MESODERMAL PATTERNING BY A GRADIENT OF THE VERTEBRATE HOMEOBOX GENE GOOSECOID

Amphibian mesoderm arises from the marginal zone of the early gastrula and generates various tissues such as notochord, muscle, kidney, and blood. Small changes (twofold) in the amount of microinjected messenge r RNA encoding the goosecoid (gsc) homeodomain protein resulted in mar ked changes in the differentiation of mesoderm in Xenopus laevis. At l east three thresholds were observed, which were sufficient to specify four mesodermal cell states. Endogenous gsc messenger RNA was expresse d in the marginal zone in a graded fashion that is congruent with a ro le for this gene in dorso-ventral patterning of mesoderm at the early gastrula stage.