PATTERNING THE XENOPUS BLASTULA

This review starts from the classical standpoint that there are at lea st two separable processes acting with respect to axis formation and t issue specification in the early Xenopus embryo: a UV-insensitive even t establishing a postgastrula embryo consisting of three concentric ge rm layers, ectoderm, mesoderm and endoderm, all of a ventral character ; and a UV-sensitive event producing tissue of a dorsal type, includin g somites, notochord and neural tissue, and concomitantly establishing the dorsoventral and anteroposterior axes. The experimental evidence suggesting the molecular basis of the dorsal and ventral pathways is r eviewed.