Biology subjects

Ribas, J. C.

Publications and source records attributed to Ribas, J. C..

3 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↗

bioRxiv2025

PP6 phosphatase and Elongator contribute to kinesin 5-dependent spindle assembly by controlling microtubule regulator levels

Eukaryotic chromosome segregation relies on the assembly of a bipolar machinery based on microtubules (MTs), named the mitotic spindle. Formation of the mitotic spindle follows a force balance mechanism that ensures the proper capture and separation of sister chromatids. Many proteins have been involved in the establishment of this force balance, although kinesin 5 is well recognized as the major outward pushing force generator, since its inactivation results in monopolar, non-functional spindles. In order to find additional players in the force balance mechanism, we have performed a suppressor screen using a conditional allele of the fission yeast kinesin 5 ortholog Cut7. This screen identified that the lack of the PP6 phosphatase partially suppresses cut7 phenotypes, at least by defective translation of MT regulators, impacting on the force balance mechanism. Additionally, our data show that the Elongator complex, a target regulated by PP6 involved in tRNA modification, also ensures the force balance, albeit to a lesser extent. Importantly, this complex has been recently involved in direct MT polymerization in metazoans, a role probably not shared by its fission yeast counterpart. AUTHOR SUMMARYThe mitotic spindle is a cellular machine made of microtubules, which become arranged in a bipolar manner to capture and segregate chromosomes into the daughter cells during cell division. Spindle bipolarization relies on a force balance mechanism established by the function of many proteins, among which, the essential kinesin 5 is the major outward force generator. To discover novel proteins involved in the force balance, we have screened for suppressors of the kinesin 5 ortholog of fission yeast Cut7. Among the hits of the screen, we found that the lack of PP6 phosphatase components allow cut7 mutants form a bipolar spindle. Our results show that this suppression is, as least in part, mediated by the inactivation of Elongator, a complex that modifies tRNAs to facilitate the translation of specific mRNAs. Our results show that PP6 and Elongator participate in the efficient production of microtubule regulators that contribute to the proper generation of the force balance for spindle assembly.

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↗