The role of the oviduct environment in embryo survival.

Context: Declining fertility is an issue in multiple mammalian species. As the site of fertilisation and early embryo development, the oviduct plays a critical role in embryo survival, yet there is a paucity of information on how the oviduct regulates this process. Aims: We hypothesised that differences in steroid hormone signalling and/or immune function would be observed in a model of poor embryo survival, the peripubertal ewe. Methods: We examined expression of steroid hormones in systemic circulation, oviductal expression of oestrogen receptor α and genes important in steroid hormone signalling, and immune function in pregnant and cyclic peripubertal and adult ewes on day 3 after oestrus. Key results: Concentrations of progesterone, but not oestradiol, were decreased in the peripubertal ewe compared to the adult ewe. Oestrogen receptor α protein expression was increased in the peripubertal ewe, but pathway analysis of gene expression revealed downregulation of the oestrogen signalling pathway compared to the adult ewe. Differential expression of several genes involved in immune function between the peripubertal and adult ewe was consistent with an unfavourable oviductal environment in the peripubertal ewe lamb. Oestradiol concentration was positively correlated with the expression of multiple genes involved in the regulation of immune function. Conclusions: Differences in the immune environment of the oviduct, potentially linked to differential modulation by steroid hormones, may partially underly the poor fertilisation and early embryo survival observed in the peripubertal ewe. Implications: A unfavourable oviductal environment may play an important role in limiting reproductive success. Declining fertility is an issue in multiple mammalian species, with around 15% of couples experiencing infertility. Differential expression of genes involved in inflammation, linked with altered steroid signalling in the oviduct, was observed in peripubertal ewes, a model of poor fertility. Ensuring that the oviductal environment does not become hostile to fertilisation and early embryo development may provide a novel approach to improve fertility, particularly in conditions associated with chronic low-grade inflammation. Photograph by Jenny Juengel. [ABSTRACT FROM AUTHOR]