Broad-Minded Links Cell Cycle-Related Kinase to Cilia Assembly and Hedgehog Signal Transduction

Abstract

SUMMARY Recent findings indicate that mammalian Sonic hedgehog (Shh) signal transduction occurs within primary cilia, although the cell biological mechanisms underlying both Shh signaling and ciliogenesis have not been fully elucidated. We show that an uncharacterized TBC domain-containing protein, Broad-minded (Bromi), is required for high-level Shh responses in the mouse neural tube. We find that Bromi controls ciliary morphology and proper Gli2 localization within the cilium. Using a zebrafish model, we further show that Bromi is required for proper association between the ciliary membrane and axoneme. Bromi physically interacts with cell cycle-related kinase (CCRK), whose Chlamydomonas homolog regulates flagellar length. Biochemical and genetic interaction data indicate that Bromi promotes CCRK stability and function. We propose that Bromi and CCRK control the structure of the primary cilium by coordinating assembly of the axoneme and ciliary membrane, allowing Gli proteins to be properly activated in response to Shh signaling.

Intestinal cell kinase, a protein associated with endocrine-cerebro-osteodysplasia syndrome, is a key regulator of cilia length and Hedgehog signaling

“…In Chlamydomonas, four different mutated proteins cause abnormally elongated flagella, including LF2 and LF4 kinases that are homologs of vertebrate CCRK and MAK/ICK, respectively (23). We previously showed that Ccrk knockdown in zebrafish results in abnormal ciliogenesis in kidney epithelial cells (24). Similarly, depletion of Ccrk in cultured cells results in elongated cilia (25).…”

The Cdc14B phosphatase contributes to ciliogenesis in zebrafish

“…Interestingly, the cdc14b morphant larvae did not display a strong body axis curvature as seen in zebrafish cilia mutants (Cao et al, 2010;Omori et al, 2008;Sullivan-Brown et al, 2008;Tsujikawa and Malicki, 2004;Zhao and Malicki, 2007). However, this weaker phenotype has previously been observed when MOs against genes encoding cilia proteins were injected (Ferrante et al, 2009;Hurd et al, 2010;Ko et al, 2010;Tsujikawa and Malicki, 2004). This difference in the phenotypes is probably due to the decreased efficiency of the MOs by this time in development.…”

The primary cilium as a multiple cellular signaling scaffold in development and disease

“…Loss of MAK in mouse model system result in abnormal long cilia in photoreceptor cells and human genetic studies revealed that mutation in MAK cause retinitis pigmentosa in human (24)(25)(26)(27). CCRK has also been shown that it affects ciliogenesis in zebrafish model system (28). In contrast to Chlamydomonas studies, knockdown of CCRK expression in vertebrate compromises ciliary structure rather than length.…”