In mouse embryos, the establishment of left-right (LR) asymmetry, which initiates the proper positioning of the internal organs, requires intracellular calcium (Cai2+) enrichment along the left side of the node. But does this mechanism also establish laterality in other vertebrates? On , Susan Smith and colleagues report that chick embryos also use a left-side enriched Cai2+ asymmetry to establish laterality. They show that Cai2+ is enriched along the front edge of Hensen's node (the chick's organizer) by the definitive primitive streak stage. Subsequent left-side enrichment of Cai2+ requires the activity of ryanodine receptors(intracellular calcium channels) and extracellular calcium, which suggests that calcium-induced calcium release supplies the Cai2+. Furthermore, the manipulation of Cai2+ across the node randomizes heart laterality and disrupts asymmetric gene expression. Finally,other established laterality mediators regulate LR identity by directly affecting node Cai2+ concentrations, the authors report. Thus, they suggest, Cai2+ asymmetry across the node may be a conserved mechanism for establishing laterality among vertebrates,despite differences in node architecture.
