![]() In the early neurula eFGF expression can be detected in the extreme posterior of the embryo. While most uninjected embryos closed their blastopore by late gastrula stage. become increasingly abundant in the dorsal blastopore lip. These results illuminate the mechanobiology of early vertebrate morphogenic mechanisms, aid interpretation of phenotypes, and give insight into the evolution of blastopore closure mechanisms. At the beginning of Xenopus gastrulation, the presumptive anterior. Uniaxial tensile stress relaxation assays show stiffening of mesodermal and ectodermal tissues around the onset of neurulation, potentially enhancing long-range transmission of convergence forces. and the pathway of chordamesoderm migration over the matrix in Xenopus. Explants from ventralized embryos, which lack tissues expressing CE but close their blastopores, produce up to 2 μN of tensile force, showing that CT alone generates forces sufficient to close the blastopore. marginal zone turns inward over the blastopore lip and then back on itself (Fig. These forces are generated by convergent thickening (CT) until the midgastrula and increasingly by convergent extension (CE) thereafter. Blastopore closure in Xenopus is driven by two morphogenic mechanisms that have strongly context dependent effects on tissue movement and that generate tensile force across tissues: convergent extension, as expected, and, unexpectedly, convergent thickening. Definitions: The opening of the archenteron to the exterior, marking the point of origin of the archenteron and the caudal end of the embryo. ![]() We show that explanted MZs generate tensile convergence forces up to 1.5 μN during gastrulation and over 4 μN thereafter. The individual blastomeres of Xenopus two- to 32-cell embryos have been fate mapped. ![]() Indirect evidence suggests that blastopore closure during gastrulation of anamniotes, including amphibians such as Xenopus laevis, depends on circumblastoporal convergence forces generated by the marginal zone (MZ), but direct evidence is lacking. ![]()
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