Beddington R S, Robertson E J
Division of Mammalian Development, MRC National Institute for Medical Research, Ridgeway, Mill Hill, London, UK.
Trends Genet. 1998 Jul;14(7):277-84. doi: 10.1016/s0168-9525(98)01499-1.
The anteroposterior axis of the vertebrate embryo becomes explicit during gastrulation, the process that converts a relatively featureless embryonic precursor population into new tissues assembled into a recognisable body pattern. Vertebrate embryos arrive at gastrulation in very different states in terms of their size, cell number and reliance on factors inherited from the unfertilized egg. However, they emerge from gastrulation looking very similar, and there is now extensive molecular genetic evidence to indicate that the bare essentials of the gastrulation process have been well conserved during evolution. Here, we review recent findings in the mouse that suggest that anterior identity is, in fact, established before gastrulation starts. They suggest that it is first manifest in extraembryonic tissue and that this tissue is essential for the embryo to develop normal anterior structures, such as the forebrain. We also argue that this precocious anterior pattern could have a counterpart in other non-mammalian vertebrates.
脊椎动物胚胎的前后轴在原肠胚形成过程中变得明确，原肠胚形成过程将相对无特征的胚胎前体细胞群转化为组装成可识别身体模式的新组织。脊椎动物胚胎在进入原肠胚形成阶段时，在大小、细胞数量以及对未受精卵中遗传因素的依赖程度方面处于非常不同的状态。然而，它们从原肠胚形成阶段出现时看起来非常相似，现在有大量分子遗传学证据表明，原肠胚形成过程的基本要素在进化过程中得到了很好的保留。在这里，我们回顾了小鼠最近的研究发现，这些发现表明，事实上，前部特征在原肠胚形成开始之前就已确立。它们表明，前部特征首先在胚外组织中显现，并且该组织对于胚胎发育正常的前部结构（如前脑）至关重要。我们还认为，这种早熟的前部模式可能在其他非哺乳动物脊椎动物中也有对应物。
