Abstract
The onset of estrus is a critical sign of female sexual maturity. The pituitary plays a vital role in this process by the secretion of reproductive hormones. To investigate the effects of nutrient restriction on reproductive function and the underlying mechanisms involved, deep RNA sequencing of pituitary gland tissue was carried out to determine the differentially expressed genes (DEGs) between gilts in normal estrus, and gilts in which anestrus was induced by nutrient restriction. Gilts which had gone through two estrus cycles were fed a normal (CON, 2.86kg/d, n = 10) or nutrient restricted (NR, 1kg/d, n = 10) diet. The NR gilts experienced another three estrus cycles, but did not express estrus symptoms at the anticipated 6th and 7th cycles. Body weight gain in NR gilts was significantly decreased by nutrient restriction. Gilts were considered as anestrus when blood progesterone concentrations lower than 1.0 ng/mL from three consecutive blood samples were recorded. Circulating concentrations of progesterone (< 1.0 ng/mL vs. 2.1 ng/mL) and estradiol (208.6 ng/mL vs. 371.8 ng/mL) were significantly lower in the NR gilts than in the CON gilts. Between 5,360,000 and 5,370,000 sequence reads per sample from the CON and NR gilts’ pituitaries were obtained and mapped to the porcine genome. Analysis of read counts revealed 185 DEGs. Expression of selected genes was validated by the use of quantitative real-time RT-PCR. Bioinformatic analysis identified that the genes identified were enriched in the GO terms “neuroactive ligand-receptor interaction”, “GnRH signaling pathway” and “immune response system”. Our findings provide a new perspective for understanding the nutrient restriction-induced reproductive impairment at the pituitary transcriptional level, and how this is linked to hormone secretion. Moreover, the transcriptomic changes in anestrus gilts associated with nutrient restriction could be a resource for targeted studies of genes and pathways potentially involved in the regulation of reproductive function and animal health.
Highlights
Throughout vertebrates the onset of estrus indicates that the female organism has reached sufficient sexual maturity to reproduce
Studies have shown that reproductive function in pigs is sensitive to the status of energy reserves suggesting that weight loss in humans by extreme dieting methods may have potential negative effects on fertility [1,2,3]
It is well known that estrus onset is a complex biological process which is initiated by hormonal signals from the brain to the gonads, involving the secretion of gonadotropin-releasing hormone (GnRH) by the hypothalamus [6], luteinizing hormone (LH) and follicle stimulating hormone (FSH) by the pituitary, and estradiol (E2) by the ovary
Summary
Throughout vertebrates the onset of estrus indicates that the female organism has reached sufficient sexual maturity to reproduce. Nutritional factors are the strongest and most obvious environmental factors affecting the timing of puberty [4], and studies have revealed that nutrient restriction in post-pubertal gilts led to cessation of estrus [3]. In the pig industry, pre-pubertal gilts and weaned sows are always kept in good body condition without too much adipose tissue to allow the onset of puberty and estrus at the appropriate time. Depressed luteinizing hormone (LH) and follicle stimulating hormone (FSH) secretion led to the inhibition of gonadal function and reproductive failure in nutrient restricted animals [2]. It is well known that estrus onset is a complex biological process which is initiated by hormonal signals from the brain to the gonads, involving the secretion of gonadotropin-releasing hormone (GnRH) by the hypothalamus [6], LH and FSH by the pituitary, and estradiol (E2) by the ovary. Understanding the neuroendocrine control of LH and FSH secretion may provide insights into both normal reproduction and disorders of the pubertal process
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