Imprinting status of genes linked to Peg1/Mest in mice

Abstract

Genomic imprinting is a mammal-specific epigenetic mechanism of the gamete or zygote leading to parent-of-origin-specific differential expression of the two alleles of a gene in somatic cells of offspring. Individual imprinted genes tend to cluster in a region of chromosome. To identify novel imprinted genes in the chromosomal vicinity of a previously identified imprinted gene, a systematic method exploiting the clustering feature was attempted in this study. Peg1/Mest, a maternally imprinted gene is located in the sub-proximal end of mouse chromosome 6, which is previously suspected to contain imprinted genes as demonstrated by uniparental disomy studies. Polymorphisms of the genes and ESTs mapped to this region in mouse and human was identified and used to physically discriminate one of parental alleles from the other in the F1 hybrids between two inbred mouse strains, Mus musculus molossinus and Mus musculus domesticus (C57BL/6J). Restriction fragment length polymorphism analysis of RT-PCR products was carried out to investigate the allele-specific expression of genes and ESTs in the F1 hybrids. Calu, Cda15a02, Ube2h and Cappa2 genes showed biallelic expression and allelic expression bias was not detected in these genes. However, one of the mouse EST, tentatively named URF1, was obviously shown to be expressed only from the paternal allele in the brain of F1 hybrids. Thus URF1 is maternally imprinted in adult mouse brain. Expression pattern in the reciprocal cross unambiguously confirmed the maternal imprinting of URF1 gene. Imprinting of URF1 seems to be delicately regulated in tissue-specific manner. In adult heart and lung, imprinting status of URF1 was relaxed. The extent of relaxation was analyzed quantitatively. It was estimated that the percentage of C57BL/6J allele was 93% for F1 hybrid of (M × C) and 29% for hybrid of (C × M) in heart and 86% for hybrid of (M × C) and 50% for hybrid of (C × M) in lung. URF1 provides an example of endogenous gene tha...