Appel B, Fritz A, Westerfield M, Grunwald D J, Eisen J S, Riley B B
Institute of Neuroscience, 1254 University of Oregon, Eugene, Oregon 97403, USA.
Curr Biol. 1999 Mar 11;9(5):247-56. doi: 10.1016/s0960-9822(99)80113-4.
Fate mapping studies have shown that progenitor cells of three vertebrate embryonic midline structures - the floorplate in the ventral neural tube, the notochord and the dorsal endoderm - occupy a common region prior to gastrulation. This common region of origin raises the possibility that interactions between midline progenitor cells are important for their specification prior to germ layer formation.
One of four known zebrafish homologues of the Drosophila melanogaster cell-cell signaling gene Delta, deltaA (dlA), is expressed in the developing midline, where progenitor cells of the ectodermal floorplate, mesodermal notochord and dorsal endoderm lie close together before they occupy different germ layers. We used a reverse genetic strategy to isolate a missense mutation of dlA, dlAdx2, which coordinately disrupts the development of floorplate, notochord and dorsal endoderm. The dlAdx2 mutant embryos had reduced numbers of floorplate and hypochord cells; these cells lie above and beneath the notochord, respectively. In addition, mutant embryos had excess notochord cells. Expression of a dominant-negative form of Delta protein driven by mRNA microinjection produced a similar effect. In contrast, overexpression of dlA had the opposite effect: fewer trunk notochord cells and excess floorplate and hypochord cells.
Our results indicate that Delta signaling is important for the specification of midline cells. The results are most consistent with the hypothesis that developmentally equivalent midline progenitor cells require Delta-mediated signaling prior to germ layer formation in order to be specified as floorplate, notochord or hypochord.
命运图谱研究表明，三种脊椎动物胚胎中线结构的祖细胞——腹侧神经管的底板、脊索和背侧内胚层——在原肠胚形成之前占据共同区域。这个共同的起源区域增加了一种可能性，即中线祖细胞之间的相互作用对于它们在胚层形成之前的特化很重要。
果蝇细胞间信号传导基因Delta的四个已知斑马鱼同源物之一，deltaA（dlA），在发育中的中线表达，在那里外胚层底板、中胚层脊索和背侧内胚层的祖细胞在占据不同胚层之前紧密相邻。我们使用反向遗传策略分离出dlA的一个错义突变体dlAdx2，它协同破坏了底板、脊索和背侧内胚层的发育。dlAdx2突变体胚胎中底板和下脊索细胞数量减少；这些细胞分别位于脊索的上方和下方。此外，突变体胚胎有过多的脊索细胞。通过mRNA显微注射驱动的Delta蛋白显性负性形式的表达产生了类似的效果。相反，dlA的过表达产生了相反的效果：躯干脊索细胞减少，底板和下脊索细胞过多。
我们的结果表明Delta信号传导对于中线细胞的特化很重要。这些结果与以下假设最一致，即发育上等效的中线祖细胞在胚层形成之前需要Delta介导的信号传导，以便被特化为底板、脊索或下脊索。
