Heat-Induced Reversal of Dorsal-Ventral Polarity in Xenopus Eggs

Heat-treatment of fertilized Xenopus laevis eggs at 30°C induced; 1. conspicuous concentration of the pigment toward the sperm entry point (SEP), 2. eccentric first cleavage furrow formation, and 3. reversal of the dorsal-ventral polarity of the embryos. The optimal treatment was for 2.5 min applied at 20 min postfertilization (p.f.). The rotation movement of the Nile-blue stained spots in the vegetal hemisphere of the heated eggs accurately located the future dorsal midline as in untreated embryos (ref. 22). Exposure of eggs to D₂O also reversed the dorsal-ventral polarity of the embryo suggesting that stabilization of microtubules is involved in the dorsal-ventral axis reversal.