Cilia are versatile, microtubule-based organelles that facilitate cellular signaling, motility, and environmental sensing in eukaryotic cells. These dynamic structures act as hubs for key developmental signaling pathways, while their assembly and disassembly are intricately regulated along cell cycle transitions. Recent findings show that factors regulating ciliogenesis and cilia dynamics often integrate their roles across other cellular processes, including cell cycle regulation, cytoskeletal organization, and intracellular trafficking, ensuring multilevel crosstalk of mechanisms controlling organogenesis. Disruptions in these shared regulators lead to broad defects associated with both ciliopathies and cancer. This review explores the crosstalk of regulatory mechanisms governing cilia assembly, disassembly, and maintenance during ciliary signaling and the cell cycle, along with the broader implications for development, tissue homeostasis, and disease.

• Keywords
• Cancer, Cell cycle regulation, Cilia, Ciliary dynamics, Ciliary signaling, Ciliopathies, Tissue development,
• Publication type
• Journal Article MeSH
• Review MeSH

BACKGROUND: Primary cilia facilitate cellular signalling and play critical roles in development, homeostasis, and disease. Their assembly is under the control of Tau-Tubulin Kinase 2 (TTBK2), a key enzyme mutated in patients with spinocerebellar ataxia. Recent work has implicated TTBK2 in the regulation of cilia maintenance and function, but the underlying molecular mechanisms are not understood. METHODS: To dissect the role of TTBK2 during cilia growth and maintenance in human cells, we examined disease-related TTBK2 truncations. We used biochemical approaches, proteomics, genetic engineering, and advanced microscopy techniques to unveil molecular events triggered by TTBK2. RESULTS: We demonstrate that truncated TTBK2 protein moieties, unable to localize to the mother centriole, create unique semi-permissive conditions for cilia assembly, under which cilia begin to form but fail to elongate. Subsequently, we link the defects in cilia growth to aberrant turnover of a microtubule-depolymerizing kinesin KIF2A, which we find restrained by TTBK2 phosphorylation. CONCLUSIONS: Together, our data imply that the regulation of KIF2A by TTBK2 represents an important mechanism governing cilia elongation and maintenance. Further, the requirement for concentrating TTBK2 activity to the mother centriole to initiate ciliogenesis can be under specific conditions bypassed, revealing TTBK2 recruitment-independent functions of its key partner, CEP164.

• Keywords
• Basal body, Cilia, Ciliogenesis, KIF2A, TTBK2,
• MeSH
• Cilia * metabolism   MeSH
• Phosphorylation MeSH
• Kinesins * metabolism   MeSH
• Humans MeSH
• Microtubules * metabolism   MeSH
• Protein Serine-Threonine Kinases * metabolism   genetics   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• KIF2A protein, human MeSH Browser
• Kinesins * MeSH
• Protein Serine-Threonine Kinases * MeSH
• tau-tubulin kinase MeSH Browser

Primary cilia are key regulators of embryo development and tissue homeostasis. However, their mechanisms and functions, particularly in the context of human cells, are still unclear. Here, we analyzed the consequences of primary cilia modulation for human pluripotent stem cells (hPSCs) proliferation and differentiation. We report that neither activation of the cilia-associated Hedgehog signaling pathway nor ablation of primary cilia by CRISPR gene editing to knockout Tau Tubulin Kinase 2 (TTBK2), a crucial ciliogenesis regulator, affects the self-renewal of hPSCs. Further, we show that TTBK1, a related kinase without previous links to ciliogenesis, is upregulated during hPSCs-derived neural rosette differentiation. Importantly, we demonstrate that while TTBK1 fails to localize to the mother centriole, it regulates primary cilia formation in the differentiated, but not the undifferentiated hPSCs. Finally, we show that TTBK1/2 and primary cilia are implicated in the regulation of the size of hPSCs-derived neural rosettes.

• MeSH
• Centrioles metabolism   MeSH
• Cilia metabolism   MeSH
• Humans MeSH
• Pluripotent Stem Cells * metabolism   MeSH
• Protein Serine-Threonine Kinases genetics   metabolism   MeSH
• Hedgehog Proteins * genetics   metabolism   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Protein Serine-Threonine Kinases MeSH
• Hedgehog Proteins * MeSH
• tau-tubulin kinase MeSH Browser