Journal of cell science最新文献

Epithelia are vital tissues in multicellular organisms, acting as barriers between external and internal environments. Simple epithelia, such as pg those in embryos and the adult gut, have the remarkable ability to repair wounds efficiently, making them ideal for studying epithelial repair mechanisms. In these tissues, wound closure involves the coordinated action of a contractile actomyosin cable at the wound edge and collective cell movements around the wound. However, the dynamics of cell-cell interactions during this process remain poorly understood. Here, we demonstrate that Dachsous (Ds), an atypical cadherin associated with Planar Cell Polarity, is crucial for efficient epithelial repair in the Drosophila embryo. We show that the absence of Ds alters tissue mechanics and cell shape changes and rearrangements, leading to slower wound closure. Additionally, we reveal that Occluding Junctions are necessary for the proper apical localization of Ds, uncovering an unanticipated interaction between these two molecular complexes. This study identifies Ds as a novel key player in epithelial repair and highlights the need for further investigating the molecular mechanisms by which Ds modulates cell shape and tissue morphogenesis.

Intrinsically disordered regions (IDRs) are known to sense the positive membrane curvature of vesicles and tubules. However, whether IDRs can sense the negative curvature of their luminal surfaces remains elusive. Here, we show that IDRs direct specific localization to ER tubules. In Saccharomyces cerevisiae, Sed4 interacts with Sec16 at the ER exit site (ERES) to promote ER export. Upon loss of this interaction, Sed4 failed to assemble at the ERES but was enriched in the ER tubules in a luminal region-dependent manner. Fusion of the Sed4 luminal region with Sec12 and Sec22, which localize throughout the ER, resulted in their enrichment in the tubules. The luminal regions of Sed4 or its homologs, predicted to be IDRs, localized to tubules when translocated alone into the ER lumen. The lumen-imported IDRs derived from cytosol-localizing Sec16 and Atg13 also exhibited tubule localization. Furthermore, Sed4 constructs with the luminal region replaced by these IDRs were concentrated at the ERES. Collectively, we suggest that the IDRs may sense the properties of the tubule lumen, such as its surface, and facilitate Sed4 assembly at the ERES.

Biomolecular condensates (BMCs) emerge as important players in RNA regulation. The RNA binding protein Smaug forms cytosolic BMCs in mammals, insects and yeasts and affects mitochondrial function and/or responses to nutrient deprivation. Here we found that the non-canonical activation of the SMO-AMPK pathway known to affect energy metabolism triggers the immediate disassembly of BMCs formed by a number of human and rodent Smaug orthologs, whereas processing bodies remained rather unaltered. A non-phosphorylatable SMO mutant abrogated the effect, involving SMO phosphorylation in hSmaug1 BMCs regulation. Three mechanistically different SMO ligands, namely SAG; GSA-10 and cyclopamine elicited a similar response, which was blocked upon AMPK pharmacological inhibition. Polysome disassembly by puromycin halted Smaug1 BMC dissolution, thus suggesting that unbound transcripts became translationally active. Single-molecule fluorescent in situ hybridization illustrated the release of UQCRC1 mRNA. Finally, Smaug1 is a phosphoprotein bound by 14-3-3 proteins and the competitive inhibitor difopein blocked the response to non-canonical SMO stimulation. We propose that the regulated condensation and dispersion of Smaug1 BMCs generate translational changes that contribute to metabolic regulation downstream of the non-canonical SMO-AMPK axis.

Evolutionarily conserved Mis4 establishes cohesion between replicated sister chromatids in vegetatively proliferating cells. In the fission yeast, Schizosaccharomyces pombe, defects in Mis4 lead to premature separation of sister chromatids, resulting in fatal chromosome mis-segregation during mitosis. In humans, NIPBL, an ortholog of Mis4, is responsible for a multisystem disorder called Cornelia de Lange syndrome. We reported that Mis4 is also essential in non-proliferating quiescent cells. Whereas wild-type fission yeast cells can maintain high viability for long periods without cell division in the quiescent G0 phase, mis4-450 mutant cells cannot. Here, we show that Mis4 is not required for cells to enter G0 phase, but is essential for them to exit from it. When resuming mitosis after passage of G0, mis4 mutant cells segregated sister chromatid successfully, but failed to separate daughter nuclei completely and consequently formed dikaryon-like cells. These findings suggest a novel role for Mis4/NIPBL in quiescent cells, which is prerequisite for full nuclear separation upon resumed mitosis. As most human cells are in a quiescent state, this study may facilitate development of novel therapies for human diseases caused by Mis4/NIPBL deficiency.

The paradoxical exacerbation of cellular injury and death during reperfusion remains a problem in treatment of myocardial infarction. Mitochondrial dysfunction plays a key role in the pathogenesis of myocardial ischemia and reperfusion injury. Dysfunctional mitochondria can be removed by mitophagy, culminating in their degradation within acidic lysosomes. Mitophagy is pivotal in maintaining cardiac homeostasis and emerges as a potential therapeutic target. Here we employ beating human engineered heart tissue (EHT) to assess mitochondrial dysfunction and mitophagy during ischemia and reperfusion simulation. Our data indicate adverse ultrastructural changes in mitochondrial morphology and impairment of mitochondrial respiration. Furthermore, our pH-sensitive mitophagy reporter EHTs, generated by CRISPR/Cas9 endogenous knock-in strategy, reveal induced mitophagy flux in EHTs after ischemia and reperfusion simulation. The induced flux requires the activity of the protein kinase ULK1, a member of the core-autophagy machinery. Our results demonstrate the applicability of the reporter EHTs for mitophagy assessment in a clinically relevant setting. Deciphering mitophagy in the human heart will facilitate development of novel therapeutic strategies.

White adipose tissue (WAT) comprises a plethora of cell types beyond adipocytes forming a regulatory network that ensures systemic energy homeostasis. Intertissue communication is facilitated by metabolites and signaling molecules that are spread by vasculature and nerves. Previous works have indicated that WAT responds to environmental cues by adapting the abundance of these 'communication routes'; however, the high intra-tissue heterogeneity questions the informative value of bulk or single-cell analyses and underscores the necessity of whole-mount imaging. The applicability of whole-mount WAT-imaging is currently limited by two factors - (1) methanol-based tissue clearing protocols restrict the usable antibody portfolio to methanol-resistant antibodies and (2) the vast amounts of data resulting from 3D imaging of whole-tissue samples require high computational expertise and advanced equipment. Here, we present a protocol for whole-mount WAT clearing, overcoming the constraints of antibody-methanol sensitivity. Additionally, we introduce TiNeQuant (for 'tissue network quantifier') a Fiji tool for automated 3D quantification of neuron or vascular network density, which we have made freely available. Given TiNeQuants versatility beyond WAT, it simplifies future efforts studying neuronal or vascular alterations in numerous pathologies.

Over the past two decades, significant progress has been made in understanding mechanotransduction to the nucleus. Nevertheless, most research has focused on outside-in signalling orchestrated by external mechanical stimuli. Emerging evidence highlights the importance of intrinsic nuclear mechanisms in the mechanoresponse. The discovery of actin and associated motor proteins, such as myosins, in the nucleus, along with advances in chromatin organisation research, has raised new questions about the contribution of intranuclear architecture and mechanics. Nuclear actin and myosins are present in various compartments of the nucleus, particularly at sites of DNA processing and modification. These proteins can function as hubs and scaffolds, cross-linking distant chromatin regions and thereby impacting local and global nuclear membrane shape. Importantly, nuclear myosins are force-sensitive and nuclear actin cooperates with mechanosensors, suggesting a multi-level contribution to nuclear mechanics. The crosstalk between nuclear myosins and actin has significant implications for cell mechanical plasticity and the prevention of pathological conditions. Here, we review the recent impactful findings that highlight the roles of nuclear actin and myosins in nuclear organisation. Additionally, we discuss potential links between these proteins and emphasize the importance of using new methodologies to unravel nuclear-derived regulatory mechanisms distinct from the cytoskeleton.

This study investigated possible mechanisms underlying differences between heterophilic and homophilic cadherin adhesions that influence intercellular mechanics and multicellular organization. Results suggest that homophilic cadherin ligation selectively activates force transduction, such that resulting signaling and mechano-transduction amplitudes are independent of cadherin-binding affinities. Epithelial (E-) and neural (N-)cadherin cooperate with distinct growth factors to mechanically activate force transduction cascades. Prior results have demonstrated that E-cadherin and epidermal growth factor receptor form force-sensitive complexes at intercellular junctions. Here, we show that the reconstitution of N-cadherin force transduction requires the co-expression of N-cadherin and fibroblast growth factor receptor. Mechanical measurements further demonstrated that homophilic ligation initiates receptor tyrosine kinase-dependent force transduction cascades, but heterophilic cadherin ligands fail to activate signaling or generate stereotypical mechano-transduction signatures. The all-or-nothing contrast between mechano-transduction by heterophilic versus homophilic cadherin adhesions supersedes differences in cadherin adhesion strength. This mechano-selectivity impacts cell spreading and traction generation on cadherin substrates. Homophilic ligation appears to be a key that selectively unlocks cadherin mechano-transduction. These findings might reconcile the roles of cadherin recognition and cell mechanics in the organization of multicellular assemblies.

Budding yeast cells multiply by asymmetric cell division. During this process, the cell organelles are transported by myosin motors along the actin cytoskeleton into the growing bud, and, at the same time, some organelles must be retained in the mother cell. The ordered partitioning of organelles depends on highly regulated binding of motor proteins to cargo membranes. To search for novel components involved in this process, we performed a protein fragment complementation screen using the cargo-binding domain of Myo2, the major organelle transporter in yeast, as bait and a genome-wide strain collection expressing yeast proteins as prey. One robust hit was Alo1, a poorly characterized D-arabinono-1,4-lactone oxidase located in the mitochondrial outer membrane. We found that mutants lacking Alo1 exhibited defects in mitochondrial morphology and inheritance. During oxidative stress, dysfunctional mitochondria are immobilized in the mother in wild-type cells. Intriguingly, overexpression of ALO1 restored bud-directed transport of mitochondria under these conditions. We propose that Alo1 supports the recruitment of Myo2 to mitochondria and its activity is particularly important under oxidative stress.

Microtubules are cytoskeletal filaments important for various cellular processes such as intracellular transport, cell division, polarization and migration. Microtubule organization goes hand in hand with cellular function. Motile cells, such as immune cells or fibroblasts, contain microtubule asters attached to the centrosome and the Golgi complex, whereas in many other differentiated cells, microtubules form linear arrays or meshworks anchored at membrane-bound organelles or the cell cortex. Over the past decade, new developments in cell culture, genome editing and microscopy have greatly advanced our understanding of complex microtubule arrays. In this Cell Science at a Glance article and the accompanying poster, we review the diversity of microtubule arrays in interphase animal cells. We describe microtubule network geometries present in various differentiated cells, explore the variety in microtubule-organizing centers responsible for these geometries, and discuss examples of microtubule reorganization in response to functional changes and their interplay with cell motility and tissue development.