TTBK2

Cilia effects upon perturbation of TTBK2

Cilia number / % ciliated:

Decreased cilia number

Loss-of-function effect:

Shorter cilia

Overexpression effect:

No effect

Ciliogenesis screen results (3 screens)

• Wheway et al. 2015 (siRNA) [siRNA]: Ciliogenesis Defect (z=-6.30) PMID:26167766
• Breslow et al. 2018 (CRISPR) [CRISPR]: Positive Regulator (Hh signaling, casTLE effect=-2.92) PMID:29459680
• Roosing et al. 2015 (siRNA) [siRNA]: No effect PMID:26595381

Phenotypes

Mouse phenotype:

preweaning lethality, complete penetrance, pretal lethality prior to heart atrial septation, embryonic lethality prior to tooth bud stage

Human ciliopathy phenotype:

spinocerebellar ataxia type 11

Ciliopathy associations

• Spinocerebellar Ataxia

Subcellular localization

basal body, centrosome, cilia, cytosol, nucleus, transition zone

Functional category

• Ciliary assembly/disassembly
• Actin & cytoskeleton regulation
• Cell migration & adhesion
• Transition zone
• Cilia length regulation

Function

Regulator of the initiation of ciliogenesis in vivo. Ttbk2 mutants lack cilia. Promotes the removal of CP110 from the mother centriole, the recruitment and retention of IFT proteins at the distal end of basal body, to initiate the assembly of the ciliary axoneme (23141541). Mutations have been associated with domi nt human neurodegenerative disorder Spinocerebellar Ataxia type 11 (18037885). Interacts in a complex with CP164, which is required for its ciliary localisation. Promotes assembly of distal appendages at both centrioles and Cep83 localisation (24982133). Phosphorylates Cep164, Cep97 and inhibits the interaction between Cep164 and Dvl3 (25297623). Phosphorylated CEP83, which is required for ciliary vesicle docking and CP110 removal (31455668). To investigate if elevated TTBK2 expression promoted ciliogenesis or extended cilia length, cells were subjected to serum starvation to induce cilia formation, but neither cilia formation nor cilia length was affected by TTBK2 overexpression (Fig. 3E–G), indicating that the increased frequency of ciliation by TTBK2 overexpression was not attributable to a promotion of ciliogenesis or cilia elongation.ciliogenesis, to regulate cilium stability (30532139). To examine if TTBK2 kinase activity is required for its function in GNP proliferation, we mutated TTBK2 residue D163 from aspartic acid to alanine (TTBK2KD) [24, 26] and expressed TTBK2KD in GNPs. Surprisingly, a majority of TTBK2KD-expressing cells exited the cell cycle and migrated prematurely to the IGL, indicating that TTBK2-dependent GNP proliferation relies on TTBK2 activity (Fig. 2E, F). By performing Arl13b staining, TTBK2 overexpression in GNPs increased the percentage of ciliated GNPs, indicating that elevated TTBK2 levels in GNPs stabilize primary cilia (Figs. 2G and S2B). Furthermore, in developing cerebella electroporated with TTBK2KD, proportions of ciliated GNPs were greatly reduced (Figs. 2G and S2B), confirming that TTBK2 supports GNP proliferation through TTBK2’s activity-dependent stabilization of primary cilia. (38879724)

Model organism evidence