Studies on thefunction of centrosomal proteins, CPAP and CP110

Abstract

A centrosome consists of a pair of centrioles embedded in pericentriolar materials (PCM). Like chromosomes, centrioles duplicate and segregate into the daughter cells. Centriole duplication is strictly regulated to occur once per cell cycle. Abnormalities in the number of centrioles lead to chromosome instability and tumor formation. During mitosis, centrosomes prepare to become spindle poles and undergo maturation which PCM is accumulated at the centrosome to possess a strong microtubule organizing activity. If the centrosomes fail to become mature, the chromosomes do not properly segregate to daughter cells. Therefore, it is essential to elucidate precise mechanisms of centrosome duplication and maturation during the cell cycle. Here, I investigated the functions of two centrosomal proteins, CPAP (Centrosomal protein 4.1-associated protein) and CP110 (Centrosomal protein of 110kDa) to study centrosome maturation and duplication. In Chapter 1, I investigated biological roles of CPAP in centrosome maturation. It is known that CPAP functions in centriole assembly and elongation. I found that CPAP is also critical for centrosome maturation during mitosis. The CPAP function in centrosome maturation is independent of centriole duplication. Depletion of CPAP eventually resulted in asymmetric spindle pole formation during mitosis. Asymmetric spindle pole indicates that the mitotic spindle pole have uneven amount of PCM. In chapter 2, I investigated biological roles of CP110 in centriole duplication. PLK4 is a critical kinase in centriole assembly. However, direct substrates of PLK4 remain elusive. I demonstrated that CP110 is phosphorylated by PLK4 in vivo. This phosphorylation is prerequisite of the centriole assembly. The phosphorylated CP110 is recruited at the proximal end of the daughter centrioles at an early stage of centriole assembly. Based on these results, I propose that phosphorylation of CP110 by PLK4 is a critical step for stabilization of the recruited centriole components.