Differences in in vitro responses of the hypothalamo-pituitary-gonadal hormonal axis between low and high egg producing turkey hens

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

Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2020
Publication Date: 9/30/2020
Citation: Brady, K.M., Long, J.A., Liu, H., Porter, T.E. 2020. Differences in in vitro responses of the hypothalamo-pituitary-gonadal hormonal axis between low and high egg producing turkey hens. Poultry Science. https://doi.org/10.1016/j.psj.2020.08.048.
DOI: https://doi.org/10.1016/j.psj.2020.08.048

Interpretive Summary: Turkey hens have the capacity to lay an egg on a daily basis (every 24 to 26 hours or 6-7 eggs/week); however, there are hens that routinely produce fewer eggs (3-4 eggs per week). Understanding the mechanism of why low egg producing hens (LEPH) ovulate less frequently than high egg producing hens (HEPH) is important to improve reproduction in commercial operations. The expression of genes related to the production of steroid hormones by the ovary differed between LEPH and HEPH. HEPH display increased expression of genes related to progesterone and estradiol production, in the granulosa layer of the largest follicle (F1G) and small white follicles (SWF), respectively, whereas LEPH display increased expression of genes related to progesterone and androgen production in the granulosa of the fifth largest follicle (F5G) and theca interna layer of the fifth largest follicle (F5I), respectively. Transcriptome analysis was performed on F1G, F5G, F5I, and SWF samples from LEPH and HEPH to identify novel regulators of ovarian steroidogenesis that could ultimately impact egg production rates. Pathway analysis inferred differential regulation of the hypthalamo-pituitary-thyroid (HPT) axis, particularly thyroid hormone transporters and thyroid hormone receptors, and of estradiol signaling in LEPH and HEPH. Differential regulation of steroid hormone production may contribute to differences in egg production rates seen in LEPH and HEPH.

Technical Abstract: Background: Low egg producing hens (LEPH) and high egg producing hens (HEPH) exhibit gene expression differences related to steroidogenesis in ovarian follicles. HEPH display increased expression of genes related to progesterone and estradiol production, in the granulosa layer of the largest follicle (F1G) and small white follicles (SWF), respectively, whereas LEPH display increased expression of genes related to progesterone and androgen production in the granulosa of the fifth largest follicle (F5G) and theca interna layer of the fifth largest follicle (F5I), respectively. Transcriptome analysis was performed on F1G, F5G, F5I, and SWF samples from LEPH and HEPH to identify novel regulators of ovarian steroidogenesis that could ultimately impact egg production rates. Results: In total, 12,221 differentially expressed genes (DEGs) were identified between LEPH and HEPH, with 6,212 genes up-regulated in LEPH and 6,009 genes up-regulated in HEPH. Consistent with previous results, HEPH displayed enrichment of steroidogenic genes in the F1G and SWF, whereas LEPH displayed enrichment of steroidogenic genes in the F5G and F5I. Pathway analysis inferred differential regulation of the hypthalamo-pituitary-thyroid (HPT) axis, particularly thyroid hormone transporters and thyroid hormone receptors, and of estradiol signaling in LEPH and HEPH. The HPT axis showed up-regulation in HEPH in less mature follicles but up-regulation in LEPH in more mature follicles. Estradiol signaling exclusively exhibited up-regulation in HEPH and beta-estradiol was identified as a top upstream regulator in three of the four tissue examined. Treatment with thyroid hormone in SWF cells from LEPH and HEPH in vitro decreased estradiol production from HEPH cells to the levels seen in LEPH cells, whereas thyroid hormone treatment did not impact estradiol production in LEPH cells. Conclusions: Transcriptome analysis of the major cell types involved in ovarian steroid hormone production inferred the involvement of the HPT axis and estradiol signaling in the regulation of differential steroid hormone production seen in LEPH and HEPH. Differential regulation of steroid hormone production may contribute to differences in egg production rates seen in LEPH and HEPH.