302 IMPRINTED microRNA ARE DIFFERENTIALLY EXPRESSED IN ADULT MOUSE TESTES-DERIVED MALE GERM-LINE STEM CELLS

Testis-derived male germ-line stem (GS) cells, the in vitro counterpart of spermatogonial stem cells, can acquire multipotency under appropriate culture conditions to become multipotent adult germ-line stem (maGS) cells, which, upon testicular transplantation, produce teratomas instead of initiating spermatogenesis. This study evaluated the DNA methylation and expression of imprinted microRNA (miRNA) in mouse GS and maGS cells. The GS and maGS cell lines were established essentially as described earlier (Jung et al. 2010 Mol. Hum. Reprod. PMID: 20610616) and were quantified for maternally (miR-296-3p, miR-296-5p, miR-483) and paternally (miR-127, miR-127-5p) imprinted miRNA by real-time TaqMan® MicroRNA assay and for DNA methylation at imprinting control regions of respective miRNA (Gnas-Nespas DMR, Igf2-H19 ICR, and Dlk1-Dio3 IG-DMR) by bisulfite genomic sequencing. Sperm and embryonic stem (ES) cells were used as controls for comparison. Results showed that, similar to sperm, expression of maternally imprinted miRNA was consistently higher (P < 0.001), whereas that of paternally imprinted miRNA was consistently lower (P < 0.001) in GS cells than in control ES cells. The DNA methylation analyses further confirmed that imprinted miRNA were androgenetic in GS cells. On the other hand, DNA methylation of maGS cells resembled that of ES cells, but the expression pattern of imprinted miRNA was intermediate between that of GS cells and ES cells. The expression of imprinted miRNA in GS and maGS cells was also altered during their in vitro differentiation but varied with both the differentiation stage and the miRNA. In conclusion, our data suggest that GS cells have androgenetic DNA methylation and expression of imprinted miRNA which changes to an ES cell-like pattern upon their conversion to maGS cells and, therefore, may serve as an epigenetic miRNA signature or molecular marker to distinguish GS cells from maGS cells. This work was supported by a grant (Code #200901FHT010305191) from BioGreen 21 Program, RDA, Republic of Korea.