Separate Na,K-ATPase genes are required for otolith formation and semicircular canal development in zebrafish

We have investigated the role of Na,K-ATPase genes in zebrafish ear development. Six Na,K-ATPase genes are differentially expressed in the developing zebrafish inner ear. Antisense morpholino knockdown of Na,K-ATPase α1a.1 expression blocked formation of otoliths. This effect was phenocopied by treatment of embryos with ouabain, an inhibitor of Na,K-ATPase activity. The otolith defect produced by morpholinos was rescued by microinjection of zebrafish α1a.1 or rat α1 mRNA, while the ouabain-induced defect was rescued by expression of ouabain-resistant zebrafish α1a.1 or rat α1 mRNA. Knockdown of a second zebrafish α subunit, α1a.2, disrupted development of the semicircular canals. Knockdown of Na,K-ATPase β2b expression also caused an otolith defect, suggesting that the β2b subunit partners with the α1a.1 subunit to form a Na,K-ATPase required for otolith formation. These results reveal novel roles for Na,K-ATPase genes in vestibular system development and indicate that different isoforms play distinct functional roles in formation of inner ear structures. Our results highlight zebrafish gene knockdown-mRNA rescue as an approach that can be used to dissect the functional properties of zebrafish and mammalian Na,K-ATPase genes.