A CCRK and a MAK Kinase Modulate Cilia Branching and Length via Regulation of Axonemal Microtubule Dynamics in Caenorhabditis elegans

Abstract

The diverse morphologies of primary cilia are tightly regulated as a function of cell type and cellular state. CCRK and MAK-related kinases have been implicated in ciliary length control in multiple species, although the underlying mechanisms are not fully understood. Here we show that in C. elegans , DYF-18/CCRK and DYF-5/MAK act in a cascade to generate the highly arborized cilia morphologies of the AWA olfactory neurons. Loss of kinase function results in dramatically elongated AWA cilia that lack branches. IFT motor protein localization but not velocities in AWA cilia are altered upon loss of dyf-18 . We instead find that axonemal microtubules are decorated by the EBP-2 end-binding protein along their lengths, and that the tubulin load is increased, and tubulin turnover is reduced, in AWA cilia of dyf-18 mutants. Moreover, we show that predicted microtubule-destabilizing mutations in two tubulin subunits, as well as mutations in IFT proteins predicted to disrupt tubulin transport, restore cilia branching and suppress AWA cilia elongation in dyf-18 mutants. Loss of dyf-18 is also sufficient to elongate the truncated rod-like unbranched cilia of the ASH nociceptive neurons in animals carrying a microtubule-destabilizing mutation in a tubulin subunit. We suggest that CCRK/MAK activity tunes cilia length and shape in part via modulation of axonemal microtubule stability, suggesting that similar mechanisms may underlie their roles in ciliary length control in other cell types. Cilia are microtubule-based organelles that exhibit cell-specific morphologies. CCRK and MAK-related kinases restrict cilia length in multiple organisms. Maurya et al . show that a CCRK and a MAK kinase act in a cascade to control cilia shape and structure by regulating axonemal microtubule dynamics in multiple sensory neuron types in C. elegans .