The unfertilized frog egg is radially symmetric abut its primary, animal-vegetal axis, but events after fertilization lead to completely different developmental fates for various cytoplasmic regions. The earliest steps in this regional specialization probably involve relocalization of components already present in the egg. The aims of this project are to define the major cellular mechanisms whereby such determinants might be localized in early Xenopus laevis embryogenesis and evaluate the developmental importance of those localizations. Two extensive rearrangements of the deep cytoplasm during early embryogenesis will be examined. The first of these movements occurs during the first cell cycle, and appears to result from the directed translocation of the vegetal yolk mass- a complicated shift of ventral egg cytoplasm toward the prospective dorsal side. the second movement is an extensive ingression of subcortical cytoplasm along cleavage furrows during each early cell division. These rearrangements will be followed in eggs in which yolk platelets in specific regions have been fluorescently labelled, to produce a 3-dimensional picture of egg cytoplasmic movements. The importance of these rearrangements for specification of the embryonic body axis will be evaluated by comparing them in normal and experimental embryos, the latter treated in a variety of ways to disrupt normal cytoplasmic rearrangements. %%% How a radially symmetric egg develops into an adult with a dorsal/ventral and anterior/posterior axis is a fundamental question of developmental biology. These axes are set up very early in development. This study is to examine some of those very early events that lead to axis formation.
