ALU REPEATED DNAS ARE DIFFERENTIALLY METHYLATED IN PRIMATE GERM-CELLS

A significant fraction of Alu repeats in human sperm DNA, previously f ound to be unmethylated, is nearly completely methylated in DNA from m any somatic tissues. A similar fraction of unmethylated Alus is observ ed here in sperm DNA from rhesus monkey. However, Alus are almost comp letely methylated at the restriction sites tested in monkey follicular oocyte DNA. The Alu methylation patterns in mature male and female mo nkey germ cells are consistent with Alu methylation in human germ cell tumors. Alu sequences are hypomethylated in seminoma DNAs and more me thylated in a human ovarian dysgerminoma. These results contrast with methylation patterns reported for germ cell single-copy, CpG island, s atellite, and L1 sequences. The function of Alu repeats is not known, but differential methylation of Alu repeats in the male and female ger m lines suggests that they may serve as markers for genomic imprinting or in maintaining differences in male and female meiosis.