Development of the enteric nervous system

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***The enteric nervous system is often referred to as the second brain due to the number and diversity of its neural cell types. Enteric neurons and glia are organized in interconnected networks of ganglia, which control key gastrointestinal functions such as digestive motility and selective epithelial permeability. ******The enteric nervous system forms during prenatal development from neural crest cells that migrate from the neural tube. Following their entry in the foregut mesenchyme, the so-called enteric neural crest-derived cells (ENCCs) then migrate posteriorly to colonize the midgut and hindgut. Incomplete colonization (due to defective migration or insufficient number of ENCCs) leads to a lack of neural ganglia over varying lengths of the distal gut, and consequently to functional bowel obstruction, which is lethal soon after birth. In mice, this phenotype is known as aganglionic megacolon and has allowed the identification of key regulators of enteric nervous system development (e.g. Gdnf/Ret pathway members). Neurogenesis and gliogenesis are initiated during the colonization phase, yet defects in these processes generally result in more subtle phenotypes. This is likely why, compared to the mechanisms governing ENCC migration/proliferation/survival, the molecular mechanisms underlying enteric neurogenesis and gliogenesis remain poorly defined. ******Taking advantage of the murine aganglionic megacolon phenotype in a transgenic insertional mutation screen, we generated three mutant mouse lines, named TashT, Holstein and Spot. These mutants allowed us to make major discoveries about the regulation of ENCC migration and proliferation. In Spot, we found that both processes are impaired because of premature glial differentiation. The Spot insertional mutation disrupts a long-range interaction between a silencer element and the Nr2f1-A830082K12Rik overlapping gene pair, resulting in overexpression of both genes in Spot ENCCs. We further discovered that Nr2f1 directly regulates the expression of glial markers downstream of gliogenic cues, whereas A830082K12Rik is a lncRNA regulating gene expression in cis. All these data provide a solid framework for studies aimed at elucidating the currently enigmatic molecular mechanisms at play during enteric gliogenesis.******Initiated 10 years ago, this NSERC-funded basic research program is aimed at unravelling the molecular mechanisms that control enteric nervous system development. For the next 5 years, this work will be focused on enteric gliogenesis. Our aims are to: ***1) Elucidate the regulatory interactions between the Spot-associated silencer element, A830082K12Rik and Nr2f1; ***2) Determine the hierarchical position of Nr2f1 relative to other regulators of enteric gliogenesis; ***3) Identify new regulators of enteric gliogenesis. ***This work is expected to have a significant and long-lasting impact on the enteric nervous system field as well as on the wider field of neurobiology.**