Progress 10/01/05 to 09/30/07
Outputs
OUTPUTS: There were three primary outputs for this work. First, the information were presented at national meetings of the American Dairy Science Association and the American Society for Animal Science (see abstracts, below). Second, it was presented to other university researchers at invited seminars. For example, these data were presented at the University of Florida, Gainesville, Animal Reproductive Biology Seminar Series in a seminar entitled "Local versus systemic control of IGF system genes in the whole animal" (September 26, 2007).Farmers and veternarians learned about these data at regional conferences (Intermountain Nutrition Conference, Salt Lake City, UT; Texas Animal Nutrition Council Meeting, Stevensville, TX; Southwest Nutrition & Management Conference, Tempe, AZ; Mid-Atlantic Consortium Dairy Extension In-Service. Wilkes Barre, PA; Midwest Dairy Veterinary Meeting, Minneapolis, MN). PARTICIPANTS: Joseph Meyer and Shelly Rhoads worked on the project. They were both graduate students in Animal Science. This project was part of their professional development during graduate school. Both students graduated with their Ph.D. degrees. Joe now owns a farm in Wisconsin. Shelly is an Assistant Professor of Animal Science at the University of Arizona. TARGET AUDIENCES: The target audiences were fellow scientists (reached through scientific meetings) and farmers/veternarians (reached through regional conferences). PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
The objective of these studies was to investigate the expression of repressors, intermediaries, and end-products of the IGF1 and insulin signaling pathways within hepatic and reproductive tissues of dairy cattle. We monitored the signaling of the GH/IGF1/insulin pathways through the use of quantitative real-time polymerase chain reaction (qRT-PCR). The qRT-PCR assay was designed so that a single sample could be analyzed on a single 96-well plate. A literature search for key genes was done and 32 genes were selected. Each gene product was PCR amplified and sequenced to verify its identity. Liver samples from four cows were tested to generate preliminary information. From these results, we concluded that gene expression can be measured by using this bovine specific qRT-PCR 96 well plate array. The objective of the first study was to measure insulin/IGF1 signaling in the liver of periparturient dairy cows by using the qRT-PCR plate that we developed. Cows were sampled once before calving and once after calving (d 3). The 32 mRNA were detected in all cows on both sample days. Hepatic gene expression (reported as Ct) differed prepartum compared with postpartum for Grb2 (increased postpartum), Insr (increased postpartum), Irs2 (increased postpartum), and Ptp1b (increased postpartum) but these changes in gene expression were relatively minor. The greatest change in gene expression was observed for IGF1 that differed by nearly 3 cycles from prepartum to postpartum (approximately 6-fold decrease). We concluded that there are differences between prepartum and postpartum expression of multiple genes in the insulin/IGF signaling pathway but that the largest change in gene expression occurs for IGF1 which is a principle ligand for the insulin/IGF1 system. Major changes within this system, therefore, appear to be orchestrated by the ligand (IGF1) and not by individual components of the signaling pathway that were included on our assay plate. In the second study, gene expression was compared across hepatic and uterine tissues in lactating dairy cattle that were sampled at approximately 60 days postpartum. All 32 mRNA products were detected in liver but 8 genes in the uterus had very low expression (Acc, Bclx, ERas, Ets2, G6pc, Insr, Pdk1, and Ucp3). For detected mRNA, the effects of tissue and cow were significant for mRNA amount. Across all expressed genes, there was a 30-fold increase in expression of pathway genes in liver compared with uterus. Individual cows differed for mRNA expression across numerous pathway genes and those differences may encode a different degree of insulin sensitivity in individual cows. Within a sample and tissue, the expression of genes were generally correlated with one another. The pathways genes as a whole, therefore, appeared to be highly expressed in some cows and poorly expressed in others. Across tissues, there was little correlation between gene expression. From that result we learned that the two tissues (liver and uterus) were not coordinated in terms of gene expression. Instead, gene expression of the studied genes appeared to be independently regulated in the two tissues.
Publications
- Rhoads, M.L., Meyer, J.P., Kolath, S.J., Lamberson, W.R., and M.C. Lucy. 2008. Growth hormone receptor, insulin-like growth factor (IGF) 1 and IGF binding protein 2 expression in the reproductive tissues of early postpartum dairy cows. J Dairy Sci. 91:1802-1813.
- Meyer J, Radcliff R, and M Lucy. 2006. Expression of insulin receptor substrate-1 (IRS1) mRNA in hepatic tissue of periparturient Holstein cows. Proceedings of the Annual Meeting of the Midwest Section of the American Society of Animal Science. March 20-22, 2006, Des Moines, IA.
- Meyer, J.P., Rhoads, M.L. and M.C. Lucy 2007. Uterine and hepatic mRNA expressioni for insulin and IGF-I signaling intermediaries, end-products and repressors in lactating Holstein cows. Soc Reprod Fertil Suppl. 64:491.
- Rhoads, M.L., Meyer, J.P., Lamberson, W.R., Keisler, D.H., and M.C. Lucy. 2008. Uterine and hepatic gene expression in relation to days postpartum, estrus, and pregnancy in postpartum dairy cows. J Dairy Sci. 91:140-150.
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