DEMETHYLATION IN THE 5'-FLANKING REGION OF MOUSE CELLULAR RETINOIC ACID-BINDING PROTEIN-I GENE IS ASSOCIATED WITH ITS HIGH-LEVEL OF EXPRESSION IN MOUSE EMBRYOS AND FACILITATES ITS INDUCTION BY RETINOIC ACID INP19 EMBRYONAL CARCINOMA-CELLS

The mouse cellular retinoic acid binding protein-I (CRABP-I) gene is s pecifically up-regulated by retinoic acid (RA) in P19 mouse embryonal carcinoma cells, and its expression in animals is spatially and tempor ally restricted to RA-sensitive tissues during embryonic development. This study demonstrates that, in adult mouse tissues and P19 cells whe re the expression of CRABP-I is detected at the basal level, the 5'-fl anking region of the CRABP-I gene is hypermethylated at the C residues of all the Hpa II sites. Conversely, in mouse embryos during early st ages of development when the expression of CRABP-I gene is detected at a much higher level, this region is demethylated at these Hpa II site s. In P19, enhancement on the RA-induced up-regulation of CRABP-I can be observed in cells treated with 5-azacytidine (5-AzaC) in conjunctio n with RA, where partial demethylation in the 5'-flanking region of CR ABP-I gene is observed. Nuclear run-on experiments indicate that incre ased message levels of CRABP-I in P19 cells can be accounted for, at l east partially, by increases in its transcription rates. The induction of retinoic acid receptor (RAR) beta by RA can also be enhanced by 5- AzaC, but to a much lesser degree. In contrast, all the Hpa II sites i n the structural gene portion, at least in the first two exons, are fu lly demethylated at the C residues. (C) 1994 Wiley-Liss, Inc.