Dorsal lip vs blastopore lip3/11/2024 Deuterostome phylogeny reveals monophyletic chordates and the new phylum Xenoturbellida. Multigene analyses of bilaterian animals corroborate the monophyly of Ecdysozoa, Lophotrochozoa, and Protostomia. Molecular phylogeny and divergence times of deuterostome animals. Did the first chordates organize without the organizer? Trends Genet. Evolution of the organizer and the chordate body plan. In light of recent phylogenetic analyses placing cephalochordates basally in the chordate lineage, we propose that separate signalling centres for patterning the D/V and A/P axes may be an ancestral chordate character. These results suggest evolutionary conservation of the mechanisms for both D/V and A/P patterning of the early gastrula. In addition, Wnt-antagonists (for example, Dkks and sFRP2-like) are expressed anteriorly, whereas Wnt genes themselves are expressed posteriorly, consistent with a role for Wnt signalling in anterior/posterior (A/P) patterning. Here we show that the gastrula of the cephalochordate amphioxus expresses dorsal/ventral (D/V) patterning genes (for example, bone morphogenetic proteins ( BMPs), Nodal and their antagonists) in patterns reminiscent of those of their vertebrate orthlogues, and that amphioxus embryos, like those of vertebrates, are ventralized by exogenous BMP protein. Although a topic of long-standing interest, the evolutionary origin of the organizer remains unclear. The organizer of the vertebrate gastrula is an important signalling centre that induces and patterns dorsal axial structures.
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