The paternally imprinted DLK1-GTL2 locus is differentially methylated in embryonal and alveolar rhabdomyosarcomas

Parental imprinting of differentially methylated regions (DMRs) contributes to appropriate expression of several developmentally important genes from paternally or maternally derived chromosomes. Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma in children and is associated with altered expression of certain parentally imprinted genes. As previously reported, RMS cells display loss of imprinting (LOI) of the DMR at the IGF2-H19 locus, resulting in insulin-like growth factor 2 (IGF2) transcription from both paternally and maternally inherited chromosomes, and overall IGF2 overexpression. As the DLK1-GTL2 locus is structurally similar to the IGF2-H19 locus, the status of parental imprinting of the DLK1-GTL2 locus was studied in RMS. We observed that while both embryonal and alveolar rhabdomyosarcomas (ERMS and ARMS, respectively) show LOI of the DMR at the IGF2-H19 locus, imprinting of the DMR at the DLK1-GTL2 locus varies in association with the histological subtype of RMS. We found that, while ERMS tumors consistently show LOI of the DMR at the DLK1-GTL2 locus, ARMS tumors have erasure of imprinting (EOI) at this locus. These changes in imprinting status of the DLK1-GTL2 locus result in a higher GTL2/DLK1 mRNA ratio in ARMS as compared to ERMS. This difference in imprinting elucidates a novel genetic difference between these two RMS subtypes and may provide a potential diagnostic tool to distinguish between these subtypes.