A Conserved Domain ofCfap298Governs Left-Right Symmetry Breaking in Vertebrates

Cfap298is a highly conserved gene required for ciliary motility and dynein arm assembly. It plays a known role in Left-Right (LR) patterning in zebrafish and is linked to human ciliopathies. Here we describe a newCfap298mutant allele,Cfap298^Δ3aa, which selectively interferes with LR axis establishment in mice. Mutant embryos display a range of laterality defects includingsitus solitus,situs inversus, andsitus ambiguous,as indicated by abnormal heart, lung, and stomach positioning. At embryonic day 8.5, mutant embryos display abnormalNodal,Pitx2, andLefty1expression patterns in the lateral plate mesoderm and midline, consistent with an early disruption in LR symmetry breaking. In mice, LR asymmetry is established by leftward fluid flow in the node, generated by planar-polarized cilia. Althoughcfap298mutations are reported to affect cell polarity, we did not observe changes in cilia position, length, or planar cell polarity protein localization within the node, suggesting thatCfap298^Δ3aafunctions at the level of cilia motility. Consistently, motile cilia lining the trachea ofCfap298^Δ3aamutants fail to beat. Expression of theCfap298^Δ3aavariant in zebrafish fails to rescue the LR defects ofcfap298(kurly)loss-of-function mutants. These results confirm thatCfap298functions in LR axis formation in mammals and uncover a novel region of CFAP298 protein with a conserved and essential role in cilia motility.