Characterization of the Chibby family of centrosomal proteins
- The Chibby protein antagonizes Wnt/Beta-Catenin signaling, a prominent regulator pathway of development, via direct interaction with the transcriptional activator domain of Beta-Catenin. Chibby mutant mice have a defect in the formation of motile cilia in the airway epithelium. The centrosome is the major microtubule organizing center of animal cells and includes two centrioles, termed mother and the daughter based on their age and replicative history. The mother harbors subdistal and distal appendages, which, respectively, anchor the interphase microtubule array and are required for ciliation. Several lines of published evidence suggest a link between the primary cilium, a single, non-motile structure found on many cells, and Wnt/Beta-Catenin signaling. Based on this evidence I investigated Chibby, and related members of the Chibby protein family, to determine its role in centrosome and cilium structure and function. I report here that the Chibby family of proteins is associated physically and functionally with the centrioles of the centrosome in mammalian cells. The Chibby family consists of Chibby (Cby1), Nurit/Cby2, and the previously uncharacterized, Chibby3 (Cby3). Fluorescence microscopy revealed that Cby1 localized to the mother centriole of the centrosome, and that this localization was partially shared with Nurit/Cby2 and Cby3. Cby1 colocalizes at the mother centriole with phospho-Beta-Catenin, a modified form of Beta-Catenin that, in some contexts it is targeted for proteasome-mediated degradation. I also found that Cby1 partially colocalized with phospho-Beta-Catenin at a ring-like structure at the midbody during cytokinesis, where they might regulate abscission. The localization of Cby1 to the mother centriole was similar to that described for proteins for the distal appendages of the mother centriole. I found that Cby1 colocalized with, and exhibited cell cycle dynamics similar to, Cep164, a known distal appendage protein that is required for primary cilium formation. Consistent with a role for Cby1 in these centriolar structures, Cby1-/- mouse embryonic fibroblasts exhibited a strong reduction in primary cilium formation that could be complemented by expression of the wild-type Cby1 protein. Remarkably, overexpression of either GFP-tagged Beta-Catenin or GFP-Cby1 in hTERT-RPE1 cells resulted in fewer, but longer, cilia than controls suggesting that both of these proteins are important for structure and function of the primary cilium. In summary, I propose that Cby1 is associated with the distal appendages of the mother centriole, that defects in those structures are the likely cause of the failure of cilium formation in cells lacking Cby1, and that both primary and motile cilia display this requirement for Cby1.
|Type of resource
|electronic; electronic resource; remote
|1 online resource.
|Santé, Joshua Martin
|Stanford University, Department of Biological Sciences
|Nelson, W. J. (W. James)
|Nelson, W. J. (W. James)
|Statement of responsibility
|Joshua Martin Santé.
|Submitted to the Department of Biological Sciences.
|Thesis (Ph.D.)--Stanford University, 2010.
- © 2010 by Joshua Martin Sante
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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