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 p57Kip2 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 H19 gene region, suggesting that these more telomeric genes are not regulated by the mechanism that controls H19, Igf2, and Ins2. Mutations in human p57Kip2 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; p57Kip2 is activated, Kvlqt1 is silenced, and Mash2 is unaffected in mice lacking DNA methyltransferase. We conclude that H19 is not a global regulator of imprinting on distal chromosome 7 and that the telomeric genes are imprinted by a separate mechanism(s).

Epigenetic deregulation of imprinting in congenital diseases of aberrant growth

“…Furthermore, in the mouse, deletion of the H19 ICR does not affect the KCNQ1 domain and, conversely, targeting of the KvDMR1 does not alter imprinting at the IGF2-H19 domain. (17,34,35) An emerging question is whether, as opposed to what happens in BWS, increased expression of CDKN1C could be causally involved in SRS. In the novel SRS studies, this was explored by analysis of the KvDMR1, but no methylation changes were detected in the patients analysed.…”

Role of De Novo DNA Methyltransferases in Initiation of Genomic Imprinting and X-Chromosome Inactivation

“…Mash2 is located within a large imprinted cluster on mouse distal chromosome 7 and is exclusively expressed from the maternal allele (Guillemot et al 1995). However, the imprinting of this gene is unique in that its maintenance is highly resistant to hypomethylation, as shown by the analysis of the Dnmt1-deficient embryos (Caspery et al 1998;Tanaka et al 1999). It is therefore interesting to ask whether the imprinting of this gene is initiated normally in the germ line of [Dnmt3a 2lox/1lox , TNAP-Cre] females.…”

“…By contrast, in the trophoblast, the role of DNA methylation seems more relaxed (Table 1) (Caspery et al 1998;Tanaka et al 1999;Sado et al 2000). However, whether DNA methylation is involved in their initiation has not been addressed.…”

Igf2 imprinting does not require its own DNA methylation or H19 RNA

“…All of these properties are evident within an ∼800-kb cluster of genes that resides on the distal end of mouse chromosome 7 (Caspary et al 1998). This cluster contains the paternally expressed insulin-like growth factor 2 (Igf2) and insulin-2 (Ins2) genes, which are flanked on the telomeric side by the maternally expressed p57 Kip2 ,Mash2,and K v lqt1 genes and on the centromeric side by the maternally expressed H19 gene.…”