| The eukaryotic primary cilium is a solitary, antenna-like projection from the surface of a cell, critical for sensing the extracellular environment. Many mammalian cell types have a primary cilium, which acts as a hub for different signaling pathways depending upon the cell type. Primary cilia play an important role in cell differentiation and cell fate determination in response to rapidly switching cues during embryonic development. Due to the widespread occurrence of primary cilium in different tissues, mutation in proteins affecting cilia structure can present a wide variety of developmental defects and sensory disorders, collectively termed ciliopathies.;A microtubule-based scaffold, known as the axoneme, forms the core of the primary cilium. The structure of the axoneme is highly conserved across different eukaryotic species. However, mechanisms that regulate the structure and microtubule dynamics in the axoneme are poorly understood. TOG domain array-containing proteins ch-TOG and CLASP are key regulators of cytoplasmic microtubules. Whether TOG array proteins also regulate ciliary microtubules is unknown. In this dissertation, we have identified the conserved Crescerin protein family as a cilia-specific TOG array-containing microtubule regulator. We present the crystal structure of mammalian Crescerin1 TOG2, revealing a canonical TOG fold with conserved tubulin-binding determinants. Crescerin1's TOG domains possess inherent microtubule-binding activity and promote microtubule polymerization in vitro. Using Cas9-triggered homologous recombination in Caenorhabditis elegans, we demonstrate that the worm Crescerin family member CHE-12 requires TOG domain-dependent tubulin-binding activity for sensory cilia development. Thus, Crescerin expands the TOG domain array-based MT regulatory paradigm beyond ch-TOG and CLASP, representing a distinct regulator of cilia structure. |
