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Shifting into high gear: how Interstitial Cells of Cajal change the motility pattern of the developing intestine.

The first contractile waves in the developing embryonic gut are purely myogenic, they only involve smooth muscle. Here, we provide evidence for a transition from smooth-muscle to Interstitial Cell of Cajal (ICC) driven contractile waves in the developing chicken gut. In-situ hybridization staining for ANO1, a known ICC marker, shows that ICCs are already present throughout the gut as from embryonic day 7 (E7). We devised a protocol to reveal ICC oscillatory and propagative calcium activity in embryonic gut whole-mount and find that the first steady calcium oscillations in ICCs occur at E14. We show that the activation of ICCs leads to an increase in contractile wave frequency, regularity, directionality and velocity between E12 and E14. We finally demonstrate that application of the c-KIT antagonist imatinib mesylate in organ culture specifically depletes the ICC network and inhibits the transition to a regular, rhythmic wave pattern. We compare our findings to existing results in the mouse and predict that a similar transition should take place in the human fetus between 12 and 14 weeks of development. Together, our results point to an abrupt physiological transition from smooth-muscle mesenchyme self-initiating waves to ICC-driven motility in the fetus, and clarify the contribution of ICCs to the contractile wave pattern.