Ovine conceptus transcriptome

Establishment of pregnancy depends on successful implantation to the maternal endometrium. In ruminants, various molecules are involved in regulating conceptus attachment; however, the mechanisms regulating the conceptus attachment have not been well characterized. We hypothesized that conceptus must produce a molecule(s), yet uncharacterized or overlooked, which enhances conceptus attachment to the uterine epithelium. In this study, we aimed to identify new candidate(s) in conceptus secretory proteins responsible for conceptus attachment in sheep. We thus performed RNA-sequence analysis with ovine conceptuses obtained from pregnant animals on day 15 (P15: pre-attachment), 17 (P17: right after attachment), and 21 (P21: post-attachment) and iTRAQ analysis of uterine flushing on P15 and P17. To identify the proteins secreted uniquely from conceptuses, we cross-referenced the transcriptome and proteome data to those from the ovine uterine epithelium available publicly. Together, these analyses identified 48 and 34 proteins as conceptus secretory proteins on P15 and P17, respectively. Gene ontology analysis revealed that the conceptus secretory proteins were enriched in those categorized to fibrinolysis and coagulation. RT-qPCR analysis verified that the expression levels of transcripts in conceptuses encoding coagulation factors, fibrinogen subunits, and fibrinolysis factors were significantly higher on P21 than on P15 or P17. Histology analysis revealed that fibrin formed at the conceptus attachment region on P21. These results suggest that in addition to the numerous attachment molecules so far characterized, fibrin is a new candidate molecule for facilitating conceptus attachment for successful pregnancy in ruminants.