Asymmetric distribution of dynamic calcium signals in the node of mouse embryo during left-right axis formation

In the node of mouse embryo, rotational movements of cilia generate an external liquid flow known as nodal flow, which determines left-right asymmetric gene expression. How nodal flow is converted into asymmetric gene expression is still controversial, but the increase of Ca2+ levels in endodermal cells to the left of the node has been proposed to play a role. However, Ca2+ signals inside the node itself have not yet been described. By our optimized Ca2+ imaging method, we were able to observe dynamic Ca2+ signals in the node in live mouse embryos. Pharmacological disruption of Ca2+ signals did not affect ciliary movements or nodal flow, but did alter the expression patterns of the Nodal and Cerl-2 genes. Quantitative analyses of Ca2+ signal frequencies and distributions showed that during left-right axis establishment, formerly symmetric Ca2+ signals became biased to the left side. In iv/iv mutant embryos that showed randomized laterality due to ciliary immotility, Ca2+ signals were found to be variously left-sided, right-sided, or bilateral, and thus symmetric on average. In Pkd2 mutant embryos, which lacked polycystin-2, a Ca2+-permeable cation channel necessary for left-right axis formation, the Ca2+ signal frequency was lower than in wild-type embryos. Our data support a model in which dynamic Ca2+ signals in the node are involved in left-right patterning. (C) 2013 Elsevier Inc. All rights reserved.