Figure legend. Generation and regulation of testicular germ cell-specific genes. Testicular isoform genes are generated by conventional gene duplication or retroposition. In the case of retroposons, the inserted cDNA, which is reverse-transcribed from mRNA, cannot be expressed in any tissue because the mRNAs lack a promoter in the 5'-flanking sequence of the genomic DNA. This implies that testicular germ cells provide an appropriate environment for retroposon transcription and facilitate gene expression from promoter-like sequences. This in turn suggests that the rules governing gene transcription during the later stages of spermatogenesis differ drastically from those in other cell types. |
- DNA methylation during spermatogenesis.
Many of the testicular germ cell-specific genes are retroposons, most of which contain a CpG-rich region within their ORFs. We discovered that the methylation of the CpG dinucleotides in the ORF represses its promoter in somatic cells and that demethylation is necessary for gene expression in spermatogenic cells. We are analyzing the molecular basis of the epigenetic modifications, including DNA methylation and histone methylation, which occur in a distinct genomic region in germ cells. - Unique structure of sperm chromatin.
In the mammalian sperm nucleus, the haploid genome is packaged into a highly compact structure that contains protamines and some remaining histones. We are analyzing the physiological importance of the somatic-like, histone-containing regions of sperm chromatin. - Establishment of an in vitro germ cell differentiation system
To examine the genetic requirements that are needed for germ cell formation and epigenetic reprogramming, we are in the process of establishing an in vitro developmental system based on ES cell differentiation.