Abstract
Ovarian follicular development is an extremely complex and precise process in which the hypothalamic-pituitary-ovarian (HPO) axis plays a crucial role. However, research on the regulatory factors of the HPO axis is sparse. In this study, transcriptomes of the tissues in the entire HPO axis at 15, 20, 30, and 68 w of age were analyzed. In total, 381, 622, and 1090 differentially expressed genes (DEGs) were found among the hypothalamus, pituitary, and ovary, respectively. In particular, the greatest number of DEGs (867) was identified from the comparison of ovary at 30 and 15 w, which might be related to ovarian development and function at high ovulation capacity. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses indicated that most of these DEGs in the significantly enriched biological process (BP) terms and pathways were primarily involved in tissue development and the regulation of reproductive hormone biosynthesis and secretion. The latter is highly related to the HPO axis. Therefore, a number of hub candidate genes strongly associated with the HPO axis in each tissue were filtered by analyzing the Protein-protein interaction (PPI) network and seven known reproductive hormone-associated key genes were obtained: PGR, HSD3B2, CYP17A1, CYP11A1, CYP21A2, STS, and CYP19A1, and 12 novel genes: ROCK2, TBP, GTF2H2, GTF2B, DHCR24, DHCR7, FDFT1, LSS, SQLE, MSMO1, CYP51A1, and PANK3. These will be utilized for further research into the function of the HPO axis. This study has highlighted the major role of the HPO axis in the reproduction of hens at the four developmental stages and explored the novel factors that might regulate reproduction, thus providing new insights into the function of the HPO axis on the reproductive system.
Highlights
Egg production is an essential trait for laying hens and for breeding in poultry
To investigate the key genes of the HPO axis that were involved in follicular development and ovarian function, the differentially expressed genes (DEGs) of the hypothalamus, pituitary, and ovary at the four stages of development of laying hens were analyzed (Figures 1, 2)
A larger number of DEGs were found in the ovary compared to the other tissues, and most of them were upregulated at 30 and 68 w and were downregulated at 15 and 20 w, indicating that these genes may be associated with ovarian function and ovulation process
Summary
The growth and development of chicken ovarian follicles has been found to be directly related to the egg-laying performance (Williams and Sharp, 1978b). Ovary weight increases exponentially and gradually generates prehierarchical follicles before sexual maturity (around 18–20 weeks of age) (Robinson et al, 2001). The chicken ovary continues to develop to its largest size until reaching peak egg production. The ovary contains multiple follicles of various sizes and developmental stages during the active laying period to maintain ovulation and produce eggs. The number of viable follicles declines gradually and the proportion of atretic follicles increases, leading to a reduction in egg production (Waddington et al, 1985; Lillpers and Wilhelmson, 1993)
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