Global gene expression of the turkey hen reproductive axis during the preovulatory hormonal surge

Authors: Brady, Kristen; LIU, HSIAO-CHING - North Carolina State University; HICKS, JULIE - North Carolina State University; Long, Julie; PORTER, TOM - University Of Maryland

Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2023
Publication Date: 2/2/2023
Citation: Diehl, K.M., Liu, H., Hicks, J., Long, J.A., Porter, T.E. 2023. Global gene expression of the turkey hen reproductive axis during the preovulatory hormonal surge. Poultry Science. 102(4). Article e102547. https://doi.org/10.1016/j.psj.2023.102547.
DOI: https://doi.org/10.1016/j.psj.2023.102547

Interpretive Summary: The first step to egg production in poultry is ovarian follicle ovulation. Ovulation is triggered by increased circulating hormones, luteinizing hormone and progesterone, termed the preovulatory hormonal surge. The upstream events leading to the preovulatory hormonal surge and the downstream impact of the preovulatory hormonal surge on the reproductive axis to eventually lead to ovulation is poorly understood. We utilized RNA sequencing technology to examine gene expression changes in the key tissues of the reproductive axis (hypothalamus, pituitary, ovarian follicle granulosa cells) that occur during the preovulatory hormonal surge. Using lists of differentially expressed genes for each tissue examined, we were able to look upstream at potential regulators driving the preovulatory hormonal surge. We were also able use the list of differentially expressed genes to look downstream to determine biological processes that ultimately lead to ovulation. Through this analysis we were able to identify a total 3435 differentially expressed genes and 565 potential upstream regulators. This study increased our knowledge surrounding the preovulatory hormonal surge, which may allow for manipulation of the frequency of the preovulatory hormonal surge after further studies.

Technical Abstract: The preovulatory hormonal surge consists of elevated circulating luteinizing hormone and progesterone levels and serves as the primary trigger for ovarian follicle ovulation. Increased luteinizing hormone and progesterone, produced by the pituitary and the granulosa layer of the largest ovarian follicle (F1), respectively, result from hypothalamic stimulation and steroid hormone feedback on the hypothalamo-pituitary-gonadal (HPG) axis. The hypothalamus, pituitary, F1 granulosa, and granulosa layer of the fifth largest follicle (F5) were isolated from hens outside and during the preovulatory surge and subjected to RNA sequencing (n=6). Differentially expressed genes were subjected to functional annotation using DAVID and IPA. A total of 12, 250, 1235, and 1938 DEGs were identified in the hypothalamus, pituitary, F1 granulosa, and F5 granulosa respectively. Gene Ontology (GO) analysis revealed key roles for metabolic processes, steroid hormone feedback, and hypoxia induced gene expression changes. Upstream analysis identified a total of 4, 42, 126, and 393 potential regulators of downstream gene expression in the hypothalamus, pituitary, F1G, and F5G respectively, with a total of 63 potential regulators exhibiting differential expression between samples collected outside and during the preovulatory hormonal surge. The results from this study serve to increase the current knowledge base surrounding the regulation of the preovulatory hormonal surge within turkey hens. Through GO analysis, downstream processes and functions associated with the preovulatory hormonal surge were linked to identified DEGs and through upstream analysis, potential regulators of DEGs were identified for further analysis. Linking upstream regulators to downstream preovulatory surge and ovulation events could allow for manipulation of ovulation frequencies in turkey hens.