ABSTRACT
Primary cilia are microtubule (MT)-based organelles that mediate sensory functions in multiple cell types. Disruption of cilia structure or function leads to a diverse collection of diseases termed ciliopathies (1–3). Mutations in the DUF3719 domain-containing protein FAM149B1 have recently been shown to elongate cilia via unknown mechanisms and result in the ciliopathy Joubert syndrome (4). The highly conserved CCRK and MAK/RCK kinases negatively regulate cilia length and structure in Chlamydomonas, C. elegans, and mammalian cells (5–11). How the activity of this kinase cascade is tuned to precisely regulate cilia architecture is unclear. Here we identify XBX-4, a DUF3719 domain-containing protein related to human FAM149B1, as a novel regulator of the DYF-18 CCRK and DYF-5 MAK kinase pathway in C. elegans. As in dyf-18 and dyf-5 mutants (11), sensory neuron cilia are elongated in xbx-4 mutants and exhibit altered axonemal MT stability. XBX-4 promotes DYF-18 CCRK activity to regulate DYF-5 MAK function and localization. We find that Joubert syndrome-associated mutations in the XBX-4 DUF3719 domain also elongate cilia in C. elegans. Our results identify a new metazoan-specific regulator of this highly conserved kinase pathway, and suggest that FAM149B1 may similarly act via the CCRK/MAK kinase pathway to regulate ciliary homeostasis in humans.
Competing Interest Statement
The authors have declared no competing interest.
