Journal of Cell Biology最新文献

The cell biology of tissues challenges us to understand how fundamental processes found in free living as well as communal cells are coordinated to achieve complex patterns of behavior on the scale of cellular populations. In this issue, Soffer et al. (https://doi.org/10.1083/jcb.202502071) reveal how cell-cell adhesion co-opts the spectrin membrane skeleton to achieve this goal in the epidermis of the skin.

The cell biology community mourns the loss of Catherine Rabouille, an exceptional scientist whose determination, innovation, and fearless engagement with ideas reshaped how we think about cellular organization. After a brave battle with metastatic breast cancer, Catherine chose to bring her life to a peaceful close on 7 August 2025, in a manner consistent with the clarity, resolve, and agency that defined her approach to science and life. She was an extraordinary mentor, whose generosity, attentiveness, and unwavering support shaped generations of scientists and left a profound mark on all those she guided. Catherine leaves behind a legacy defined by intellectual courage and an enduring passion for science.

Vertebrate genes function in specific tissues and stages, so their functional studies require conditional knockout or editing. In zebrafish, spatiotemporally inducible genome editing, particularly during early embryogenesis, remains challenging. Here, we establish inducible Cas9-based editing in defined cell types and stages. The nCas9ERT2 fusion protein, consisting of Cas9 and an estrogen receptor flanked by two nuclear localization signals, is usually located in the cytoplasm and efficiently translocated into nuclei upon 4-hydroxytamoxifen (4-OHT) treatment in cultured cells or embryos. As a proof of concept, we demonstrate that genes in primordial germ cells in embryos and germ cells in adult ovaries from a transgenic line with stable expression of nCas9ERT2 and gRNAs can be mutated by 4-OHT induction. The system also works in early mouse embryos. Thus, this inducible nCas9ERT2 approach enables temporospatial gene editing at the organismal level, expanding the tissue- and stage-specific gene-editing toolkit.

Cell shape and fate are tightly linked, yet how the cortical cytoskeleton integrates regulation of shape and fate remains unclear. Using the multilayered epidermis as a paradigm for cell shape-guided changes in differentiation, we identify spectrin as an essential organizer of the actomyosin cortex to integrate transitions in cell shape with spatial organization of signaling. Loss of αII-spectrin (Sptan1) in mouse epidermis altered cell shape in all layers and impaired differentiation and barrier formation. High-resolution imaging and laser ablation revealed that E-cadherin organizes gradients of cortical actin and spectrin into layer-specific submembranous networks with discrete structural and mechanical properties that coordinate cell shape and fate. This layer-specific organization dissipates tension and, in upper layers, retains activated growth factor receptor EGFR and the calcium channel TRPV3 at the membrane to induce terminal differentiation. Together, these findings reveal how polarized organization of the cortical cytoskeleton directs transitions in cell shape and cell fate at the tissue scale necessary to establish epithelial barriers.

SQSTM1/p62 is a master regulator of the autophagic and ubiquitination pathways of protein degradation and the antioxidant response. p62 functions in these pathways via reversible assembly and sequestration of additional factors into cytoplasmic phase-separated structures termed p62 bodies. The physiological roles of p62 in these various pathways depend on numerous mechanisms for regulating p62 body formation and dynamics that are incompletely understood. Here, we identify a new mechanism for regulation of p62 oligomerization and incorporation into p62 bodies by SHKBP1, a cullin-3 E3 ubiquitin ligase adaptor, that is independent of its potential functions in ubiquitination. We map an SHKBP1-p62 protein-protein interaction outside of p62 bodies that limits p62 assembly into p62 bodies and affects the antioxidant response involving sequestration of Keap1 and nuclear translocation of Nrf2. These studies provide a non-ubiquitination-based mechanism for an E3 ligase adaptor in regulating p62 body formation and cellular responses to oxidative stress.

Segregating a complete set of chromosomes into the gametes relies on exchanges of genetic material that occur during meiosis. It is only exchanges that form between the homologous chromosomes (homologs), rather than between the identical sister chromatids, that enable correct chromosome segregation. Understanding how the homologs and the sisters are distinguished requires knowledge of how they are organized relative to each other. Here, we use selective labeling of a single sister in Caenorhabditis elegans to define the organization of the sister chromatids when meiotic exchanges form. We find that pairs of sisters are well separated (resolved) throughout pachytene, despite being tethered to each other along their length. Depleting the cohesin loader NIPBLSCC-2 impairs sister resolution, suggesting that an active process-likely loop extrusion-demixes the sisters. Our work shows that meiotic exchanges form in C. elegans when the sisters and homolog are roughly the same distance from one another, suggesting that repair template choice is unlikely to rely on relative proximity.

Loss-of-function studies are a central approach to understanding gene/protein function. In mice, this often relies upon heritable recombination at the DNA level. This approach is slow and nonreversible, which limits both spatial and temporal resolution of analysis. Recently, degron techniques that directly target proteins for degradation have been successfully used to quickly and reversibly knock down proteins. Currently, these systems have been limited by lack of tissue/cell type specificity. Here, we generated mice that allow spatial and temporal control of GFP-tagged protein degradation. This DegronGFP line leads to degradation of GFP-tagged proteins in different cellular compartments and in distinct cell types. Further, it is rapid and reversible. We used DegronGFP to probe the function of the glucocorticoid receptor in the epidermis and demonstrate that it has distinct functions in proliferative and differentiated cells-an analysis that would not have been possible with traditional recombination approaches. We propose that the ability to use GFP knock-in lines for loss-of-function analysis will provide additional motivation for generation of these useful tools.

Micronuclei (MN), a hallmark of chromosome instability, frequently rupture, leading to protumorigenic consequences. MN rupture requires nuclear lamina defects, yet their underlying causes remain unclear. Here, we demonstrate that MN lamina gaps are linked to excessive MN growth resulting from impaired protein export. This export defect arises from reduced levels of the transport protein RCC1 in MN. Overexpressing RCC1 increases protein export and protects MN from rupture. Differences in RCC1 levels linked to chromatin state also explain why high euchromatin content increases the stability of small MN. Additional RCC1 loss in euchromatic MN results in impaired protein import. For these MN, increasing RCC1, directly or through increasing histone methylation, accelerates rupture. Our findings define a new model of MN rupture, where defects in protein export drives continuous MN growth causing nuclear lamina gaps that predispose MN to membrane rupture and where chromatin-specific features can alter rupture of small MN by further impairing nuclear transport.

Hundreds of mitochondrial proteins rely on N-terminal presequences for organellar targeting and import. While generally described as positively charged amphiphilic helices, presequences lack a consensus motif and thus likely promote protein import into mitochondria with variable efficiencies. Indeed, the concept of presequence strength underlies biological models such as stress sensing, yet a quantitative analysis of what dictates strong versus weak presequences is lacking. Furthermore, the extent to which presequence strength affects mitochondrial function and cellular fitness remains unclear. Here, we capitalize on the MitoLuc protein import assay to define multiple aspects of presequence strength. We find that select presequences, including those that regulate the mitochondrial unfolded protein response (UPRmt), impart differential import efficiencies during mitochondrial uncoupling. Surprisingly, we find that presequences beyond those associated with stress signaling promote highly variable import efficiency in vitro, suggesting presequence strength may influence a broader array of processes than currently appreciated. We exploit this variability to demonstrate that only presequences that promote robust in vitro import can fully rescue defects in respiratory growth in complex IV-deficient yeast, suggesting that presequence strength dictates metabolic potential. Collectively, our findings demonstrate that presequence strength can describe numerous metrics, such as total imported protein, maximal import velocity, or sensitivity to uncoupling, suggesting that the annotation of presequences as weak or strong requires more nuanced characterization than typically performed. Importantly, we find that such variability in presequence strength meaningfully affects cellular fitness beyond stress signaling, suggesting that organisms may broadly exploit presequence strength to fine-tune mitochondrial import and thus organellar homeostasis.

BAR domain-containing proteins are key regulators of endocytosis and actin remodeling. Their function in morphogenesis remains to be investigated. We report that the I-BAR domain-containing protein, missing-in-metastasis (MIM) (also called MTSS1), promotes branched actin network formation and endocytosis to drive rapid, cyclical plasma membrane remodeling during syncytial divisions in Drosophila embryos. Actin-rich villous protrusions in the apical caps in interphase are depleted in metaphase, concurrent with furrow extension between adjacent nuclei. MIM depletion results in a loss of furrow extension and in longer, more abundant apical protrusions containing the formin diaphanous. Branched actin networks promoted by MIM are in balance with bundled actin networks induced by RhoGEF2 and diaphanous. Cyclical recruitment of MIM to the cortex promotes localization of active Rac, the WAVE regulatory complex, and the Arp2/3 complex to drive endocytic membrane remodeling. These findings identify MIM as an integrator of actin and endocytic dynamics that enables rapid membrane remodeling during Drosophila syncytial division cycles.