Proteins involved in cell division have broad developmental functions.

Several proteins that are known to play a crucial role in mitosis may have alternative functions in embryogenesis. To test this hypothesis, we examined the spatial and temporal expression of the transcripts that encode proteins involved in mitosis throughout development, including those that encode for motor proteins, cytoskeletal elements and their modulators, vesicular transport, and cell cycle regulators. Results indicate that these transcripts have different expression patterns in various cell types. Interestingly, Cyclin Dependent Kinase 1 (CDK1), Polo Like Kinase 1 (PLK1), and Aurora kinase (Aurk) transcripts are expressed by endomesodermal cells of the blastula, the multipotent stem cells in coelomic pouches and/or the skeletogenic mesoderm of the gastrula that are not actively dividing. To further test that proteins important for mitosis may perform additional functions during embryogenesis, we treated embryos with CDK1, PLK1, and Aurk inhibitors, which resulted in a dose-dependent developmental arrest or delay and defects in gastrulation, skeletogenesis, and epithelial to mesenchymal transition. Further analysis indicates that the number of mesodermally-derived pigment cells is significantly less in CDK1 and PLK1 inhibited embryos and significantly increased in Aurk inhibited embryos. Importantly, the percentage of pigment cells undergoing cell proliferation in drug-treated embryos was not different than the control, indicating additional functions of CDK1, PLK1, and Aurk. Furthermore, PLK1 and Aurk may regulate ERK signaling to impact various developmental processes.