DNA methylation and DNA methyltransferases are essential for spermatogenesis. 
Mutations in the DNA methyltransferase Dnmt1 gene exert a paternal effect on 
epigenetic states and phenotypes of offspring, suggesting that DNMT1 is 
important for the epigenetic remodeling of the genome that takes place during 
spermatogenesis. However, the specific role of DNMT1 in spermatogenesis and the 
establishment of genomic imprints in the male germ line remains elusive. To 
further characterize the effect of DNMT1 deficiency on the resetting of 
methylation imprints during spermatogenesis, we analyzed the methylation 
profiles of imprinted regions in the spermatozoa of mice that were heterozygous 
for a Dnmt1 loss-of-function mutation. The mutation did not affect the H19 or IG 
differentially methylated regions (DMRs) that are usually highly methylated but 
led to a partial hypermethylation of the Snrpn DMR, a region that should 
normally be unmethylated in mature spermatozoa. This defect does not appear in 
mouse models with mutations in Dnmt3a and Mthfr genes and, therefore, it is 
specific for the Dnmt1 gene and is suggestive of a role of DNMT1 in imprint 
resetting or maintenance in the male germ line.