Abstract
BackgroundGenomic imprinting is an epigenetic source of variation in quantitative traits that results from monoallelic gene expression, where commonly either only the paternally- or the maternally-derived allele is expressed. Imprinting has been shown to affect a diversity of complex traits in a variety of species. For several such quantitative traits sex-dependent genetic effects have been discovered, but whether imprinting effects also show such sex-dependence has yet to be explored. Moreover, theoretical work on the evolution of sex-dependent genomic imprinting effects makes specific predictions about the phenotypic patterns of such effects, which, however, have not been assessed empirically to date.ResultsUsing a genome-scan for loci affecting a set of complex growth and body composition traits from an intercross between two divergent mouse strains, we investigated possible sex-dependent imprinting effects. Our results demonstrate for the first time the existence of genomic imprinting effects that depend on sex and are not related to sex-chromosome effects. We detected a total of 13 loci on 11 chromosomes that showed significant differences between the sexes in imprinting effects. Most loci showed imprinting effects in only one sex, with eight imprinted effects found in males and six in females. One locus showed sex-dependent imprinting effects in both sexes for different traits. The absence of an imprinting effect in one sex was not necessarily indicative of the overall inactivity of the locus in that sex, as for several loci a significant additive or dominance effect was detected. Moreover, three loci exhibited significant additive effects in both sexes but their imprinting effect was restricted to one sex.ConclusionOur results clearly show that imprinting effects can be sex-dependent and also suggest that new candidate imprinted loci can be detected when taking account of sex-specific imprinting effects. However, predictions made about the evolution of sex-dependent imprinting effects and associated phenotypic patterns cannot be unequivocally supported at present and further research into the selection pressures applied to the strains of mice used in our study is required.
Highlights
Genomic imprinting is an epigenetic source of variation in quantitative traits that results from monoallelic gene expression, where commonly either only the paternally- or the maternally-derived allele is expressed
We detected a total of 13 quantitative trait loci (QTL) on 11 chromosomes affecting both body and organ weight measures that showed a significant interaction of sex and genomic imprinting effect (SbiQTL, where 'Sbi' refers to sex by imprinting interaction)
For all QTL, we confirmed that these sex interactions were true genomic imprinting effects rather than maternal genetic effects
Summary
Genomic imprinting is an epigenetic source of variation in quantitative traits that results from monoallelic gene expression, where commonly either only the paternally- or the maternally-derived allele is expressed. Imprinting has been shown to affect a diversity of complex traits in a variety of species. While most genes are expressed from both the paternally and maternally derived allele, imprinted loci show parentof-origin-dependent gene expression such that either the paternal or the maternal allele only is expressed [1,2] This monoallelic pattern of gene expression is usually caused by differential methylation of the paternal and maternal allele [3] and results in phenotypic differences between the two heterozygotes (where the only difference is the parent-of-origin of the parental alleles) at a given locus [4]. Among traits affected by imprinting are weight-related [8] and body composition traits [10] cognitive abilities [11,12] and associated disorders (e.g. Prader-Willi and Angelman syndrome), and obesity [7,13,14,15,16], highlighting the impact of epigenetic sources to variation in complex traits
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