Copenhaver P F, Taghert P H
Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, Missouri 63110.
Dev Biol. 1989 Jan;131(1):85-101. doi: 10.1016/s0012-1606(89)80040-5.
The enteric plexus is a discrete portion of the enteric nervous system (ENS) in the larval moth Manduca sexta. It consists of a stereotyped array of nerves extending across specific regions of both the foregut and midgut. Within these nerves are approximately 400 neurons (the EP cells), which do not appear to be uniquely identifiable but exhibit a spectrum of morphological and biochemical phenotypes. In this report we have described the morphogenetic events by which the enteric plexus is created during embryogenesis and have characterized the morphological differentiation of the EP neurons. In particular, we have demonstrated a prominent role for stereotyped cellular migration in the formation of this region of the ENS. The neurons of the enteric plexus arise from the dorsal epithelium of the foregut in the form of a dense, triangular packet. Between 40 and 65% of embryogenesis, the cells of this packet become progressively dispersed by a sequence of migratory events: an initial, slow phase of migration that is circumferentially directed around the foregut, and a rapid, dispersing phase by which the EP cells achieve their mature distributions across the foregut and midgut surface. These migratory phases occur along defined pathways on the gut and result in cellular translocations of up to 250 microns. In the early phase, some migrating neurons extend long axons in stereotyped directions, while others retain a simple bipolar morphology. Neurons of both morphological types are interspersed throughout the initial packet of cells and participate equally in the migratory process. Toward the end of migration, cells with the simpler morphology also extend axons along predictable pathways. Several additional subtypes subsequently differentiate in various regions within the plexus. The expression of specific peptidergic substances (related to the molluscan peptide Phe-Met-Arg-Phe-NH2, as described in the accompanying paper (P. F. Copenhaver and P. H. Taghert, 1988, Dev. Biol. 130, 70-84) commences within the EP cell population only after these migratory phases are complete and can be correlated with the outcome of cellular migration: only neurons that navigate onto the midgut regions of the plexus subsequently exhibit the peptidergic phenotype. This system should provide an excellent model with which to examine the mechanisms underlying the migratory process and the potential roles of cellular migration in regulating neuronal differentiation.
肠神经丛是幼虫烟草天蛾中肠神经系统（ENS）的一个离散部分。它由一系列规则排列的神经组成，这些神经延伸穿过前肠和中肠的特定区域。在这些神经中大约有400个神经元（EP细胞），它们似乎没有独特的可识别特征，但呈现出一系列形态和生化表型。在本报告中，我们描述了胚胎发育过程中肠神经丛形成的形态发生事件，并对EP神经元的形态分化进行了特征描述。特别是，我们证明了规则的细胞迁移在ENS这个区域形成过程中发挥了重要作用。肠神经丛的神经元以前肠背侧上皮中密集的三角形细胞团形式产生。在胚胎发育的40%至65%阶段，这个细胞团的细胞通过一系列迁移事件逐渐分散：最初是围绕前肠圆周方向的缓慢迁移阶段，以及EP细胞在前肠和中肠表面实现成熟分布的快速分散阶段。这些迁移阶段沿着肠道上确定的路径发生，导致细胞移位可达250微米。在早期阶段，一些迁移的神经元沿规则方向延伸长轴突，而其他神经元则保持简单的双极形态。两种形态类型的神经元都散布在最初的细胞团中，并平等地参与迁移过程。在迁移接近尾声时，形态较简单的细胞也沿可预测的路径延伸轴突。随后，几种额外的亚型在神经丛内的不同区域分化。只有在这些迁移阶段完成后，特定肽能物质（与软体动物肽苯丙氨酸-甲硫氨酸-精氨酸-苯丙氨酸-氨基有关，如随附论文（P.F. 科彭哈弗和P.H. 塔格特，1988年，《发育生物学》130卷，70 - 84页）所述）的表达才在EP细胞群体中开始，并且可以与细胞迁移的结果相关联：只有迁移到神经丛中肠区域的神经元随后才表现出肽能表型。这个系统应该为研究迁移过程的潜在机制以及细胞迁移在调节神经元分化中的潜在作用提供一个极好的模型。
