![fate of a blastopore fate of a blastopore](https://d2vlcm61l7u1fs.cloudfront.net/media/882/882c3441-6df0-481f-9687-eaa6354c0333/phpbu2Y2U.png)
![fate of a blastopore fate of a blastopore](https://media.springernature.com/full/springer-static/image/art%3A10.1186%2Fs13227-015-0019-1/MediaObjects/13227_2015_19_Fig3_HTML.gif)
In deuterostomes, the blastopore forms the anus, but its fate in protostome groups is. Comparisons of the embryos of amphioxus and vertebrates indicate that in spite of large differences in the mechanics of cleavage and gastrulation, anterior/posterior and dorsal/ventral patterning occur by homologous genetic mechanisms. Dorsal lip of the blastopore yolk plug ventral lip of the blastopore. The fate of the blastopore during development in the bilaterian ancestor is currently not well understood. During the gastrula stage, the animal pole shifts ventrally, coming to lie about 20° ventral to the anterior tip of the late gastrula/early neurula. Involution or ingression of cells over the blastopore lip is negligible, and the blastopore, which is posterior, closes centripetally as if by a purse string.
![fate of a blastopore fate of a blastopore](https://media.springernature.com/lw785/springer-static/image/art%3A10.1186%2Fs13227-015-0019-1/MediaObjects/13227_2015_19_Fig15_HTML.gif)
It shows (1) that the anterior pole of the amphioxus embryo is offset dorsally from the animal pole only by about 20°, (2) that the ectoderm/mesendoderm boundary (the future rim of the blastopore) is at the equator of the blastula, which approximately coincides with the 3rd cleavage plane, and (3) that there is no ventral mesoderm during the gastrula stage. This difference reflects the fate of a structure called the blastopore (Figure 6), which becomes the mouth in protostomes and the anus in deuterostomes. The revised fate map is substantially different from that of ascidians. Although detailed cell lineage tracing in amphioxus has not been done because of limited availability of the embryos and because cleavage is radial and holoblastic with the blastomeres nearly equal in size and not tightly adherent until the mid-blastula stage, a compilation of data from gene expression and function, blastomere isolation and dye labeling allows a more realistic fate map to be drawn. It does not ‘recapitulate’ any early evolutionary process during animal evolution, either. Previous embryonic fate maps of the cephalochordate amphioxus (Branchiostoma) were influenced by preconceptions that early development in amphioxus and ascidian tunicates should be fundamentally the same and that the early amphioxus embryo, like that of amphibians, should have ventral mesoderm. Altogether, our study indicates that the fate of the blastopore is a consequence of the axial and cell-fate architecture of each embryo, and not an intrinsic property of the lineage given by its phylogenetic position.
#Fate of a blastopore plus#
The chordates include vertebrates plus two groups of invertebrates (the cephalochordates and tunicates).