Role of ciliopathy proteins in the regulation of ciliogenesis and mitosis

Abstract

Primary cilia, antenna-like structures protruding from the cell surface, play roles in the reception and transduction of extracellular signals. Mutations in genes involved in the formation or function of cilia cause a broad spectrum of diseases referred as “ciliopathies” that include Joubert syndrome, Bardet-Biedl syndrome, and Oral-facial-digital syndrome. Frequent symptoms of ciliopathies are brain malformation, retinal degeneration, cystic kidney, bone malformation and obesity. Our laboratory has identified genes that are required for ciliogenesis, using genome-wide siRNA screening. Myosin heavy chain 10 (MYH10), one of the isoforms of non-muscle myosin II, was selected as a top screen hit. Here, I demonstrate that MYH10 is required for centriole migration to the apical plasma membrane, which is a prerequisite for ciliogenesis. The ciliogenesis defect in MYH10-depleted cells coincided with a reduction in the level of cortical actin filaments and its binding protein EZRIN. MYH10 knockdown interfered with centriolar migration and centrosomal recruitment of IFT88, which is required for the transport of building blocks to the ciliary tip.

JBTS17 is a newly identified ciliopathy gene mutated in Joubert syndrome and Oral-facial-digital syndrome. Here, I elucidate the subcellular localization of JBTS17 and its unexpected roles in mitotic progression. I found that JBTS17 is recruited to the ciliary basal body and required for the assembly of primary cilia. Remarkably, JBTS17 was detected at the kinetochores in mitotic cells. Depletion of JBTS17 caused a delay in the metaphase-anaphase transition. In addition, mitotic spindle angles were disturbed in JBTS-depleted cells. JBTS17 knockdown in mouse embryos inhibited both the mitotic progression of neural progenitors and the migration of differentiating neurons. Moreover, I present evidence that JBTS17 interacts with the Dynein regulator LIS1, and regulates the recruitment and mitotic functions of the Dynein-LIS1 complex. Therefore, I suggest cilia-independent roles of JBTS17, which may provide new insight on ciliopathy pathogenesis.