Search

VAMP-associated protein (VAP) is a type II integral transmembrane protein at the endoplasmic reticulum (ER). Mutations in human VAPB/ALS8 are associated with amyotrophic lateral sclerosis (ALS). The N-terminal major sperm protein (MSP) domain of VAPB (Drosophila Vap33) is cleaved, secreted, and acts as a signaling ligand for several cell-surface receptors. Although extracellular functions of VAPB are beginning to be understood, it is unknown how the VAPB/Vap33 MSP domain facing the cytosol is secreted to the extracellular space. Here we show that Vap33 uses the ER-Golgi conventional secretion pathway to reach the plasma membrane, where the MSP domain is exposed extracellularly by topological inversion. The externalized MSP domain is cleaved by Matrix metalloproteinase 1/2 (Mmp1/2). Overexpression of Mmp1 restores decreased levels of extracellular MSP domain derived from ALS8-associated Vap33 mutants. We propose an unprecedented secretion mechanism for an ER-resident membrane protein, which may contribute to ALS8 pathogenesis.

The periodic circumferential cytoskeleton supports various tubular tissues1-5. Radial expansion of the tube lumen causes anisotropic tensile stress, which can be exploited as a geometric cue6. However, the molecular machinery linking anisotropy to robust circumferential patterning is poorly understood. Here, we aimed to reveal the emergent process of circumferential actin cable formation in a Drosophila tracheal tube7. During luminal expansion, sporadic actin nanoclusters emerge and exhibit circumferentially biased motion and fusion. RNAi screening revealed the formin family protein, DAAM, as an essential component of tensile stress sensing, and non-muscle myosin II as a component required for nanocluster fusion. A coarse-grained molecular dynamics simulation demonstrated that crosslinkers play a crucial role in nanocluster formation and cluster-to-cable transition occurs in response to mechanical anisotropy. Altogether, we propose that an actin nanocluster is an organizational unit that senses stress in the cortical membrane and builds a higher-order cable structure.

Actin-mediated mechanical forces are central drivers of cellular dynamics. They generate protrusive and contractile dynamics, the latter of which are induced in concert with myosin II bundled at the site of contraction. These dynamics emerge concomitantly in tissues and even each cell; thus, the tight regulation of such bidirectional forces is important for proper cellular deformation. Here, we show that contractile dynamics can eventually disturb cell–cell junction contraction in the absence of p21-activated kinase 3 (Pak3). Upon Pak3 depletion, contractility induces the formation of abnormal actin protrusions at the shortening junctions, which causes decrease in E-cadherin levels at the adherens junctions and mislocalization of myosin II at the junctions before they enough shorten, compromising completion of junction shortening. Overexpressing E-cadherin restores myosin II distribution closely placed at the junctions and junction contraction. Our results suggest that contractility both induces and perturbs junction contraction and that the attenuation of such perturbations by Pak3 facilitates persistent junction shortening.

SummaryNanometer-level patterned surface structures form the basis of biological functions including superhydrophobicity, structural coloration, and light absorption [1-3]. In insects, the cuticle overlying the olfactory sensilla has multiple small (50–200-nm diameter) pores [4-8], which are supposed to function as a filter that admits odorant molecules, while preventing the entry of larger airborne particles and limiting water loss. However, the cellular processes underlying the patterning of extracellular matrices into functional nano-structures remain unknown. Here we show that cuticular nanopores inDrosophilaolfactory sensilla originate from a curved ultrathin film that is formed in the outermost envelope layer of the cuticle, and secreted from specialized protrusions in the plasma membrane of the hair forming (trichogen) cell. The envelope curvature coincides with plasma membrane undulations associated with endocytic structures. Thegore-tex/Osiris23gene encodes an endosomal protein that is essential for envelope curvature, nanopore formation, and odor receptivity, and is expressed specifically in developing olfactory trichogen cells. The 24-memberOsirisgene family is expressed in cuticle-secreting cells, and is found only in insect genomes. These results reveal an essential requirement for nanopores for odor reception and identifyOsirisgenes as a platform for investigating the evolution of surface nano-fabrication in insects.

Messenger RNA (mRNA) plays a critical role in cellular growth and development. However, there have been limited methods available to visualize endogenous mRNA in living cells with ease. We have designed RNA-based fluorescence “turn-on” probes that target mRNA by fusing an unstable form of Spinach with target-complementary sequences. These probes have been demonstrated to be selective, stable, and capable of targeting various mRNAs for live E. coli imaging.

A central challenge of the post-genomic era is to comprehensively characterize the cellular role of the ∼20,000 proteins encoded in the human genome. To systematically study protein function in a native cellular background, libraries of human cell lines expressing proteins tagged with a functional sequence at their endogenous loci would be very valuable. Here, using electroporation of Cas9/sgRNA ribonucleoproteins and taking advantage of a split-GFP system, we describe a scalable method for the robust, scarless and specific tagging of endogenous human genes with GFP. Our approach requires no molecular cloning and allows a large number of cell lines to be processed in parallel. We demonstrate the scalability of our method by targeting 48 human genes and show that the resulting GFP fluorescence correlates with protein expression levels. We next present how our protocols can be easily adapted for the tagging of a given target with GFP repeats, critically enabling the study of low-abundance proteins. Finally, we show that our GFP tagging approach allows the biochemical isolation of native protein complexes for proteomic studies. Together, our results pave the way for the large-scale generation of endogenously tagged human cell lines for the proteome-wide analysis of protein localization and interaction networks in a native cellular context.SIGNIFICANCE STATEMENTThe function of a large fraction of the human proteome still remains poorly characterized. Tagging proteins with a functional sequence is a powerful way to access function, and inserting tags at endogenous genomic loci allows the preservation of a near-native cellular background. To characterize the cellular role of human proteins in a systematic manner and in a native context, we developed a method for tagging endogenous human proteins with GFP that is both rapid and readily applicable at a genome-wide scale. Our approach allows studying both localization and interaction partners of the protein target. Our results pave the way for the large-scale generation of endogenously tagged human cell lines for a systematic functional interrogation of the human proteome.

Estrogenic activity by recombinant yeast screen assay of the commercial NP was considerably higher when compared with that of n-nonylphenol (n-NP). Fractionation of the commercial NP by high performance liquid chromatography (HPLC) afforded seven isomers: 4-(1,3-dimethyl-1-propyl-butyl)-phenol, 4-(1,1,3-trimethyl-hexyl)-phenol, 4-(1,1-dimethyl-3-ethyl-pentyl)-phenol, 4-(1,1,4-trimethyl-hexyl)-phenol, 4-(1-methyl-1-propyl-pentyl)-phenol, 4-(1,1,2-trimethyl-hexyl)-phenol and 4-(1-ethyl-1-methyl-hexyl)-phenol. The structures of these isomers were determined by GC–MS and nuclear magnetic resonance spectroscopy (NMR). All of these isomers possessed tertiary α-carbon in their chemical structures. Another tertiary NP, 4-(1,1-dimethyl-heptyl)-phenol was synthesized in the present study and this synthetic NP also exhibited the estrogenic activity. One fractionated compound was identified as one of decylphenol, 4-(1-ethyl-1,4,4-trimethyl-pentyl)-phenol. The isomer, 4-(1,1,4-trimethyl-hexyl)-phenol exhibited the highest estrogenic activity corresponding to 1/10 000 that of 17β-estradiol (E2). The activity of n-NP was the least. This suggests that it may be possible to develop a technical NP mixture with relatively low estrogenic activity.

Neural circuit assembly requires precise dendrite and axon targeting. We identified an evolutionarily conserved endoplasmic reticulum (ER) protein, Meigo, from a mosaic genetic screen in Drosophila melanogaster. Meigo was cell-autonomously required in olfactory receptor neurons and projection neurons to target their axons and dendrites to the lateral antennal lobe and to refine projection neuron dendrites into individual glomeruli. Loss of Meigo induced an unfolded protein response and reduced the amount of neuronal cell surface proteins, including Ephrin. Ephrin overexpression specifically suppressed the projection neuron dendrite refinement defect present in meigo mutant flies, and ephrin knockdown caused a similar projection neuron dendrite refinement defect. Meigo positively regulated the level of Ephrin N-glycosylation, which was required for its optimal function in vivo. Thus, Meigo, an ER-resident protein, governs neuronal targeting specificity by regulating ER folding capacity and protein N-glycosylation. Furthermore, Ephrin appears to be an important substrate that mediates Meigo’s function in refinement of glomerular targeting.

Eukaryotic cells contain multiple intracellular organelles which are structurally and functionally distinct membrane-delimited compartments. Organelles play vital roles in many cellular events in essentially all eukaryotic cells. Although the canonical roles of organelles are well described by classical in vitro studies, little is known about the specific physiological roles of organelles in neurons, which possess extremely polarized cellular structures and have a massive cellular volume compared with most eukaryotic cells. Studies that make use of recently developed genetic and microscopic techniques are currently elucidating the unexpectedly specialized roles of intracellular, membrane-delimited organelles in neuronal morphogenesis and function, and in human disease. Here we review recent advances in understanding the roles of organelles (the ER-Golgi secretory pathway, endosomes and mitochondria) in developing neurons.

Epidermal growth factor (EGF) family members, including epiregulin (EP), play a fundamental role in epithelial tissues; however, their roles in immune responses and the physiological role of EP remain to be elucidated. The skin has a versatile system of immune surveillance. Biologically active IL-1α is released to extracellular space upon damage from keratinocytes and is a major player in skin inflammation. Here, we show thatEPis expressed not only in keratinocytes but also in tissue-resident macrophages, and thatEP-deficient (EP–/–) mice develop chronic dermatitis. Wound healing in the skin inEP–/–mice was not impairedin vivo, nor was the growth rate of keratinocytes fromEP–/–mice different from that of WT micein vitro. Of interest is that in WT keratinocytes, both IL-1α and the secreted form of EP induced down-regulation ofIL-18mRNA expression, which overexpression in the epidermis was reported to induce skin inflammation in mice, whereas the down-regulation ofIL-18induced by IL-1α was impaired inEP–/–keratinocytes. Although bone marrow transfer experiments indicated that EP deficiency in non-bone-marrow-derived cells is essential for the development of dermatitis, production of proinflammatory cytokines byEP–/–macrophages in response to Toll-like receptor agonists was much lower, compared with WT macrophages, whose dysfunction inEP–/–macrophages was not compensated by the addition of the secreted form of EP. These findings, taken together, suggested that EP plays a critical role in immune/inflammatory-related responses of keratinocytes and macrophages at the barrier from the outside milieu and that the secreted and membrane-bound forms of EP have distinct functions.