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Title: ONTOGENIC AND NUTRITIONAL REGULATION OF STEROID RECEPTOR AND IGF-I TRANSCRIPT ABUNDANCE IN THE PREPUBERTAL BOVINE MAMMARY GLAND

Author
item MEYER, M - CORNELL UNIVERSITY
item RHOADS, R - CORNELL UNIVERSITY
item Capuco, Anthony
item Connor, Erin
item BOISCLAIR, Y - CORNELL UNIVERSITY
item VAN AMBURGH, MIKE - CORNELL UNIVERSITY

Submitted to: Journal of Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/13/2007
Publication Date: 9/2/2007
Citation: Meyer, M.J., Rhoads, R.P., Capuco, A.V., Connor, E.E., Boisclair, Y.R., Van Amburgh, M.E. 2007. Ontogenic and nutritional regulation of steroid receptor and igf-i transcript abundance in the prepubertal bovine mammary gland. Journal of Endocrinology. 195:59-66.

Interpretive Summary: We performed a study to evaluate regulation of five genes that are potentially related to ovarian effects on mammary growth in cattle. These genes were estrogen receptor alpha, ERá; estrogen receptor beta, ERâ; estrogen-related receptor alpha-1, ERRá1; progesterone receptor, PR; and insulin-like growth factor-I, IGF-I. Expression of the genes was evaluated within the portion of the mammary gland containing tissue (parenchyma) that ultimately gives rise to the secretory tissue of the mammary gland as well as from a portion of the mammary gland containing the fatty matrix (fat pad) in which the parenchyma develops. Gene expression was evaluated at multiple times between birth and just beyond puberty. Because of its exceedingly low level of expression in both tissues, ERâ does not appear to be an important regulator of mammary growth. However, expression of the genes for both ERá and IGF-I were expressed at high levels and decreased linearly within both compartments of the mammary gland with increasing age of heifers. No marked changes in expression of these genes were evident to explain the parenchyma's transition from a rapid phase of growth to a slower phase of growth around the time of puberty. However, the decreased expression of ERá and IGF-I as the heifers develop may play a role in this process.

Technical Abstract: In the bovine, an obligatory role of the ovaries in coordinating prepubertal mammary development has been previously demonstrated, as has the unique dynamics of allometric and isometric prepubertal parenchyma growth. The current study describes transcriptional regulation of five genes (estrogen receptor alpha, ERá; estrogen receptor beta, ERâ; estrogen-related receptor alpha-1, ERRá1; progesterone receptor, PR; and IGF-I) thought to provide means by which the ovaries influence mammary development in the bovine. Their expression within the mammary fat pad and epithelium-rich mammary parenchyma was investigated at multiple points between birth and just beyond puberty. Additionally, the role that plane of nutrition plays in their transcriptional regulation is also described. Starting at 45 kg body weight, Holstein heifers (n = 72) were assigned to either an elevated (E) or restricted (R) plane of nutrition supporting body growth rates of 950 (E) or 650 (R) g/d. Transcript abundance of ERá, ERâ, ERRá1, PR and IGF-I was determined at 50 kg increments of body weight from 100 to 350 kg by quantitative real-time RT-PCR. All five genes were expressed within both the mammary parenchyma and mammary fat pad; however, ERâ transcript abundance was extremely low. ERá protein was localized to both adipocytes and fibroblasts within the mammary fat pad, demonstrating that this tissue posses the capability to influence the parenchyma via estrogen-responsive paracrine acting hormones. Transcript abundance of both ERá and IGF-I decreased linearly with increasing slaughter weight within both compartments of the mammary gland. No marked changes in transcript abundance of these genes were evident to explain the parenchyma's transition from allometric to isometric growth; however, ontogenic downregulation of ERá and IGF-I expression possibly plays some role in this process.