Effect of CpG methylation on expression of the mouse imprinted gene Mest

We previously reported isolation of the mouse gene, Mest (mesoderm-specific transcripts), which is mapped to the proximal part of chromosome 6 and pre dominantly expressed in the mesoderm and its derivatives during development . Peg1, a paternally expressed gene isolated by a systematic screening of i mprinted genes, was recently demonstrated to be identical to Mest. We and o thers have shown that the human homolog (MEST) of Mest is also imprinted so as to be expressed from the paternal copy and maps to 7q32. lo study trans criptional regulation of Mest/Peg1, we examined the effect of DNA methylati on on its expression. In the embryonal carcinoma (EC) cell line, MC12, from which Mest was originally isolated, the 5'-region harboring presumptive pr omoter of the gene was undermethylated. On the other hand, C4XX, a subclone of MC12 which had lost expression of Mest, was characterized by extremely high levels of methylation in the 5'-region, demethylation of which resulte d in activation of Mesa. Furthermore, a methylated reporter construct with the luciferase gene under the control of the putative promoter region of Me st was not competent to produce luciferase activity in MC12 cells. These re sults suggest a suppressive role for DNA methylation in Mest expression. Ho wever, neither methylated nor unmethylated reporter constructs showed lucif erase activity in a primary culture from the adult kidney, in which Mest is down-regulated despite apparent unmethylation of the paternal allele. Take n together, the data suggest that there are probably two modes of regulatio n for the Mest gene; one being a methylation-dependent mechanism that regul ates imprinted expression of Mest during development, and the other being a methylation-independent mechanism that is involved in down-regulation of M est in adult tissues. (C) 1999 Elsevier Science B.V. All rights reserved.