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Genomic imprinting is a phenomenon whereby genes are differentially expressed according to their parental origin.1,2 Mutations which affect the epigenetic states of imprinted domains underlie a number of diseases, including developmental abnormalities, malignant tumours, and psychiatric diseases.3 To date, >50 imprinted genes have been identified in human and mouse (www.otago.ac.nz/IGC). For some genes, imprinting has been shown to be tissue specific4–9 and/or developmentally regulated.10,11 For others, polymorphic imprinting (the term for the imprinting of a gene that is variable between individuals) has also been observed.12,13 These variations in gene expression are considered to be a source of phenotypic heterogeneity in human disease with parent-of-origin effects.4
Three imprinted loci have been identified on human chromosome 7.14 One of the loci is located on 7q21.3 and two genes, SGCE and PEG10, are known to be imprinted (fig 1A). Initially the mouse Sgce gene (encoding sarcoglycan-epsilon) was identified as a maternally imprinted (paternally expressed) gene in a subtractive screening experiment using cDNA libraries derived from parthenogenetic and wild-type fibroblast lines.15 The human SGCE gene has also been confirmed to be imprinted.16–18PEG10 (paternally expressed gene 10), which is immediately telomeric to SGCE, was also shown to be imprinted in embryonic villi.19 Moreover, the mouse Asb4 gene (ankyrin repeat and SOCS box-containing protein 4), which is 800 kb telomeric to Sgce, was found to be maternally expressed by cDNA micro-array based high-throughput screening for genes differentially expressed between mouse parthenogenetic and androgenetic embryos.6 The imprinting status of the human ASB4 and other genes adjacent to SGCE/PEG10 has not yet been determined, but systematic imprinting analyses of mouse genes indicate that the 1 Mb interval encompassing Sgce/Peg10 is part of a large imprinted locus; …
Footnotes
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↵* These two authors contributed equally to this manuscript.
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↵† Current address: Kihara Institute for Biological Research, Graduate School of Integrated Science, Yokohama City University, Yokohama, 244-0813, Japan.
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↵‡ Current address: Faculty of Medicine, Yamaguchi University, Yamaguchi, 753-8511, Japan.
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This research is supported by grants from the Canadian Institutes of Health Research (CIHR) and Genome Canada.
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Conflict of interest: none declared.
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Data deposition: GenBank accession number, AY308065.