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Abstract Cdc42, a Rho-family GTPase, is a master regulator of cell polarity. Recently, it has been shown that Cdc42 also facilitates proper cytokinesis in the fission yeast Schizosaccharomyces pombe. Cdc42 is activated by two partially redundant GEFs, Gef1 and Scd1. Although both GEFs activate Cdc42, their deletion mutants display distinct phenotypes, indicating that they are differentially regulated by an unknown mechanism. During cytokinesis, Gef1 localizes to the division site and activates Cdc42 to initiate ring constriction and septum ingression. Here, we report that the F-BAR protein Cdc15 promotes Gef1 localization to its functional sites. We show that cdc15 promotes Gef1 association with cortical puncta at the incipient division site to activate Cdc42 during ring assembly. Moreover, cdc15 phospho-mutants phenocopy the polarity phenotypes of gef1 mutants. In a hypermorphic cdc15 mutant, Gef1 localizes precociously to the division site and is readily detected at the cortical patches and the cell cortex. Correspondingly, the hypermorphic cdc15 mutant shows increased bipolarity during interphase and precocious Cdc42 activation at the division site during cytokinesis. Finally, loss of gef1 in hypermorphic cdc15 mutants abrogates the increased bipolarity and precocious Cdc42 activation phenotype. We did not see any change in the localization of the other GEF Scd1 in a Cdc15-dependent manner. Our data indicate that Cdc15 facilitates Cdc42 activation at the division site during cytokinesis at the cell cortex to promote bipolarity and this is mediated by promoting Gef1 localization to these sites.
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Endocytic patch dynamics are differentially regulated at distinct cell sites in fission yeast
Endocytosis promotes polarity and growth in eukaryotes. In Schizosaccharomyces pombe fission yeast, endocytosis occurs at the polarized cell ends and division site and at the non-polarized cell sides. Our characterization of endocytic actin patches show that they are differentially regulated. The patches at the cell ends and division site internalize successfully while those at the sides are weak and erratic. The major regulator of cell polarity, Cdc42, and its target Pak1 kinase only localize to the cell ends and division site. We find that these proteins regulate assembly and internalization of patches at these sites but not at the cell sides. Moreover, Cdc42 specifically activated by the GEF Gef1 promotes proper patch dynamics. Endocytosis requires phosphorylation of the Type I Myosin Myo1 by the Pak1 kinase. Myo1 localizes to the cell ends, division site, and the cell sides. We find that unlike Cdc42 and Pak1, Myo1 also promotes patch assembly at the cell sides. Our data indicate that while Myo1 can globally promote branched actin assembly, successful endocytic patch dynamics and internalization at polarized sites require Cdc42 and Pak1 kinase.
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- Award ID(s):
- 2309328
- PAR ID:
- 10631627
- Publisher / Repository:
- The Company of Biologists
- Date Published:
- Journal Name:
- Journal of Cell Science
- ISSN:
- 0021-9533
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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