Hager Reinmar, Cheverud James M, Leamy Larry J, Wolf Jason B
Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, UK.
BMC Evol Biol. 2008 Oct 31;8:303. doi: 10.1186/1471-2148-8-303.
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. 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.
Using 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.
Our 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.
基因组印记是数量性状变异的一种表观遗传来源，其源于单等位基因表达，通常只有父源或母源等位基因表达。印记已被证明会影响多种物种的多种复杂性状。对于一些这样的数量性状，已经发现了性别依赖性遗传效应，但印记效应是否也表现出这种性别依赖性尚待探索。此外，关于性别依赖性基因组印记效应进化的理论研究对这种效应的表型模式做出了具体预测，然而，迄今为止尚未进行实证评估。
通过对两个不同小鼠品系杂交后代中影响一组复杂生长和身体组成性状的基因座进行全基因组扫描，我们研究了可能的性别依赖性印记效应。我们的结果首次证明了存在依赖于性别的基因组印记效应，且与性染色体效应无关。我们在11条染色体上共检测到13个基因座，这些基因座在印记效应上存在显著的性别差异。大多数基因座仅在一种性别中表现出印记效应，其中在雄性中发现8种印记效应，在雌性中发现6种。一个基因座在两种性别中对不同性状表现出性别依赖性印记效应。在一种性别中不存在印记效应并不一定表明该基因座在该性别中整体不活跃，因为对于几个基因座检测到了显著的加性或显性效应。此外，三个基因座在两种性别中都表现出显著的加性效应，但其印记效应仅限于一种性别。
我们的结果清楚地表明印记效应可能是性别依赖性的，也表明考虑性别特异性印记效应时可以检测到新的候选印记基因座。然而，目前关于性别依赖性印记效应进化及相关表型模式的预测不能得到明确支持，需要进一步研究应用于我们研究中所使用小鼠品系的选择压力。
