|Mclean, D -|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 5, 2010
Publication Date: March 18, 2011
Repository URL: http://hdl.handle.net/10113/48939
Citation: Roberts, A.J., Mclean, D.J. 2011. Differential gene expression in anterior pituitary glands from anestrous and cycling postpartum beef cows. Journal of Animal Science. 89:1035-1041. Interpretive Summary: A major limitation to successful reproduction is failure of cows to resume reproductive activity following parturition. Research to date indicates that many factors influence the transition from non-reproductive to reproductive state, and that this transition involves hormone signals from the pituitary gland. The complex nature of numerous interactions among physiological and environmental factors that affect this gland has repressed progress in this area of research. Development of microarrays specific for bovine provides an opportunity to perform near genome wide evaluations of gene expression. The present research utilized this new technology to compare gene expression profiles in anterior pituitary glands collected from cows that had or had not resumed cycling after calving. A total of 47 genes were found to be expressed at greater levels, and 31 genes were expressed at lower levels in cows that had resumed reproductive cycles compared to cows that had not. Only a few of these 78 genes have been previously associated with reproductive function. Thus, this study has identified numerous genes that may be involved in the transition back to cycling status after calving. It is expected that this new knowledge will eventually lead to methods to improve reproductive efficiency in cattle.
Technical Abstract: Oligionucleotide microarrays (GeneChip Bovine Genome Arrays, Affymetrix Inc., Santa Clara, CA) were used to evaluate gene expression profiles in anterior pituitary glands collected from 4 anestrous and 4 cycling postpartum primiparous beef cows to provide insight into genes associated with transition for an anestrous to cycling status. Tissue was collected 40 to 61 d after calving for anestrous cows or on d 7 to 13 of the estrous cycle (luteal phase) at 54 to 77 d after calving. Comparison of hybridization signals (normalized across arrays) for which the log 2 transformation of the ratio of signal for anestrous to cycling was > 0.6 (expression in cycling animals is increased by at least 1.5 fold) or < –0.6 (expression decreased by at least 35% in cycling cows), and change in signal intensity was > 10 units revealed 47 transcripts that were increased (P < 0.025) and 31 transcripts that were decreased (P < 0.025) in cycling compared to anestrous cows. Few transcripts identified in this analysis have been previously associated with reproductive function. To provide greater detail into influence that stage of cycle (i.e. collected during the luteal phase) might have on the detected differences in gene expression, quantitative rtPCR was used to compare expression in anterior pituitaries from anestrous cow RNA samples isolated from an independent additional set of anterior pituitary samples collected at four different stages of the estrous cycle; 0.5 to 2 d, 5 to 6.5 d, 11.4 to 13.7 d and 17.9 to 19 d after onset of estrus. Gastrin-releasing peptide (GRP), the gene that exhibited the largest fold increase in expression in the microarray experiment, and IGFPB-3 were expressed at greater (P < 0.004) levels in samples from the different stages of the cycle than in anestrous cow samples. In addition, expression of IGFBP-3 was inversely proportional to serum progesterone concentrations throughout the cycle. Expression of versican was decreased (P = 0.03) in samples from the different stages of the cycle when compared to anestrous cow samples. Results identify numerous genes that may be involved in the transition from anestrous to cycling status, providing novel insight into mechanisms regulating reproductive function.