RXR Expression Profiles in Yak Reproductive Tissues During Follicular, Luteal, and Pregnancy Phases

The yak is a large ruminant that lives in the high-altitude and hypoxic environment of the Qinghai-Tibet Plateau in China and typically exhibits limited reproductive capacity, posing a significant challenge to the advancement of animal husbandry in the region. Retinoid X receptors (RXRs), as an important member of the NR superfamily, play a key role in the regulation of reproductive hormone synthesis, follicular development, and embryo implantation. However, there is still a lack of systematic research on the expression characteristics and potential functions of RXRs in the yak's reproductive system. This study characterized RXR expression in ovarian, uterine, and oviductal tissues from three yaks per reproductive phase (follicular, luteal, and pregnancy). Using Quantitative Real-Time PCR Experiments (RT-qPCR), Western blot (WB), immunohistochemistry (IHC), and immunofluorescence (IF), we analyzed RXR mRNA and protein expression and localization. RXR expression varied significantly (p ≤ 0.05), peaking in ovaries during the follicular phase, oviducts during the luteal phase, and uteri during pregnancy. RXRs were localized in ovarian granulosa and theca cells, oviductal epithelium, and uterine endometrial glands, with dynamic nuclear-cytoplasmic shifts. These findings suggest RXRs regulate key reproductive processes in yaks, offering insights on improving fertility in high-altitude environments.