NEURAL INDUCTION AND ANTERO-POSTERIOR PATTERNING IN THE AMPHIBIAN EMBRYO - PAST, PRESENT AND FUTURE

Neural induction and patterning in competent ectoderm occurs during ga strula and early neurula stages in response to signals from dorsal mes oderm. The earliest views of antero-posterior (A-P) patterning were mo dified beginning in the 1930s, as complexities concerning the timing o f the pattern-forming process and potential sources of the patterning signals were revealed. In the 1950s and 1960s several different models for A-P patterning were proposed, all of which, however, bear a numbe r of similarities, including a two-component system for generating A-P axial information in the embryo. Early attempts to identify neural-in ducing molecules were largely unsuccessful due to technical limitation s in biochemical analyses and concerns about assaying neural responses . The advent of modern molecular genetic technology has permitted more precise tests of a number of classic observations about the timing of A-P patterning and the sources of patterning signals. While some earl y observations have been confirmed, a number of new concepts have emer ged in recent years, particularly concerning the source of patterning signals in the embryo. Striking progress has been made in identifying putative neural-inducing molecules, and recent experiments have begun to suggest how these might contribute to A-P patterning. While the suc cesses in recent years have been revealing, many of the classic issues concerning neural induction and patterning remain essentially as they were when first defined many decades ago. The power of modern molecul ar genetics, however, should permit many of these issues to be signifi cantly clarified in the decades to come.