The neural plate can be explanted together with the underlying dorsal mesoderm/endoderm at the same stages by cutting completely through the anterior, lateral, and ventral walls of the archenteron (88). This type of explant was first used to analyze Xenopus mesodermal cell behavior by stripping off the endoderm of the archenteron roof, exposing the deep somitic and notochordal cells (see ref. 88). However, it can also be used to compare autonomous development of the neural plate isolated and cultured alone, with development under the continued influence of the underlying mesoderm. In this explant, the ventral mesoderm that is destined to contribute to posterior somitic tissue moves around both sides of the blastopore, which is pushed posteriorly by the extending notochord (see refs. 88,89). This is the only explant preparation that allows the posterior somitic mesoderm, which lies at the ventrolateral and even ventral IMZs of the gastrula, to move beneath the neural plate in a relatively normal fashion (see Fig. 5 in ref. 29).
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