Paraxial and lateral plate influences on reinitiation of wing development in chicken embryos.

Stephens et al. ([1993] Dev. Dynam. 197:157-168) hypothesized that the chick embryo wing territory is not an equipotential system. They proposed that following extirpation of the wing territory, limb formation is reinitiated, stimulated by more paraxial tissues. It was the purpose of this study to test this hypothesis. Four sets of procedures were undertaken in stage 11-12 chick embryos: 1) the wing territory lateral plate was removed (negative controls); 2) medial (between the central axis and somites), lateral (between the mesonephros and lateral plate), and intermediate (between the somites and mesonephros) foil barriers were placed adjacent to the wing territory (positive controls); 3) barriers were placed as above, with the removal of the lateral plate (experimental); and 4) barriers were placed lateral to the area of lateral plate extirpation (experimental). Normal limbs developed in 89% of the embryos without foil barriers with the lateral plate removed. In 93% of the embryos that contained medial barriers, normal wings developed whether or not the limb territory was extirpated, and in 100% of the embryos with intermediate or lateral barriers, with or without extirpation, deficient limbs occurred. When foil barriers were placed lateral to the wound, 87% of the chick wings were either reduced or absent. Closure of the wound following extirpation appeared to progress from lateral to medial. The data from this study appear to support the hypothesis that the limb territory is not equipotential but is reformed from cells closing the wound from lateral to medial, and is reinitiated from paraxial tissues (medial to lateral) following wound healing.