Regulation of region-specific neural genes in zebrafish early embryos

对两栖动物胚胎的分析表明，中枢神经系统的诱导和前后模式是由组织者和组织者衍生的轴向中胚层产生的信号启动的。然而，我们在这里表明，斑马鱼中枢神经系统的初始前后模式取决于外胚层的差异能力，而不是由组织者衍生的信号强加的。这种前后信息存在于通常产生神经和非神经衍生物的外胚层细胞的整个外胚层。由于这些信息，移植到胚胎腹侧的组织者组织可以诱导神经组织，但诱导神经组织的前后身份取决于诱导组织在外胚层内的位置。因此，无论移植物的位置如何，前神经标记物otx2只在胚胎的前区被诱导。同样，hoxa-1，一种后侧神经标记物，只在后侧区域被诱导。此外，每个异位表达域在胚胎腹侧的边界始终与胚胎背侧的内源性表达域处于相同的纬度。外胚层的正反面特征与胚胎的背腹侧特征无关，因为在腹侧胚胎中诱导的神经组织也表现出正反面特征。细胞移植和RNA注射实验表明，非轴向边缘中胚层和FGF信号是外胚层正向分化所必需的。然而，对FGF信号的要求是间接的，因为对FGF反应能力受损的细胞仍然可以对前后位信息作出反应。

Analyzes using amphibian embryos proposed that induction and anteroposterior patterning of the central nervous system is initiated by signals that are produced by the organizer and organizer-derived axial mesoderm. However, we show here that the initial anteroposterior pattern of the zebrafish central nervous system depends on the differential competence of the epiblast, and is not imposed by organizer derived signals. This anteroposterior information is present throughout the epiblast in ectodermal cells that normally give rise both to neural and non-neural derivatives. Because of this information, organizer tissues transplanted to the ventral side of the embryo induce neural tissue but the anteroposterior identity of the induced neural tissue is dependent upon the position of the induced tissue within the epiblast. Thus, otx2, an anterior neural marker, was only ever induced in anterior regions of the embryo, irrespictive of the position of the grafts. Similarly, hoxa-1, a posterior neural marker was induced only in the posterior regions. Furthermore, the boundary of each ectopic expression domain on the ventral side was always at an equivalent latitude to that of the endogenous expression of the dorsal side of the embryo. The anteroposterior specification of the epiblast is independent of the dorsoventral specification of the embryo because neural tissues induced in the ventralized embryos also showed anteroposterior polarity. Cell transplantation and RNA injection experiments showed that non-axial marginal mesoderm and FGF signalling is required for anteroposterior specification of the epiblast. However, the requirement for FGF signalling is indirect in that cells with compromised ability to respond to FGF can still respond to anteroposterior positional information.