Gatm, a creatine synthesis enzyme, is imprinted in mouse placenta

To increase our understanding of imprinting and epigenetic gene regulation, we undertook a search for new imprinted genes. We identified Gatm, a gene that encodes L-arginine:glycine amidino-transferase, which catalyzes the rate-limiting step in the synthesis of creatine. In mouse, Gatm is expressed during development and is imprinted in the placenta and yolk sac, but not in embryonic tissues. The Gatm gene maps to mouse chromosome 2 in a region not previously shown to contain imprinted genes. To determine whether Gatm is located in a cluster of imprinted genes, we investigated the expression pattern of genes located near Gatm: Duoxl-2, Slc28a2, Slc30a4 and a transcript corresponding to LOC214616. We found no evidence that any of these genes is imprinted in placenta. We show that a CpG island associated with Gatm is unmethylated, as is a large CpG island associated with a neighboring gene. This genomic screen for novel imprinted genes has elucidated a new connection between imprinting and creatine metabolism during embryonic development in mammals.