Regulation of the ovine interferon-tau gene by a blastocyst-speciflic transcription factor, Cdx2

Expression of ovine interferon-tau (oIFN tau), a factor essential for the process of maternal recognition of pregnancy in ruminant ungulates, is restricted to the trophoblast. However, the molecular mechanisms by which olFN tau expression is restricted to the trophectoderm have not been fully elucidated, The objective of this study was to determine whether oIFN tau gene transcription could be regulated through Cdx2 expression, a transcription factor implicated in the control of cell differentiation in the trophectoderm. Human choriocarcinoma JEG3 cells were co-transfected with an oIFN tau (-654 base pair, bp)-luciferase reporter (-654-oIFN tau-Luc) construct and several transcription factor expression plasmids. Compared to -654-oIFN tau-Luc alone, transcription of the -654oIFN tau-Luc increased more than 30 times when this construct was co-transfected with Cdx2, Ets-2, and c-jun. The degree of transcription decreased to 1/4 levels when the upstream region was reduced to -551 bp, and became minimal with further deletions; this was confirmed with the use of the reporter constructs with mutated c-jun, Ets-2, and/or Cdx2 sites. In trophoblast unrelated NIH3T3 cells, which do not support IFN tau gene transcription, the olFN tau-Luc transcription was enhanced approximately eightfold when the cells were co-transfected with the Cdx2/Ets-2 or Cdx2/Ets-2/c-jun expression plasmids. These findings were confirmed by gel-shift assays examining Cdx binding site on the oIFN tau gene's upstream region, by immunohistochemical study identifying the presence of Cdx2 in day 15 and 17 ovine conceptuses, and by Western blot detecting Cdx2 in day 17 conceptuses. Our results indicate that oIFN tau gene transcription is regulated by Cdx2, and suggest that Cdx2 could be a key molecule in determining oIFN tau gene transcription by the trophectoderm.