Epigenetic regulation of the expression on of [i]ELF5[/i] in different bovine cell lineages
Résumé
ELF5 is a transcription factor specifically expressed in adult epithelia and in trophectoderm cells at the blastocyst stage. In the mouse, ELF5 plays a decisive role as gatekeeper of the trophoblast and its expression peaks at the time of implantation. In human placenta, its expression is maintained in the villous cytotrophoblast (Hemberger et al., 2009, 2010). Moreover, the transcriptional regulation of ELF5 is ensured by epigenetic modifications such as DNA methylation in the proximal part of the promoter region (Ng et al., 2008). In the bovine species, ELF5 expression peaks at Day 12 (Degrelle et al., 2005) and decreases with conceptus length during the elongation process (Smith et al., 2010). In order to analyze the role of ELF5 as gatekeeper of the trophoblast lineage at implantation (day 18-20) and during the early fetal development (umtil day 60), we analysed its expression and methylation profiles at these two stages in tissues from different lineages. Since placenta development is one of the main defects observed after somatic cel! nuclear transfer (or cloning; Chavatte-Palmer et al, 2011), tissues from bovine conceptuses generated by artificial insemination (control) and by cloning have been used. ELF5 expression was measured by real lime RT-PCR and DNA methylation by DNA bisulfite conversion and pyrosequencing at tw*o proximal regions of the bovine ELF5 promoter containing 14CpG and 13CpG, respectively. Tite ELF5 transcript was weakly expressed in bovine extra-embryonic tissues at Day 18 and faintly expressed at Day 60. In addition, ELF5 expression patterns were similar in these tissues after SCNT or Al. The two regions of the proximal promoter that were analysed exhibited subtle differences in their methylation levels, in relation with the lineage and with the gestation stage. These data suggest that the transcriptional regulation of this gene through DNA methylation is finely-tuned in the bovine species, depending on the promoter region, the developmental stage and the cell lineage.