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Livestock phenotypes are determined by the interaction of a variety of factors, including the genome, the epigenome and the environment. Epigenetics refers to gene expression changes without DNA sequence alterations. Epigenetic markers mainly include DNA methylation, histone modifications, non-coding RNAs, and imprinting genes. More and more researches show that epigenetic markers play an important role in the traits of pigs by modulating phenotype changes via gene expression. However, the role of epigenetic markers has caught little attention in swine breeding. The mechanism that influences important traits of swine has not been analyzed in detail, and it still lacks adequate scientific basis for practical applications. From the aspects of nutrition, diseases, important economic traits and trans-generational inheritance, we summarize the research, application prospects and challenges in the field of utilizing epigenetic markers in molecular breeding of pigs, thus providing a more comprehensive theoretical basis to promote more rapid research development in this field.

Mammalian ovulation is a complicated process that includes development of follicles, ovulation, formation of corpus luteum and luteolysis. The three different stages of the ovulation activity are affected by hypoxic microenvironment and hypoxia-induced factors (HIF), which play a crucial role in physiologyical processes, such as angiogenesis and inflammation. Although the process of ovulation has been well elucidated, the molecular mechanism regulated by hypoxia needs an in depth study. In this review, we summarize how hypoxic and HIF regulate gene expression during mammalian ovulation in order to provide a better understanding of ovulation mechanism, which may lay a theoretical basis for prevention and therapy of various ovarian diseases.

MicroRNAs (miRNAs) are involved in several physiological processes as important post-transcriptional regulators. Progesterone (P4), an important steroid hormone, produces physiological effect through binding specific receptor progesterone receptors (PGR) which regulates functions of both reproductive and non-reproductive tissues as a member of the nuclear receptor superfamily. P4/PGR and miRNAs could regulate female reproduction independently, however, it is still unclear how miRNAs and P4/PGR interaction regulates female reproductive activities such as ovulation in female reproduction. In this review, we summarize the possible ways in which miRNAs regulate P4 production and PGR gene expression as well as P4/PGR regulate miRNAs expression, which provide a theoretical basis for further studying the role of miRNAs and P4/PGR in female reproduction.

The hypothalamo-pituitary-gonadal (HPG) axis integrates internal and external cues via a balance of stimulatory and inhibitory neurochemical systems to regulate reproductive function in mammals. However, RFRP-3 is a unique inhibitor of HPG axis at the hypothalamuic level in mammals to date. A large number of previous studies have confirmed that RFamide-related peptide (RFRP-3) suppresses gonadotropin-releasing hormone (GnRH) system and luteinizing hormone (LH) secretion, thereby affecting the reproduction. However, whether the inhibition of LH secretion by RFRP-3 occurs at the pituitary level or the hypothalamus level is not clear. It is interesting that RFRP-3 is also related to signal pathway of melatonin modulating mammal seasonal reproduction, but little is known about the effects of melatonin on the RFRP-3 neuron up to now. In addition, RFRP-3 also plays an important role in the regulation of energy balance and behavior. The regulatory mechanism of RFRP-3 in HPG axis and role of RFRP-3 in modulating mammalian energy balance, as well as behavior, are systematically elaborated and the remaining unsolved problems are also discussed in this paper.

The seasonal reproduction of mammal means the reproduction experiences an annual period from quiescence to renaissance. Studies have shown that kisspeptin and RFRP play an important role in the reproductive seasonality. The non-breeding season is characterized by an increase in the negative feedback effect of estrogen on GnRH, and this effect is transmitted by kisspeptin neurons, which may be an important factor affecting the reproduction activities. The expression of RFRP depends on melatonin secretion, and shows an apparent inhibition on reproduction in non-breeding season. In addition, thyroid hormones influence termination of the breeding season. Dopaminergic neuron A14/A15 also contributes to the seasonal changes in estrogen negative feedback. These neural systems may synergistically modulate the seasonal changes of reproductive function with the photoperiod. This review makes a systematic expatiation on the relationship between seasonal reproduction and these neural systems.

The steroid hormone, progesterone, plays a key role in diverse events associated with female reproduction. In humans and other vertebrates, the biological activity of progesterone is mediated by modulation of the transcriptional activity of two progesterone receptors, PGR-A and PGR-B. This review introduced the structure, expression regulation and polymorphism of progesterone receptor gene. The relationship between progesterone receptor gene and reproductive function was also discussed in mammals.