Specification of germ layer identity in the chick gastrula.
Specification of germ layer identity in the chick gastrula.
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DOI：
10.1186/1471-213x-7-91
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发表时间：
2007-07-30
影响因子：
--
通讯作者：
Schoenwolf GC
中科院分区：
文献类型：
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作者：
Chapman SC;Matsumoto K;Cai Q;Schoenwolf GC
鸡定形内胚层是早期胚胎形成中心结构的重要信号来源，围绕该中心结构构建体平面。虽然确定的内胚层的起源已被映射在鸡，主要是由嘴条在延长线阶段，它是不知道当这层第一次成为完全致力于其胚层的命运，一个重要的问题，以解决在早期胚胎的后续图案的关键作用。通过鸡原肠胚基因表达筛选，我们确定了限定性内胚层的分子标记，仅限于吻侧（Sox 17）和尾侧（Gata 5/6）区域，这表明在侵入过程中至少存在两个限定性内胚层细胞亚群。我们发现：（1）假定的中胚层细胞迁移到中层，并保持间充质移植到吻原条，和预期的内胚层细胞进入下层，并成为上皮细胞移植到尾原条;和（2）假定的内胚层细胞和中胚层细胞失去正常的基因表达（Sox 17和Wnt 8 c，分别）时，移植到其正常的位置的起源。此外，当吻侧或尾侧原条片段被移植到吻侧胚盘分离物（RBIs）中时，两种类型的移植物在4-6小时后表达Sox 17-与它们的新位置一致，而不管它们假定的胚层来源-并且预期的中胚层移植物（其通常表达Wnt 8 c）关闭表达，这表明吻侧胚盘内的信号诱导内胚层基因表达，并在原肠胚形成期间抑制中胚层基因表达。我们的研究结果表明，胚层身份是固定的时间内胚层和中胚层细胞的人口通过原条入境，而他们的基因表达模式仍然不稳定。此外，我们的研究结果表明，诱导和抑制信号的存在，这些信号调节基因表达的侵入内胚层和中胚层细胞。因此，原肠胚细胞显示出前图案化和可塑性的元素，内胚层是第一胚层，在原肠胚形成早期阶段被赋予其命运。
Chick definitive endoderm is an important source of signals that pattern the early embryo forming a central structure around which the body plan is constructed. Although the origin of definitive endoderm has been mapped in the chick, arising principally from rostral streak at elongating streak stages, it is not known when this layer first becomes fully committed to its germ layer fate, an important issue to resolve in light of its critical role in subsequent patterning of the early embryo. Through gene expression screening of chick gastrula, we identified molecular markers of definitive endoderm restricted to rostral (Sox17) and caudal (Gata5/6) regions, suggesting that at least two subpopulations of definitive endodermal cells exist during ingression. We show (1) that presumptive mesoderm cells migrate to the middle layer and remain mesenchymal when transplanted to rostral primitive streak, and prospective endoderm cells enter the lower layer and become epithelial when transplanted to caudal primitive streak; and (2) that presumptive endoderm cells and mesoderm cells lose normal gene expression (Sox17 and Wnt8c, respectively) when transplanted outside of their normal position of origin. Moreover, when rostral or caudal primitive streak segments are transplanted into rostral blastoderm isolates (RBIs), both types of transplants express Sox17 4–6 hours later–consistent with their new position, regardless of their presumptive germ layer origin–and prospective mesoderm transplants, which normally express Wnt8c, turn off expression, suggesting that signals within the rostral blastoderm induce endoderm gene expression, and repress mesoderm gene expression, during gastrulation. Our results demonstrate that germ layer identity is fixed at the time populations of endoderm and mesoderm cells ingress through the primitive streak, whereas their gene expression patterns remain labile. In addition, our results show that inductive and repressive signals are present, and that these signals regulate gene expression of both ingressed endoderm and mesoderm cells. Thus, gastrula cells display elements of both pre-patterning and plasticity, with endoderm the first germ layer becoming committed to its fate during early gastrulation stages.