The mouse cellular retinoic acid binding protein-I (CRABP-I) gene is specifically up-regulated by retinoic acid (RA) in P19 mouse embryonal carcinoma cells, and its expression in animals is spatially and temporally restricted to RA-sensitive tissues during embryonic development. This study demonstrates that, in adult mouse tissues and P19 cells where the expression of CRABP-I is detected at the basal level, the 5'-flanking region of the CRABP-I gene is hypermethylated at the C residues of all the H p a I1 sites. Conversely, in mouse embryos during early stages of development when the expression of CRABP-I gene is detected at a much higher level, this region is demethylated at these H p a I1 sites. In P19, enhancement on the RA-induced up-regulation of CRABP-I can be observed in cells treated with 5-azacytidine (5-AzaC) in conjunction with RA, where partial demethylation in the 5'-flanking region of CRABP-I gene is observed. Nuclear run-on experiments indicate that increased message levels of CRABP-I in P19 cells can be accounted for, at least partially, by increases in its transcription rates. The induction of retinoic acid receptor (RAR) p by RA can also be enhanced by 5-AzaC, but to a much lesser degree. In contrast, all the H p a I1 sites in the structural gene portion, at least in the first two exons, are fully demethylated at the C residues. o 1994 WiIey-Liss, Inc.

Transgenic mice with ectopic expression of bovine CRABP under the control of the human metallotheionein IIA promoter have shown a variety of pathological consequences. Expression of the transgene has been detected in most of the tissues examined, including heart, lung, liver, spleen, kidney, intestine, testis, and ovary, except pancreas. Two independent lines have been able to produce normal non‐transgenic F1 animals of both sexes but only female transgenic progenies. All of these F1 female transgenic animals derived from both lines are sterile, and the ovaries from these animals appear to be significantly smaller as compared to their non‐transgenic littermates. Histopathological examinations have shown no maturing follicles in these transgenic ovaries in which abnormal cells have been observed. Another independent line has generated transgenic F1 animals which have been growing retardly. These animals all have small spleen and liver and have become very sick at the age of 4 to 5 weeks. Histopathological examinations on these transgenic progenies have shown hepatocytes to be reduced in the cytoplasmic portion in which glycogen is highly depleted. The spleen is poorly developed as no well organized germinal centers can be observed in the spleen sections of these transgenic animals.