Ventral vs. dorsal chick dermal progenitor specification.

The dorsal and the ventral trunk integuments of the chick differ in their dermal cell lineage (originating from the somatic and somatopleural mesoderm respectively) and in the distribution of their feather fields. The dorsal macropattern has a large spinal pteryla surrounded by semi-apteria, whereas the ventral skin has a true medial apterium surrounded by the ventral pterylae. Comparison of the results of heterotopic transplantations of distal somatopleure in place of somatic mesoderm (Mauger 1972) or in place of proximal somatopleure (our data), leads to two conclusions. These are that the fate of the midventral apterium is not committed at day 2 of incubation and that the signals from the environment which specify the ventral and dorsal featherforming dermal progenitors are different. Effectively, Shh, but not Wnt -1 signalling can induce the formation of feather forming dermis from the embryonic somatopleure. Shh is not able, however, to trigger the formation of a feather forming dermis from the extra embryonic somatopleure. This brief report constitutes the first attempt, by comparing old and new preliminary results, to understand whether dermal progenitors at different sites are specified by different signalling pathways.