Cell cycle control of septin ring dynamics in the budding yeast.
ABSTRACT Septins constitute a cytoskeletal structure that is conserved in eukaryotes. In Saccharomyces cerevisiae, the Cdc3, Cdc10, Cdc11, Cdc12 and Shs1/Sep7 septins assemble as a ring that marks the cytokinetic plane throughout the budding cycle. This structure participates in different aspects of morphogenesis, such as selection of cell polarity, localization of chitin synthesis, the switch from hyperpolar to isotropic bud growth after bud emergence and the spatial regulation of septation. The septin cytoskeleton assembles at the pre-bud site before bud emergence, remains there during bud growth and duplicates at late mitosis eventually disappearing after cell separation. Using a septin-GFP fusion and time-lapse confocal microscopy, we have determined that septin dynamics are maintained in budding zygotes and during unipolar synchronous growth in pseudohyphae. By means of specific cell cycle arrests and deregulation of cell cycle controls we show that septin assembly is dependent on G1 cyclin/Cdc28-mediated cell cycle signals and that the small GTPase Cdc42, but not Rho1, are essential for this event. However, during bud growth, the septin ring shapes a bud-neck-spanning structure that is unaffected by failures in the regulation of mitosis, such as activation of the DNA repair or spindle assembly checkpoints or inactivation of the anaphase-promoting complex (APC). At the end of the cell cycle, the splitting of the ring into two independent structures depends on the function of the mitotic exit network in which the protein phosphatase Cdc14 participates. Our data support a role of cell cycle control mechanisms in the regulation of septin dynamics to accurately coordinate morphogenesis throughout the budding process in yeast.
Article: Spore germination in Saccharomyces cerevisiae: global gene expression patterns and cell cycle landmarks.[show abstract] [hide abstract]
ABSTRACT: Spore germination in the yeast Saccharomyces cerevisiae is a process in which non-dividing haploid spores re-enter the mitotic cell cycle and resume vegetative growth. To study the signals and pathways underlying spore germination we examined the global changes in gene expression and followed cell-cycle and germination markers during this process. We find that the germination process can be divided into two distinct stages. During the first stage, the induced spores respond only to glucose. The transcription program during this stage recapitulates the general transcription response of yeast cells to glucose. Only during the second phase are the cells able to sense and respond to other nutritional components in the environment. Components of the mitotic machinery are involved in spore germination but in a distinct pattern. In contrast to the mitotic cell cycle, growth-related events during germination are not coordinated with nuclear events and are separately regulated. Thus, genes that are co-induced during G1/S of the mitotic cell cycle, the dynamics of the septin Cdc10 and the kinetics of accumulation of the cyclin Clb2 all exhibit distinct patterns of regulation during spore germination, which allow the separation of cell growth from nuclear events. Taken together, genome-wide expression profiling enables us to follow the progression of spore germination, thus dividing this process into two major stages, and to identify germination-specific regulation of components of the mitotic cell cycle machinery.Genome biology 02/2007; 8(11):R241. · 6.63 Impact Factor