The COUP-adjacent repressor (CAR) element participates in the tissue-specific expression of the ovalbumin gene

The ovalbumin (Ov) gene is an excellent model for the study of tissue-speci fic gene regulation as it is only active in the estrogen-stimulated oviduct . Previous studies have demonstrated that the negative regulatory element ( NRE) in the Ov gene 5'-flanking region is responsible for silencing the gen e in oviduct in the absence of steroids. Linker scanning analysis defined a n element within the NRE designated the COUP-adjacent repressor (CAR) eleme nt as a repressor of Ov gene expression. However, the role of the CAR eleme nt in non-oviduct tissues has not been addressed. Using transient transfect ion analysis of various Ov 5'-flanking region constructs into the estrogen- responsive chicken hepatocyte cell line LMH/2A, we demonstrate that Ov gene expression is not induced by estrogen and that an active repressor element exists in the NRE. Deletion analysis indicates that the region from -134 t o -87, which includes the CAR element, mediates this repression. Mutation o f the CAR element relieves repression, leading to high levels of gene expre ssion. These data support a model where the inhibition of Ov gene expressio n in non-oviduct cells is a combination of the lack of essential positive f actors and the presence of an active repressor, which binds to the CAR elem ent. (C) 2000 Elsevier Science B.V. All rights reserved.