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Title: Investigation of a functional role for Titin in the bovine ovary based on the results of an initial whole genome scan for antral follicle count

Author
item Cushman, Robert - Bob
item Echternkamp, Sherrill

Submitted to: Biology of Reproduction Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 3/21/2011
Publication Date: 7/30/2011
Citation: Cushman, R.A., Echternkamp, S.E. 2011. Investigation of a functional role for Titin in the bovine ovary based on the results of an initial whole genome scan for antral follicle count [abstract]. Biology of Reproduction. 85 (1 Supplement):199 (Abstract # 642).

Interpretive Summary:

Technical Abstract: A world-wide food shortage is predicted by the year 2050, and biotechnologies are needed to improve production efficiency in agriculture. Biotechnologies that improve reproductive efficiency in domestic farm species will improve the availability and price of food for the growing world population. Identifying and validating genetic markers of reproductive longevity in beef heifers would be of great economical value to the cow-calf producer because replacement heifers could be chosen early in life and developed accordingly, thereby maximizing outputs while minimizing inputs. Initial results using the Bovine SNP50 BeadChip in a pedigreed population of crossbred beef heifers at USMARC identified a series of single nucleotide polymorphisms (SNP) on bovine chromosome 2 within the Titin (TTN) gene that associated with antral follicle counts (P = 0.008). TTN is expressed in muscle, and polymorphisms in TTN have been associated with marbling in Japanese Black beef cattle. Therefore, using TTN as a genetic marker for beef cattle could be hampered by antagonistic relationships between reproductive traits and carcass traits. However, no study has reported expression of TTN in the mammalian ovary. Therefore, we hypothesized that TTN mRNA was transcribed in the bovine ovary, and that its expression would correlate positively with that of anti-Müllerian Hormone (AMH), a known biomarker of follicle numbers in the mammalian ovary. Non-lactating crossbred beef cows were ovariectomized on day 3 (n = 5), day 6 (n = 6), or day 9 (n = 6) of the estrous cycle. The ovaries were weighed and visible antral follicles were counted. Pieces of the ovaries were fixed and embedded in paraffin. Ovaries from day 3 (n = 4) or day 9 (n =3) were processed for in situ hybridization using probes specific for bovine TTN and bovine AMH. There was a tendency (P = 0.08) for antral follicle numbers to be greater on day 6 (61.5 ± 8.5 follicles) than day 3 (31.2 ± 9.4 follicles); however, the average weight of the combined ovaries within a cow did not differ across days of the estrous cycle (P = 0.22). Hybridization of the AMH probe was clearly identified in small antral follicles (= 5 mm), but a greater percentage of follicles = 3 mm in diameter expressed AMH mRNA than follicles > 3 mm in diameter (P = 0.04, 97.2 ± 20.0% vs. 53.7 ± 20.0%). Day of the estrous cycle did not influence the percentage of small antral follicles expressing AMH (P = 0.86). We were unable to detect hybridization of the TTN probe in any ovarian tissues. From this, we conclude: 1) that expression of TTN mRNA in the bovine ovary is below the sensitivity of in situ hybridization to detect, or 2) that the SNP are in linkage disequilibrium with the functional polymorphism that influences follicle numbers in the bovine ovary. Further sequencing efforts in this region of bovine chromosome 2 will be needed to confirm and fine map the causative polymorphism influencing follicle numbers and to determine any role of TTN in ovarian function in beef cows. USDA is an equal opportunity provider and employer.