SpTpCdr2 · Spatio-temporal Control of Cell Division in Fission Yeast

Cytokinesis is a critical and irreversible step of cell cycle, which eventually separates daughter cells. This event is consequently subject to strict spatial and temporal regulations. Spatial integration of the DNA distribution and the global geometry of the cell are necessary to determine the proper division plane and ensure the successful genome and cytoplasmic segregation. Additionally, cells of a given cell type usually grow to a similar size, suggesting that cell dimensions can be monitored and controlled. Consequently, coordination of cell growth and cell division is essential for an appropriate cell size homeostasis. The fission yeast SAD kinase Cdr2 assembles a novel structure termed “midsome”, which is organized as medial cortical nodes. This structure includes a variety of proteins, including the anillin-like protein Mid1, a key factor in division plane positioning, and Wee1, which inhibits the entry into mitosis by phosphorylating Cdk. Two recent articles have demonstrated that the DYRK kinase Pom1 phosphorylates Cdr2, inhibiting it and excluding it from the cell tips. A gradient of Pom1 from the cell tips allows a differential inhibition of Cdr2 depending on its distance to the cell tips, thus, coupling cell size to the determination of the division plane and the cell cycle progression. Therefore, I propose to study the assembly and maintenance of the “midsome” analysing Cdr2 anchorage to the membrane, the molecular mechanism underlying the phosphorylaton of Cdr2 by Pom1, and the importance of membrane lipid composition on the localization of the “midsome”. Defining the role of the Cdr2 kinase in reading the spatial cues given by the cell tip protein Pom1 will also contribute to a better understanding of intracellular signals that trigger entry into mitosis.