Cell Polarization and Cytokinesis in Budding Yeast

Abstract

Asymmetric cell division, which includes cell polarization and cytokinesis, is essential for generating cell diversity during development. The budding yeast Saccharomyces cerevisiae reproduces by asymmetric cell division, and has thus served as an attractive model for unraveling the general principles of eukaryotic cell polarization and cytokinesis. Polarity development requires G-protein signaling, cytoskeletal polarization, and exocytosis, whereas cytokinesis requires concerted actions of a contractile actomyosin ring and targeted membrane deposition. In this chapter, we discuss the mechanics and spatial control of polarity development and cytokinesis, emphasizing the key concepts, mechanisms, and emerging questions in the field.

Endocytic Accessory Factors and Regulation of Clathrin-Mediated Endocytosis

“…In yeast, the endocytic budding events are distributed in a nonrandom manner dependent on the cell-cycle state (Bi and Park 2012). Initially, in unbudded cells the endocytic sites are equally distributed throughout the cell, but when the budding starts the endocytic events become highly concentrated into the growing daughter cell.…”

Fungal Morphogenesis

“…In budding yeast, the cell surface protein Axl2 acts in conjunction with the septin-associated proteins Bud3 and Bud4 to specify the axial budding pattern of mating-type a or a cells, whereas a distinct set of cell surface proteins (i.e., Bud8, Bud9, Rax1, Rax2) specify the bipolar pattern observed in a/a cells (Chant 1999). In either case, the landmarks trigger local activation of Cdc42 via the Ras-like GTPase Bud1 (Bi and Park 2012). In fission yeast, the plasma membrane-anchored protein Mod5 provides a target for the delivery of Tea1 via the plus ends of cytoplasmic microtubules (Snaith and Sawin 2003).…”

“…Nevertheless, careful regulation of depolarization presumably underlies much of the variation in cell shape that is observed in fungi. In S. cerevisiae, depolarization manifests as the "apical-to-isotropic" switch that enables the formation of an ellipsoidal yeast cell as opposed to more elongated pseudohyphae (Bi and Park 2012). In contrast, hyphae, by definition, undergo sustained polarized growth.…”

Protein kinase Gin4 negatively regulates flippase function and controls plasma membrane asymmetry

“…Given that inner leaflet PtdEth promotes inactivation of Cdc42-GTP by its GAPs and/or GDI (Cherfils and Zeghouf, 2013), our results connect Gin4 action to modulation of the level of active Cdc42, an essential and pivotal regulator of cell polarity and morphogenesis (Etienne-Manneville, 2004;Bi and Park, 2012). Gin4, by negatively regulating Fpk1, inhibits the flippases under Fpk1 control, lowers inner leaflet PtdEth content, thus reducing PtdEth-stimulated GAP Cdc42 (Rga1 and Rga2; Saito et al, 2007) and/or Rho GDI (Rdi1; Das et al, 2012) function, thereby maintaining or increasing the concentration of PM-associated GTP-bound Cdc42 (Fig.…”