An animal-vegetal axis exists in the unfertilized eggs of the ascidian Halocynthia roretzi. The first phase of ooplasmic segregation brings the egg cortex to the vegetal pole very soon after fertilization. In the present study, when 5-8% of the egg cytoplasm in the vegetal pole region was removed between the first and second phase of segregation, most embryos exhibited failure of gastrulation, ...

All endodermal and mesenchymal cells of the sea urchin embryo descend from the vegetal plate, a thickened epithelium of approximately 50 cells arising at the early blastula stage. Cell types that derive from the vegetal plate are specified conditionally by inductive interactions with underlying micromeres, but the molecular details of vegetal-plate specification remain unresolved. In a search f...

The patterns of proteins synthesized in animal and vegetal regions of Xenopus oocytes, eggs and embryos were examined by 2D gel electrophoresis. In oocytes and eggs, the only proteins synthesized asymmetrically along the animal-vegetal axis were a small number of proteins synthesized predominantly in the vegetal hemisphere. At the cleavage stage there were a total of four proteins synthesized u...

In sea urchin embryos, the animal-vegetal axis is specified during oogenesis. After fertilization, this axis is patterned to produce five distinct territories by the 60-cell stage. Territorial specification is thought to occur by a signal transduction cascade that is initiated by the large micromeres located at the vegetal pole. The molecular mechanisms that mediate the specification events alo...

We have shown in defect experiments that an 8-cell embryo of Xenopus laevis consists of three kinds of cells, that is, animal, vegetal dorsal and vegetal ventral cells, and that cells of different kinds are distinctly different in their developmental capacity. Complete pattern formation occurs in any defect embryo which contains at least two animal, one vegetal dorsal and one vegetal ventral ce...

C H I L D (1936) has described reduction gradients in different stages of developing sea-urchin and starfish larvae. His results concerning the gradients in seaurchin mesenchyme blastulae and early gastrulae have been confirmed with Janus green. There exists a stronger vegetal (acropetal) reduction gradient and a weaker animal one, appearing later, in the normal whole larva. Isolated vegetal ha...

To examine the nature of cytoplasm determinants for dorsal specification in zebrafish, we have developed a method in which we remove the vegetal yolk hemisphere of early fertilized eggs (vegetal removed embryos). When the vegetal yolk mass was removed at the 1-cell stage, the embryos frequently exhibited typical ventralized phenotypes: no axial structures developed. The frequency of dorsal defe...

beta-Catenin has a central role in the early axial patterning of metazoan embryos. In the sea urchin, beta-catenin accumulates in the nuclei of vegetal blastomeres and controls endomesoderm specification. Here, we use in-vivo measurements of the half-life of fluorescently tagged beta-catenin in specific blastomeres to demonstrate a gradient in beta-catenin stability along the animal-vegetal axi...

In the unfertilized egg, germ plasm is widely distributed throughout the vegetal subcortex in small islets. Following fertilization or artificial activation, the location and organization changes, and by the 4- to 8-cell stage the germ plasm forms a small number of large patches overlying the vegetal pole. We distinguish three processes that produce these changes. The first of these is aggregat...

In many animal embryos, a specific gene expression pattern is established along the animal-vegetal axis soon after zygotic transcription begins. In the embryo of the ascidian Ciona intestinalis, soon after the division that separates animal and vegetal hemispheres into distinct blastomeres, maternal Gata.a and β-catenin activate specific genes in the animal and vegetal blastomeres, respectively...