EXPRESSION OF THE GLUCOCORTICOID RECEPTOR GENE IS REGULATED DURING EARLY EMBRYOGENESIS OF XENOPUS-LAEVIS

To study the possible role of the glucocorticoid receptor (GR) in earl y embryogenesis, we isolated a Xenopus glucocorticoid receptor cDNA fr om an embryonic stage 17 cDNA library. Overexpression of this Xenopus GR in COS cells confers the ability to transactivate a GRE-tk CAT prom oter construct in a ligand dependent manner. Expression of the Xenopus GR gene at the RNA level was analyzed by Northern blot hybridization. Transcripts of 4 and 6 kb are present in oocytes. The 4 kb mRNA is ab undant and is degraded together with the 6 kb mRNA during cleavage sta ges of early development. Between stages 17 and 24, GR messengers are extremely rare. From stage 32 onwards, both GR transcripts start to be expressed again at intermediate levels. These results provide the fir st evidence that expression of the GR gene is regulated during early e mbryonic development.