Idiopathic scoliosis (IS) affects 3% of children worldwide, yet mechanisms underlying spinal deformity remain unknown. Here we show that ptk7 mutant zebrafish, a faithful genetic model of IS, exhibit ependymal cell (EC) cilia development and cerebrospinal fluid (CSF) flow defects. Transgenic re-introduction of Ptk7 in motile ciliated lineages prevents scoliosis in ptk7 mutants, while mutation of multiple independent cilia motility genes yield IS phenotypes. We define a finite developmental window for motile cilia in spine morphogenesis. Notably, restoration of cilia motility, after scoliosis onset, blocks spinal curve progression. Together, our results indicate a critical role for cilia-driven CSF flow in spine development, implicate irregularities in CSF flow as an underlying biological cause of IS and provide proof-of-principle that non-invasive therapeutic intervention could prevent severe scoliosis.

A diverse family of cytoskeletal dynein motors powers various cellular transport systems, including axonemal dyneins generating the force for ciliary and flagellar beating essential to movement of extracellular fluids and of cells through fluid. Multisubunit outer dynein arm (ODA) motor complexes, produced and preassembled in the cytosol, are transported to the ciliary or flagellar compartment and anchored into the axonemal microtubular scaffold via the ODA docking complex (ODA-DC) system. In humans, defects in ODA assembly are the major cause of primary ciliary dyskinesia (PCD), an inherited disorder of ciliary and flagellar dysmotility characterized by chronic upper and lower respiratory infections and defects in laterality. Here, by combined high-throughput mapping and sequencing, we identified CCDC151 loss-of-function mutations in five affected individuals from three independent families whose cilia showed a complete loss of ODAs and severely impaired ciliary beating. Consistent with the laterality defects observed in these individuals, we found Ccdc151 expressed in vertebrate left-right organizers. Homozygous zebrafish ccdc151(ts272a) and mouse Ccdc151(Snbl) mutants display a spectrum of situs defects associated with complex heart defects. We demonstrate that CCDC151 encodes an axonemal coiled coil protein, mutations in which abolish assembly of CCDC151 into respiratory cilia and cause a failure in axonemal assembly of the ODA component DNAH5 and the ODA-DC-associated components CCDC114 and ARMC4. CCDC151-deficient zebrafish, planaria, and mice also display ciliary dysmotility accompanied by ODA loss. Furthermore, CCDC151 coimmunoprecipitates CCDC114 and thus appears to be a highly evolutionarily conserved ODA-DC-related protein involved in mediating assembly of both ODAs and their axonemal docking machinery onto ciliary microtubules.

SUMMARY Cilia are microtubule-based projections that function in the movement of extracellular fluid. This requires cilia to be: (1) motile, driven by dynein complexes and (2) correctly polarized on the surface of cells, which requires planar cell polarity (PCP). Few factors that regulate both processes have been discovered. We reveal that C21orf59/Kurly (Kur), a cytoplasmic protein with some enrichment at the base of cilia, is needed for motility; zebrafish mutants exhibit characteristic developmental abnormalities and dynein arm defects. kur was also required for proper cilia polarization in the zebrafish kidney and the larval skin of Xenopus laevis. CRISPR/Cas9 coupled with homologous recombination to disrupt the endogenous kur locus in Xenopus resulted in the asymmetric localization of the PCP protein Prickle2 being lost in mutant multi-ciliated cells. Kur also makes interactions with other PCP components including Disheveled. This supports a model wherein Kur plays a dual role in cilia motility and polarization.

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