Read E M, Rodaway A R, Neave B, Brandon N, Holder N, Patient R K, Walmsley M E
Developmental Biology Research Centre, King's College London, The Randall Institute, United Kingdom.
Int J Dev Biol. 1998 Sep;42(6):763-74.
Recent studies in early Xenopus and zebrafish embryos have demonstrated that posteriorizing, non-axial signals arising from outside the organizer (or shield) contribute to A/P patterning of the neural axis, in contradiction to the classical Spemann model in which such signals were proposed to be solely organizer derived. Our studies on the early expression of the transcription factors GATA-2 and 3 in both Xenopus and zebrafish nonneural ectoderm lend support to the existence of such non-axial signaling in the A/P axis. Thus we find that the earliest expression of GATA-2 and 3 is located in nonneural ectoderm and is strongly patterned in a graded manner along the A/P axis, being high anteriorly and absent from the most posterior regions. This results by early neurula stages in three broad zones: an anterior region which is positive for both GATA-2 and 3, a middle region which is positive for GATA-2 alone and a posterior region in which neither gene is expressed. These regions correspond to head, trunk and tail ectoderm and may represent the beginnings of functional segmentation of nonneural ectoderm, as suggested in the concept of the 'ectomere'. We find that A/P patterning of GATA expression in nonneural ectoderm may occur as early as late blastula/early gastrula stages. We investigate which posteriorizing signals might contribute to such distinct non axial ectodermal patterning in the A/P axis and provide evidence that both FGF and a Wnt family member contribute towards the final A/P pattern of GATA expression in nonneural ectoderm.
近期对非洲爪蟾和斑马鱼早期胚胎的研究表明，来自组织者（或胚盾）之外的使胚胎后部化的非轴向信号，对神经轴的前后模式形成有影响，这与经典的施佩曼模型相矛盾，在经典模型中，这类信号被认为仅源自组织者。我们对非洲爪蟾和斑马鱼非神经外胚层中转录因子GATA - 2和3的早期表达进行的研究，支持了在前后轴存在这种非轴向信号传导的观点。因此我们发现，GATA - 2和3最早的表达位于非神经外胚层，并且沿前后轴以梯度方式强烈形成模式，前部表达高，最后部区域则无表达。到神经胚早期阶段，这导致形成三个大致区域：对GATA - 2和3均呈阳性的前部区域、仅对GATA - 2呈阳性的中部区域以及两个基因均不表达的后部区域。这些区域分别对应头部、躯干和尾部外胚层，可能代表了非神经外胚层功能分段的开端，就如同“外节”概念中所提出的那样。我们发现，非神经外胚层中GATA表达的前后模式形成可能早在囊胚晚期/原肠胚早期阶段就已发生。我们研究了哪些使胚胎后部化的信号可能导致前后轴上这种独特的非轴向外胚层模式形成，并提供证据表明，FGF和一个Wnt家族成员都对非神经外胚层中GATA表达的最终前后模式有贡献。
