Methylation of CpG dinucleotides alters binding and silences testis-specific transcription directed by the mouse lactate dehydrogenase C promoter

The mouse lactate dehydrogenase c gene (mldhc) is transcribed only in cells of the germinal epithelium. Cloning and analysis of the mldhc promoter rev ealed that a 100-base pair fragment was able to drive testis-specific trans cription in vitro and in transgenic mice. Several testis-specific genes are believed to be regulated at least in part through differential methylation of CpG dinucleotides. We investigated the possibility that transcriptional repression of the mldhc gene is mediated in somatic tissues by hypermethyl ation of CpG dinucleotides. The CpG dinucleotides within a fragment of the mldhc promoter containing a GC box and tandem activating transcription fact or/cAMP-responsive element binding sites are hypermethylated in somatic tis sues and hypomethylated in testis. Methylation of the activating transcript ion factor/cAMP-responsive elements altered the protein binding pattern obs erved in electrophoretic mobility shift assays using mouse liver but not te stis nuclear extract. Furthermore, methylation of an extended mldhc promote r fragment driving lac Z silenced transcription from the promoter in a tran sient transfection assay. These data suggest that tissue-specific different ial methylation plays a role in mldhc silencing in somatic tissues.