GR TRANSCRIPTS ARE LOCALIZED DURING EARLY XENOPUS-LAEVIS EMBRYOGENESIS AND OVEREXPRESSION OF GR INHIBITS DIFFERENTIATION AFTER DEXAMETHASONE TREATMENT

We have studied the spatial expression of the Xenopus GR in early embr yos by whole-amount in situ hybridization. At the gastrula stage, GR m RNA is localized in the dorsal ectoderm. By the early neurula stage, G R transcripts were detected along the notoplate. Between mid and late neurula stages, GR mRNA was not detectable. At the tailbud stage, GR m RNA was found in the anterior part of the embryo, including the cement gland, eyes, brain, the foregut, stomodeal-hypophyseal anlage, the ol factory placodes, head mesenchyme and somites. Injection of Xenopus GR RNA into zygotes followed by treatment with dexamethasone from the bl astula stage onwards inhibits early differentiation. Expression of Xbr a, gsc and histone H3 genes in these embryos is not inhibited, indicat ing that the GR effects are not due to a general squelching effect on transcription. (C) 1994 Academic Press, Inc.