Biology subjects

Osumi, M.

Publications and source records attributed to Osumi, M..

4 recordsLinked to original sources

bioRxiv2026

Ectopic overproduction of cell wall glucan through membrane perturbation by an antifungal peptide theonellamide A in fission yeast

Ergosterol has multiple functions in filamentous fungi and yeasts, although only a part of the functions seems to be understood. An antifungal peptide, theonellamide A (TNM-A) induces drastic morphological changes in fission yeast cells by targeting plasma membrane ergosterol. TNM-A induces overproduction and ectopic accumulation of cell wall glucan at both growing tips and septum through a yet unknown mechanism. Here we show that TNM-A treatment causes accumulation of 1,3-{beta}-glucan at cell-polarity sites, not by increased activity of 1,3-{beta}-glucan synthase, but by an increased, persistent localization of the glucan synthase enzymes. Screening based on subcellular localization of proteins at periphery or polarity sites suggested the involvement of the Rho family GTPase Cdc42. In agreement, TNM-A induced both activation of Cdc42 and enhancement of membrane trafficking of glucan synthase enzymes. In conclusion, our chemical genetics analyses using TNM-A suggest that membrane ergosterol regulates the activity of Cdc42, which further regulates the localization of glucan synthases and cell wall biosynthesis. Highlights (four sentences)- Thenoellamide A (TNM-A) induces an ectopic overproduction of cell wall glucan. - TNM-A treatment causes increased, persistent localization of glucan synthases at the cell tips and septum. - TNM-A activates Cdc42 and upregulates membrane trafficking of glucan synthases. - Ergosterol is involved in proper activation/inactivation of Cdc42.

cell biology↗

bioRxiv2022

Fission yeast Smi1p participates in the synthesis of the primary septum by regulating β-1,3-glucan synthase Bgs1p function

Cytokinesis is the concluding step of the cell cycle. Coordination between multiple cellular processes is essential for the success of cytokinesis. The fission yeast, Schizosaccharomyces pombe, like other fungal cells is contained within a cell wall. During cell division, the external cell wall is extended inwards to form a special septum wall structure in continuity with the cell wall. The primary septum, the central component of the three-layered division septum, is enriched with linear {beta}-1,3-glucan formed by Bgs1p, a {beta}-1,3-glucan synthase. In this study we uncover a novel essential protein, Smi1p, that functions as a suppressor of the Bgs1p temperature-sensitive mutant, cps1-191. We observe a rescue in the cell wall composition and ultrastructure and also in actomyosin ring dynamics. Further, we identify a colocalization and physical association between Bgs1p and Smi1p. Altogether, our results indicate that Smi1p regulates the function of Bgs1p during cytokinesis.

cell biology↗

bioRxiv2020

Inhibition of cell membrane ingression at the division site by cell wall in fission yeast

Eukaryotic cells assemble an actomyosin ring during cytokinesis to function as a force-generating machine to drive membrane invagination, and to counteract the intracellular pressure and the cell surface tension. It is unclear whether additional factors such as the extracellular matrix (cell wall in yeasts and fungi) affect the actomyosin ring contraction. While studying the fission yeast {beta}-glucan synthase mutant cps1-191, which is defective in division septum synthesis and actomyosin ring contraction, we found that significantly weakening of the extracellular glycan matrix caused the spheroplasts to divide at the non-permissive condition. This division was dependent on a functional actomyosin ring and vesicular trafficking, but independent of normal septum synthesis. cps1-191 cells with weakened extracellular glycan matrix divide non-medially with a much slower ring contraction rate compared to wild type cells under similar conditions, which we term as cytofission. Interestingly, the high turgor pressure appears to play minimal roles in inhibiting ring contraction in cps1-191 mutants as decreasing the turgor pressure alone does not enable cytofission. We propose that during cytokinesis, the extracellular glycan matrix restricts actomyosin ring contraction and membrane ingression, and remodeling of the extracellular components through division septum synthesis relieves the inhibition and facilitates actomyosin ring contraction.

cell biology↗

bioRxiv2019

Nuclear actin cable with multiple branches during yeast meiosis

Actin polymerizes to form filaments/cables for motility, transport, and structural framework in a cell. Recent studies show that actin polymers are present not only in cytoplasm, but also in nuclei of vertebrate cells, and their formation is induced in response to stress. Here, by electron microscopic observation with rapid freezing and high-pressure freezing, we found a unique bundled structure containing actin in nuclei of budding yeast cells undergoing meiosis. The nuclear bundle/cable during meiosis consists of multiple filaments with a rectangular lattice arrangement often showing "feather-like" appearance. The bundle is immuno-labeled with anti-actin antibody and sensitive to an actin-depolymerizing drug. Like cytoplasmic bundles, nuclear bundles with actin are rarely seen in pre-meiotic cells and spores, and are induced during meiotic prophase-I. The formation of the nuclear bundles/cables is independent of meiotic DNA double-stranded breaks. We speculate that nuclear bundles/cables containing actin play a role in nuclear events during meiotic prophase I.

cell biology↗