Submitted to: Molecular Reproduction and Development
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/10/2003
Publication Date: 4/20/2004
Citation: Nojima, H., Nagaoka, K., Christenson, R.K., Shiota, K., Imakawa, K. 2004. Increase in DNA methylation downregulates conceptus interferon-tau gene expression. Molecular Reproduction and Development. 67(4):396-405. Interpretive Summary: Reproductive loss during early pregnancy is one of the most costly factors influencing the livestock industry. A large majority of reproductive failure in sheep occur as a result of an impaired signal from the developing conceptus to the maternal system during implantation. In sheep, the gene controlling the conceptus signaling product (ovine interferon-tau, oIFNtau) is known, but molecular mechanisms of tissue-specific gene expression and down-regulation of the IFNtau gene are not known. The objective of this study was to determine the methylation patterns of promoter and enhancer regions of the conceptus oIFNtau gene at different stages of gestation. These results provide evidence that changes in the degree of DNA methylation are fundamental mechanisms resulting in the down-regulation of the oIFNtau gene during early gestation in sheep. Thorough understanding of conceptus gene regulation should enable improvement in survival throughout gestation.
Technical Abstract: Expression of ovine interferon-tau (oIFNtau) genes is restricted to the trophoblast and is not detected in any other cell types or tissues. Substantial secretion of oIFNtau starts on day 12-13 of pregnancy (day 0 = day of estrus), reaches the highest on day 16-17, and then declines rapidly. To gain insight into a molecular mechanism of tissue-specific gene expression of IFNtau genes, the methylation status within 1 kb of the 5'-flanking region of oIFNtau-o10 gene was investigated: CpG dinucleotides of this gene in day 14 ovine conceptuses were hypomethylated compared to day 20 conceptuses or other tissues. In vitro methylation of oIFNtau-o10-reporter constructs caused suppression of reporter activity in transient transfections. Cotransfection of methyl-CpG-binding protein (MeCP2) with the reporter construct elicited further suppression of the reporter activity. Day 17, not day 14, conceptuses cultured in vitro and treated with 5-aza-2'-deoxycytidine, an inhibitor of DNA methylation, resulted in up-regulation of oIFNtau expression. These results provide evidence that changes in the degree of DNA methylation could be one of the major mechanisms leading to down-regulation of the oIFNtau-o10 gene during early gestation, and possibly its silencing in non-conceptus tissues.