inverted formin sub-family in mammals, zebrafish, fruit flies, and worms.

In this study, we describe a Japanese family with progressive hearing loss and macrothrombocytopenia. Using next-generation and Sanger sequencing analyses, we identified a heterozygous variant in exon 27 of the DIAPH1 gene (NM_005219), c.3637C>T, p.R1213X. All patients in the family had sensorineural hearing loss and macrothrombocytopenia. None of the patients exhibited a tendency to bleed. No pathogenic variants were found in the MYH9 gene. Hearing loss began with high-frequency loss during early childhood and progressed to severe hearing loss involving all frequencies. Analyses of the mean platelet volume and platelet distribution width indicated that the macrothrombocytopenia is progressive in patients with DIAPH1 related disease.There are no reports describing progressive macrothrombocytopenia in patients with pathogenic variants of DIAPH1. Thus, progressive macrothrombocytopenia may be a novel feature of deafness patients with pathogenic variants in DIAPH1.

Formins are regulators of actin filament dynamics. We demonstrate here that two formins, FHOD-1 and EXC-6, are important in the nematode Caenorhabditis elegans for ovulation, during which actomyosin contractions push a maturing oocyte from the gonad arm into a distensible bag-like organ, the spermatheca. EXC-6, a homolog of the disease-associated mammalian formin INF2, is highly expressed in the spermatheca, where it localizes to cell-cell junctions and to circumferential actin filament bundles. Loss of EXC-6 does not noticeably affect the organization the actin filament bundles, and causes only a very modest increase in the population of junction-associated actin filaments. Despite absence of a strong cytoskeletal phenotype, approximately half of ovulations in exc-6 mutants exhibit extreme defects, including failure of the oocyte to enter the spermatheca, or breakage of the oocyte as the distal spermatheca entrance constricts during ovulation. Loss of FHOD-1 alone has little effect, and we cannot detect FHOD-1 in the spermatheca. However, combined loss of these formins in double fhod-1;exc-6 mutants results in profound ovulation defects, with significant slowing of the entry of oocytes into the spermatheca, and failure of nearly 80% of ovulations. We suggest that EXC-6 plays a role directly in the spermatheca, perhaps by modulating the ability of the spermatheca wall to rapidly accommodate an incoming oocyte, while FHOD-1 may play an indirect role relating to its known importance in the growth and function of the egg-laying muscles. © 2016 The Authors. Cytoskeleton Published by Wiley Periodicals, Inc.

The cytoskeleton has a central role in eukaryotic biology, enabling cells to organize internally, polarize, and translocate. Studying cytoskeletal machinery across the tree of life can identify common elements, illuminate fundamental mechanisms, and provide insight into processes specific to less-characterized organisms. Red algae represent an ancient lineage that is diverse, ecologically significant, and biomedically relevant. Recent genomic analysis shows that red algae have a surprising paucity of cytoskeletal elements, particularly molecular motors. Here, we review the genomic and cell biological evidence and propose testable models of how red algal cells might perform processes including cell motility, cytokinesis, intracellular transport, and secretion, given their reduced cytoskeletons. In addition to enhancing understanding of red algae and lineages that evolved from red algal endosymbioses (e.g., apicomplexan parasites), these ideas may also provide insight into cytoskeletal processes in animal cells.

Actin is a major component of the plant cytoskeleton. Filamentous actin (F-actin) contributes to the maintenance of the internal architecture of the cell, drives cytoplasmic streaming (the movement of components around the cytosol) and contributes to the process of cell division. The biochemistry of plant actin has many similarities to that of yeast and animals, but has developed its own strategies and molecular machinery to organize actin filaments. F-actin provides tracks for myosin molecular motors to transport organelles at high velocities and actin is required for specific stages of vesicle trafficking that underpin cell growth and development. The means by which plant cells control the nucleation of new actin filaments from G-actin have diverged considerably from yeast and metazoans. The unique aspects of the plant actin cytoskeleton are likely to have arisen from a combination of the environmental challenges to a sessile multicellular existence and a complex evolutionary history. Key concepts The basic principles of actin biochemistry applicable to animals, fungi and protists are conserved in plants but there are a number of specific modifications as plants do not possess the full complement of animal actin-binding proteins. Actin filaments in plants have to fulfil unique functions. Actin focuses on the expansion of tip growing cells, maintains cytoarchitecture and responds to the environment (e.g. polarizing in response to pathogen stimulation). During cell division actin filaments participate in all major plant-specific arrays. A stationary cell is NOT a physically inactive cell. Actin cables are exploited for organelle transport. Actin-based transport tends to dominate over microtubule-based movement. Plants utilize the fastest known type V myosin (known in plants as type XI) within the eukaryote kingdom. Polymerization dynamics are thought to add to trafficking capabilities as low levels of antiactin drugs disrupt vesicle delivery and fusion during cell growth yet preserve myosin-mediated transport. New proteins and new domain combinations have become established in plants to regulate the actin cytoskeleton in accordance with the unusual demands placed on them. Importantly, these radical adaptations should not be considered purely in terms of a response to a sedentary way of life as the fungal kingdom has achieved such a conversion using arguably less radical cytoskeletal solutions. Consequently the impact of other unique facets of plant evolutionary history and niches must be considered. Keywords: actin; myosin; plant; microtubules; trafficking

Formin-like2 (FMNL2) is a member of the diaphanous-related formins family, which act as effectors and upstream modulators of Rho GTPases signaling and control the actin-dependent processes, such as cell motility or invasion. FMNL2 has been identified as promoting the motility and metastasis in colorectal carcinoma (CRC). However, whether FMNL2 regulates Rho signaling to promote cancer cell invasion remains unclear. In this study, we demonstrated an essential role for FMNL2 in the activations of Rho/ROCK pathway, SRF transcription or actin assembly, and subsequent CRC cell invasion. FMNL2 could activate Rho/ROCK pathway, and required ROCK to promote CRC cell invasion. Moreover, FMNL2 promoted the formation of filopodia and stress fiber, and activated the SRF transcription in a Rho-dependent manner. We also demonstrated that FMNL2 was necessary for LPA-induced invasion, RhoA/ROCK activation, actin assembly and SRF activation. FMNL2 was an essential component of LPA signal transduction toward RhoA by directly interacting with LARG. LARG silence inhibited RhoA/ROCK pathway and CRC cell invasion. Collectively, these data indicate that FMNL2, acting as upstream of RhoA by interacting with LARG, can promote actin assembly and CRC cell invasion through a Rho/ROCK-dependent mechanism.

Polymerization of actin monomers into filaments requires the initial formation of nuclei composed of a few actin subunits; however, their instability has hindered their detailed study. Therefore we used chemically crosslinked actin oligomers to analyse their effect on actin polymerization. Actin dimer (upper dimer, UD), trimer and tetramer intermolecularly crosslinked by phenylene-bismaleimide along the genetic helix (between Lys199 and Cys374) were isolated by gel filtration and found to increasingly stimulate actin polymerization as shown by the pyrene assay and total internal reflection fluorescence microscopy. In contrast, the so-called lower actin dimer (LD) characterized by a Cys374-Cys374 crosslink stimulated actin polymerization only at low but inhibited it at high concentrations. UD and trimer stimulated the repolymerization of actin from complexes with thymosin β4 (Tβ4) or profilin, whereas the LD stimulated repolymerization only from the profilin : actin but not the actin : Tβ4 complex. In vivo, actin polymerization is stimulated by nucleation factors. Therefore the interaction and effects of purified LD, UD and trimer on the actin-nucleating activity of gelsolin, mouse diaphanous related (mDia) formin and the actin-related protein 2/3 (Arp2/3) complex were analysed. Native gel electrophoresis demonstrated binding of LD, UD and trimer to gelsolin and its fragment G1-3, to the FH2 domains of the formins mDia1 and mDia3, and to Arp2/3 complex. UD and trimer increased the nucleating activity of gelsolin and G1-3, but not of the mDia-FH2 domain nor of the Arp2/3 complex. In contrast, LD at equimolar concentration to Arp2/3 complex stimulated its nucleating activity, but inhibited that of mDia-FH2 domains, gelsolin and G1-3, demonstrating differential regulation of their nucleating activity by dimers containing differently oriented actin subunits.

Huntington's disease (HD) is an autosomal dominant neurodegenerative disease caused by an expansion of the CAG repeat in the huntingtin gene. One of the brain changes that occurs in HD is the expression of the receptor for advanced glycation end products (RAGE), a receptor protein capable of activating multiple signalling pathways by interacting with a range of ligands leading to either beneficial or harmful effects to the cell. Here, we demonstrate in human HD brains a high degree of co-localization of RAGE with its putative ligands S100B and N-carboxymethyllysine (CML) in the caudate nucleus (CN) and the subependymal layer (SEL). The level of co-staining for both RAGE-S100B and RAGE-CML was the highest in the astrocytes but was low in neurons and microglia. The immunostaining for RAGE, S100B and CML extended in a medio-lateral (SEL-CN) direction with increasing grade, such that any change in the expression and co-localization pattern between grades was less prominent in the lateral CN. Additionally, signalling molecules that are downstream of RAGE activation showed changes in their activation status in HD brains. A larger number of RAGE-positive astrocytic cells had NF-kB translocated to the nucleus and the level of phospho-ERK1/2 was also increased in HD brains. Interestingly, the level of mDia-1, that interacts directly with the cytoplasmic domain of RAGE, decreased in HD. Overall, the results suggest a correlation between the functions of RAGE and the HD pathology, but the influence of RAGE on astrocytes and the impact of this on HD progression requires further study. RAGE (receptor for advanced glycation end products) binds multiple types of ligand to produce either neurotrophic or neurotoxic effects. Immunohistochemical staining of HD human brains showed that both RAGE and its ligands were expressed primarily in astrocytes. The pattern of staining corresponded to the grade and region-wise pattern of neurodegeneration suggesting a possible role for RAGE in HD pathology.

Types 1 and 2 diabetes are on the rise worldwide. Although the treatment of hyperglycemia has benefited from recent advances, aggressive efforts to maintain euglycemia may be fraught with risk, especially in older subjects or in subjects vulnerable to hypoglycemic unawareness. Hence, strategies to prevent and treat the complications of hyperglycemia are essential. In this review we summarize recent updates on the biology of the receptor for advanced glycation endproducts (RAGE) in the pathogenesis of both micro- and macrovascular complications of diabetes, insights from the study of mouse models of obesity and diabetic complications, and from associative studies in human subjects. The study of the mechanisms and consequences of the interaction of the RAGE cytoplasmic domain with the formin, mDia1, in RAGE signal transduction, will be discussed. Lastly, we review the “state-of-the-art” on RAGE-directed therapeutics. Tackling RAGE/mDia1 may identify a novel class of therapeutics preventing diabetes and its complications.

The cytoskeletal polymers--actin, microtubules, and intermediate filaments--are interlinked by coordinated protein interactions to form a complex three-dimensional cytoskeletal network. Association of actin filaments with microtubules is important for various cellular processes such as cell division, migration, vesicle and organelle transport, and axonal growth. Several proteins including signaling molecules, motor proteins, and proteins directly or indirectly associated with microtubules and actin are involved in bridging the cytoskeletal components. Microtubule-associated proteins (MAPs) belonging to the MAP1, 2, 4 family and Tau proteins have been identified as key players that directly crosslink the two cytoskeletons. This review summarizes the current understanding of the interactions of these MAPs with actin filaments and their role in forming the actin-microtubule network and further discusses how the in vitro reconstitution assays can be used to study the dynamics of coordinated networks. Understanding the mechanisms by which actin and microtubules interact is key to decipher cancer, wound healing, and neuronal regeneration.

The Drosophila formin Cappuccino (Capu) creates an actin mesh-like structure that traverses the oocyte during midoogenesis. This mesh is thought to prevent premature onset of fast cytoplasmic streaming which normally happens during late-oogenesis. Proper cytoskeletal organization and cytoplasmic streaming are crucial for localization of polarity determinants such as osk, grk, bcd, and nanos mRNAs. Capu mutants disrupt these events, leading to female sterility. Capu is regulated by another nucleator, Spire, as well as by autoinhibition in vitro. Studies in vivo confirm that Spire modulates Capu's function in oocytes; however, how autoinhibition contributes is still unclear. To study the role of autoinhibition in flies, we expressed a Capu construct that is missing the Capu Inhibitory Domain, CapuΔN. Consistent with a gain of activity due to loss of autoinhibition, the actin mesh was denser in CapuΔN oocytes. Further, cytoplasmic streaming was delayed and fertility levels decreased. Localization of osk mRNA in early stages, and bcd and nanos in late stages, were disrupted in CapuΔN-expressing oocytes. Finally, evidence that these phenotypes were due to a loss of autoinhibition comes from coexpression of the N-terminal half of Capu with CapuΔN, which suppressed the defects in actin, cytoplasmic streaming and fertility. From these results, we conclude that Capu can be autoinhibited during Drosophila oocyte development. © 2014 Wiley Periodicals, Inc.

Members of the formin family are known to be involved in the regulation of the actin cytoskeleton. We have recently identified a muscle specific splice variant of the formin FHOD3 and demonstrated its role in the maintenance of the contractile filaments of cardiomyocytes. Here, we characterize the expression and subcellular localization of FHOD3's closest relative, FHOD1, in the heart. Confocal microscopy shows that FHOD1 is mainly located at the intercalated disc, the special type of cell-cell contact between cardiomyocytes, but also partially associated with the myofibrils. Subcellular targeting of FHOD1 is probably mediated by its N-terminal domain, since expression constructs lacking this domain show aberrant localization in primary cultures of neonatal rat cardiomyocytes. Finally, we show that in contrast to FHOD3, FHOD1 shows increased expression levels in dilated cardiomyopathy, suggesting that the two formins play distinct roles and are differentially regulated in cardiomyocytes. Anat Rec, 297:1560–1570, 2014. © 2014 Wiley Periodicals, Inc.

Classic functions of the actin cytoskeleton include control of cell size and shape and the internal organization of cells. These functions are manifest in cellular processes of fundamental importance throughout biology such as the generation of cell polarity, cell migration, cell adhesion, and cell division. However, studies in the unicellular model eukaryote Saccharomyces cerevisiae (Baker's yeast) are giving insights into other functions in which the actin cytoskeleton plays a critical role. These include endocytosis, control of protein translation, and determination of protein 3-dimensional shape (especially conversion of normal cellular proteins into prions). Here, we present a concise overview of these new "moonlighting" roles for the actin cytoskeleton and how some of these roles might lie at the heart of important molecular switches. This is an exciting time for researchers interested in the actin cytoskeleton. We show here how studies of actin are leading us into many new and exciting realms at the interface of genetics, biochemistry, and cell biology. While many of the pioneering studies have been conducted using yeast, the conservation of the actin cytoskeleton and its component proteins throughout eukaryotes suggests that these new roles for the actin cytoskeleton may not be restricted to yeast cells but rather may reflect new roles for the actin cytoskeleton of all eukaryotes.

Mutations in the inverted formin-2 (INF2) gene were recently identified in patients with autosomal dominant intermediate Charcot-Marie-Tooth (DI-CMT) disease and focal segmental glomerulosclerosis (FSGS). Here, we identified a novel p.L132P INF2 mutation in a Korean family with DI-CMT and FSGS by whole-exome sequencing. This mutation was cosegregated with affected individuals in the family and was not found in the 300 controls. The two affected members exhibited juvenile onset sensorimotor polyneuropathy and FSGS. Nerve conduction studies showed an intermediate range of motor nerve conduction velocities. We report a novel INF2 mutation in a family with DI-CMT and FSGS as the first case in Koreans. The INF2 mutation appears to be a major cause of CMT with FSGS.

Filopodia are essential for the development of neuronal growth cones, cell polarity and cell migration. Their protrusions are powered by the polymerization of actin filaments linked to the plasma membrane, catalyzed by formin proteins. The acceleration of polymerization depends on the number of profilin–actins binding with the formin-FH1 domain. Biophysical characterization of the disordered formin-FH1 domain remains a challenge. We analyzed the conformational distribution of the diaphanous-related formin mDia1-FH1 bound with one to six profilins. We found a coil-to-elongation transition in the FH1 domain. We propose a cooperative “jack” model for the Formin-Homology-1 (FH1) domain of formins stacked by profilin–actins.

The host actin nucleation machinery is subverted by many bacterial pathogens to facilitate their entry, motility, replication, and survival. The majority of research conducted in the past primarily focused on exploitation of a host actin nucleator, the Arp2/3 complex, by bacterial pathogens. Recently, new studies have begun to explore the role of formins, another family of host actin nucleators, in bacterial pathogenesis. This review provides an overview of recent advances in the study of the exploitation of the Arp2/3 complex and formins by bacterial pathogens. Secreted bacterial effector proteins seem to manipulate the regulation of these actin nucleators or functionally mimic them to drive bacterial entry, motility and survival within host cells. An enhanced understanding of how formins are exploited will provide us with greater insight into how a fundamental eurkaryotic cellular process is utilized by bacteria and will also advance our knowledge of host-pathogen interactions.

Formins are well-known regulators that participate in the organization of the actin cytoskeleton in organisms. The Arabidopsis thaliana L. genome encodes 21 formins, which can be divided into two distinct subfamilies. However, type II formins have to date been less well characterized. Here, we cloned a type II formin, AtFH16, and characterized its biochemical activities on actin and microtubule dynamics. The results show that the FH1FH2 structure of AtFH16 cannot nucleate actin polymerization efficiently, but can bind and bundle microfilaments. AtFH16 FH1FH2 is also able to bind and bundle microtubules, and preferentially binds microtubules over microfilaments in vitro. In addition, AtFH16 FH1FH2 co-localizes with microtubules in onion epidermal cells, indicating a higher binding affinity of AtFH16 FH1FH2 for microtubules rather than microfilaments in vivo. In conclusion, AtFH16 is able to interact with both microfilaments and microtubules, suggesting that AtFH16 probably functions as a bifunctional protein, and may thus participate in plant cellular processes.

Many actin-binding proteins (ABPs) use complex multidomain architectures to integrate and coordinate multiple signals and interactions with the dynamic remodeling of actin cytoskeleton. In these proteins, small segments that are intrinsically disordered in their unbound native state can be functionally as important as identifiable folded units. These functional intrinsically disordered regions (IDRs) are however difficult to identify and characterize in vitro. Here, we try to summarize the state of the art in understanding the structural features and interfacial properties of IDRs involved in actin self-assembly dynamics. Recent structural and functional insights into the regulation of widespread, multifunctional WH2/β-thymosin domains, and of other IDRs such as those associated with WASP/WAVE, formin or capping proteins are examined. Understanding the functional versatility of IDRs in actin assembly requires apprehending by multiple structural and functional approaches their large conformational plasticity and dynamics in their interactions. In many modular ABPs, IDRs relay labile interactions with multiple partners and act as interaction hubs in interdomain and protein-protein interfaces. They thus control multiple conformational transitions between the inactive and active states or between various active states of multidomain ABPs, and play an important role to coordinate the high turnover of interactions in actin self-assembly dynamics.

Diabetic peripheral nerve dysfunction is a common complication occurring in 30-50% of long-term diabetic patients. The pathogenesis of this dysfunction remains unclear but growing evidence suggests that it might be attributed, in part, to alteration in axonal transport. Our previous studies demonstrated that RAGE (Receptor for Advanced Glycation Endproducts) contributes to the pathogenesis of diabetic peripheral neuropathy and impairs nerve regeneration consequent to sciatic nerve crush, particularly in diabetes. We hypothesize that RAGE plays a role in axonal transport impairment via the interaction of its cytoplasmic domain with mammalian Diaphanous 1 (mDia1) - actin interacting molecule. Studies showed that mDia1-RAGE interaction is necessary for RAGE-ligand-dependent cellular migration, AKT phosphorylation, macrophage inflammatory response and smooth muscle migration. Here, we studied RAGE, mDia1 and markers of axonal transport rates in the peripheral nerves of wild-type C57BL/6 and RAGE null control and streptozotocin-injected diabetic mice at 1, 3 and 6 h after sciatic nerve crush. The results show that in both control and diabetic nerves, the amount of RAGE accumulated at the proximal and distal side of the crush area is similar, indicating that the recycling rate for RAGE is very high and that it is evenly transported from and towards the neuronal cell body. Furthermore, we show that slow axonal transport of proteins such as Neurofilament is affected by diabetes in a RAGE-independent manner. Finally, our study demonstrates that mDia1 axonal transport is impaired in diabetes, suggesting that diabetes-related changes affecting actin binding proteins occur early in the course of the disease.

WH2 domains are multifunctional regulators of actin assembly that can either sequester G-actin or allow polarized barbed end growth. They all bind similarly to a hydrophobic pocket at the barbed face of actin. Depending on their electrostatic environment, WH2 domains can nucleate actin assembly by facilitating the formation of prenuclei dimers along the canonical spontaneous assembly pathway. They also modulate filament barbed end dynamics in a versatile fashion, acting either as barbed end cappers or assisting barbed end growth like profilin or uncapping barbed ends and potentially mediating processive elongation like formins when they are dimerized. Tandem repeats of WH2 domains can sever filaments and either remain bound to created barbed ends like gelsolin, or strip off an ADP-actin subunit from the severed polymer end, depending on their relative affinity for terminal ADP-F-actin or ADP-G-actin. In summary, WH2 domains recapitulate all known elementary regulatory functions so far found in individual actin-binding proteins. By combining different discrete sets of these multifunctional properties, they acquire specific functions in various actin-based processes, and participate in activities as diverse as filament branching, filopodia extension, or actin remodeling in ciliogenesis and asymmetric meiotic division. They also integrate these functions with other actin-binding motifs present either in the same protein or in a complex with another protein, expanding the range of complexity in actin regulation. The details of their molecular mechanisms and the underlying structural basis provide exciting avenues in actin research. © 2013 Wiley Periodicals, Inc.

Formins are actin-binding proteins conserved across species from plants to humans. The formin family is defined by their common formin homology (FH2) domains. The 15 distinct human formins are involved in a broad range of cellular functions, including cell adhesion, cytokinesis, cell polarity, and cell morphogenesis. Their commonality is actin polymerization activity inherent to FH2 domains. Although still requiring much study, biochemical activity of formins has been carefully described. In contrast, much less is known of their activities in complex living systems. With the diversity of the formin family and the actin structures that they affect, an extensive future of study beckons. In this study, we report the expression level of all 15 formins in 22 different human cell and tissue types using quantitative real-time PCR. Identification of major themes in formin expression and documentation of expression profiles should facilitate the cellular study of formins. © 2013 Wiley Periodicals, Inc.

The fission yeast Schizosaccharomyces pombe is an excellent model organism to study cytokinesis. Here, we review recent advances on contractile-ring assembly in fission yeast. First, we summarize the assembly of cytokinesis nodes, the precursors of a normal contractile ring. IQGAP Rng2 and myosin essential light chain Cdc4 are recruited by the anillin-like protein Mid1, followed by the addition of other cytokinesis node proteins. Mid1 localization on the plasma membrane is stabilized by interphase node proteins. Second, we discuss proteins and processes that contribute to the search, capture, pull, and release mechanism of contractile-ring assembly. Actin filaments nucleated by formin Cdc12, the motor activity of myosin-II, the stiffness of the actin network, and severing of actin filaments by cofilin all play essential roles in contractile-ring assembly. Finally, we discuss the Mid1-independent pathway for ring assembly, and the possible mechanisms underlying the ring maturation and constriction. Collectively, we provide an overview of the current understanding of contractile-ring assembly and uncover future directions in studying cytokinesis in fission yeast. © 2012 Wiley Periodicals, Inc

Rho proteins are key regulators of cellular morphogenesis, but their function in filamentous fungi is poorly understood. By generating conditional rho-1 mutants, we dissected the function of the essential GTPase RHO1 in cell polarization and maintenance of cell wall integrity in Neurospora crassa. We identified NCU00668/RGF1 as RHO1-specific exchange factor, which controls actin organization and the cell wall integrity MAK1 MAP kinase pathway through the direct interaction of active RHO1 with the formin BNI1 and PKC1 respectively. The activity of RGF1 is controlled by an intramolecular interaction of its DEP and GEF domains that blocks the activation of the GTPase. Moreover, the N-terminal region including the DEP domain of RGF1 interacts with the plasma membrane sensor NCU06910/WSC1, potentially to activate the cell wall integrity pathway. RHO1 also functions as regulatory subunit of the glucan synthase. N. crassa possesses a second GTPase, RHO2, that is highly homologous to RHO1. RHO2 is of minor importance for growth and does not interact with BNI1. Conditional rho-1;rho-2 double mutants display strong synthetic growth and cell polarity defects. We show that RHO2 does not regulate glucan synthase activity and the actin cytoskeleton, but physically interacts with PKC1 to regulate the cell wall integrity pathway.

Membrane protrusion at the leading edge of migrating cells is driven by the polymerization of actin. Recent studies using advanced imaging techniques raised a lively controversy about the morphology of these filaments; however, common ground between the two sides now appears to have been found. Here we discuss how the controversy has led to a deeper consideration of the architecture of actin networks underlying cell migration, and has helped define new challenges that lie ahead.

FMNL2 is a member of diaphanous-related formins which act as effectors of Rho family GTPases and control the actin-dependent processes such as cell motility or invasion. We previously found that FMNL2 overexpression in metastatic cell lines and tissues of colorectal carcinoma is associated with more aggressive tumour behaviour. Here we used gain-of-function and loss-of-function approaches to investigate the effects of FMNL2 on colorectal carcinoma in vitro and in vivo. Forced expression of FMNL2 caused a significant increase in tumour cell proliferation, motility, invasion in vitro, and metastasis in vivo, whereas FMNL2 depletion showed opposite effects. We examined gene expression profiles following knockdown of FMNL2 in SW480/M5 cells. Expression of 323 genes was up-regulated by more than two-fold, whereas 222 genes were down-regulated by more than two-fold in FMNL2-depleting SW480/M5 cells. Gene ontology analysis showed that most of genes belong to functional categories such as cell cycle, cytoskeleton, transcription factor, and G-protein modulator. Pathway analysis revealed that cytoskeletal regulation by the Rho GTPase pathway, the Wnt pathway, the G-protein pathway, and the P53 pathway were affected by FMNL2. Many of these genes are in functional networks associated with cell proliferation, metastasis, Wnt or the Rho signalling pathway involved in the regulation of FMNL2. The expression of five differentially expressed genes including CXXC4, CD200, VAV1, CSF1, and EPHA2 was validated by real-time PCR and western blot analysis. Thus, FMNL2 is a positive regulator of cell motility, invasion, and metastasis of colorectal carcinoma.

Proper cell morphogenesis requires the co-ordination of cell polarity, cytoskeletal organization and vesicle trafficking. The Schizosaccharomyces pombe mutant pob1-664 has a curious lemon-like shape, the basis of which is not understood. Here, we found abundant vesicle accumulation in these cells, suggesting that Pob1 plays a role in vesicle trafficking. We identified Rho3 as a multicopy suppressor of this phenotype. Because Rho3 function is related to For3, an actin-polymerizing protein, and Sec8, a component of the exocyst complex, we analyzed their functional relationship with Pob1. Pob1 was essential for the formation of actin cables (by interacting with For3) and for the polarized localization of Sec8. Although neither For3 nor Sec8 is essential for polarized growth, their simultaneous disruption prevented tip growth and yielded a lemon-like cell morphology similar to pob1-664. Thus, Pob1 may ensure cylindrical cell shape of S. pombe by coupling actin-mediated vesicle transport and exocyst-mediated vesicle tethering during secretory vesicle targeting.

Formin proteins are nucleators of actin filaments and regulators of the microtubule cytoskeleton. As such, they play important roles in the development of yeast and other fungi. We show here that AgBnr2, a homologue of the ScBnr1 formin from the filamentous fungus Ashbya gossypii, localizes to the spindle pole body (SPB), the fungal analogue of the centrosome of metazoans. This protein plays an important role in the development of the typical needle-shaped spores of A. gossypii, as suggested by several findings. First, downregulation of AgBNR2 causes defects in sporangium formation and a decrease in the total spore number. Second, a fusion of AgBNR2 to GFP that is driven by the native AgBNR2 promoter is only visible in sporangia. Third, AgBnr2 interacts with a AgSpo21, a sporulation-specific component of the SPB. Furthermore, we provide evidence that AgBnr2 might nucleate actin cables, which are connected to SPBs during sporulation. Our findings add to our understanding of fungal sporulation, particularly the formation of spores with a complex, elongated morphology, and provide novel insights into formin function.

Summary Actin microfilament (MF) organization and remodelling is critical to cell function. The formin family of actin binding proteins are involved in nucleating MFs in Arabidopsis thaliana. They all contain formin homology domains in the intracellular, C-terminal half of the protein that interacts with MFs. Formins in class I are usually targeted to the plasma membrane and this is true of Formin1 (AtFH1) of A. thaliana. In this study, we have investigated the extracellular domain of AtFH1 and we demonstrate that AtFH1 forms a bridge from the actin cytoskeleton, across the plasma membrane and is anchored within the cell wall. AtFH1 has a large, extracellular domain that is maintained by purifying selection and that contains four conserved regions, one of which is responsible for immobilising the protein. Protein anchoring within the cell wall is reduced in constructs that express truncations of the extracellular domain and in experiments in protoplasts without primary cell walls. The 18 amino acid proline-rich extracellular domain that is responsible for AtFH1 anchoring has homology with cell-wall extensins. We also have shown that anchoring of AtFH1 in the cell wall promotes actin bundling within the cell and that overexpression of AtFH1 has an inhibitory effect on organelle actin-dependant dynamics. Thus, the AtFH1 bridge provides stable anchor points for the actin cytoskeleton and is probably a crucial component of the signalling response and actin-remodelling mechanisms.

Ena/VASP proteins are implicated in a variety of fundamental cellular processes including axon guidance and cell migration. In vitro, they enhance elongation of actin filaments, but at rates differing in nearly an order of magnitude according to species, raising questions about the molecular determinants of rate control. Chimeras from fast and slow elongating VASP proteins were generated and their ability to promote actin polymerization and to bind G-actin was assessed. By in vitro TIRF microscopy as well as thermodynamic and kinetic analyses, we show that the velocity of VASP-mediated filament elongation depends on G-actin recruitment by the WASP homology 2 motif. Comparison of the experimentally observed elongation rates with a quantitative mathematical model moreover revealed that Ena/VASP-mediated filament elongation displays a saturation dependence on the actin monomer concentration, implying that Ena/VASP proteins, independent of species, are fully saturated with actin in vivo and generally act as potent filament elongators. Moreover, our data showed that spontaneous addition of monomers does not occur during processive VASP-mediated filament elongation on surfaces, suggesting that most filament formation in cells is actively controlled.

Actin-dependent finger-like protrusions such as filopodia and microvilli are widespread in eukaryotes, but their assembly mechanisms are poorly understood. Filopodia assembly requires at least three biochemical activities on actin: actin filament nucleation, prolonged actin filament elongation, and actin filament bundling. These activities are shared by several mammalian formin proteins, including mDia2, FRL1 (also called FMNL1), and FRL2 (FMNL3). In this paper, we compare the abilities of constructs from these three formins to induce filopodia. FH1-FH2 constructs of both FRL2 and mDia2 stimulate potent filopodia assembly in multiple cell types, and enrich strongly at filopodia tips. In contrast, FRL1 FH1-FH2 lacks this activity, despite possessing similar biochemical activities and being highly homologous to FRL2. Chimeric FH1-FH2 experiments between FRL1 and FRL2 show that, while both an FH1 and an FH2 are needed, either FH1 domain supports filopodia assembly but only FRL2’s FH2 domain allows this activity. A mutation that compromises FRL2’s barbed end binding ability abolishes filopodia assembly. FRL2’s ability to stimulate filopodia assembly is not altered by additional domains (GBD, DID, DAD), but is significantly reduced in the full-length construct, suggesting that FRL2 is subject to inhibitory regulation. The data suggest that the FH2 domain of FRL2 possesses properties not shared by FRL1 that allow it to generate filopodia.

Cytoskeletal alterations in both Sertoli cells and germ cells are important during many facets of mammalian spermatogenesis. Diaphanous-related formin proteins are known to control many aspects of actin-based cytoskeletal rearrangements, yet nothing is known regarding the expression of formins in the testis. Accordingly, here we present the first data describing mDia1 and mDia2 mRNA and protein expression in primary Sertoli cell isolates, established tissue culture cell lines often used as models for Sertoli cell analysis, and mixed populations of adult rat male germ cells. Furthermore, we have examined intact sections of rat testis. The results suggest strongly that mDia1 and mDia2 are indeed involved in the regulation of Sertoli cell and germ structure during mammalian spermatogenesis, and provide strong indications of the future directions for mechanistic studies. Developmental Dynamics 237:2170–2176, 2008. © 2008 Wiley-Liss, Inc.

The TRPP2 cation channel is directly responsible for approximately 15% of all cases of autosomal dominant polycystic kidney disease. However, the mechanisms underlying fundamental properties of TRPP2 regulation, such as channel gating and activation, are unknown. We have shown that TRPP2 was activated by EGF and physically interacted with the mammalian diaphanous-related formin 1 (mDia1), a downstream effector of RhoA. Now, we show that mDia1 regulates TRPP2 by specifically blocking its activity at negative but not positive potentials. The voltage-dependent unblock of TRPP2 by mDia1 at positive potentials is mediated through RhoA-induced molecular switching of mDia1 from its autoinhibited state at negative potentials to its activated state at positive potentials. Under physiological resting potentials, EGF activates TRPP2 by releasing the mDia1-dependent block through the activation of RhoA. Our data reveal a new role of mDia1 in the regulation of ion channels and suggest a molecular basis for the voltage-dependent gating of TRP channels.

Formin-family proteins, in the active state, form actin-based structures such as stress fibres. Their activation mechanisms, however, are largely unknown except that mDia and its closely related formins can be activated by direct binding of the small GTPase Rho or Cdc42. Here we show that the Rho-dependent protein kinase ROCK phosphorylates the C-terminal residues Ser1131, Ser1137, and Thr1141 of formin homology domain protein 1 (FHOD1), a major endothelial formin that is normally autoinhibited by intramolecular interaction between the N- and C-terminal regions. Phosphorylation of FHOD1 at the three residues fully disrupts the autoinhibitory interaction, which culminates in formation of stress fibres. We also demonstrate that, in vascular endothelial cells, thrombin, a vasoactive substance leading to Rho activation, elicits both FHOD1 phosphorylation and stress fibre formation in a ROCK-dependent manner, and that FHOD1 depletion by RNA interference impairs thrombin-induced stress fibre formation. Based on these findings we propose a novel mechanism for activation of formin-family proteins: ROCK, activated by G protein-coupled receptor ligands such as thrombin, directly phosphorylates FHOD1 at the C-terminal region, which renders this formin in the active form, leading to stress fibre formation.

Reorganization of the actin filament is an essential process for cell motility, cell–cell attachment and intracellular transport. Formin proteins promote nucleation and elongation of the actin filament, and thus are key regulators for this process. The formin homology 2 (FH2) domain forms a head-to-tail ring-shaped dimer, and processively moves towards the barbed end. Dishevelled-associated activator of morphogenesis (DAAM) is a Rho-regulated formin implicated in neuronal development. Here, we present the crystal structure of human DAAM1 FH2 dimer at 2.8 A resolution. This is the first dimeric structure of the mammalian formin. The core structure of human DAAM1 is similar to those of mouse mDia1 and yeast Bni1p, whereas the orientations of the FH2 dimeric rings are different between human DAAM1 and yeast Bni1p, despite their similar dimer interactions. This difference supports the previous prediction that the dimer architecture of the formin is highly flexible in the actin-free state. The results of the actin assembly assays using the DAAM1 mutants demonstrated that the length of the linker connecting the N-terminal domain and the core region is crucial for the activity.

Formins are a class of actin binding proteins that regulate the elongation and nucleation of actin filaments and they are key to maintaining cellular morphology. The mammalian formin-like 3 (FMNL3) protein is essential for the formation of filopodia, projections of the plasma membrane that enable cell motility. Formins contain a highly conserved formin homology 2 (FH2) domain that dimerizes through interactions of the lasso and post subdomains. These dimers bind to actin filament barbed ends to mediate elongation and prevent inhibition of filament growth by capping proteins, thereby ensuring the formation of long, linear actin filaments. The FH2 dimer is able to remain associated with the growing end of the filament during elongation through the flexibility of linker regions that connect the FH2 subunits. A previous structural study of the yeast formin Bni1p FH2 domain was found to form a complex with three adjacent actin subunits, supporting a simple stepping model of formin-mediated actin polymerization...

Our studies have shown the cytoplasmic domain of the receptor for advanced glycation endproducts (RAGE) binds to the formin molecule, diaphanous-1 (mDia1). mDia1 is a member of the formin family of...