Biology subjects

Dudin, O.

Publications and source records attributed to Dudin, O..

22 records · Page 2Linked to original sources

bioRxiv2019

A unicellular relative of animals generates an epithelium-like cell layer by actomyosin-dependent cellularization

In animals, cellularization of a coenocyte is a specialized form of cytokinesis that results in the formation of a polarized epithelium during early embryonic development. It is characterized by coordinated assembly of an actomyosin network, which drives inward membrane invaginations. However, whether coordinated cellularization driven by membrane invagination exists outside animals is not known. To that end, we investigate cellularization in the ichthyosporean Sphaeroforma arctica, a close unicellular relative of animals. We show that the process of cellularization involves coordinated inward plasma membrane invaginations dependent on an actomyosin network, and reveal the temporal order of its assembly. This leads to the formation of a polarized layer of cells resembling an epithelium. We show that this epithelium-like stage is associated with tightly regulated transcriptional activation of genes involved in cell adhesion. Hereby we demonstrate the presence of a selforganized, clonally-generated, polarized layer of cells in a unicellular relative of animals.

evolutionary biology↗

bioRxiv2018

Yeast-to-hypha transition of Schizosaccharomyces japonicus in response to natural stimuli

Many fungal species are dimorphic, exhibiting both unicellular yeast-like and filamentous forms. Schizosaccharomyces japonicus, a member of the fission yeast clade, is one such dimorphic fungus. Here, we first identify fruit extracts as natural, stress-free, starvation-independent inducers of filamentation, which we use to describe the properties of the dimorphic switch. During the yeast-to-hypha transition, the cell evolves from a bipolar to a unipolar system with 10-fold accelerated polarized growth but constant width, vacuoles segregated to the non-growing half of the cell, and hyper-lengthening of the cell. We demonstrate unusual features of S. japonicus hyphae: these cells lack a Spitzenkorper, a vesicle distribution center at the hyphal tip, but display more rapid cytoskeleton-based transport than the yeast form, with actin cables being essential for the transition. S. japonicus hyphae also remain mononuclear and undergo complete cell divisions, which are highly asymmetric: one daughter cell inherits the vacuole, the other the growing tip. We show these elongated cells scale their nuclear size, spindle length and elongation rates but display altered division size controls. This establishes S. japonicus as a unique system that switches between symmetric and asymmetric modes of growth and division.

microbiology↗

bioRxiv2017

Feedback inhibition of Ras activity coordinates cell fusion with cell-cell contact

In fission yeast Schizosaccharomyces pombe, pheromone signalling engages a GPCR-Ras-MAPK cascade to trigger sexual differentiation leading to gamete fusion. Cell-cell fusion necessitates local cell wall digestion, the location of which relies on an initially dynamic actin fusion focus that becomes stabilized upon local enrichment of the signalling cascade. We constructed a live-reporter of active Ras1 (Ras1-GTP), also functional in S. cerevisiae, which revealed Ras activity at polarity sites peaking on the fusion structure before fusion. Remarkably, constitutive Ras1 activation promoted fusion focus stabilization and fusion attempts irrespective of cell-cell pairing, leading to cell lysis. Ras1 activity is restricted by the GTPase activating protein (GAP) Gap1, itself recruited to sites of Ras1-GTP. While the GAP domain on its own does not suffice for this localization, its recruitment to Ras1-GTP sites is essential to block untimely fusion attempts. We conclude that negative feedback control of Ras activity restrains the MAPK signal and couples fusion with cell-cell engagement.

cell biology↗

bioRxiv2017

A systematic screen for morphological abnormalities during fission yeast sexual reproduction identifies a mechanism of actin aster formation for cell fusion

In non-motile fungi, sexual reproduction relies on stron morphogenetic changes in response to pheromone signaling. We report here on asystematic screen for morphological abnormalities o the mating process in fission yeast Schizosaccharomyces pombe. We derived a homothallic (self-fertile) collection of viable deletions which, upon visual screening, revealed a plethora of phenotype affecting all stages of the mating process, including cell polarizati cell fusion and sporulation. Cell fusion relies onthe formation of the fusion focus, an aster-like F-actin structure that is marked by stron local accumulation of the myosin V Myo52, which concentrates secretion at the fusion site. A secondaryscreen for fusion-defective mutants identified the myosin V Myo51-associated coiled-coil proteins Rng8 and Rng9 as critical forthe coalescence of the fusion focus Indeed, rng8{triangleup} and rng9{triangleup} mutant cells exhibitmultiple stable dots a the cell-cell contact site, instead of the single cusfo observed in wildtype. Rng8 and Rng9 accumulate on the fusion focus, depende on Myo51 and tropomyosin Cdc8A. tropomyosin mutant allele, whic compromises Rng8/9 localization but not actin binding, similarly lea to multiple stable dots instead of a single focus.By contrast, myo51 deletion does not strongly affect fusion focus coalescenceWe. propose that focusing of the actinfilaments in the fusionaster primarily relies on Rng8/9-dependent cross-linking of tropomyosin-actin filaments.

cell biology↗