Cby1 promotes Ahi1 recruitment to a ring-shaped domain at the centriole-cilium interface and facilitates proper cilium formation and function.
Bottom Line: Defects in centrosome and cilium function are associated with phenotypically related syndromes called ciliopathies.Superresolution microscopy using both three-dimensional SIM and STED reveals that Cby1 localizes to an ∼250-nm ring at the distal end of the mature centriole, in close proximity to Ofd1 and Ahi1, a component of the transition zone between centriole and cilium.This suggests that Cby1 is required for efficient recruitment of Ahi1, providing a possible molecular mechanism for the ciliogenesis defect in Cby1(-/-) cells.
Affiliation: Department of Biology, Stanford School of Medicine, Stanford University, Stanford, CA 94305.Show MeSH
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Mentions: The primary cilium is a signaling center for several pathways, and concentration of signaling proteins in the cilium compartment is essential to proper signaling (Berbari et al., 2009; Mahjoub and Stearns, 2012). Arl13b is a cilium-localized small GTPase that regulates cilium morphology and ciliary trafficking (Caspary et al., 2007; Duldulao et al., 2009; Cevik et al., 2010; Larkins et al., 2011). Loss of Arl13b in the zebrafish scorpion mutant results in cystic kidneys (Sun et al., 2004; Cantagrel et al., 2008), and mutations in ARL13B are causative for the ciliopathy Joubert syndrome (Cantagrel et al., 2008). We examined the localization of Arl13b to cilia in Cby1+/+ and Cby1−/− MEFs. The amount of ciliary Arl13b in Cby1−/− MEFs was reduced twofold compared with Cby1+/+ MEFs (Figure 3, A and B), and this reduction could be complemented by a human GFP-Cby1 construct (Figure 3, D and E). The amount of ciliary acetylated α-tubulin was similar in Cby1+/+ and Cby1−/− MEFs (Figure 3, A and C). Despite the reduction of ciliary Arl13b in Cby1−/− MEFs, these cells retained the ability to control protein access to the ciliary compartment, as assessed by recruitment of the transmembrane protein Smoothened (Smo) in response to treatment with Smo agonist (SAG), an activator of the pathway (Supplemental Figure S1).
Affiliation: Department of Biology, Stanford School of Medicine, Stanford University, Stanford, CA 94305.