One ring to bind them all at the centre of the cell
Résumé
In animal cells and fungi, cytokinesis is achieved by constriction of an actomyosin-based ring assembled during mitosis. The fission yeast Schizosaccharomyces pombe is an excellent model organism for unraveling cell division controls by combining molecular genetics with cell biology approaches. Once spatially defined, the ring assembly site is the place of sequential incorporation of a set of proteins during mitotic progression, most of which are evolutionarily conserved. Then, fission yeast divides medially to produce equally sized daughter cells. In the past years, several studies have explored mechanisms of division site determination. It has been demonstrated that positive signals for division plane positioning originate from the central region. Position of the predivided nucleus and the anilin-related protein Mid1 give spatial cues to establish the place of ring formation. In addition, negative signals controlled by the DYRK Pom1 kinase and emanating from the cell ends restrict ring formation in the central region. This dual system prevents illegitimate cell division outside the centre of the cell and subsequent polyploid cell formation. Recently, it has been shown that the mitotic regulator Cdr2 kinase is intrinsically involved in division plane specification by binding to Mid1 at the cell equator during interphase. Moreover, nuclear-to-cytoplasm shuttling of Mid1 is another independent crucial mechanism that couples nuclear position with the actomyosin ring assembly site late in the G2 phase. Kin1, another kinase that regulates morpho-genesis and intracellular organization, shares an essential function with Pom1 in cytokinesis. Recent advances have also identified distinct pathways involved in completion of CAR formation. Therefore, multiple regulatory mechanisms act in parallel to accurately specify and build up the actomyosin ring at the centre of the cell. Concomitant inhibition of these pathways dramatically affects cytokinesis and cell viability. Here we present these redundant pathways that contribute to faithful distribution of the genetic material into daughter cells.