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United States Department of Agriculture

Agricultural Research Service

Title: Localization of Period 1 Mrna in the Ruminant Oocyte and Investigations of Its Role in Ovarian Function

Authors
item CUSHMAN, ROBERT
item Allan, Mark
item JONES, SHUNA
item Rupp, Gary - UNIV NEBRASKA-GPVEC
item Echternkamp, Sherrill

Submitted to: Animal Reproduction Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 28, 2006
Publication Date: May 20, 2007
Citation: Cushman, R.A., Allan, M.F., Jones, S.A., Rupp, G.P., Echternkamp, S.E. 2007. Localization of Period 1 mRNA in the ruminant oocyte and investigations of its role in ovarian function. Animal Reproduction Science. 99(1-2):93-105.

Interpretive Summary: Oocyte or egg quality is an important component of reproductive efficiency in cattle, because cattle oocytes produce factors which control follicle development, ovulation, fertilization and early embryonic development. The clock gene Period 1 (Per1) may be an important oocyte-specific factor, because it is produced by the mouse oocyte and fruit flies that lack Per1 shed fewer eggs. Ovaries were collected at slaughter on Days 5, 12, 15, 17, and 20 after estrus for evaluation of Per1 gene expression in Dorset, Romanov, Romanov/Dorset, and Composite ewes. Ovaries were also collected from cows selected for increased ovulation rate or unselected controls on days 4, 5, and 6 of the estrous cycle to measure Per1 gene expression. To examine the role of Per1 in early follicle development, pieces of ovaries from neonatal calves (n = 5) were cultured for ten days and Per1 mRNA levels were measured on Day 0 and on Day 10 of culture. Per1 gene expression was unaffected by prolificacy, day of the cycle, or pregnancy status in ewes or cows. Per1 gene expression occurred only in oocytes of bovine preantral and antral follicles. In bovine ovarian cortical cultures on Day 0, the tissue contained mostly primordial follicles (i.e., the earliest stage); however, after 10 days in culture, the number of primordial follicles per section decreased and the number of primary follicles (i.e., entered into further development. Per1 gene expression did not change over time in culture. This is the first study to demonstrate expression of Per1 gene expression in rsheep and cattle oocytes; however, its physiological role remains to be elucidated.

Technical Abstract: The clock gene Period 1 (Per1) may be a prolificacy gene, because it localized to the mouse oocyte and Per1-null drosophila shed fewer eggs. Because Per1 mapped to a region of mouse chromosome 11 syntenic to bovine chromosome 19 where a quantitative trait loci (QTL) for ovulation rate existed, we hypothesized that Per1 influenced folliculogenesis and ovulation rate in ruminants. Ovarian cortex was collected at slaughter on Days 5, 12, 15, 17, and 20 after estrus for real-time RT-PCR evaluation of Per1 mRNA expression in Dorset (n = 18); Romanov (n = 10); Romanov/Dorset (n = 21); and Composite (n = 22) ewes. Ovarian cortex was also collected from cows selected for increased ovulation rate (n = 37) or unselected controls (n = 28) on days 4, 5, and 6 of the estrous cycle for in situ hybridization and real-time RT-PCR. To examine the role of Per1 in early follicular development, ovarian cortex from neonatal calves (n = 5) was cultured for ten days and Per1 mRNA levels were measured on Day 0 and on Day 10 of culture. The primers generated a 483 bp amplicon with 100% homology to bovine RIGUI-like protein (Per1) which is 20 cM from the QTL. Per1 mRNA expression was unaffected by prolificacy, day of the cycle, or pregnancy status in ewes or cows. The riboprobe hybridized to oocytes of bovine preantral and antral follicles. In bovine ovarian cortical cultures on Day 0, the tissue contained mostly primordial follicles (5.6 +/ 0.6 follicles/section); however, after 10 days in culture, the number of primordial follicles per section decreased (0.5 follicles/section) and the number of primary follicles increased as follicles activated (Day 0 = 0.5 +/ 0.6 vs. Day 10 = 10.4 +/ 0.6 primary follicles/ section; P < 0.001). Per1 mRNA did not change over time in culture. We conclude that Per1 mRNA is expressed by ruminant oocytes in preantral and antral follicles; however, its physiological role in mammalian ovarian function remains to be elucidated.

Last Modified: 9/29/2014
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