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 shows that they are differentially regulated. The patches at the cell ends and division site internalize successfully, whereas those at the sides are weak and erratic. The major regulator of cell polarity, Cdc42, and its target Pak1 kinase (also known as Shk1 and Orb2) 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 guanine-nucleotide-exchange factor (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 although Myo1 can globally promote branched actin assembly, successful endocytic patch dynamics and internalization at polarized sites require Cdc42 and Pak1 kinase.