While there is a good conceptual framework of dorsoventral and anterioposterior axes formation in most vertebrate groups, understanding of left-right axis initiation is fragmentary. Diverse mechanisms have been implied to contribute to the earliest steps of left-right asymmetry, including small molecule signals, gap junctional communication, membrane potential, and directional flow of extracellular liquid generated by monocilia in the node region. Here we demonstrate that a mutation in the zebrafish Na,K-ATPase subunit atp1a1a causes left-right defects including isomerism of internal organs at the anatomical level. The normally left-sided Nodal signal spaw as well as its inhibitor lefty are expressed bilaterally, while pitx2 may appear random or bilateral. Monocilia movement and fluid circulation in Kupffer's vesicle are normal in atp1a1a(m883) mutant embryos. Therefore, the Na,K-ATPase is required downstream or in parallel to monocilia function during initiation of left-right asymmetry in zebrafish.
(c) 2006 Wiley-Liss, Inc.