Maternal age influences folliculogenesis and gene networks in the ovaries of beef heifers

Authors: Cushman, Robert - Bob; TENLEY, SARAH - University Of Nebraska; SPURI GOMES, RENATA - University Of Nebraska; ROSASCO, SHELBY - New Mexico State University; NORTHROP, EMMALEE - South Dakota State University; RICH, JERICA - South Dakota State University; McNeel, Anthony; SUMMERS, ADAM - New Mexico State University; Miles, Jeremy; Chase, Chadwick - Chad; Lents, Clay; PERRY, GEORGE - South Dakota State University; WOOD, JENNIFER - University Of Nebraska; CUPP, ANDREA - University Of Nebraska

Submitted to: Society for the Study of Reproduction Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 5/1/2018
Publication Date: 7/2/2018
Citation: Cushman, R.A., Tenley, S.C., Spuri Gomes, R., Rosasco, S.L., Northrop, E.J., Rich, J.J., McNeel, A.K., Summers, A.F., Miles, J.R., Chase, C.C., Lents, C.A., Perry, G.A., Wood, J.R., Cupp, A.S. 2018. Maternal age influences folliculogenesis and gene networks in the ovaries of beef heifers [abstract]. Society for the Study of Reproduction Annual Meeting. Abstract Program p. 137-138. Available: https://www.ssr.org/sites/ssr.org/files/2018_annual_meeting_abstracts_updated.pdf.

Interpretive Summary:

Technical Abstract: The size of the ovarian reserve is an important component of fertility and reproductive longevity in bovine females. Ultrasonographic determination of antral follicle count is the best method for estimating the size of the ovarian reserve in heifers and cows in a production setting. Antral follicle count is highly repeatable, moderately heritable, and correlates positively with the number of primordial follicles in the ovaries. Maternal age may influence the size of the ovarian reserve in daughters, because heifers born to mature cows have more antral follicles detectable by ultrasonography at a year of age than heifers born to heifers. Therefore, we hypothesized that heifers born to mature cows would have more primordial follicles than heifers born to heifers. Ovaries were collected from yearling Angus heifers born to heifers (n = 20) or mature cows (n = 63), all surface follicles were counted and a representative sample of each ovary was processed for histological evaluation of primordial follicle number. Ovarian cortex from four heifers born to heifers and four heifers born to mature cows was processed for RNA sequencing to identify differences in transcript abundance in the ovary based on age of dam. In agreement with previously published ultrasonographic data, antral follicle number was decreased in yearling heifers born to heifers compared to yearling heifers born to mature cows (P < 0.01; 37.9 ± 8.0 follicles and 64.4 ± 4.0 follicles, respectively). Yearling heifers born to heifers also had fewer primordial follicles per histological section compared to yearling heifers born to mature cows (P = 0.02; 40.3 ± 9.5 follicles per section and 67.4 ± 5.0 follicles per section, respectively). There was a tendency for primary follicle number to be decreased in ovaries of heifers born to heifers (P = 0.06; 7.9 ± 1.7 follicles per section and 12.3 ± 0.9 follicles per section, respectively). The number of secondary follicles per histological section was decreased in heifers born to heifers compared to heifers born to mature cows (P = 0.02; 1.6 ± 0.5 follicles per section and 3.0 ± 0.3 follicles per section, respectively). Pathway analysis clustered genes into biological processes involved in development of the circulatory system (P = 0.02) and cellular components involved in extracellular matrix formation (P < 0.001). Among genes that were differentially expressed after Benjamini-Hochberg correction, transcript abundance for connective tissue growth factor was decreased in the ovaries of heifers born to heifers compared to heifers born to mature cows (P = 0.01) . Conditional knockout of this gene in the murine ovary has been associated with disrupted follicle development. These data corroborate previously published ultrasonographic data demonstrating that antral follicle numbers are greater in heifers born to mature cows and demonstrate that this difference in antral follicle number is correlated with the size of the ovarian reserve. Mechanistically, decreased vascular development and increased formation of extracellular matrix may contribute to the decreased numbers of follicles in ovaries of heifers born to heifers.