Key pointsr Neurogenic gut movements start after longitudinal smooth muscle differentiation in three species (mouse, zebrafish, chicken), and at E16 in the chicken embryo.r The first activity of the chicken enteric nervous system is dominated by inhibitory neurons. r The embryonic enteric nervous system electromechanically couples circular and longitudinal spontaneous myogenic contractions, thereby producing a new, rostro-caudally directed bolus transport pattern: the migrating motor complex.r The response of the embryonic gut to mechanical stimulation evolves from a symmetric, myogenic response at E12, to a neurally mediated, polarized, descending inhibitory, 'law of the intestine'-like response at E16. r High resolution, whole-mount 3D reconstructions are presented of the enteric nervous system of the chicken embryo at the neural-control stage E16 with the iDISCO+ tissue clarification technique.Abstract Gut motility is a complex transport phenomenon involving smooth muscle, enteric neurons, glia and interstitial cells of Cajal. Because these different cells differentiate and become active at different times during embryo development, studying the ontogenesis of motility offers a unique opportunity to 'time-reverse-engineer' the peristaltic reflex. Working on chicken embryo intestinal explants in vitro, we found by spatio-temporal mapping and signal processing of diameter and position changes that motility follows a characteristic sequence of increasing complexity: (1) myogenic circular smooth muscle contractions from E6 to E12 that propagate as waves along the intestine, (2) overlapping and independent, myogenic, low-frequency, bulk longitudinal smooth muscle contractions around E14, and (3) tetrodotoxin-sensitive coupling of longitudinal and circular contractions by the enteric nervous system as from E16. Inhibition of nitric oxide synthase neurons shows that the coupling consists in nitric oxide-mediated relaxation of circular smooth muscle when the longitudinal muscle layer is contracted. This mechanosensitive coupling gives rise to a directional, cyclical, propagating bolus transport pattern: the migrating motor complex. We further reveal a transition to a polarized, descending, inhibitory Nicolas R. Chevalier, a native of Bailly (France) and Vienna (Austria), is a researcher at Laboratoire Matière Systèmes Complexes, CNRS/Université Paris Diderot. He holds an MSc. degree in physics from Ecole Polytechnique Fédérale de Lausanne (Switzerland), and a PhD degree from Université Pierre et Marie Curie (France) in the field of crystal growth. His current investigations pertain to embryonic gut development. He is particularly interested in neural crest cell migration, enteric nervous system development and intestinal motility, and has elucidated the crucial effects of mechanical forces in driving embryonic gut elongation. N. R. Chevalier and others J Physiol 597.10 reflex response to mechanical stimulation after neuronal activity sets in at E16. This asymmetric response is the elementary mechanism responsible for ...

While the colonization of the embryonic gut by neural crest cells has been the subject of intense scrutiny over the past decades, we are only starting to grasp the morphogenetic transformations of the enteric nervous system happening in the fetal stage. Here, we show that enteric neural crest cell transit during fetal development from an isotropic cell network to a square grid comprised of circumferentially-oriented cell bodies and longitudinally-extending interganglionic fibers. We present ex-vivo dynamic time-lapse imaging of this isotropic-to-nematic phase transition and show that it occurs concomitantly with circular smooth muscle differentiation in all regions of the gastrointestinal tract. Using conditional mutant embryos with enteric neural crest cells depleted of β1-integrins, we show that cell-extracellular matrix anchorage is necessary for ganglia to properly reorient. We demonstrate by whole mount second harmonic generation imaging that fibrous, circularly-spun collagen I fibers are in direct contact with neural crest cells during the orientation transition, providing an ideal orientation template. We conclude that smooth-muscle associated extracellular matrix drives a critical reorientation transition of the enteric nervous system in the mammalian fetus.