Primary cilia are microtubule-based cellular projections that play an essential role in developmental signaling pathways, particularly the development of the central nervous system. Defects in cilia formation and structure are associated with a broad spectrum of human genetic diseases disrupt a variety of tissues, including the brain and CNS. The importance of cilia in human health is now well established, however a number of important questions remain, including how cilia assembly is regulated, and whether cilia mediate pathways important for tissue homeostasis in adults in addition to their role in regulating developmental signaling pathways. To begin to address these questions, I will make use of a unique ENU-induced mouse mutant I have begun to characterize during my postdoctoral studies, which is a null allele of Tau tubulin kinase 2 (Ttbk2). We found using this allele that Ttbk2 is required for ciliogenesis, and independent studies linked Ttbk2 to the human neurodegenerative disorder spinocerebellar ataxia type 11 (SCA11). To further examine the link between cilia and neural development and disease I will: (1) Define the pathway in which TTBK2 acts to control cilia formation;(2) Identify additional substrates of TTBK2 important in cilia formation;and (3) Characterize the requirements for TTBK2 and TTBK1 in the nervous system. The mentored phase of this award will be carried out at Sloan-Kettering Institute (SKI) under the mentorship of Dr. Kathryn Anderson. During this phase, I will have the opportunity to complement my strong foundation in developmental genetics by gaining experience in biochemistry and in neurobiology. In this period, I will use cell biological, biochemical and proteomic approaches to identify substrates of Ttbk2 required for ciliogenesis (Aims 1 and 2) with guidance from two SKI faculty members, Drs. Bryan Tsou and Prasad Jallepalli, who have agreed to serve on my advisory committee. Also during this period, I will use conditional alleles of Ttbk1 and Ttbk2 to analyze developmental phenotypes within the CNS, focusing on the cerebellum, the tissue affected in SCA11 (Aim 3), with guidance from my third advisory committee member, Dr. Alexandra Joyner, who is a leading expert on the development of the cerebellum. During the independent phase of the grant, I will continue to define the developmental phenotypes of the Ttbk2 and Ttbk1 conditional mutants and use the conditional alleles to examine the requirements for these genes in the adult nervous system. In this analysis I will test whether the phenotypes of Ttbk conditional mutants are due to disruptions in ciliary signaling by comparing these phenotypes to those of conditional mutants of Ift88 and Kif3a, two proteins essential for ciliogenesis. Thus through these studies, I will further define the requirements for cilia in the CNS as well as examine the cellular basis of a human neurodegenerative disorder, SCA11.
Primary cilia play an essential role in mediating developmental signaling pathways, but their role in adult onset neurological disorders is less clear. Ttbk2 is both essential for cilia formation, and is mutated in human patients with a neurodegenerative disease. Thus, studying the role of Ttbk2 within the developing and adult CNS could establish whether cilia-mediated signaling pathways are linked to neurodegeneration.