Coculture system that mimics in vivo attachment processes in bovine trophoblast cells

The establishment of pregnancy requires bidirectional communication between the developing conceptus and the uterine endometrium. The aim of this study was to establish an in vitro coculture system with bovine trophoblast cells and uterine epithelial cells (EECs) that mimics the in vivo attachment process. We previously reported that expression of interferon tau (IFNT), a major secretory product from the trophectoderm, decreases with changes in chromatin structure when the conceptus successfully attaches to the uterine epithelium. Thus, IFNT is a good marker to assess whether attachment has successfully occurred. In this study, bovine trophoblast CT-1 cells were cultured to generate spheroids, which were then placed on type I collagen-coated plates (monoculture) or bovine EECs (coculture) with or without uterine flushings collected from Day 15 cyclic or Days 15, 17, or 19 pregnant animals. In the coculture but not the monoculture, addition of uterine flushings from Day 15 or 17 pregnant animals resulted in decreased IFNT and CDX2 mRNA expression in CT-1 spheroids, accompanied with changes in histone modifications. In monocultured CT-1 spheroids, integrin subunit ITGA8 and ITGB3 mRNAs were minimally expressed but were induced in cocultured CT-1 spheroids with or without uterine flushings. Expression of CDH2, another marker for bovine conceptus attachment to the uterine epithelium, was also induced in the cocultured CT-1 spheroids. These results suggest that this in vitro coculture system could be used to isolate processes essential for conceptus attachment to uterine EECs.