DNA methylation of germ-cell-specific basic helix-loop-helix (HLH) transcription factors, Sohlh2 and Figl during gametogenesis

Regulation of germ-cell-specific transcription is essential for the differentiation and other physiological processes of germ cells. Germ-cell-specific transcription factors, Sohlh2 and Figla, play key roles in gametogenesis. To elucidate whether an epigenetic mechanism is involved in the controlled expression of Sohlh2 and Figlα, we examined the dynamics of DNA methylation at two gene loci. Results showed changes in methylation patterns in the promoter regions of both genes during the period of germ cell differentiation, while the methylation patterns in first exons and first introns (near the transcription initiation sites) remained constant. The methylation reprogramming at the cytosine-phosphate-guanine (CpG) locus in the Figlα promoters (P1: -812 to -568 bp and P2: -692 to -438 bp) and in the Sohlh2 promoter (sohlh2-P: -202 to 173 bp) was found to correlate with the expression of Figlα and Sohlh2 transcripts, respectively. Data therefore suggested that a dynamic DNA CpG methylation in the Sohlh2 and Figlα promoters, but not in the intron and exon sequences, is linked to the regulation of gene expressions, even though CpG islands are also present in their introns or exons.