Regulation of region-specific neural genes in zebrafish early embryos

使用两栖动物胚胎的分析提出，诱导和中枢神经系统的前后图案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，最初的前后模式的斑马鱼中枢神经系统依赖于上胚层的差异能力，而不是由组织者衍生的信号。这种前后信息存在于外胚层细胞的整个上胚层中，通常产生神经和非神经衍生物。由于这些信息，组织者组织移植到胚胎的腹侧诱导神经组织，但诱导的神经组织的前后身份取决于诱导的组织在上胚层内的位置。因此，otx 2，一种前神经标记物，只在胚胎的前区被诱导，与移植物的位置无关。同样，hoxa-1，一个后神经标记物，仅在后部区域被诱导。此外，每个异位表达域在腹侧的边界总是在一个相等的纬度上的内源性表达的背侧的胚胎。前后规范的上胚层是独立的背腹规格的胚胎，因为在腹侧化胚胎诱导的神经组织也表现出前后极性。细胞移植和RNA注射实验表明，非轴向边缘中胚层和FGF信号是必需的前后规范的上胚层。然而，对FGF信号传导的需求是间接的，因为对FGF应答能力受损的细胞仍然可以对前后位置信息应答。

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.