Differential chromatin packaging of genomic imprinted regions between expressed and non-expressed alleles

基因组印迹的染色体区域包含一个功能域，表现出亲本特异性的基因表达，因此可能具有独特的染色质结构。在这里，我们已经检查了染色质包装状态的等位基因位点的Zfpl 27/Snrpn基因座上的小鼠7号染色体和小鼠17号染色体上的Igf 2 r基因座的染色质分离和等位基因特异性检测组成的测定。结果表明，在C57 BL/6与MSM两种杂交类型的F_1代小鼠中，IgfSr的非转录等位基因比转录等位基因包装得更紧密，而Igf 2 r附近的非印迹基因Sod-2则没有这种差异。这表明印记和染色质的差异包装之间存在密切的相关性。另一方面，Zfp 127/Snrpn基因座仅在杂交的Ft杂种小鼠中显示出这种等位基因特异性分离模式，而在反交的Ft杂种小鼠中没有显示出这种分离模式。这些结果表明，印迹结构域的染色质在不同的压实水平，这是由不同的蓝图，在同源染色体，通过生殖系遗传的影响。

Chromosomal regions subject to genomic imprinting comprise a functional domain exhibiting parental-specific expression of genes and hence may take a Unique chromatin structure. Here we have examined chromatin packaging state of allelic sites in the Zfpl27/Snrpn locus on mouse chromosome 7 and in the Igf2r locus on mouse chromosome 17 with an assay consisting of chromatin fractionation and allele-specific detection. The result showed that nontranscribed alleles of IgfSr are packaged more compact than transcribed alleles in F_1 hybrid mice of both types of cross between C57BL/6 and MSM strains, while a nonimprinted gene, Sod-2, in the vicinity of Igf2r does not show such a difference. This indicates a close correlation between imprinting and the differential packaging of chromatin. On the other hand, the Zfpl27/Snrpn locus showed such an allele-specific fractionation pattern only in Ft hybrid mice of a cross but not in those of the reciprocal cross.Analysis of congenic mice produced for this locus did not provide any difference. These results suggest the chromatin of imprinted domains in different compaction level which is affected by distinct blueprints in homologous chromosomes that are heritable through the germ line.