Department of Biological Sciences, Duquesne University, Pittsburgh, PA, USA,
Dev Genes Evol. 2013 Nov;223(6):351-62. doi: 10.1007/s00427-013-0451-y. Epub 2013 Sep 17.
Unlike Xenopus laevis, Eleutherodactylus coqui develops without a tadpole. The yolk-rich vegetal region of the embryo forms a transient nutritive tissue, the nutritional endoderm (NE). The definitive endoderm (DE) in E. coqui comes from cells closer to the animal pole in contrast to its vegetal origin in X. laevis. RNA important for initiating the endoderm specification network is absent in presumptive NE cells, raising the question whether signaling occurs in them. We explored the nature of NE and asked how differences between NE and DE cells arise. We identified differences between NE and DE that first become evident at gastrula, when NE cells become multinucleated. Nuclear β-catenin, an essential cofactor of sox 17, important for endoderm formation in X. laevis, is present in NE and DE at gastrula but remains in NE long after it is not seen in DE. We cloned E. coqui homologs of TGFβs activin b and derriere and provide evidence for their maternal expression. We also detected activin b and derriere RNAs in NE at gastrula and show that NE possesses some mesoderm-inducing activity, but it is delayed with respect to DE. Our findings indicate that altered development of NE begins at gastrula. RNAs important for mesendoderm induction and some mesoderm-inducing activity are present in NE.
与非洲爪蟾不同，Eleutherodactylus coqui 的发育过程中没有蝌蚪期。胚胎富含卵黄的植物极区域形成了一种短暂的营养组织，即营养内胚层（NE）。与非洲爪蟾的植物起源相反，E. coqui 的真正内胚层（DE）来自更靠近动物极的细胞。对于启动内胚层特化网络非常重要的 RNA 在内胚层前体细胞中缺失，这引发了一个问题，即信号是否在内胚层前体细胞中发生。我们探索了 NE 的性质，并询问了 NE 和 DE 细胞之间的差异是如何产生的。我们发现，NE 和 DE 之间的差异在原肠胚阶段首先变得明显，此时 NE 细胞开始多核化。β-连环蛋白（β-catenin）是 sox17 的必需辅助因子，对于非洲爪蟾的内胚层形成至关重要，它存在于原肠胚期的 NE 和 DE 中，但在 DE 中不再存在后，它仍存在于 NE 中。我们克隆了 E. coqui 的 TGFβ 激活素 b 和 Derriere 同源物，并提供了它们母源表达的证据。我们还在原肠胚期的 NE 中检测到激活素 b 和 Derriere RNA，并表明 NE 具有一定的中胚层诱导活性，但相对于 DE 来说，这种活性是延迟的。我们的研究结果表明，NE 的发育异常始于原肠胚期。对于中内胚层诱导和一些中胚层诱导活性非常重要的 RNA 存在于 NE 中。
