Vodicka M A, Gerhart J C
University of California, Berkeley 94720, USA.
Development. 1995 Nov;121(11):3505-18. doi: 10.1242/dev.121.11.3505.
Spemann's Organizer, located in the dorsal marginal zone of the amphibian gastrula, induces and differentiates dorsal axial structures characteristic of this and other vertebrates. To trace the cellular origins of the Xenopus Organizer, we labelled dorsal blastomeres of three of the four tiers (A, B and C) of the 32-cell embryo with green, red and blue fluorescent lineage tracers. A strong vegetalward displacement of labelled clones occurs between the late blastula and early gastrula stages but clones mix only slightly at their borders. The typical early gastrula Organizer is composed of approximately 10% A1 progeny in its animalmost region, 70% B1 progeny in the central region, and 20% C1 progeny in vegetal and deep regions. Variability in the composition of the early gastrula Organizer results from variability in the position of early cleavage planes and in pregastrulation movements. As the Organizer involutes during gastrulation, forming dorsal axial mesoderm, clonal boundaries are greatly dispersed by cell intermixing. Within a clone, deep cells are displaced and intermixed more than superficial cells. Variability in the distribution of progeny in the dorsal axial mesoderm of the late gastrula results mostly from variable intermixing of cells during gastrulation. Experiments to perturb later developmental events by molecular or embryonic manipulations at an early stage must take this variability into account along with the majority distributions of the fate map. Within the early gastrula Organizer, the genes Xbra, goosecoid, noggin and xNR3 are expressed differently in the animal-vegetal and superficial-deep dimensions. In situ hybridization and lineage labelling define distinct regions of the dorsal marginal zone. By the end of gastrulation, dorsal axial mesoderm cells derived from the Organizer have altered their expression of the genes Xbra, goosecoid, noggin and xNR3. At a given stage, a cell's position in the embryo rather than its lineage may be more important in determining which genes it will express.
施佩曼组织者位于两栖类原肠胚的背侧边缘区，诱导并分化出该物种以及其他脊椎动物特有的背侧轴结构。为了追踪非洲爪蟾组织者的细胞起源，我们用绿色、红色和蓝色荧光谱系示踪剂标记了32细胞胚胎四层（A、B和C层）中三层的背侧卵裂球。在囊胚后期和原肠胚早期阶段之间，标记克隆发生了强烈的向植物极的位移，但克隆仅在其边界处略有混合。典型的早期原肠胚组织者在其最动物极区域由约10%的A1后代组成，在中央区域由70%的B1后代组成，在植物极和深部区域由20%的C1后代组成。早期原肠胚组织者组成的变异性源于早期卵裂平面位置和原肠胚形成前运动的变异性。随着组织者在原肠胚形成过程中内卷，形成背侧轴中胚层，克隆边界因细胞混合而大大分散。在一个克隆内，深层细胞比表层细胞的位移和混合更多。晚期原肠胚背侧轴中胚层中后代分布的变异性主要源于原肠胚形成过程中细胞的可变混合。在早期阶段通过分子或胚胎操作干扰后期发育事件的实验必须考虑到这种变异性以及命运图谱的多数分布情况。在早期原肠胚组织者内，基因Xbra、鹅膏蕈氨酸、头蛋白和xNR3在动物 - 植物极和表层 - 深部维度上的表达有所不同。原位杂交和谱系标记定义了背侧边缘区的不同区域。到原肠胚形成结束时，源自组织者的背侧轴中胚层细胞改变了它们对基因Xbra、鹅膏蕈氨酸、头蛋白和xNR3的表达。在给定阶段，细胞在胚胎中的位置而非其谱系在决定它将表达哪些基因方面可能更重要。
