Abstract
Intestinal smooth muscle differentiation is a complex physico-biological process involving several different pathways. Here, we reveal using GCamp6f expressing mouse embryos that calcium waves propagate in the mouse intestinal mesenchyme one day prior to the emergence of α-smooth muscle actin in the presumptive circular and longitudinal smooth muscle layers. We find that L-type calcium channel blockers and myosine light-chain kinase inhibitors halt these waves, inhibit smooth muscle differentiation and intestinal growth. We demonstrate that the effect of the calcium waves on differentiation are not mediated via mechanobiological pathways related to smooth muscle contractions. We recapitulate most of these results in the avian embryo, and show that early guts treated with L-type channel blockers up-regulate the LIX1 factor characteristic of mesenchymal stemness, whereas older guts display KIT expressing cells characteristic of Interstitial Cells of Cajal. We conclude that electrical connectivity of the mesenchyme precedes contractile function in intestinal development and that calcium waves are required for the differentiation of mesenchymal progenitors into contractile smooth muscle cells.