Genomic Imprinting in Mammals: Emerging Themes and Established Theories

Abstract

The epigenetic events that occur during the development of the mammalian embryo are essential for correct gene expression and cell-lineage determination. Imprinted genes are expressed from only one parental allele due to differential epigenetic marks that are established during gametogenesis. Several theories have been proposed to explain the role that genomic imprinting has played over the course of mammalian evolution, but at present it is not clear if a single hypothesis can fully account for the diversity of roles that imprinted genes play. In this review, we discuss efforts to define the extent of imprinting in the mouse genome, and suggest that different imprinted loci may have been wrought by distinct evolutionary forces. We focus on a group of small imprinted domains, which consist of paternally expressed genes embedded within introns of multiexonic transcripts, to discuss the evolution of imprinting at these loci.

A Genomic Imprinting Defect in Mice Traced to a Single Gene

“…Parthenogenones overexpress maternally, and lack expression of paternally expressed imprinted genes, while the opposite misexpressions occur in androgenones Mann and Lovell-Badge 1984;McGrath and Solter 1984;Surani et al 1984;Cattanach and Kirk 1985;Coan et al 2005;Fowden et al 2006). Understanding how the various misexpressions combine to bring about the death of partheno-and androgenones is important for understanding the etiology of genomic imprinting (Solter 2006;Wood and Oakey 2006;Renfree et al 2009) and the prevalence of sexual reproduction (Avise 2008). …”

Genomic imprinting effects on adult body composition in mice

“…At some imprinted loci, such as Igf2r in mice, only the maternal allele is expressed, whereas at other loci, such as Igf2, only the paternal allele is expressed (3,4). This parent-of-origin-specific expression pattern is evinced by phenotypic differences between the ordered reciprocal heterozygotes, Aa and aA, where the first allele denotes the paternally derived copy and the second denotes the maternally derived allele.…”

“…Although the two heterozygotes (Aa and aA) are genotypically equivalent, they can be phenotypically distinct because, under genomic imprinting, only one of the two parental alleles is expressed. A variety of molecular mechanisms are thought to be involved in imprinting effects, including DNA methylation, histone modification, noncoding RNAs (ncRNA), and even longdistance interchromosomal interactions (4)(5)(6)(7).…”

Cancer Survivorship Care: A perspective from an Occupational- Participation Approach

“…Nevertheless it's also proactive, to consider perspectives from a cellular dimension. Research has shown that imprinted DNA methylation [established during gametogenesis in the parental germ line [52], and their associated loss of imprinting [LOI]) have been observed in a large variety of human carcinomas [53]. Thus, survivors should be followed up for any imprinted gene associated diseases.…”