Polarity establishment is essential for cell division and growth in Schizosaccharomyces pombe, which transitions between monopolar and bipolar growth, also termed as new end take off (NETO). The contractile ring protein Fic1 has been shown to be important for NETO. In addition, phosphorylation of cytokinetic proteins can modulate their localisation and function during cell cycle progression. Building on their previous work, Kathleen Gould and colleagues (Bohnert et al., 2020) now identify the phosphorylation sites in Fic1 that influence NETO establishment. Fic1 is constitutively phosphorylated during the cell cycle on two residues in its C-terminus. By mutating both sites, the authors generated phospho-ablated (Fic1-2A) and phospho-mimetic (Fic1-2D) forms of Fic1. Similarly to fic1Δ mutants, both phosphomutants display defects in bipolar growth and promote a dimorphic change from a unicellular state to the formation of pseudohyphae. Interestingly, Fic1 is phosphorylated in vitro by Cdk1 and Orb5, kinases known to regulate polarised growth; however, single or double mutants for these kinases do not impair Fic1 phosphorylation. Also, another 111 different kinase mutants, as well as 11 kinase double mutants, did not show any defects in Fic1 phosphorylation, suggesting that several kinases act together to regulate the phospho-state of Fic1. Thus, this study provides insight into the phospho-regulatory processes that connect cytokinesis and polarised growth in S. pombe.
