Objectives were to sequence and examine the expression of the estrogen receptor beta (ER beta) in the sheep ovary, The sequence of the ovine ER beta (oER beta) was determined using reverse-transcription polymerase chain reaction (RT-PCR) and cloning techniques, The reading frame of oER beta contained 527 amino acids and exhibited high overall homology with cow (98%), rat (88%), and human (88%) ER beta, In addition, an oER beta isoform having a 139-base pair deletion (oER beta1) was identified. The predicted amino acid sequence of this isoform is tacking the ligand-binding and carboxyl-terminal transactivation domains, The oER beta protein and mRNA were determined in ovaries obtained from ewes on Days 0 (first day of estrus), 2, 6, and 10 of the estrous cycle and Day 30 of gestation. Immunohistochemistry showed that oER beta protein was located in granulosa cells, the ovarian surface epithelium, endothelium, and Day 2 corpus luteum (CL). Weak immunostaining for ERP was detected in the theca interna, Relative steady-state amounts of oER beta mRNA in the CL were determined using semiquantitative RT-PCR, Amounts of oER beta mRNA were greater (P < 0.05) during CL formation (Day 2) than at later stages. The oER beta to oER beta1 mRNA ratio was lower (P < 0.05) on Day 2 than on Day 10 or Day 30 due to a decrease in amounts of oER beta1. Results indicate that the oER beta is a 527-amino acid protein expressed in specific cells of the ovary, Changes in relative amounts of full-length oERB and a deletion isoform in CL occurred during the estrous cycle, suggesting that these two types of ER beta might regulate estrogen actions during early CL development in sheep.
