Function of a transcription factor CDX2 beyond its trophectoderm lineage specification

The transcription factor caudal-related homeobox 2 (CDX2) regulates trophectoderm differentiation, but its function beyond trophectoderm differentiation is not well characterized. CDX2 was shown to regulate a trophoblast-specific gene, interferon τ (IFNT), in the ruminants. However, its regulatory mechanism has not been determined. Here, we report a new role of CDX2 in histone modifications of the IFNT gene. Chromatin immunoprecipitation assays using ovine conceptuses obtained from d 14, 16, 16.5, or 20 of pregnancy (d 0, day of mating) revealed that H3K18 acetylation was highly detectable at the upstream and open reading frame regions of the IFNT gene on d 14 and 16, when CDX2 reached its peak expression. From d 16.5, when the conceptus initiates attachment to uterine epithelial cells, histone acetylation along with CDX2 expression declines. Two candidate CDX2 binding sites (-300 to -294 bp and -293 to -287 bp) of the bovine IFNT gene promoter region were detected from chromatin immunoprecipitation and luciferase assay. When Cdx2 constructs were transfected into bovine ear-derived fibroblast cells, histone acetylation was increased, concurrent with the recruitment of cAMP response element binding protein-binding protein, which has histone acetyltransferase activity. H3K18 acetylation was seen in the proximity of the CDX2 binding region located at the IFNT gene's upstream region in CT-1 cells, but when these cells were treated with specific CDX2 small interfering RNA, H3K18 acetylation was decreased. These findings suggest that CDX2 regulates its targeted gene through cAMP response element binding protein-binding protein recruitment, which correlates with greater histone acetylation.