Abstract

Cytokinesis is a well-conserved process where one cell divides into two daughters, and must be tightly regulated to prevent aneuploidy and fate changes. The mitotic spindle regulates the assembly and ingression of an actomyosin ring that pinches in the cortex. Though less understood, microtubule-independent mechanisms also regulate cytokinesis and their requirement may vary depending on cell type. Our lab discovered that a novel chromatin pathway signals through Ran-GTP to regulate cytokinesis in human cells, and my thesis explored the biological relevance of this pathway in Caenorhabditis elegans embryos. Our model is that importin-alpha or beta forms an inverse gradient to Ran-GTP and facilitates the recruitment and/or activation of contractile regulators. To test this model, I explored the requirement of the Ran pathway in regulating cytokinesis of P0 (one-celled zygote), AB (anterior daughter) and P1 (posterior daughter fated to be germline) cells. I found that each cell has unique ingression kinetics, and reducing Ran-GTP by partial RNAi of RCC-1 (Ran-GEF) increased their rate of ingression. Through co-depletion experiments, I found that the Ran pathway regulates ANI-1 (anillin) in P0 and AB cells, but not in P1 cells. Anillin is a scaffold that coordinates cytokinesis and is directly regulated by importin in human cells. I also found that regulators of contractility, such as ECT-2 (RhoA GEF) and LET-502 (Rho binding kinase) are in the Ran pathway in P0, AB and P1 cells. Thus, the Ran pathway regulates cytokinesis in all cell types, but the molecular effectors vary depending on cell type.