Abstract: The purpose of this study was to explore the proteomic characteristics of yak serum during pregnancy, and to screen and analyze the role of differentially expressed proteins(DEPs) in the maintenance of yak pregnancy. In this study, nine natural estrus female yaks aged from 4.5 to 6 years old with good health and no calving in the current year were selected for artificial insemination(AI). Serum samples were collected on the 30, 60 and 90 days after AI, and pregnancy diagnosis was performed on the mated female yaks. According to the diagnostic results, the collected samples were retrospectively grouped into the first, second, third month of pregnancy group and non-pregnant group(non-pregnant group samples were from non-pregnant yak individuals diagnosed by pregnancy diagnosis 90 days after AI), with 3 biological replicates in each group. The protein expression of yak serum samples was quantitatively analyzed by tandem mass spectrometry(TMT) technology, and the differentially expressed proteins were screened. Bioinformatics analysis such as GO function enrichment and KEGG pathway were carried out to further screen potential proteins related to yak pregnancy maintenance. The results showed that a total of 497 proteins were obtained from the four groups of yak serum protein samples, and a total of 68 differential proteins were obtained by screening with a fold change ≥1.2 or ≤0.83, and P<0.05. GO functional enrichment and KEGG pathway analysis showed that these DEPs were significantly enriched in biological processes such as metabolism, immune system, adhesion, and biological regulation, as well as pathways related to inflammation and immune pathways such as complement and coagulation cascades and Staphylococcus aureus infection. It is worth noting that the differential protein enrichment pathways between the groups during pregnancy include PI3K-Akt, Rap1, MAPK and other reproductive-related signaling pathways. The expression of IGFBP2, FGG, B2M, PDIA4 and AZGP1 in DEPs had a tendency to be up-regulated with the prolongation of pregnancy time, and the expression of these proteins in the third month of pregnancy was significantly higher than that in the non-pregnant state. The results showed that there were obvious changes in serum proteome in early pregnancy of yak. These DEPs play an important role in promoting cell adhesion and proliferation, maternal-fetal angiogenesis, and maintaining maternal metabolism and immune balance. In particular, IGFBP2, FGG, B2M, PDIA4 and AZGP1 may play an important role in the maintenance of yak pregnancy by participating in the regulation of placental growth and development, immune response and lipid metabolism. The results provide basic data for further exploring the regulatory mechanism of yak in maintaining pregnancy.

Key words: TMT, proteomics, yak, serum, differentially expressed proteins, pregnancy maintenance