Chromosomal mapping and quantitative analysis of estrogen-related receptor alpha-1, estrogen receptors alpha and beta and progesterone receptor in the bovine mammary gland

Steroid receptors are key transcriptional regulators of mammary growth, development and lactation. Expression of estrogen receptors alpha (ER alpha) and beta (ER beta), progesterone receptor (PR), and estrogen-related receptor alpha-1 (ERR alpha) have been evaluated in bovine mammary gland. The ERRa is an orphan receptor that, in other species and tissues, appears to function in the regulation of estrogen-response genes including lactoferrin and medium chain acvl-CoA dehydrogenase and in mitochondrial biogenesis. Expression of ER alpha, ER beta, PR and ERR alpha was characterized in mammary tissue obtained from multiple stages of bovine mammary gland development using quantitative real-time RT-PCR..Expression was evaluated in prepubertal heifers, primigravid cows, lactating non-pregnant cows, lactating pregnant cows and non-lactating pregnant coves (n=4 to 9 animals/stage). In addition, ER alpha, ER beta, PR and ERR alpha were snapped to chromosomes 9, 10, 15 and 29 respectively, by linkage and radiation hybrid mapping. Results indicated that expression of ER alpha, PR and ERR was largely coordinately regulated and they were present in significant quantity during all physiological stages evaluated. In contrast, ER alpha transcripts were present at a very low concentration during all stages. Furthermore, no ER alpha protein could be detected in bovine mammary tissue by immunohistochemistry. The ER alpha and PR proteins were detected during all physiological states, including lactation. Our results demonstrate the presence of ER alpha, PR and ERR alpha during all physiological stages, and suggest a functional role for ERRa and a relative lack of a role for ER beta in bovine mammary gland development and lactation.