Jones C M, Broadbent J, Thomas P Q, Smith J C, Beddington R S
Division of Developmental Biology, National Institute for Medical Research, The Ridgeway, Mill Hill, NW7 1AA, UK.
Curr Biol. 1999 Sep 9;9(17):946-54. doi: 10.1016/s0960-9822(99)80421-7.
Signals from anterior endodermal cells that express the homeobox gene Hex initiate development of the most rostral tissues of the mouse embryo. The dorsal/anterior endoderm of the Xenopus gastrula, which expresses Hex and the putative head-inducing gene cerberus, is proposed to be equivalent to the mouse anterior endoderm. Here, we report the origin and signalling properties of this population of cells in the early Xenopus embryo.
Xenopus anterior endoderm was found to derive in part from cells at the centre of the blastocoel floor that express XHex, the Xenopus cognate of Hex. Like their counterparts in the mouse embryo, these Hex-expressing blastomeres moved to the dorsal side of the Xenopus embryo as gastrulation commenced, and populated deep endodermal adjacent to Spemann's organiser. Experiments involving the induction of secondary axes confirmed that XHex expression was associated with anterior development. Ventral misexpression of XHex induced ectopic cerberus expression and conferred anterior signalling properties to the endoderm. Unlike the effect of misexpressing cerberus, these signals could not neuralise overlying ectoderm.
XHex expression reveals the unexpected origin of an anterior signalling centre in Xenopus, which arises in part from the centre of the blastula and localises to the deep endoderm adjacent to Spemann's organiser. Signals originating from these endodermal cells impart an anterior identity to the overlying ectoderm, but are insufficient for neural induction. The anterior movement of Hex-expressing cells in both Xenopus and mouse embryos suggests that this process is a conserved feature of vertebrate development.
表达同源框基因Hex的前肠内胚层细胞发出的信号启动了小鼠胚胎最前端组织的发育。非洲爪蟾原肠胚的背侧/前肠内胚层表达Hex和假定的头部诱导基因cerberus，被认为等同于小鼠的前肠内胚层。在此，我们报告了非洲爪蟾早期胚胎中这群细胞的起源和信号特性。
发现非洲爪蟾的前肠内胚层部分来源于囊胚腔底部中央表达XHex（Hex的非洲爪蟾同源物）的细胞。与小鼠胚胎中的对应细胞一样，随着原肠胚形成开始，这些表达Hex的卵裂球迁移到非洲爪蟾胚胎的背侧，并聚集在与施佩曼组织者相邻的深层内胚层中。涉及诱导次生轴的实验证实，XHex的表达与前部发育相关。XHex在腹侧的异位表达诱导了异位的cerberus表达，并赋予内胚层前部信号特性。与cerberus异位表达的效果不同，这些信号不能使覆盖的外胚层神经化。
XHex的表达揭示了非洲爪蟾中一个意想不到的前部信号中心的起源，该中心部分源自囊胚的中央，并定位于与施佩曼组织者相邻的深层内胚层。源自这些内胚层细胞的信号赋予覆盖的外胚层前部特征，但不足以诱导神经形成。非洲爪蟾和小鼠胚胎中表达Hex的细胞的前部迁移表明，这一过程是脊椎动物发育的一个保守特征。
