DIFFERENCES BETWEEN HUMAN SPERM AND SOMATIC-CELL DNA IN CPG METHYLATION WITHIN THE HLA CLASS-I CHROMOSOMAL REGION

PROBLEM: We investigated the possible negative regulatory mechanisms t hat repress classical human leukocyte antigen (HLA) class I gene expre ssion in human spermatozoa and searched for novel testis-specific codi ng sequences that might be present in the MHC class I chromosomal regi on. METHOD: We performed a comparative DNA methylation analysis of thi s genomic region in both purified human spermatozoa and mononuclear bl ood cells from the same donors, using methylation-sensitive restrictio n enzymes followed by classical or pulsed field gel electrophoresis an d hybridization with HLA class I locus-specific probes. RESULTS: Unmet hylated CpG sites were detected in the 3' part of HpaII tiny fragments of the HLA-F and HLA-G genes in spermatozoal DNA. In contrast, no dif ference was observed in the methylation status of the HLA-B, HLA-C, an d HLA-E genes between germ and somatic cells. CpG unmethylation events were also detected in several parts of this chromosomal region (outsi de the known loci) in spermatozoal DNA. CONCLUSIONS: These results sug gest that this genomic region undergoes changes in its DNA methylation pattern during the developmental process. We hypothesize that these d ynamic changes have functional importance, including a possible transc riptional activity of nonclassical class I genes and/or as yet undescr ibed testis-specific coding sequences.