INDUCTION OF ANTEROPOSTERIOR NEURAL PATTERN IN XENOPUS - EVIDENCE FORA QUANTITATIVE MECHANISM

The developing vertebrate nervous system arises from ectoderm in respo nse to inductive signals from the dorsal mesoderm, or Spemann organize r. It displays pronounced anteroposterior (AP) pattern, but the mechan ism that generates this pattern is poorly understood. We demonstrate t hat the inducing ability of dorsal mesoderm is regionalized along the AP axis at the early gastrula stage, using the homeodomain-encoding ge nes Xanf-2 and en-2 as markers of anterior and mid-neural pattern, res pectively. In addition, we show that changing the size ratio of poster ior dorsal mesoderm to responding ectoderm affects the type of AP patt ern induced. A low ratio leads to induction of anterior neural pattern , while a high ratio leads to expression of only mid-neural pattern. T hese and other results indicate that a quantitative mechanism specifie s AP neural pattern.