Department of Developmental Biology, 279 Campus Drive, Beckman Center B300, Stanford University, Stanford, CA 94305-5329, USA.
Development. 2010 Nov;137(21):3643-9. doi: 10.1242/dev.057521. Epub 2010 Sep 28.
Although much is known about the initial construction of the peripheral nervous system (PNS), less well understood are the processes that maintain the position and connections of nerves during postembryonic growth. Here, we show that the posterior lateral line nerve in zebrafish initially grows in the epidermis and then rapidly transitions across the epidermal basement membrane into the subepidermal space. Our experiments indicate that Schwann cells, which myelinate axons in the PNS, are required to reposition the nerve. In mutants lacking Schwann cells, the nerve is mislocalized and the axons remain in the epidermis. Transplanting wild-type Schwann cells into these mutants rescues the position of the nerve. Analysis of chimeric embryos suggests that the process of nerve relocalization involves two discrete steps - the degradation and recreation of the epidermal basement membrane. Although the outgrowth of axons is normal in mutants lacking Schwann cells, the nerve becomes severely disorganized at later stages. In wild-type embryos, exclusion of the nerve from the epidermis isolates axons from migration of their targets (sensory neuromasts) within the epidermis. Without Schwann cells, axons remain within the epidermis and are dragged along with the migrating neuromasts. Our analysis of the posterior lateral line system defines a new process in which Schwann cells relocate a nerve beneath the epidermal basement membrane to insulate axons from the postembryonic remodeling of their targets.
尽管人们对周围神经系统（PNS）的初始构建过程了解较多，但对于维持胚胎后期生长过程中神经位置和连接的过程了解较少。在这里，我们展示了斑马鱼的后外侧线神经最初在表皮中生长，然后迅速穿过表皮基底膜进入皮下空间。我们的实验表明，施万细胞（Schwann cells），即 PNS 中的轴突髓鞘形成细胞，对于重新定位神经是必需的。在缺乏施万细胞的突变体中，神经定位错误，轴突仍留在表皮中。将野生型施万细胞移植到这些突变体中可以挽救神经的位置。嵌合胚胎的分析表明，神经重新定位的过程涉及两个离散的步骤 - 表皮基底膜的降解和重建。尽管在缺乏施万细胞的突变体中轴突的生长是正常的，但在后期阶段神经变得严重紊乱。在野生型胚胎中，神经从表皮中被排除会使轴突与表皮内的目标（感觉神经丘）的迁移隔离。在没有施万细胞的情况下，轴突仍留在表皮中，并随迁移的神经丘一起被拖动。我们对后外侧线系统的分析定义了一个新的过程，其中施万细胞将神经重新定位到表皮基底膜下方，以将轴突与目标的胚胎后期重塑隔离开来。
