The mitotic exit network (MEN), a protein kinase cascade under the switch-like control of the small GTPase Tem1, triggers exit from mitosis in budding yeast. Now it emerges that signals from both Tem1 and the yeast Polo kinase Cdc5 converge onto the MEN kinase Cdc15 to accurately restrict MEN activation to late mitosis.
"The process of cell separation is regulated by the RAM network (Regulation of Ace2 and Morphogenesis) (Saputo et al., 2012), whose activation is closely linked to the completion of mitosis and cytokinesis. In S. cerevisiae exit from mitosis and entry into cytokinesis is controlled by the Mitotic Exit Network (MEN) a GTPase regulated kinase cascade (reviewed in Bardin and Amon, 2001; de Bettignies and Johnston, 2003; McCollum and Gould, 2001; Segal, 2011). A similar cascade, the Septation Initiation Network (SIN), has been reported in Schizosaccharomyces pombe and Aspergillus nidulans, although in these organisms its primary role appears to be in regulating septation rather than mitotic exit (Bruno et al., 2001; Kim et al., 2006; Kim et al., 2009; Krapp et al., 2004). "
[Show abstract][Hide abstract] ABSTRACT: Candida albicans demonstrates three main growth morphologies: yeast, pseudohyphal and true hyphal forms. Cell separation is distinct in these morphological forms and the process of separation is closely linked to the completion of mitosis and cytokinesis. In Saccharomyces cerevisiae the small GTPase Tem1 is known to initiate the mitotic exit network, a signalling pathway involved in signalling the end of mitosis and initiating cytokinesis and cell separation. Here we have characterised the role of Tem1 in C. albicans, and demonstrate that it is essential for mitotic exit and cytokinesis, and that this essential function is signalled through the kinase Cdc15. Cells depleted of Tem1 displayed highly polarised growth but ultimately failed to both complete cytokinesis and re-enter the cell cycle following nuclear division. Consistent with its role in activating the mitotic exit network Tem1 localises to spindle pole bodies in a cell cycle-dependent manner. Ultimately, the mitotic exit network in C. albicans appears to co-ordinate the sequential processes of mitotic exit, cytokinesis and cell separation.
[Show abstract][Hide abstract] ABSTRACT: Sequential transfer of information from one enzyme to the next within the confines of a protein kinase scaffold enhances signal transduction. Though frequently considered to be inert organizational elements, two recent reports implicate kinase-scaffolding proteins as active participants in signal relay.
Current biology: CB 06/2013; 23(12):R515-R517. DOI:10.1016/j.cub.2013.05.002 · 9.57 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Fifty years of genetic and molecular experiments have revealed a wealth of molecular interactions involved in the control of cell division. In light of the complexity of this control system, mathematical modeling has proved useful in analyzing biochemical hypotheses that can be tested experimentally. Stochastic modeling has been especially useful in understanding the intrinsic variability of cell cycle events, but stochastic modeling has been hampered by a lack of reliable data on the absolute numbers of mRNA molecules per cell for cell cycle control genes. To fill this void, we used fluorescence in situ hybridization (FISH) to collect single molecule mRNA data for 16 cell cycle regulators in budding yeast, Saccharomyces
cerevisiae. From statistical distributions of single-cell mRNA counts, we are able to extract the periodicity, timing, and magnitude of transcript abundance during the cell cycle. We used these parameters to improve a stochastic model of the cell cycle to better reflect the variability of molecular and phenotypic data on cell cycle progression in budding yeast.
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