National Institute for Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892, USA.
Proc Natl Acad Sci U S A. 2011 May 31;108(22):9143-7. doi: 10.1073/pnas.1018513108. Epub 2011 May 16.
Although it is well established that neural cells are ectodermal derivatives in bilaterian animals, here we report the surprising discovery that some of the pharyngeal neurons of sea urchin embryos develop de novo from the endoderm. The appearance of these neurons is independent of mouth formation, in which the stomodeal ectoderm joins the foregut. The neurons do not derive from migration of ectoderm cells to the foregut, as shown by lineage tracing with the photoactivatable protein KikGR. Their specification and development depend on expression of Nkx3-2, which in turn depends on Six3, both of which are expressed in the foregut lineage. SoxB1, which is closely related to the vertebrate Sox factors that support a neural precursor state, is also expressed in the foregut throughout gastrulation, suggesting that this region of the fully formed archenteron retains an unexpected pluripotency. Together, these results lead to the unexpected conclusion that, within a cell lineage already specified to be endoderm by a well-established gene regulatory network [Peter IS, Davidson EH (2010) Dev Biol 340:188-199], there also operates a Six3/Nkx3-2-dependent pathway required for the de novo specification of some of the neurons in the pharynx. As a result, neuroendoderm precursors form in the foregut aided by retention of a SoxB1-dependent pluripotent state.
尽管已经证实神经细胞是两侧对称动物外胚层的衍生物，但在这里我们报告了一个令人惊讶的发现，即某些海胆胚胎的咽神经元是从头从内胚层发育而来的。这些神经元的出现与口的形成无关，在口的形成过程中，原口外胚层与前肠相连。神经元不是由外胚层细胞迁移到前肠而来的，这一点通过光激活蛋白 KikGR 的谱系追踪得到了证明。它们的特化和发育依赖于 Nkx3-2 的表达，而 Nkx3-2 又依赖于 Six3，两者都在前肠谱系中表达。SoxB1 与支持神经前体细胞状态的脊椎动物 Sox 因子密切相关，在整个原肠胚形成过程中也在前肠中表达，这表明完全形成的原肠胚的这个区域保留了一种出人意料的多能性。这些结果共同导致了一个出人意料的结论，即在一个已经由一个成熟的基因调控网络指定为内胚层的细胞谱系内，还存在一个依赖于 Six3/Nkx3-2 的通路，该通路对于咽中的一些神经元的从头特化是必需的。因此，在前肠中，神经内胚层前体的形成得益于 SoxB1 依赖性多能状态的保留。
