Keller R, Jansa S
Department of Molecular and Cell Biology, University of California, Berkeley, California 94720.
Dev Dyn. 1992 Nov;195(3):162-76. doi: 10.1002/aja.1001950303.
The objective of this paper is to determine the function in gastrulation of several of the five major regional morphogenetic processes in the African clawed frog, Xenopus laevis. These regional processes are (1) epiboly of the animal cap (AC); (2) migration of the mesoderm on the roof of the blastocoel; (3) convergence and extension of the dorsal, noninvoluting marginal zone (NIMZ); (4) formation of the bottle cells at the site of blastopore formation; and (5) convergence and extension of the involuting marginal zone (IMZ). After the AC and the NIMZ were removed, thus eliminating the first three of these processes, the IMZ involuted, constricted, and closed the blastopore. It also converged and extended to form notochord and somites, although these tissues were often crooked and sank into or were covered over by the vegetal endoderm. When the AC was removed, the dorsal axial mesoderm involuted and stuck to the inner surface of the NIMZ. The IMZ and NIMZ converged and extended together to form a longer, straighter axis than that formed by the IMZ alone. Moreover, presence of the NIMZ also prevented the sinking of the IMZ into the endoderm. Misalignment of the available AC-NIMZ substratum and the IMZ at the beginning of gastrulation suggested that the IMZ determines the general direction of its own extension. Absence of the AC-NIMZ accelerated and increased the normal effects of bottle cell formation on the IMZ and vegetal endoderm. In absence of the AC-NIMZ as a substratum on which to migrate, prechordal mesoderm was pushed anteriorly by the converging and extending mesoderm behind it, but it did not spread normally. We conclude that (1) involution and blastopore closure by the IMZ can occur without pushing by epiboly and convergence and extension of the NIMZ-AC; (2) involution and blastopore closure can occur without migration of the mesoderm on the blastocoel roof; (3) convergence and extension of the IMZ are sufficient to bring about IMZ involution and blastopore closure; (4) the function of bottle cells in initiating involution is retarded by presence of the NIMZ-AC; (5) the associated dorsal NIMZ and IMZ together form an axis that extends better and is perhaps stiffer than the IMZ alone; and (6) the dorsal axial and paraxial mesoderm form the "skeleton" around which the mechanics of the other parts of the embryo are organized. These findings are important for the analysis of gastrulation by cellular, genetic, and molecular approaches.
本文的目的是确定非洲爪蟾（非洲爪蟾）五个主要区域形态发生过程中的几个在原肠胚形成中的作用。这些区域过程包括：（1）动物帽（AC）的外包；（2）中胚层在囊胚腔顶部的迁移；（3）背侧非内卷边缘区（NIMZ）的汇聚和延伸；（4）在胚孔形成部位形成瓶状细胞；（5）内卷边缘区（IMZ）的汇聚和延伸。去除AC和NIMZ后，即消除了前三个过程，IMZ内卷、收缩并关闭了胚孔。它也汇聚并延伸形成脊索和体节，尽管这些组织常常弯曲并沉入植物性内胚层或被其覆盖。去除AC后，背侧轴中胚层内卷并附着在NIMZ的内表面。IMZ和NIMZ一起汇聚并延伸，形成了比单独由IMZ形成的轴更长、更直的轴。此外，NIMZ的存在还防止了IMZ沉入内胚层。原肠胚形成开始时，可用的AC - NIMZ基质与IMZ的错位表明，IMZ决定了其自身延伸的总体方向。AC - NIMZ的缺失加速并增强了瓶状细胞形成对IMZ和植物性内胚层的正常影响。在没有AC - NIMZ作为迁移基质的情况下，脊索前中胚层被其后方汇聚和延伸的中胚层向前推，但它不能正常扩散。我们得出以下结论：（1）IMZ的内卷和胚孔关闭可以在没有NIMZ - AC的外包以及汇聚和延伸推动的情况下发生；（2）内卷和胚孔关闭可以在没有中胚层在囊胚腔顶部迁移的情况下发生；（3）IMZ的汇聚和延伸足以导致IMZ内卷和胚孔关闭；（4）NIMZ - AC的存在会延迟瓶状细胞启动内卷的功能；（5）相关的背侧NIMZ和IMZ共同形成一个延伸更好、可能更硬的轴，比单独的IMZ形成的轴更好；（6）背侧轴和近轴中胚层形成了“骨架”，围绕该骨架组织了胚胎其他部分的力学结构。这些发现对于通过细胞、遗传和分子方法分析原肠胚形成具有重要意义。
