MESODERMAL INDUCTION

Mesodermal induction is one of the most important events that lead to the establishment of the primary body plan in vertebrate embryos. Our knowledge of this process is based on concepts which have arisen essen tially from experimental embryological studies on amphibian embryos. O ur understanding of inductive processes and mesoderm patterning at the molecular level has considerably progressed in the last few years. Th ere is increasing evidence that induction of the dorsal mesoderm of th e early gastrula (Spemann organizer) results from the combined action of growth factors such as FGF and activin together with competence mod ifyers such as Wnt or noggin. The activity of the Spemann organizer re quires the expression of several homeobox genes among which goosecoid most probably plays a crucial role. These data have been obtained in X enopus embryos but investigations should certainly be extended in the near future to higher vertebrates, particularly to mammals where they are still very incomplete.