DNA methylation changes during mouse spermatogenesis.

Genomic imprinting in mammals is thought to be mediated by differences in the methylation level of cytosine residues in the genome. These differences in DNA methylation are thought to be generated during the development of the germ line. To characterize the profile of global methylation of the mouse genome during male gametogenesis, we have quantified the relative level of methylation in individual cells during meiosis and spermatogenesis. A decrease in the level of DNA methylation is observed from meiotic cells to elongated spermatids. The erasure of the somatic pattern of methylation during spermatogenesis suggests the existence of a subsequent mechanism generating the parental specific methylation patterns leading to genomic imprinting of specific alleles.