DNA methylation plays an essential role in genomic imprinting observed in 
eutherian mammals and marsupials. In mouse, one of the two de novo DNA 
methyltransferases, Dnmt3a, and a related protein, Dnmt3L have been shown to be 
essential for imprint establishment in the parental germline. To gain insights 
into the evolution of imprinting mechanisms, we have identified and 
characterized the DNMT3 family genes in other vertebrate species. We cloned 
cDNAs for chicken DNMT3A and DNMT3B, whose putative protein products shared 
81.5% and 48.6% amino acid sequence identity with their mouse orthologues. Using 
computer-assisted database searches, we also identified DNMT3A and DNMT3B 
orthologues in fish (fugu and zebrafish) and marsupials (opossum). We found 
that, while opossums had an orthologue for DNMT3L, chickens and fish did not 
have this gene. Thus, unlike the other DNMT3 members, DNMT3L was restricted to 
the species in which imprinting occurs. The acquisition of DNMT3L by a common 
ancestor of eutherians and marsupials might have been closely related to the 
evolution of imprinting.