Regulation of Centrosome Duplication and Ciliogenesis

(Kobayashi et al., 2011; Spektor et al., 2007; Tsang et al., 2006; Chen et al., 2002)

The laboratory also focuses on understanding the molecular controls that govern mammalian centrosome duplication, which plays a pivotal role in cell cycle progression and mitosis, and ciliogenesis. Centrioles are required to fulfill a number of important roles during the cell cycle, establishing a microtubule organizing center in interphase and ensuring high fidelity chromosome separation in mitosis. In addition, centrioles have the capacity to act as basal bodies that nucleate the assembly of cilia. Although it was first described by Boveri over one hundred years ago, the centrosome remains largely enigmatic, and the controls that determine how and when centrosomes replicate are poorly defined. Further, while controls must be in place to regulate different centriolar fates—microtubule organizing activity in growing cells and primary cilium formation in quiescent and differentiated cells--key components that determine their fate remain largely undefined. We had previously identified a protein, CP110, that plays a key role in centrosome duplication and cytokinesis (Image 4).

Image 4: Localization of CP110, a centriolar protein

We have subsequently used biochemical approaches to purify complexes associated with CP110 and identified a novel centriolar protein, Cep97. Knockdown of Cep97 by RNAi or expression of dominant-negative mutants leads to CP110 displacement from centrosomes, mitotic spindle defects, and cytokinesis failure. Strikingly, loss of either Cep97 or CP110 results in primary cilia formation in cycling cells (Image 5), suggesting that Cep97 and CP110 work together to inhibit a ciliogenesis program in growing cells, when free centrioles are needed to ensure chromosome segregation. The primary cilium is a remarkable and relatively poorly understood organelle required for critical signal transduction pathways involved in normal cell proliferation and development. Loss of primary cilia plays a role in a host of human ciliary diseases, including retinal degeneration, renal disease, and a plethora of developmental abnormalities. Our ongoing, detailed characterization of CP110, Cep97, and other genes involved in key centriolar processes will enrich our understanding of the basic processes of centrosome duplication and ciliogenesis and shed light on human disease mechanisms associated with centrosomal and ciliary defects, enabling novel therapeutic strategies.

Image 5: Loss of CP110 or Cep97 promotes primary cilia assembly