Isolation and characterization of a bovine blastocyst-derived trophoblastic cell line, BT-1: development of a culture system in the absence of feeder cell.

We established a trophoblastic cell line, bovine trophoblast-1 (BT-1), derived from in vitro matured and fertilized blastocyst. While several trophoblastic cell lines have been previously reported using feeder cell, BT-1 could be cultured in the absence of feeder cell. BT-1 was cultured for more than 18 months (over 75 passage) in the absence of feeder cells, using bovine endometrial fibroblast-conditioned medium (fibroblast-conditioned medium). We found that the cell growth was accelerated in fibroblast-conditioned medium. In bromodeoxyuridine incorporation analysis, BT-1 cells growth rate in fibroblast-conditioned medium was about two-fold higher than that in conventional medium. Furthermore, fibroblast-conditioned medium accelerated attachment of BT-1 cells to culture dishes following plating. BT-1 showed epithelial morphology and expressed cytokeratin. During continuous culture, cells accumulated fluid under the cell sheet and form dome-like structure that eventually transformed into free floating vesicles. Reverse transcription polymerase chain reaction analysis and immunoblot analysis demonstrated that BT-1 cells expressed interferon-tau as well as placental lactogen (PL). Immunofluorescence analysis demonstrated that a small number of cells were PL-positive, and these cells were binucleate. The BT-1 trophoblastic cell line could serve as a powerful model system for the study of trophoblast cell lineage and proliferation.