Polarity of Xenopus Oocytes and Early Embryos

The Xenopus oocyte/egg contains maternal information (factors) stored in the form of RNAs and proteins, which are necessary and sufficient for cell proliferation after fertilization and early development of the embryo. A large subpopulation of these maternal molecules has a polarized distribution along the animal-vegetal (A-V) axis within the oocyte cytoplasm. Polarity along the A-V axis develops during the elaborate process of oogenesis. It is maintained during egg maturation, fertilization, and subsequent cortical rotation and is required for the developmental transformation of the animal hemisphere into the ectodermal fate (future epidermis and neural cells), the vegetal hemisphere into the endodermal fate (gut) and the germ cell fate, and the marginal zone between into the mesodermal fate (muscle, bone, and blood). In this review, we will describe the factors, mechanisms, developmental functions, and consequences of Xenopus oocyte/egg polarity.