Calcium fluxes in dorsal forerunner cells antagonize -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 -catenin inhibition as a Ca²⁺-signaling target and demonstrate that localized loss of Ca²⁺ within the DFC region or DFC-specific activation of -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 -catenin and altered laterality. Overall, our data support a conserved early Ca²⁺ requirement in DFC-like cell function in zebrafish and Xenopus.