Journal of cell science最新文献

Tip growth is closely tied to fungal pathogenicity. Budding yeast Spa2 (the homolog of GIT1 and GIT2 in mammals), a multi-domain protein and member of the polarisome, orchestrates tip growth in yeasts and other fungi. We identified a conserved short linear motif in the Rab GTPase-activating proteins (RabGAPs) Msb3 and Msb4, and the MAP kinase kinases Ste7 and Mkk1, which mediates their interaction with Spa2. AlphaFold predictions suggest that these initially unstructured motifs adopt an α-helical conformation upon binding to the hydrophobic cleft in the N-terminal domain of Spa2. Altering the predicted key contact residues in either Spa2 or the motif reduces complex stability. Such mutations also cause mis-localization of Msb3, Msb4 and Ste7 within the cell. Deleting the motif in Msb3 or Msb4 abolishes tip-directed growth of the yeast bud. Protein assemblies that spatially confine secretion to specific membrane regions are a common feature of eukaryotic cells. Accordingly, complexes between proteins with this motif and Spa2 were predicted in orthologs and paralogs across selected Opisthokonta, including pathogenic fungi and humans. A search for functional motifs in conformationally flexible regions of all yeast proteins identified Dse3 as a novel Spa2-binding partner.

Cell shape regulation is important for many biological processes. Some cell shape-regulating proteins harbor mechanoresponsive properties that enable them to sense and respond to mechanical cues. In Dictyostelium discoideum, mechanoresponsive network proteins formed by proteins such as myosin II, cortexillin I and IQGAP1 assemble in the cytoplasm into macromolecular complexes, which we term contractility kits (CKs). In our previous studies, we identified the RNA-binding protein RNP1A as a genetic interactor with the cytoskeletal machinery of the cell and as a biochemical interactor of cortexillin I, using in vivo fluorescence cross-correlation spectroscopy. In this study, we show that Dictyostelium rnp1A knockdown cells have reduced cell proliferation, reduced adhesion, defective cytokinesis, and a gene expression profile that indicates rnp1A knockdown cells shift away from the vegetative growth state. Some of the transcripts RNP1A binds encode proteins involved in macropinocytosis, a crucial cell shape change process. Loss of other CK proteins leads to macropinocytotic defects characterized by reduced macropinocytotic crown size. RNP1A interacts with IQGAP1, leading to crosstalk during macropinocytosis. Overall, RNP1A binds transcripts and contributes to cell mechanics and cell shape change processes through interactions with CK proteins.

A significant challenge in studying the biology of the Drosophila centriole is its small size. Advanced super-resolution techniques have provided valuable insights but require specialized equipment and can be difficult to implement in tissues. Expansion microscopy (ExM) offers an accessible alternative, yet its application in Drosophila centriole research has been sparse. We provide an ExM protocol for cultured S2 cells and fly tissues that reveals new insights into procentriole biology. In S2 cells we document overduplication in the form of the classic 'rosettes', while in spermatids we uncover an unexpected movement of the procentriole-like structure (PCL). ExM has also refined existing molecular models. In S2 cells we document the distal tip protein Cep97 as a ring, which clarifies its role in capping the growing centriole. In spermatids, we spatially segregate the inner nuclear membrane protein Spag4 and the cytoplasmic protein Yuri, leading to the new hypothesis that they play independent roles at the centriole-nucleus contact site. Finally, we show that our ExM protocol is a hypothesis generator and discovery tool applicable beyond Drosophila centrioles by imaging synaptonemal complexes in the Plodia interpunctella moth.

As a community of early-career researchers in cell biology, biochemistry and public health, we stand at a pivotal moment regarding both our careers and the fate of our planet. The climate crisis demands urgent, transformative action from the scientific community, yet current research priorities and structures often impede meaningful contributions from cell biologists to this global challenge. As early-career researchers, we present two calls to action: (1) we urge funders, institutions and policymakers to foster collaborative, interdisciplinary and globally inclusive environmental research through equitable international partnerships that prioritise researchers from vulnerable regions; (2) we call for expanded opportunities for early-career cell biologists beyond traditional research career paths, including structured pathways for engagement in policy, science communication and decision-making processes within organisations such as the Intergovernmental Panel on Climate Change and the United Nations. This requires institutional reforms that support alternative career pathways, funding mechanisms that value diverse contributions beyond publications, and meaningful - rather than tokenistic - inclusion of young cell biologists, particularly from the Global South, in climate-related decision-making structures.

Our changing climate poses increasingly severe threats to human and environmental health. Scientific research is essential for understanding and mitigating these effects, but how can cell biologists support this goal? In this Essay, Journal of Cell Science has invited cell biologists from across disciplines and career stages to share their perspectives on how cell biology can address climate-related questions. Their research ranges from practical innovations to fundamental functional studies. How can we re-route metabolic pathways to reduce industrial emissions? What can plankton-microbe interactions tell us about the impact of marine pollution? How can an in-depth understanding of cellular processes help us design more resilient crops to address specific challenges faced in West African countries? Could developments in stem cell biology help safeguard biodiversity? What can we learn from the way deep-sea squid adapt to changing environments on the cellular level? These examples illustrate an increasing drive to apply broad insights and techniques from the world of cell biology to this urgent, global challenge.

Actin microfilaments (F-actin) serve as tracks for myosin-driven organelle movement in plants. To understand how the F-actin network supports organelle movement, we examined the motility of peroxisomes as a common proxy for overall organelle motility in Arabidopsis thaliana. Using mutants of three villin (VLN) genes encoding major actin-bundling proteins that are actively expressed in vegetative tissues, we found that the vln4 mutation exacerbated the growth and subcellular F-actin defects in the vln2 vln3 double mutant. Compared to wild-type cells, the double and triple vln mutants exhibited progressive reduction of stable F-actin bundles and rapid remodeling of the fine filaments into a dynamic mesh. The defective F-actin organization caused significantly reduced mean speed and displacement distance of peroxisomes, although both rapid and slow movements were observed. Correlation analysis grouped complex heterogeneous peroxisome movement patterns into clusters reflecting distinct movement patterns. The vln2 vln3 vln4 triple mutant had significantly fewer peroxisomes with long-range and linear movement but produced an actin mesh network sufficient to retain basal peroxisome function. Our results provide insights into how VLN-dependent F-actin organization is coupled with the complex patterns of actomyosin-mediated organelle movement.

Throughout the life cycle of the unicellular parasite Trypanosoma brucei, its single flagellum remains laterally attached to the cell body by FLA and FLABP proteins, even as the parasite differentiates from the bloodstream form (BSF), found in the mammalian host, to the procyclic form (PCF), in the insect midgut. This differentiation is accompanied by changes in the dominant surface coat protein, from the variable surface glycoprotein to procyclins. There are stage-specific variants of the FLA and FLABP proteins, with FLA2 and FLA2BP found in BSFs, and FLA1 and FLA1BP in PCFs. Yet, how these proteins maintain flagellum attachment during the differentiation from BSFs to PCFs and the accompanying change in surface coat environment is unknown. Here, we used a double-induction system to test whether FLA2 and FLA2BP can maintain flagellum attachment in cells expressing procyclins. Whereas FLA2 compensated for the loss of FLA1, FLA2BP was mislocalised in PCFs and could not compensate for the loss of FLA1BP. Interestingly, when FLA2 was expressed alongside FLA2BP, FLA2BP localised to the flagellum attachment zone and flagellum attachment was maintained. Thus, we conclude that FLA2 and FLA2BP, together, will maintain flagellum attachment as the surface coat environment changes during BSF to PCF differentiation.

Chromera velia is a photosynthetic, free-living alga closely related to the apicomplexan parasites, a phylum of intracellular pathogens responsible for many devastating diseases, including malaria, cryptosporidiosis and toxoplasmosis. With molecular and cellular landmarks clearly related to but distinguishable from those found in apicomplexan parasites, Chromera provides an opportunity to investigate the evolutionary origin of the structures and processes needed for intracellular parasitism. However, tools for defining localization and functions of gene products do not exist for Chromera, which creates a major bottleneck for exploring its biology. Here we report two major advances in exploring the cell biology of this free-living relative of a large group of intracellular parasites: (1) successful cell transformation and (2) the implementation of expansion microscopy. The initial analysis enabled by these tools generated new insights into subcellular organization in different life stages of Chromera. These new developments boost the potential of Chromera as a model system for understanding the evolution of parasitism in apicomplexans.

The first step to probing any potential interaction between two biomolecules is to determine their spatial association. In other words, if two biomolecules localize similarly within a cell, then it is plausible they could interact. Traditionally, this is quantified through various colocalization metrics. These measures infer this association by estimating the degree to which fluorescent signals from each biomolecule overlap or correlate. However, these metrics are, at best, proxies, and they depend strongly on various experimental choices. Here, we define a new strategy that leverages multispectral imaging and phasor analysis, termed the phasor mixing coefficient (PMC). The PMC measures the precise mixing of fluorescent signals in each pixel. We demonstrate how the PMC captures complex biological subtlety by offering two distinct values, a global measure of overall color mixing and the homogeneity thereof. We additionally show that the PMC exhibits less sensitivity to signal-to-noise ratio, intensity threshold and background signal compared to canonical methods. Moreover, this method provides a means to visualize color mixing at each pixel. We show that the PMC offers users a nuanced and robust metric to quantify biological association.

Tumor protein p53 inducible nuclear protein 2 (TP53INP2; also known as DOR) is a multifunctional protein involved in transcriptional coactivation, ribosomal RNA synthesis and autophagy, regulated by subcellular localization. Using CRISPR/Cas9-generated TP53INP2-knockout HeLa cells reconstituted with EGFP-TP53INP2, we show that TP53INP2 is predominantly degraded by nuclear proteasomes under basal conditions. Under stress, including starvation and various chemical stress inducers, TP53INP2 accumulates in the cytoplasm independently of ATG5, CRM1-mediated export, phosphorylation, ubiquitylation or acetylation. We identify a nuclear localization signal (NLS) overlapping a nucleolar localization signal (NoLS) in the C-terminus, which mediates nuclear import and nucleolar enrichment. Deletion of this region redirects TP53INP2 to LC3B-positive puncta. A conserved nine-amino-acid cytoplasmic retention motif (CRM) in the C-terminus prevents nuclear re-entry under stress. This motif and regulation of subcellular localization is conserved in the related TP53INP1 protein. Fluorescence recovery after photobleaching (FRAP) and importin-binding assays show that nutrient starvation disrupts nuclear import of TP53INP2. Finally, we show that starvation enhances TP53INP2 translation via the m6A demethylase FTO, without altering mRNA stability. These findings uncover coordinated regulation of TP53INP2 localization and turnover by cellular stress.