A gene-specific promoter in transgenic mice directs testis-specific demethylation prior to transcriptional activation in vivo

Transcription of the autosomal phosphoglycerate kinase gene, Pgk-2, is initiated at the onset of meiosis during spermatogenesis in mammals. However, in the mouse, the 5' portion of the endogenous Pgk-2 coding sequence undergoes a specific demethylation event that precedes transcriptional activation by 10-12 days. Here we show that transgenes consisting of the Pgk2 core promoter ligated to the CAT reporter gene undergo a similar tissue-, stage-, and cell type-specific demethylation in the 5' portion of the CAT coding sequence, whereas transgenes consisting of the CAT reporter sequence alone, or of the CAT sequence ligated to the CpG island-containing transferrin gene promoter, demonstrate different patterns of demethylation. These results indicate that specific promoter sequences can influence the pattern of tissue-specific demethylation within different genes and that a signal for spermatogenic cell-specific demethylation resides within the core promoter of the mammalian Pgk-2 gene.