Jen W C, Wettstein D, Turner D, Chitnis A, Kintner C
Salk Institute for Biological Studies, San Diego, CA 92186, USA.
Development. 1997 Mar;124(6):1169-78. doi: 10.1242/dev.124.6.1169.
Segmentation of the vertebrate embryo begins when the paraxial mesoderm is subdivided into somites, through a process that remains poorly understood. To study this process, we have characterized X-Delta-2, which encodes the second Xenopus homolog of Drosophila Delta. Strikingly, X-Delta-2 is expressed within the presomitic mesoderm in a set of stripes that corresponds to prospective somitic boundaries, suggesting that Notch signaling within this region establishes a segmental prepattern prior to somitogenesis. To test this idea, we introduced antimorphic forms of X-Delta-2 and Xenopus Suppressor of Hairless (X-Su(H)) into embryos, and assayed the effects of these antimorphs on somite formation. In embryos expressing these antimorphs, the paraxial mesoderm differentiated normally into somitic tissue, but failed to segment properly. Both antimorphs also disrupted the segmental expression of X-Delta-2 and Hairy2A, a basic helix-loop-helix (bHLH) gene, within the presomitic mesoderm. These observations suggest that X-Delta-2, via X-Notch-1, plays a role in segmentation, by mediating cell-cell interactions that underlie the formation of a segmental prepattern prior to somitogenesis.
脊椎动物胚胎的分割始于轴旁中胚层被细分为体节，然而这一过程仍未被充分理解。为了研究这一过程，我们对X-Delta-2进行了表征，它编码果蝇Delta的第二个非洲爪蟾同源物。引人注目的是，X-Delta-2在体节形成前的中胚层内呈条纹状表达，这些条纹对应于未来的体节边界，这表明该区域内的Notch信号在体节形成之前建立了一种节段性的预模式。为了验证这一想法，我们将X-Delta-2和非洲爪蟾无毛抑制因子（X-Su(H)）的反形态形式导入胚胎，并检测这些反形态对体节形成的影响。在表达这些反形态的胚胎中，轴旁中胚层正常分化为体节组织，但未能正常分割。这两种反形态还破坏了体节形成前的中胚层内X-Delta-2和Hairy2A（一种基本的螺旋-环-螺旋（bHLH）基因）的节段性表达。这些观察结果表明，X-Delta-2通过X-Notch-1，在分割过程中发挥作用，通过介导细胞间相互作用，这些相互作用是在体节形成之前形成节段性预模式的基础。
