The Spemann organizer meets the anterior-most neuroectoderm at the equator of early gastrulae in amphibian species.
Bottom Line: However, we found that this physical contact was already established at the equatorial region of very early gastrula in a wide variety of amphibian species.After the contact is established, the dorsal axis is formed posteriorly, but not anteriorly.The model also implies the possibility of constructing a common model of gastrulation among chordate species.
Affiliation: JT Biohistory Research Hall, 1-1 Murasaki-cho, Takatsuki, Osaka, 569-1125, Japan; Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka, 560-0043, Japan.Show MeSH
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Mentions: From these observations, we hypothesized that the blastocoel roof at ACE is dispensable for the formation of dorsal structures. To check this hypothesis, we removed blastocoel roofs at ACE in R. rugosa, X. laevis, B. orientalis, C. pyrrhogaster, and A. mexicanum embryos, and monitored how the embryos would develop. In all the blastocoel roof-less embryos, dorsal structures, including complete head structures, showed normal development, but the ventral epidermises were absent (Fig.4A–E 3/3 in B. orientalis B. orientalis, 4/5 in R. rugosa, 17/20 in X. laevis, 5/6 in A. mexicanum, and 5/5 in C. pyrrhogaster). In addition, we recognized the cement gland in the blastocoel roof-less anuran embryos (Fig.4A–C, black arrows), reinforcing our conclusion that the anterior-most neural structure was completely formed in the embryo. Interestingly, when the blastocoel roof was removed before ACE, at stages corresponding to type-A or -B, the dorsal structure was absent or formed only posteriorly, according to the timing of blastocoel roof removal (Fig.5). From these results, we concluded that the blastocoel roof at ACE contributes not to neural tissue but to ventral epidermis.
Affiliation: JT Biohistory Research Hall, 1-1 Murasaki-cho, Takatsuki, Osaka, 569-1125, Japan; Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka, 560-0043, Japan.