![]() 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. Absence of the AC‐NIMZ accelerated and increased the normal effects of bottle cell formation on the IMZ and vegetal 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. Moreover, presence of the NIMZ also prevented the sinking of the IMZ into the endoderm. The IMZ and NIMZ converged and extended together to form a longer, straighter axis than that formed by the IMZ alone. When the AC was removed, the dorsal axial mesoderm involuted and stuck to the inner surface of the NIMZ. 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. After the AC and the NIMZ were removed, thus eliminating the first three of these processes, the IMZ involuted, constricted, and closed the blastopore. 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). 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. Xenopus gastrulation without a blastocoel roof Xenopus gastrulation without a blastocoel roof ![]()
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