Calcium asymmetry signals left from right

In mouse embryos, the establishment of left-right (LR) asymmetry, which initiates the proper positioning of the internal organs, requires intracellular calcium (Ca_i²⁺) enrichment along the left side of the node. But does this mechanism also establish laterality in other vertebrates? On p. 3271, Susan Smith and colleagues report that chick embryos also use a left-side enriched Ca_i²⁺ asymmetry to establish laterality. They show that Ca_i²⁺ 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 Ca_i²⁺ requires the activity of ryanodine receptors(intracellular calcium channels) and extracellular calcium, which suggests that calcium-induced calcium release supplies the Ca_i²⁺. Furthermore, the manipulation of Ca_i²⁺ across the node randomizes heart laterality and disrupts asymmetric gene expression. Finally,other established laterality mediators regulate LR identity by directly affecting node Ca_i²⁺ concentrations, the authors report. Thus, they suggest, Ca_i²⁺ asymmetry across the node may be a conserved mechanism for establishing laterality among vertebrates,despite differences in node architecture.