Hypomethylation and expresion of L1 and HERV-W elements in ovarian cancer. Genomic DNA was digested either with MspI (left) or HpaII (right), and hybridized with probes specific for the promoter regions of L1 (A) or HERV-W (B) elements. The restriction enzymes MspI and HpaII recognize the sequence CCGG but HpaII only cuts when the recognition sequence is unmethylated at the inner cytosine (i.e., CC GG) while MspI is indifferent to the methylation status of the inner cytosine. Brackets indicate bands from restriction cut sites internal to the elements (B = benign cystic mass; LMP = low-malignancy potential or borderline tumor; N = normal ovary. (C) Real time RT-PCR was performed to determine expression levels of LINE-1 and HERV-W elements in representative malignant and non-malignant samples. Normalized values (retroelement expression value divided by expression value of the RPS27A control gene. Shown is the average of 3 replicate assays per sample ± SE. RPS27A expression has been previously determined to be unchanged between the malignant and non-malignant samples examined in this study (see text for details).