Expression of c-fos and jun protooncogenes in ovine trophoblasts in relation to interferon-tau expression and early implantation process.

Expression of c-fos and jun protooncogenes was analyzed in the ovine extraembryonic trophoblast from days 14-18 of gestation, using Northern and Western blotting and immunohistochemistry. This study was carried out in relation to the early implantation process and the expression of interferon-tau, which is secreted in large amounts for a few days before implantation. Our results demonstrated that c-fos, c-jun, and junB were differently expressed in the ovine trophoblast around the time of implantation. The c-fos mRNA and protein were detected at high levels prior to attachment and decreased thereafter, following the pattern of expression of interferon-tau, whereas c-jun expression was maintained at relatively high levels during the implantation process. By contrast, the levels of junB mRNA and protein decreased prior to attachment. Immunohistochemical studies indicated that JunB, like C-Fos and interferon-tau, was no longer expressed in the trophoblastic cells which had established cellular contacts with the uterine epithelium. A striking finding in this study is the temporal correlation between the accumulation of c-Fos and c-Jun proteins and the expression of the interferon-tau (days 14 and 15 of gestation). We also showed by gel-retardation assays that an AP-1-like site present in the promoter of one interferon-tau gene was functional in vitro, as judged by its ability to bind day-15 trophoblast nuclear protein extracts. Nuclear proteins binding to this site had the characteristics of AP-1, as judged by the ability to be competed efficiently by a consensus TRE (12.0-tetradecanoyl phorbol 13-acetate-responsive element)-site oligonucleotide and by antibodies to c-Fos and Jun proteins. These results suggest that Fos and Jun could form regulatory complexes of interferon-tau expression and/or are regulated by common mechanisms which are still unknown.