Multiple Mechanisms Regulate Imprinting of the Mouse Distal Chromosome 7 Gene Cluster

ABSTRACT

Genomic imprinting is an epigenetic process that results in the preferential silencing of one of the two parental copies of a gene. Although the precise mechanisms by which genomic imprinting occurs are unknown, the tendency of imprinted genes to exist in chromosomal clusters suggests long-range regulation through shared regulatory elements. We characterize a 800-kb region on the distal end of mouse chromosome 7 that contains a cluster of four maternally expressed genes, H19, Mash2, Kvlqt1, and p57^Kip2 , as well as two paternally expressed genes, Igf2 and Ins2, and assess the expression and imprinting of Mash2, Kvlqt1, and p57^Kip2 during development in embryonic and extraembryonic tissues. Unlike Igf2 and Ins2, which depend on H19 for their imprinting,Mash2, p57^Kip2 , and Kvlqt1 are unaffected by a deletion of the H19gene region, suggesting that these more telomeric genes are not regulated by the mechanism that controls H19,Igf2, and Ins2. Mutations in humanp57^Kip2 have been implicated in Beckwith-Wiedemann syndrome, a disease that has also been associated with loss of imprinting of IGF2. We find, however, that a deletion of the gene has no effect on imprinting within the cluster. Surprisingly, the three maternally expressed genes are regulated very differently by DNA methylation; p57^Kip2 is activated, Kvlqt1 is silenced, and Mash2 is unaffected in mice lacking DNA methyltransferase. We conclude thatH19 is not a global regulator of imprinting on distal chromosome 7 and that the telomeric genes are imprinted by a separate mechanism(s).

ACKNOWLEDGMENTS

We thank Steve Elledge and Pumin Zhang, Baylor College of Medicine, for p57^Kip2 mutant mice and the sequence of the p57^Kip2 locus, and we thank Rudolph Jaenisch and En Li for the Dnmt mutant mice. We also thank R. S. Ingram for DNA sequencing, B. K. Jones for developing the Dnmt genotyping assay, and members of the laboratory for critical discussion.

This work was supported by a grant from the National Institute for General Medical Sciences (GM 51460).

T.C. and M.A.C. contributed equally to this work.