MOLECULAR BIOLOGY AND GENETICS PhD THESIS DEFENSE BY MELİS DİLARA ARSLANHAN GÜL

Title: Dissecting the regulation of the centrosome/cilium complex biogenesis using proximity-based proteomics

 Speaker: Melis Dilara Arslanhan Gül

 Time: August, 12, 2022, 13:00

 Thesis Committee Members:

Assoc. Prof.  Elif Nur Fırat Karalar (Advisor, Koç University)

Assist. Prof. Ayşe Koca Çaydaşı (Koç University)

Assoc. Prof. Umut Şahin (Boğaziçi University)

Prof. Dr. Kemal Sami Korkmaz (Ege University)

Prof. Dr. Yusuf Baran (İzmir Institute of Technology)

Abstract:

Centrosome is the main microtubule organizing center composed of a pair of centrioles which are cylindrical shaped microtubule-based structures are characterized by a nine-fold symmetry of microtubule triplets. The rigid structure of the centrioles is essential for proper functioning of not only the centrosome in cellular processes such as cell division but also formation of centrosome-based structures such as primary cilium. Primary cilium acts as the antenna of the cells to sense the signals. Defects in primary cilium formation and function causes many diseases including ciliopathies and cancer. Regulation of centrosome/cilium complex by the centrosomal proteins are crucial for the biogenesis and proper function. However, the proteins involved in these processes and their functions in centrosome/cilium complex are not completely understood.

In the first chapter of my thesis, I investigated the mechanisms by which the centrosome/cilium complex biogenesis is regulated by studying the very well characterized kinase implicated in cell cycle called Aurora Kinase A (AURKA). I applied BioID technique to AURKA to investigate the cell cycle independent functions of it and I found that AURKA interacts with PCM1 which is the scaffolding proteins of the centriolar satellites. Depletion of centriolar satellites by RNAi treatment showed that the abundance of AURKA and p-AURKA increased at the centrosome which is caused by an increased stability of AURKA. Finally, loss of satellites activated AURKA at the basal body, decreased centrosomal IFT88 levels and caused ciliogenesis defects. Collectively, my results uncover proteostatic regulation of AURKA by satellites as a new mechanism for its ciliary functions.

In the second chapter of my thesis, I focused on understanding the regulation of centrosome/cilium complex by studying the centriolar core proteins that have structural roles for the stability of the centrioles. I have applied BioID technique to the previously characterized centriolar proteins POC5 and Centrin-2 and identified a novel centriolar core protein called CCDC15. With the help of a new technique called ultrastructural expansion microscopy (U-ExM), I have showed that CCDC15 localizes to the centriolar inner core where it interacts with POC1B, POC5, FAM161A, Centrin-2 and Centrin-1. Loss of function studies showed that CCDC15 regulates the centriole length and stability. Moreover, I showed that the depletion of CCDC15 caused defective and non-functional cilium formation. Altogether these results reveal new components of centriole core and its crucial functions during centriole structure and primary cilium biogenesis.