Regulation of epithelial to mesenchymal transition in bovine conceptuses through the interaction between follistatin and activin A

• iTRAQ analysis identified 2063 proteins in pregnant bovine uterine flushing media.
• FST existed in day 20 conceptuses and uterine flushing media.
• Increase in Activin A was found in day 22 pregnant endometria and uterine flushings.
• FST down-regulated Activin A-induced EMT markers in cultured trophoblast cells.

Dynamic changes in bovine conceptus and endometrium occur during early gestation, in which the conceptus undergoes epithelial to mesenchymal transition (EMT) after the conceptus attachment to endometrium. To characterize EMT inducing factors, we initially undertook iTRAQ analysis with bovine uterine flushing (UF) obtained from pregnant animals on days 17 (P17: pre-attachment) and 20 (P20: post-attachment). The iTRAQ analysis demonstrated that follistatin (FST), an inhibitor of activin A, increased in P20 UF. We then found that FST decreased in P22 conceptuses, whereas elevated activin A found in P20 UF and endometria was further increased on P22. In addition, phosphorylated SMAD2 increased in P22 conceptuses. In bovine trophoblast cells, the treatment with P22 UF or activin An up-regulated EMT marker expressions, which were inhibited by FST. These results suggest that the initiation of bovine conceptus EMT could be regulated through the spatiotemporal expression of FST or activin A during the peri-attachment period.