ARS | Publication request: Developmental and Nutritional Regulation of Steroid Receptor Mrna Expression and Epithelial Cell Proliferation in the Prepubertal Bovine Mammary Gland

Submitted to: Joint Abstracts Of The American Dairy Science And Society Of Animal Science
Publication Acceptance Date: March 18, 2004
Publication Date: July 29, 2004
Citation: Meyer, M.J., Capuco, A.V., Hummel, A.S., Connor, E.E., Boisclair, Y.R., Van Amburgh, M.E. 2004. Developmental And Nutritional Regulation Of Steroid Receptor Mrna Expression And Epithelial Cell Proliferation In The Prepubertal Bovine Mammary Gland. Abstract. Adsa/asas/pas Joint Meeting, St. Louis, Mo, P. 353.

Technical Abstract: Estrogen and its alpha receptor (ERalpha) mediate the ovaries' influence on prepubertal mammary epithelial cell proliferation (MEP) in the bovine. The ER beta isoform (ERbeta) and the estrogen-related receptor alpha1 (ERRalpha1) may also play a role in estrogen mediated MEP. To better understand these relationships, the developmental and nutritional regulation of ERalpha, ERbeta, and ERRalpha1 mRNA abundance was determined in prepubertal bovine mammary parenchyma (PAR) and fat pad (FP) by real-time RT-PCR. Holstein heifers (n = 72) were fed from birth either elevated (E) or restricted (R) levels of energy and were slaughtered at 50kg increments from 100 to 350kg. MEP was assessed by BrdU labeling and estrogen responsiveness by quantity of progesterone receptor (PR) transcript. ERbeta mRNA abundance was exceedingly low in all tissues and will not be discussed. PAR abundance of ERalpha, ERRalpha1, and PR mRNA tended (P < 0.10) to be greater in E- than R-heifers. ERalpha mRNA expression within the FP was greater (P < 0.05) in E- than R-heifers. Furthermore, expression of the ERalpha protein was localized within FP fibroblasts by immunohistochemistry. PAR ERalpha, ERRalpha1 and PR mRNA abundance decreased linearly (P < 0.08) with increasing BW. This was not observed in FP, implying tissue-specific regulation of these genes. At 100kg, E- had greater MEP than R-heifers (P < 0.05). Beyond 100kg, MEP decreased rapidly with increasing BW and was similar between treatments. Among all heifers, a correlation between PAR ERalpha mRNA abundance (but not FP ERalpha) and MEP was observed (r = 0.42, P < 0.05). Likewise, a correlation between the abundance of PAR ERalpha mRNA and PAR PR mRNA was observed (r = 0.80, P < 0.05). Data suggest that expression of ERalpha, ERRalpha1 and PR are developmentally regulated within PAR but not FP. Energy intake also tends to influence PAR expression of these transcripts, but has no effect on MEP.