Joint Study on Nature of Histone Variants by Gene Disruption

44个鸡H1和核心组蛋白基因中有39个位于一个110 kb的主要组蛋白基因簇中。在这项研究中，我们使用基因靶向技术，分别产生了几个dt40o突变体，它们缺乏一个或两个特定的组蛋白基因，110 kb的主基因簇中的一个等位基因，大约57 kb的片段携带21个基因，以及12个H1基因拷贝中的11个。对结果突变体的系统分析使我们得出了一些值得注意的结论，如下所示。1)所有组蛋白基因家族都有内在的能力来弥补大约一半的自身成分的缺失，并根据剩余基因表达的增加来维持每种组蛋白亚型的化学计量平衡，而不管主要基因簇的一个等位基因完全中断或两个等位基因的大约一半片段中断。因此，一个主要组蛋白基因簇的等位基因就足以使细胞增殖。2) 12个H1基因拷贝中的11个拷贝的缺失不影响细胞功能，即生长速度和整体染色质结构。这些结果表明，只有一个拷贝的H1基因是足够的细胞增殖。3)由于组蛋白变体的组成没有变化，当缺失一个等位基因时，蛋白质模式不会改变，但当缺失大约一半的组蛋白片段时，蛋白质模式会发生变化，而后者加上更多的Hl基因(s)，这是由于H1和核心变体的质量变化。4)突变体中的蛋白质模式分别发生改变，缺乏特定的Hl和H2B变体。可变蛋白对相应的突变体是特异性的，这表明H1和核心变异体应该单独参与特定基因表达的调控，通过改变特定基因组区域的染色质结构。

Thirty-nine of the 44 chicken H1 and core histone genes are located in a major histone gene cluster of 110 kb. In this study, using gene targeting techniques, we generated several DT4O mutants, respectively, which are devoid of one or two particular histone genes, one allele of the major gene cluster of 110 kb, an approximately 57 kb segment of the cluster carrying 21 genes, and 11 of the 12 H1 gene copies. Systematic analyses of the resultant mutants led us to some noticeable conclusions, as follows.1)All of the histone gene families have the inherent ability to compensate for the deletion of approximately half of their own constituents, and to maintain the amount of each of the histone subtypes in stoichiometric balance, based on increases in the expression of the remaining genes, regardless of the complete disruption of one allele of the major gene cluster or the disruption of approximately half segments of the two alleles. Therefore, one allele of the major histone gene cluster is enough for cell proliferation.2)The deletion of 11 of the 12 H1 gene copies does not affect cell functions, i.e. the growth rate and global chromatin structure. These results indicate that only one copy of the H1 genes is enough for cell proliferation.3)The protein patterns are not altered in the case of the deletion of one allele of the cluster, due to no changes in the composition of any histone variant, but vary in the case of the deletion of approximately half segments of the cluster, and the latter plus more Hl gene(s), due to changes in the quality of the H1 and core variants.4)The protein patterns are altered in the mutants, respectively, lacking particular Hl and H2B variants. The variable proteins are specific for the corresponding mutants, suggesting that the H1 and core variants should be individually involved in regulation of the expression of specific genes, through alterations in the chrornatin structure localized in specific genomic regions.