Polarization of cell growth in yeast II. The role of the cortical actin cytoskeleton

The actin cytoskeleton provides the structural basis for cell polarity in S accharomyces cerevisiae as well as most other eukaryotes, In Part I of this two-part commentary, presented in the previous issue of Journal of Cell Sc ience, we discussed the basis by which yeast establishes and maintains diff erent states of polarity through Rho GTPases and cyclin-dependent protein k inase signaling. Here we discuss how, in response to those signals, the act in cytoskeleton guides growth of the yeast cell. A polarized array of actin cables at the cell cortex is the primary structural determinant of polarit y. Motors such as class V myosins use this array to transport secretory ves icles, mRNA and organelles towards growth sites, where they are anchored by a cap of cytoskeletal and regulatory proteins. Cortical actin patches enha nce and maintain this,polarity, probably through endocytic recycling, which allows reuse of materials and prevents continued growth at old sites, The dynamic arrangement of targeting and recycling provides flexibility for the precise control of morphogenesis.