Shain D H, Ramírez-Weber F A, Hsu J, Weisblat D A
Department of Molecular and Cell Biology, 385 LSA, University of California, Berkeley, CA 94720-3200, USA.
Dev Genes Evol. 1998 Mar;208(1):28-36. doi: 10.1007/s004270050150.
Using intracellular lineage tracers to study the main neurogenic lineage (N lineage) of the glossiphoniid leech embryo, we have characterized events leading from continuous columns of segmental founder cells (nf and ns primary blast cells) to discrete, segmentally iterated ganglia. The separation between prospective ganglia was first evident as a fissure between the posterior boundary of nf- and the anterior boundary of ns-derived progeny. We also identified the sublineages of nf-derived cells that contribute parallel stripes of cells to each segment. These stripes of cells project ventrolaterally from the dorsolateral margin of each nascent ganglion to the ventral body wall. The position and orientation of the stripes suggests that they play a role in forming the posterior segmental nerve; they are not coincident with the ganglionic boundary, and they form well after the separation of ganglionic primordia. Previous work has shown that cells in the anterior stripe express the leech engrailed-class gene. Thus, in contrast to the role of cells expressing engrailed in Drosophila, the stripes of N-derived cells expressing an engrailed-class gene in leech do not seem to play a direct role in segmentation or segment polarity.
利用细胞内谱系示踪剂来研究舌蛭胚胎的主要神经源性谱系（N谱系），我们已经确定了从连续的节段性奠基细胞柱（nf和ns初级胚细胞）到离散的、节段重复的神经节的发育过程。预期神经节之间的分离最初表现为nf衍生后代的后边界与ns衍生后代的前边界之间的裂缝。我们还确定了nf衍生细胞的亚谱系，这些细胞为每个节段贡献平行的细胞条纹。这些细胞条纹从每个新生神经节的背外侧边缘向腹侧体壁腹外侧投射。条纹的位置和方向表明它们在形成后节段神经中起作用；它们与神经节边界不一致，并且在神经节原基分离后才形成。先前的研究表明，前条纹中的细胞表达水蛭engrailed类基因。因此，与果蝇中表达engrailed的细胞的作用相反，水蛭中表达engrailed类基因的N衍生细胞条纹似乎在分割或节段极性中不发挥直接作用。
