Journal of Cell Biology最新文献

Migrating cells form retraction fibers (RFs) at their trailing edge, where migrasomes, ranging from 0.5 to 3 μm, grow at the tips or intersections of RF. Migrasomes play crucial roles when released extracellularly, but before release, they remain physically connected to cell body via RFs, facilitating long-range signal transmission. Since many signaling molecules are highly localized, the mechanism of long-range signal transmission has not been fully understood. Here, we demonstrated that tubular ER extended into RFs and localized to migrasomes, which depended on microtubule-regulated ER extension. Tubular ER adhered to migrasome biogenesis site through ER-plasma membrane contact sites (ER-PM MCSs). Notably, tubular ER functions as cholesterol and calcium reservoir, facilitating the transfer of cholesterol and calcium to migrasomes, potentially at ER-PM MCSs that promoted membrane expansion, stability, and localized secretion of migrasome. Our findings revealed a novel dynamic of tubular ER and provided a new mechanism for long-range site-specific calcium and cholesterol transmission through RFs and migrasomes in migrating cells.

The small, tubulin-binding protein STMN2 is highly expressed in neurons and is implicated in amyotrophic lateral sclerosis. STMN2 degrades rapidly and accumulates at axotomy sites, suggesting fast turnover is crucial for its neuroprotective function. We show that STMN2 was primarily degraded by the ubiquitin-proteasome system. Its membrane-targeting N-terminal domain promoted fast turnover, whereas its tubulin-binding domain promoted stabilization. Proximity labeling and imaging showed that tubulin binding reduced STMN2 targeting to trans-Golgi network membranes. Pull-down assays showed that tubulin binds preferentially to soluble over membrane-bound STMN2. Our observations suggest that STMN2 interconverts between a soluble, tubulin-bound form and a membrane-bound, tubulin-free form, and is rapidly degraded when released from both membranes and tubulin. We propose that tubulin binding sequesters and stabilizes STMN2, while its neuroprotective function involves an unknown membrane activity.

Neuronal morphogenesis depends on extracellular guidance cues accurately instructing intracellular cytoskeletal remodeling. Here, we describe a novel role of the actin binding protein coronin 1A (Coro1A) in neuronal morphogenesis, where it mediates responses to the axon guidance cue netrin-1. We found that Coro1A localizes to growth cones and filopodial structures and is required for netrin-dependent axon turning, branching, and corpus callosum development. We previously discovered that Coro1A interacts with TRIM67, a brain-enriched E3 ubiquitin ligase that binds the netrin receptor DCC, and is also required for netrin-mediated neuronal morphogenesis. Loss of Coro1A and loss of TRIM67 shared similar phenotypes, suggesting that they may function together in the same netrin pathway. A Coro1A mutant deficient in binding TRIM67 was unable to rescue loss of Coro1A phenotypes, indicating that the interaction between Coro1A and TRIM67 is required for netrin responses. Together, our findings reveal that Coro1A is required for proper neuronal morphogenesis, where it collaborates with TRIM67 downstream of netrin.

The spatiotemporal coordination of septins and myosin-II in processes like cytokinesis is not well understood. In Saccharomyces cerevisiae, Bni5 links the myosin-II heavy chain Myo1 to the septin hourglass at the bud neck prior to cytokinesis, but the underlying mechanisms and functions remain unclear. Here, we show that Bni5 binds septin filaments, the septin-associated kinase Elm1, and Myo1 via distinct domains. Bni5 regulates the architecture and stability of the septin hourglass until it dissociates from the bud neck at the onset of cytokinesis. This dissociation, facilitated through phosphorylation of Bni5 by Gin4, an Elm1-interacting kinase, enables timely remodeling of the septin hourglass into a double ring. Bni5 also mediates the role of Myo1 in retrograde actin cable flow during polarized growth and ensures maximal accumulation of Myo1 at the bud neck before cytokinesis, reinforcing the actomyosin ring and buffering it against perturbations. These findings establish Bni5 as a key regulator and coordinator of septins and myosin-II at the division site.

NoCut safeguards genome integrity against persistent DNA bridges, but how these missegregation events are sensed is not understood. In this issue, Dam et al. (https://doi.org/10.1083/jcb.202502014) identify the Srs2 and PARI helicases as conserved NoCut sensors that initiate signalling to delay cytokinetic abscission.

Adherens junctions regulate tissue architecture, mediating robust yet dynamic cell-cell adhesion and, via cytoskeletal linkage, allowing cells to change shape and move. Adherens junctions contain thousands of molecules linked by multivalent interactions of folded protein domains and intrinsically disordered regions (IDRs). One key challenge is defining mechanisms conferring robust linkage and mechanosensing. Drosophila Canoe and mammalian Afadin provide superb entry points to explore how their complex protein structures and shared IDRs enable function. We combined genetic, cell biological, and biochemical tools to define how Canoe's IDR functions during morphogenesis. Unlike many of Canoe's folded domains, the proximal IDR is critical for junctional localization, mechanosensing, and function. In its absence, the mutant protein localizes to nuclei. We took the IDR apart, identifying two conserved stickers that directly bind F-actin, separated by less-conserved spacers. Surprisingly, while mutants lacking the IDR die as embryos with morphogenesis defects, no IDR subregion is essential for viability. Instead, stickers and spacers act combinatorially to ensure localization, mechanosensing, and function.

In this issue, Calvo et al. (https://doi.org/10.1083/jcb.202410094) report a new bioluminescent Ca2+ probe (ELGA) targeted to acidic endo-lysosomes (ELs) to permit selective and dynamic recording of endo-lysosomal Ca2+ uptake and release. Ca2+ was not only released by canonical EL channels but, surprisingly, by IP3 receptors.

Endo-lysosomes are considered acidic Ca2+ stores, but direct measurements of luminal Ca2+ within them are limited. Here, we report that the Ca2+-sensitive luminescent protein aequorin does not reconstitute with its cofactor at highly acidic pH but that a significant fraction of the probe is functional within a mildly acidic compartment when targeted to the endo-lysosomal system. We leveraged this probe (ELGA) to report Ca2+ dynamics in this compartment. We show that Ca2+ uptake is ATP-dependent and sensitive to blockers of ER Ca2+ pumps. We find that the Ca2+ mobilizing messenger IP3 evokes robust luminal responses in wild-type cells, but not in IP3R knockout cells. Responses were comparable to those evoked by activation of the endo-lysosomal ion channels TPCs and TRPMLs. Stimulation with IP3-forming agonists also mobilized the store in intact cells. Super-resolution microscopy analysis was consistent with the presence of IP3Rs within the endo-lysosomal system. Our data reveal a physiologically relevant, IP3-sensitive store of Ca2+ within the endo-lysosomal system.

Peroxisome biogenesis in humans is not governed by PPARα, overturning a paradigm established in rodents. PPARα agonists fail to induce canonical peroxisomal genes, and functional response elements are absent from key promoters. Human peroxisomes nonetheless expand through PPAR-independent pathways, positioning them as organelles tuned to immunometabolic and redox demands and redefining strategies for therapeutic intervention.

Centrosomes are highly dynamic organelles, and maintaining their stability is crucial for spindle pole integrity and bipolar spindle formation. Centrosomes consist of a pair of centrioles surrounded by the PCM. In Caenorhabditis elegans, interactions between the scaffold protein SPD-5 and kinase PLK-1 are essential for PCM formation. However, how PCM stability is established and maintained remains unclear. We address this by analyzing the function of PCMD-1, a protein mainly localizing to centrioles. We show that CDK-1 primes PCMD-1 for PLK-1 phosphorylation. Mutations in PLK-1 docking sites abolish PCMD-1 phosphorylation and SPD-5 binding in vitro and destabilize the PCM scaffold in vivo. As a result, microtubule-pulling forces cannot be relayed to centrioles, delaying their separation. Our findings reveal that PCMD-1 is critical for PCM stability and timely centriole separation during PCM disassembly. We propose that PCMD-1 initiates scaffold assembly by biasing the PCM core toward intrinsic order, acting as a seed that propagates throughout the scaffold to ensure structural integrity.