Roles of Cytokinetic Ring Proteins GCK-1 and CCM-3 in the C. elegans Zygote

Cancer often involves abnormalities at the cellular level, such as errors in cytokinesis, the physical partitioning of two daughter cells by means of an actomyosin contractile ring. Novel cytokinetic ring proteins, GCK-1, a serine/threonine kinase, and CCM-3, its cofactor, had been implicated in cell shape changes and Rho activity. While it was clear that both proteins regulate contractility, it was not clear what role they played in C. elegans zygote polarization and cytokinesis, two Rho-regulated contractile events. Here, we determined the roles of GCK-1 and CCM-3 during polarization and cytokinesis. We first tested their interdependence and found that GCK-1 is required for the cytoplasmic stability of CCM-3 and that CCM-3 targets GCK-1 to the cortex. We then examined protein enrichment on the cortex of the C. elegans zygote and found that both GCK-1 and CCM-3 were segregated to the anterior cortex in patches. To assess whether GCK-1 and CCM-3 regulated or were regulated by polarity proteins, we first depleted both proteins and found no resulting perturbance of polarity. We then depleted polarity proteins and found that the asymmetric distributions of GCK-1 and CCM-3 were diminished. Together, these results allowed us to conclude that GCK-1 and CCM-3 act downstream of polarity establishing proteins. Lastly, we measured contractility by tabulating ingression time, the size of the anterior polarity cap, and myosin recruitment to the cortex in order to assess the roles of GCK-1 and CCM-3 in cytokinesis. In doing so, we found that GCK-1 and CCM-3 negatively regulate contractility during cytokinesis in the C. elegans zygote by acting on RhoA. Understanding the regulation of cytokinesis has important implications in understanding the cytokinetic abnormalities that result in the formation of diseases such as cancer.Bachelor of Scienc