ELINSON, R.P.*; NINOMIYA, H.; Duquesne University, Pittsburgh, PA: Parallel microtubules and other conserved elements of dorsal axial specification in the Puerto Rican tree frog, Eleutherodactylus coqui

In the frogs Xenopus laevis and Rana pipiens, a transient array of parallel microtubules in the vegetal cortex of the egg moves a dorsal determinant asymmetrically. This movement is the initial step in dorsal axial specification. The egg of Eleutherodactylus coqui has twenty times the volume of the X. laevis egg. To assess the impact of large egg size on early development, we investigated dorsal axial specification in E. coqui. Immunocytochemistry revealed an extensive array of parallel microtubules in the vegetal cortex. The microtubules were present before and during first cleavage, so they persisted longer than in the other frogs. Gravity can override the microtubule-based axial specification in X. laevis, and that was the case also in E. coqui. Unlike in X. laevis, gravity remained effective through the 8-cell stage. Finally, injection of Xwnt8 RNA into E. coqui embryos gave secondary axes, indicating that the �-catenin pathway is active in axial specification in these frogs. Dorsal axial specification appears to be conserved in E. coqui, with interesting differences. The microtubule array in E. coqui is much larger, and the array, as well as sensitivity to gravity, persists longer than in other frogs.