A novel gene, ITM, located between p57KIP2 and IPL, is imprinted in mice

We searched for new imprinted genes using a positional cloning method in a region of human chromosome 11p15.5, which contains several imprinted genes including p57KIP2 and IPL, and found a novel ITM gene located between p57KIP2 and IPL. We also obtained the mouse homologue Itm in its syntenic region of mouse chromosome 7. In humans, its location is 17 kb centromeric to p57KIP2 and 3 kb telomeric to IPL, and in mice, 15 kb and 2.5 kb, respectively. They are expressed in most tissue, but especially in the kidney and liver, and moderately in the heart, lung and testis. Mice exhibit a functional imprinting resulting in higher expression of maternal alleles in fetal, newborn and most adult tissues, but it is biallelically expressed in the adult kidney and liver where expression is the highest. In addition to the discrepancy between the level of expression and the strength of the imprint, Itm has several unusual features for an imprinted gene, including large introns, moderate GC content and the absence of direct repeats. Our results will be helpful in understanding the intricate regulatory mechanism of imprinted genes.