Article Abstract:
Investigations on dorsoventral patterning reported that the structural formations of the germ layers ectoderm and mesoderm were directed by molecules associated with decapentaplegic genes/bone morphogenetic protein 4 (dpp/Bmp-4), and short gastrulation/Xenopus chordin (sog/chd). This mechanism was especially evidenced in Drosophila and also believed to be feasible with vertebrates. In the latter case, the organizer will release the signals that induce dorsal differentiation which in turn will be opposed by ventral positioning information released by Bmp-4.
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Article Abstract:
The suggestion of D. Arendt and K. Nubler-Jung that decapentaplegic gene is expressed ventrally in the fruitfly Drosophila, while the homologous gene BMP-4 is expressed dorsally in vertebrates, does not agree with the calcihordate theory of chordate origins. This calcihordate theory states that chordates and echinoderms are descendants of an ancestor such as the pterobranch Cephalodiscus. The expression of decapentaplegic depends on the site of the gastrulation-neurulation process.
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Article Abstract:
Auricularia hypothesis, an alternative hypothesis for the peculiar pattern in the developmental control genes of vertebrates and insects, is proposed in contrast to Arendt and Nubler-Jung's theory that the differences in gene patterns are caused by the vertebrate's being turned upside-down during evolution. The hypothesis indicates that this can occur by a partial inversion during the chordate evolution stage.
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