Cloning, Sequencing, and Localization of Bovine Estrogen Receptor-β within the Ovarian Follicle

The potential role of estrogen receptor-β (ERβ) in normal ovarian folliculogenesis and in reproductive disorders such as ovarian follicular cysts has not been well defined. Therefore, we were interested in cloning, sequencing, and localizing ERβ mRNA and protein within the bovine ovary. Bovine ERβ (bERβ) was amplified by reverse transcription-polymerase chain reaction (RT-PCR), then cloned and sequenced. Results showed that the open reading frame of bERβ cDNA spanned 1584 nucleotides encoding a protein of 527 amino acids. The N-terminal region of bERβ was found to be 80% homologous to human and mouse ERβ and 79% homologous to rat ERβ. Bovine ERβ DNA-binding domain was 100% homologous to human, mouse, and rat ERβ sequences. The C-terminal/ligand-binding domain of bERβ was 89% homologous to human, 86% homologous to mouse, and 88% homologous to rat ERβ. Human and bovine ERβ amino acid sequences are similar in that their coding region extended farther 5′ than initially reported for the published rat ERβ sequence. Using in situ hybridization and immunohistochemistry, ERβ mRNA and protein, respectively, were demonstrated to be present in granulosa cells of antral follicles in various stages of follicular growth. These findings suggest a role for bERβ in ovarian follicular growth and maturation.