Shankland M
Nature. 1984;307(5951):541-3. doi: 10.1038/307541a0.
Segmented animals are divided into a longitudinal array of developmentally homologous subunits known as metameres. The embryonic origin of the segmental body plan has been studied in a variety of organisms, with particular emphasis on the mechanisms underlying the delineation of the individual metameres and their secondary diversification. I have examined the embryonic events which determine the total number of segments in the glossiphoniid leech Helobdella triserialis. The germinal band of the leech consists of chains of segmental founder cells, called blast cells, and is normally reduced to 32 segments by the degeneration of supernumerary blast cells located at its caudal end. By using a novel technique for selective cell ablation, the segmental register of the four ectodermal cell lines can be altered so that lineally identifiable blast cells take part in the formation of ectopic segments. I show here that the survival or death of ectodermal blast cells is determined by position independent of their cell lineage identities, implying that the final number of segments is imposed on the ectoderm by interactions with the other embryonic tissues.
分节动物被分为一系列纵向排列的、发育同源的亚单位，称为体节。人们在多种生物体中研究了分节身体模式的胚胎起源，特别关注个体体节划分及其二次分化的潜在机制。我研究了决定三带蛭（Helobdella triserialis）体节总数的胚胎事件。水蛭的胚带由称为胚细胞的分节奠基细胞链组成，通常通过位于其尾端的多余胚细胞的退化而减少到32个节段。通过使用一种选择性细胞消融的新技术，可以改变四个外胚层细胞系的节段排列，以便线性可识别的胚细胞参与异位节段的形成。我在此表明，外胚层胚细胞的存活或死亡取决于位置，与其细胞谱系身份无关，这意味着体节的最终数量是通过与其他胚胎组织的相互作用施加在外胚层上的。
