Developmental changes of DNA methylation pattern of embryonic chick pepsinogen gene.

Embryonic chick pepsinogen (ECPg) is one of the pepsinogen isozymogens and its expression is restricted to epithelial cells of the embryonic chick proventriculus (glandular stomach). To examine whether DNA methylation is involved in the regulation of organ-specific and developmental stage-specific expression of ECPg gene, we analyzed the extent of methylation of ECPg gene in normal embryonic and hatched chick organs using methylation-sensitive restriction enzymes. In the proventriculus some CCGG sites underwent demethylation in the gene region after the onset of transcription of the ECPg gene. By contrast, these sites were kept methylated throughout the development in the other organs which do not express ECPg gene. GCGC sites in the gene region became methylated in organs which do not express the ECPg gene, after the initiation of transcription of the ECPg gene in the proventriculus. In the proventriculus, GCGC sites, which were methylated in other organs, were kept unmethylated throughout the development. The methylation state of CpG sites showed no change in the proventriculus of a chick 2 weeks after hatching when the expression of the ECPg gene had completely ceased. The data presented here demonstrate that the DNA methylation is involved in the regulation of organ-specific expression, but stage-specific expression might be brought about by some other mechanisms.