A New Histochemical Approach to Localize Methylation Sites of DNA: HELMET

Abstract

Epigenetic modification such as DNA methylation is implicated in the induction of cell differentiation and its maintenace in eukaryotes. In spite of potential importance of the analysis of methylation states of sequence specific DNA in indivisual cells, it was impossible. Here we presented a new histochemical method, HELMET, which permits us to analyze methylated levels of specific sites of DNA using an isoshizomeric set of restriction enzymes. When the method was applied to examine the methylation states of CCGG sequences in mouse testis, we effectively found differetiation stage-dependent changes in the ratio of the number of nonmethylated CCGG sites to that of methylated ones during spermatogenesis.