Control of dorsoventral patterning of somitic derivatives by notochord and floor plate.

We have examined the effect of implantation of a supernumerary notochord or floor plate on dorsoventral somitic organization. We show that notochord and floor plate are able to inhibit the differentiation of the dorsal somitic derivatives--i.e., axial muscles and dermis--thus converting the entire somite into cartilage, which normally arises only from its ventral part. We infer from these results that the dorsoventral patterning of somitic derivatives is controlled by signals provided by ventral axial structures.