Abstract：Oviductin (Ovn) plays crucial role during fertilization and early embryonic development. The objective of this study was to clone the full open reading frame of yak (Bos grunniens) oviductin and to detect its different expression during the estrous cycle from mRNA and protein level. In this study, we cloned oviductin cDNA by RT-PCR, and analysed the expression of oviductin in oviductal ampulla and isthmus of yak in early follicular (follicles 3~6 mm), late follicular (with preponderant follicles＞6 mm), early luteal (one or more corpora hemorrhagica visible) and late luteal (one or more corpora lutea visible) by qRT-PCR (quantitative Real-time PCR) and immunohistochemistry. The oviductin cDNA of yak was successfully cloned, and the sequences had been submitted to GenBank, and accession number was KF303541, which contained the full open reading frame and determined to be 1 443 nucleotides encoding for a deduced protein of 480 amino acids. The sequence analysis revealed that oviductin cDNA sequences of yak shared very high homology with cattle and buffalo. The phylogenetic tree based on amino acid sequences of oviductin indicated that yak oviductin was closely related to its cattle counterpart, reached 99.1% with Bos taurus, followed by 93.7% with buffalo (Bubalus bubalis), 88.1% with sheep (Ovis aries), 79.8% with Macaca radiata. qRT-PCR results showed highest oviductin mRNA oviductin expression in the stage of late follicle, reduce in the stages of early luteal and late luteal. The expression of mRNA was lowest in the stages of early follicle. However, there was no difference between ampulla and isthmus. The prominent immunolabeling were observed in the late follicle and early luteal stages, which was reduced in other stages. In this study, we obtained cDNA sequence of yak oviductin containing an open reading frame, and found the highest expression in the stage of late follicle. It showed that oviductin has an important biological role in oocyte maturation and the process of ovulation. The present study provides certain theoretical references for increasing yak fertilization rate and the development of early embryos.
