DNA methylation-dependent modulator of Gsg2/Haspin gene expression

The Gsg2 (Haspin) gene encodes a serine/threonine protein kinase and is predominantly expressed in haploid germ cells. In proliferating somatic cells, Gsg2 is shown to be expressed weakly but plays an essential role in mitosis. Although the Gsg2 minimal promoter recognized by the spermatogenic cell-specific nuclear factor(s) has been found, to date, the molecular mechanism that differentially controls Gsg2 expression levels in germ and somatic cells remains to be sufficiently clarified. In this study, we analyzed the DNA methylation status of the upstream region containing the Gsg2 promoter. We found a tissue-dependent and differentially methylated region (T-DMR) upstream (-641 to -517) of the authentic promoter that is hypomethylated in germ cells but hypermethylated in other somatic tissues. Profiling of Gsg2 expression and DNA methylation status at the T-DMR in spermatogenic cells indicated that the hypomethylation of the T-DMR is maintained during spermatogenesis. Using the reporter assay, we also demonstrated that DNA methylation at the T-DMR of Gsg2 reduced the promoter activity by 60-80%, but did not fully suppress it. Therefore, the T-DMR functions as a modulator in a DNA methylation-dependent manner. In conclusion, Gsg2 is under epigenetic control.