Analysis of the Formation of the Animal-Vegetal Axis during Xenopus Oogenesis Using Monoclonal Antibodies

Maternally accumulated materials in Xenopus oocytes, in particular mRNAs and proteins, are considered to participate in the determination of the developmental specification of embryonic cells. In this study, a large number of monoclonal antibodies was raised against bulk oocyte antigens to examine patterns of intracellular distribution of oocyte proteins. Immunohistochemical experiments with mature oocytes showed that there are five different patterns of distribution of oocyte proteins, with enrichment on the animal side (type A₁, and A₂ ptoteins), vegetal side (type V₁ and V₂ proteins), and in the peripheral cytoplasm (type P proteins). Clear localization of type A and V antigen proteins occurred at Dumont's stages IV-VI. However, at the preceding stages, the distributions of these antigen proteins appeared to be homogeneous. By contrast, the pattern of distribution of type P protenis did not change markedly throughout oogenesis. The presence of type A and type V antigen proteins reflected the animal-vegetal axis in the cytoplasm of the mature oocyte. Furthermore, there were two boundaries of the distributions of proteins at the equatorial region, excluding or including the cytoplasm around the germinal vesicle. Thus, the cytoplasm of mature oocytes was multilayered with respect to the different proteins distributed along the animal-vegetal axis.