Epidermis and neural tissues differentiate from the ectoderm in animal embryos. Although epidermal fate is thought to be induced in vertebrate embryos, embryological evidence has indicated that no intercellular interactions during early stages are required for epidermal fate in ascidian embryos. To test this hypothesis, we determined the gene regulatory circuits for epidermal and neural specification in the ascidian embryo. These circuits started with Tfap2-r.b and Sox1/2/3, which are expressed in the ectodermal lineage immediately after zygotic genome activation. Tfap2-r.b expression was diminished in the neural lineages upon activation of fibroblast growth factor signaling, which is known to induce neural fate, and sustained only in the epidermal lineage. Tfap2-r.b specified the epidermal fate cooperatively with Dlx.b, which was activated by Sox1/2/3. This Sox1/2/3-Dlx.b circuit was also required for specification of the anterior neural fate. In the posterior neural lineage, Sox1/2/3 activated Nodal, which is required for specification of the posterior neural fate. Our findings support the hypothesis that the epidermal fate is specified autonomously in ascidian embryos.
The authors declare no competing or financial interests.
K.S.I. and Y.S. conceived the project and wrote the paper. K.S.I, H.H., K.K., and Y.S. performed experiments.
This research was supported by a Grant-in-Aid from the Japan Society for the Promotion of Science (26711014 to K.S.I.), and the CREST program of the Japan Science and Technology Agency to Y.S.
Supplementary information available online at http://dev.biologists.org/lookup/doi/10.1242/dev.142109.supplemental
- Received July 12, 2016.
- Accepted November 14, 2016.