Preview

PDF, English Download (23MB) | Terms of use

Abstract

The centrosome is a membrane-less organelle and in eukaryotes the main microtubuleorganizing center (MTOC). Due to its ability to nucleate and organize microtubules (MT), it plays an important role in cell division, ciliogenesis, cell polarity and cell migration. Therefore, it is not surprising that disfunction of centrosomes has devastating consequences for an organism, leading to various diseases ranging from cancer and ciliopathies to mental and behavioural disorders. The centriole, as the basic structure of the centrosome, is crucial to ensure centrosomal function. Structural defects of centrioles have direct consequences on centrosome function. One factor contributing to the centriolar stability is the inner scaffold, a ring-like substructure in the lumen of the central-to-distal half of the centriole. Based on their localization, POC1B (proteome of centriole 1B), POC5, FAM161A and CCDC15 are suggested inner scaffold components, however, the relationship between these proteins and if other proteins are part of the inner scaffold is still unclear. Here, I identified POC1A, the human paralogue of POC1B, as a novel inner scaffold component and investigated the function of the two human POC1 proteins within the inner scaffold. Both POC1 proteins are inner centriole proteins with overlapping localization. However, while POC1A resides closer towards the centriole lumen, POC1B is in proximity to the centriole wall. Loss of POC1A or POC1B affects the centriolar localization of inner scaffold components like POC5, FAM161A, Centrin and CCDC15. Based on the results presented in this study, POC1APOC1B heterodimers organize the complex protein network of the inner scaffold by crosslinking different proteins. This is achieved by the ability to interact with various proteins through different interaction modes mediated by their N-terminal WD40 domain, C-terminal coiled-coil region, or both. Crucial for the inner scaffold is the interaction between POC1A and POC5, and the ability of POC5 to form a tetramer. POC1A-POC1B heterodimers interact with the MT-binding proteins FAM161A and MDM1, which may lead to a positioning of the POC5 tetramer close to the centriolar wall. Disruption of the inner scaffold leads to broken centrioles and mitotic defects, confirming the importance of the inner scaffold in maintaining centriole integrity. In addition, this study shows that combined loss of POC1A and POC1B results in complete disintegration of centrioles, highlighting their role in centriole biogenesis and stability.