DORSAL DIFFERENTIATION OF NEURAL PLATE CELLS INDUCED BY BMP-MEDIATED SIGNALS FROM EPIDERMAL ECTODERM

The cellular interactions that control the differentiation of dorsal c ell types from neural progenitors have been examined in neural plate e xplants. Certain genes that are expressed in the dorsal neural tube ar e initially expressed uniformly within the neural plate and appear to achieve their dorsal restriction through a Sonic hedgehog (SHH)-mediat ed repressive signal from the notochord. The acquisition of definitive dorsal cell fates, however, requires a contact-dependent signal from the epidermal ectoderm, BMP4 and BMP7 are expressed in the epidermal e ctoderm, and both proteins mimic its inductive activity, BMP4 and a re lated gene, DSL1, are subsequently expressed by cells in the dorsal ne ural tube. The differentiation of dorsal cell types, therefore, appear s to be initiated at the neural plate stage and to involve the opponen t activities of a BMP-mediated dorsalizing signal from the epidermal e ctoderm and a SHH-mediated ventralizing signal from the notochord.