Development of the enteric nervous system

肠道神经系统通常被称为第二脑，因为它的神经细胞类型的数量和多样性。肠神经细胞和神经胶质细胞被组织成相互连接的神经节网络，这些神经节控制着关键的胃肠功能，如消化动力和选择性上皮通透性。 肠道神经系统是在胎儿发育过程中从神经管中迁移出来的神经脊细胞形成的。在进入前肠间充质后，所谓的肠神经脊源性细胞(ENCC)向后迁移，在中肠和后肠定植。不完全定植(由于有缺陷的移行或ENCC数量不足)导致远端肠道不同长度的神经节缺乏，从而导致功能性肠梗阻，这在出生后不久就是致命的。在小鼠中，这种表型被称为无神经节细胞巨结肠，可以识别肠道神经系统发育的关键调节因子(例如GDNF/Ret通路成员)。神经发生和神经胶质形成是在定植阶段启动的，但这些过程中的缺陷通常会导致更微妙的表型。这可能是为什么与调控ENCC迁移/增殖/存活的机制相比，肠神经发生和神经胶质形成的分子机制仍然缺乏明确的原因。 利用小鼠无神经节细胞巨结肠在转基因插入突变筛选中的表型，我们产生了三个突变小鼠系，命名为TashT，Holstein和Spot。这些突变使我们在ENCC迁移和增殖的调控方面有了重大发现。在Spot中，我们发现这两个过程都由于神经胶质细胞的过早分化而受损。点插入突变破坏了沉默元件与Nr2f1-A830082K12Rik重叠基因对之间的长距离相互作用，导致这两个基因在Spot ENCC中过表达。我们进一步发现，Nr2f1直接调节胶质形成线索下游的胶质标志物的表达，而A830082K12Rik是一个调节顺式基因表达的lncRNA。所有这些数据为旨在阐明目前在肠道胶质形成过程中起作用的神秘分子机制的研究提供了坚实的框架。 这项由NSERC资助的基础研究项目于10年前启动，旨在揭开控制肠道神经系统发育的分子机制。在接下来的5年里，这项工作将集中在肠道胶质发生上。我们的目标是： 1)阐明斑点相关沉默元件A830082K12Rik和Nr2f1之间的调控相互作用； 2)确定Nr2f1相对于肠神经胶质发生的其他调节因子的等级位置； 3)寻找肠神经胶质形成的新调节因子。 这项工作预计将对肠道神经系统领域以及更广泛的神经生物学领域产生重大而持久的影响。

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.