Zona pellucida protein B2 messenger ribonucleic acid expression varies with follicular development and granulosa cell location

Trimethylamine N-oxide (TMAO) treatment triggers premature ovarian insufficiency (POI) via the activation of mitochondrial pathway apoptosis in granulosa cells

Premature ovarian insufficiency (POI) is characterized by follicular development failure or follicular dysplasia, therefore causing the lack of normal ovarian function before 40 years of age. Trimethylamine N-oxide (TMAO) is a metabolite of high choline diet rich in red meat and directly associated with gut microbiota. Correlation of TMAO level with female fertility decline has been shown; however, its mechanism is largely unknown. To unveil the mechanism by which TMAO affects female reproductive function, we established a TMAO-treated mouse model which exhibited the pathological manifestations of POI including increased follicle-stimulating hormone and luteinizing hormone levels, decreased estradiol and anti-Müllerian hormone levels, reduced growing and mature follicles, increased atretic follicles, and decreased fertility. Meanwhile, these mice showed an increased apoptosis ratio and damaged mitochondrial function in granulosa cells, the nursing and supporting cells for oocyte development. Moreover, TMAO treatment significantly elevated oxidative stress and reduced antioxidative capacity in granulosa cells, whereas the antioxidants N-acetylcysteine alleviated such detriment. Mechanism investigation demonstrated that TMAO treatment up-regulated phosphatase and tensin homolog expression levels in granulosa cells, thereby inhibiting the phosphorylation of AKT and subsequently causing high expression of BCL-2-associated X protein, a key molecule in the mitochondria pathway, leading to increased cell apoptosis. Our findings documented the pathological mechanism of TMAO-induced POI, which may provide a potential target for curing POI clinically.

Quantitative Protein Analysis of ZPB2, ZPB1 and ZPC in the Germinal Disc and a Non-Germinal Disc Region of the Inner Perivitelline Layer in Two Genetic Lines of Turkey Hens That Differ in Fertility

The avian inner perivitelline layer (IPVL), containing the zona pellucida (ZP) family of proteins, surrounds the ovulated ovum. In mammalian species, ZP proteins serve as key component(s) in binding sperm and initiating the acrosome reaction. Sperm binding at the germinal disc (GD) region of the IPVL initiates fertilization in avian species, and the amount of sperm binding at the GD reflects female fertility. The current research determined whether reported differences in mRNA expression in two genetic lines of turkey hens (E, high fertility and F, low fertility) translated to the protein level. ZPB2 in the IPVL is greater in the GD region compared with the nongerminal disc (NGD) region, as indicated by both mRNA and protein expression. However, protein expressions of ZPB1 and ZPC in the IPVL of E- and F-line turkey hens was in contrast to previously reported mRNA expression. The results indicate that the mRNA expression of ZP proteins at their site of synthesis in E- and F-line hens often does not directly correlate with the IPVL abundance of these proteins. The greater protein concentration of ZPB2 in the GD region compared with the NGD regions suggests that this protein may be critical for sperm binding at the GD region.

Physiological factors influencing female fertility in birds

Fertility is fundamental to reproductive success, but not all copulation attempts result in a fertilized embryo. Fertilization failure is especially costly for females, but we still lack a clear understanding of the causes of variation in female fertility across taxa. Birds make a useful model system for fertility research, partly because their large eggs are easily studied outside of the female's body, but also because of the wealth of data available on the reproductive productivity of commercial birds. Here, we review the factors contributing to female infertility in birds, providing evidence that female fertility traits are understudied relative to male fertility traits, and that avian fertility research has been dominated by studies focused on Galliformes and captive (relative to wild) populations. We then discuss the key stages of the female reproductive cycle where fertility may be compromised, and make recommendations for future research. We particularly emphasize that studies must differentiate between infertility and embryo mortality as causes of hatching failure, and that non-breeding individuals should be monitored more routinely where possible. This review lays the groundwork for developing a clearer understanding of the causes of female infertility, with important consequences for multiple fields including reproductive science, conservation and commercial breeding.