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- Title
A maternally established Sox B1/ Sox F axis is a conserved feature of chordate germ layer patterning.
- Authors
Cattell, Maria V.; Garnett, Aaron T.; Klymkowsky, Michael W.; Medeiros, Daniel M.
- Abstract
SUMMARY Despite deep evolutionary roots in the metazoa, the gene regulatory network driving germ layer specification is surprisingly labile both between and within phyla. In Xenopus laevis, Sox B1- and Sox F-type transcription factors are intimately involved in germ-layer specification, in part through their regulation of Nodal signaling. However, it is unclear if X. laevis is representative of the ancestral vertebrate condition, as the precise roles of Sox F and Sox B1 in germ-layer specification vary among vertebrates, and there is no evidence that Sox F mediates germ-layer specification in any invertebrate. To better understand the evolution of germ-layer specification in the vertebrate lineage, we analyzed the expression of sox B1 and sox F genes in embryos and larvae of the basal vertebrate lamprey, and the basal chordate amphioxus. We find that both species maternally deposit sox B1 m RNA in the animal pole, sox F m RNA in the vegetal hemisphere, and zygotically express sox B1 and sox F throughout nascent ectoderm and mesendoderm, respectively. We also find that sox F is excluded from the vegetalmost blastomeres in lamprey and that, in contrast to vertebrates, amphioxus does not express sox F in the oral epithelium. In the context of recent work, our results suggest that a maternally established animal/vegetal Sox axis is a deeply conserved feature of chordate development that predates the role of Nodal in vertebrate germ-layer specification. Furthermore, exclusion of this axis from the vegetal pole in lamprey is consistent with the presence of an extraembryonic yolk mass, as has been previously proposed. Finally, conserved expression of Sox F in the forming mouth across the vertebrates, but not in amphioxus, lends support to the idea that the larval amphioxus mouth is nonhomologous to the vertebrate mouth.
- Subjects
GENE regulatory networks; XENOPUS laevis; METAZOA evolution; ELEUTHERODACTYLUS coqui; BLASTOMERES
- Publication
Evolution & Development, 2012, Vol 14, Issue 1, p104
- ISSN
1520-541X
- Publication type
Article
- DOI
10.1111/j.1525-142X.2011.00525.x