The human/mouse imprinted genesIGF2, H19, SNRPN andZNF127 map to two conserved autosomal clusters in a marsupial

Abstract

The four genesIGF2, H19, SNRPN andZNF127 are imprinted in mouse and human.IGF2 andH19 form one conserved cluster on the distal part of mouse chromosome 7 and human chromosome 11p15.5, whereasSNRPN andZNF127 form another on the middle of mouse chromosome 7 and on human chromosome 15q11-13. We have explored the evolution of these imprinted regions by cloning and mappingIGF2, H19, SNRPN andZNF127 homeologues in marsupials. Specifically, we wished to determine whether the arrangements were shared in eutherian and marsupial mammals, and to determine whether they lay on autosomes, or on the X, as might be predicted by the hypothesis that imprinting evolved from X inactivation. Using fluorescencein situ hybridization, we localized the marsupial homeologues ofIGF2 andH19 to the distal part of tammar wallaby chromosome 2p and the marsupial homeologues ofSNRPN andZNF127 to the middle of chromosome 1q. Thus, these genes were originally organized in two separate autosomal clusters in the therian ancestor 180 million years ago, the conservation of which may suggest a functional relationship. The autosomal location of these clusters does not suggest a recent evolutionary relationship between imprinting and X chromosome inactivation.