Calcium fluxes in dorsal forerunner cells antagonize β-catenin and alter left-right patterning

Establishment of the left-right axis is essential for normal organ morphogenesis and function. Ca2+ signaling and cilia function in the zebrafish Kuppfer's Vesicle (KV) have been implicated in laterality. Here we describe an endogenous Ca2+ release event in the region of the KV precursors (dorsal forerunner cells, DFCs), prior to KV and cilia formation. Manipulation of Ca2+ release to disrupt this early flux does not impact early DFC specification, but results in altered DFC migration or cohesion in the tailbud at somite stages. This leads to disruption of KV formation followed by bilateral expression of asymmetrical genes, and randomized organ laterality. We identify beta-catenin inhibition as a Ca2+-signaling target and demonstrate that localized loss of Ca2+ within the DFC region or DFC-specific activation of beta-catenin is sufficient to alter laterality in zebrafish. We identify a previously unknown DFC-like cell population in Xenopus and demonstrate a similar Ca2+-sensitive stage. As in zebrafish, manipulation of Ca2+ release results in ectopic nuclear beta-catenin and altered laterality. Overall, our data support a conserved early Ca2+ requirement in DFC-like cell function in zebrafish and Xenopus.