PRODUCTION OF HYPERDORSAL LARVAE BY EXPOSING UNCLEAVED XENOPUS EGGS TO A CENTRIFUGAL FORCE DIRECTED FROM THE ANIMAL POLE TO THE VEGETAL POLE

Exposure of uncleaved Xenopus eggs to a centrifugal force directed fro m the animal pole to the vegetal pole produces larvae with enhanced do rsal structures, which resemble 'hyperdorso-anterior' larvae produced by D2O-treatment at 0.3 normalized time (NT). Optimal conditions are 7 0 g for 6 min at 20% of the first cell cycle (0.2 NT). Exposure before removal of vegetal pole cortical cytoplasm, which we find has an effe ct of eliminating dorsal structures, protects eggs from losing their a bility to form dorsal axial structures upon removal. In contrast, expo sure after a slight ultraviolet (UV)-irradiation, which has virtually no effect on dorsal development, produces larvae with heavily reduced dorsal structures, which resemble 'ventralized' larvae produced by hea vy UV-irradiation. Interestingly, none of these treatments prevents co rtical rotation. Morphological and histological examinations reveal th at exposure to the force causes displacement of both cortical and deep egg components from around the vegetal pole to subequatorial regions. We conclude that exposure to the centrifugal force enhances dorsal st ructures by displacing dorsal determinants from around the vegetal pol e to subequatorial regions broader than normal. This is the first expe riment in which displacement of egg components, by methods independent of the rotation, are shown to perturb larval body pattern.