Wardle Fiona C, Smith James C
Wellcome Trust/Cancer Research UK Gurdon Institute and Department of Zoology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK.
Development. 2004 Oct;131(19):4687-96. doi: 10.1242/dev.01340. Epub 2004 Aug 25.
During blastula and gastrula stages of Xenopus development, cells become progressively and asynchronously committed to a particular germ layer. We have analysed the expression of genes normally expressed in ectoderm, mesoderm or endoderm in individual cells from early and late gastrula embryos, by both in situ hybridization and single-cell RT-PCR. We show that at early gastrula stages, individual cells in the same region may express markers of two or more germ layers, and 'rogue' cells that express a marker outside its canonical domain are also observed at these stages. However, by the late gastrula stage, individual cells express markers that are more characteristic of their position in the embryo, and 'rogue' cells are seen less frequently. These observations exemplify at the gene expression level the observation that cells of the early gastrula are less committed to one germ layer than are cells of the late gastrula embryo. Ectodermal cells induced to form mesendoderm by the addition of Activin respond by activating expression of different mesodermal and endodermal markers in the same cell, recapitulating the response of marginal zone cells in the embryo.
在非洲爪蟾发育的囊胚期和原肠胚期，细胞逐渐且异步地定向分化为特定的胚层。我们通过原位杂交和单细胞逆转录聚合酶链反应，分析了原肠胚早期和晚期胚胎单个细胞中通常在外胚层、中胚层或内胚层表达的基因的表达情况。我们发现，在原肠胚早期阶段，同一区域的单个细胞可能会表达两个或更多胚层的标志物，并且在这些阶段也会观察到表达其正常区域以外标志物的“异常”细胞。然而，到原肠胚晚期时，单个细胞表达的标志物更能体现其在胚胎中的位置特征，“异常”细胞出现的频率也更低。这些观察结果在基因表达水平上例证了以下现象：原肠胚早期的细胞比原肠胚晚期胚胎的细胞对单一胚层的定向分化程度更低。通过添加激活素诱导形成中内胚层的外胚层细胞，会通过在同一细胞中激活不同的中胚层和内胚层标志物的表达来做出反应，这重现了胚胎中边缘区细胞的反应。
