Spatiotemporal expression of regulatory kinases directs the transition from mitotic growth to cellular morphogenesis

Abstract Embryogenesis depends on a tightly regulated balance between mitotic growth, differentiation, and morphogenesis. Understanding how the embryo uses a relatively small number of proteins to transition between growth and morphogenesis is a central question of developmental biology, but the mechanisms controlling mitosis and differentiation are considered to be fundamentally distinct. Here we show the mitotic kinase Polo, which regulates all steps of mitosis from mitotic entry to cytokinesis, also directs cellular morphogenesis after cell cycle exit. In mitotic cells, Aurora B (AurB) activates Polo to control a cytoskeletal regulatory module that directs cytokinesis. In the post-mitotic mesoderm of late stage embryos, the control of Polo activation transitions to the uncharacterized kinase Back Seat Driver (Bsd), where Bsd activates Polo to direct muscle morphogenesis. The transition between mitotic growth and morphogenesis is accomplished through the spatiotemporal transcriptional regulation of AurB and Bsd. The functions of Bsd and Polo are conserved, arguing that regulating kinase expression to activate cytoskeletal regulatory modules is a widely used strategy to direct cellular morphogenesis.