Cloning of bovine estrogen receptor beta (ERβ): expression of novel deleted isoforms in reproductive tissues ☆

Abstract cDNAs coding for bovine estrogen receptor beta (ERβ) isoforms were cloned from bovine granulosa cells using a combination of several RT-PCR strategies. The cloned full-length receptor contains an open reading frame of 474 amino acids encoding a protein with high homology to the ERβ sequences from other species. A second isoform nearly totally lacking the ligand binding domain was cloned that is expressed to relatively high levels in reproductive tissues. Expression of both ERβ isoforms is down-regulated in corpus luteum and endometrium during the luteal phase of the female cycle. In addition, in granulosa cells several ERβ isoforms carrying major internal deletions were detected by RT-PCR and cloned. Transient transfection studies expressing the two major bovine ERβ isoforms together with an ERE reporter construct show estrogen-dependent transactivation by the full-length isoform, whereas the isoform lacking the ligand binding domain did not show any transactivation.