Amplified sequences constitute a large part of mammalian genomes. A chromosome 1 containing 2 large (up to 50 Mb) homogeneously staining regions (HSRs) separated by a small inverted euchromatic region is present in many natural populations of the house mouse (Mus musculus musculus). The HSRs are composed of a long-range repeat cluster, Sp100-rs, with a repeat length of 100 kb. In order to understand the organization and function of HSRs in meiotic chromosomes, we examined synapsis and recombination in male mice hetero- and homozygous for the HSR-carrying chromosome using FISH with an HSR-specific DNA probe and immunolocalization of the key meiotic proteins. In all homozygous and heterozygous pachytene nuclei, we observed fully synapsed linear homomorphic bivalents 1 marked by the HSR FISH probe. The synaptic adjustment in the heterozygotes was bilateral: the HSR-carrying homolog was shortened and the wild-type homolog was elongated. The adjustment was reversible: desynapsis at diplotene was accompanied by elongation of the HSRs. Immunolocalization of H3K9me2/3 indicated that the HSRs in the meiotic chromosome retained the epigenetic modification typical for C-heterochromatin in somatic cells. MLH1 foci, marking mature recombination nodules, were detected in the proximal HSR band in heterozygotes and in both HSR bands of homozygotes. Unequal crossing over within the long-range repeat cluster can cause variation in size of the HSRs, which has been detected in the natural populations of the house mouse.
Cytogenet Genome Res

中文翻译：

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家鼠染色体1的均质染色区（HSR）：减数分裂的突触和重组。

扩增的序列构成哺乳动物基因组的很大一部分。将含有2大的（高达50 MB）1号染色体均匀染色区域（过敏反应）分离由一个小反转常染色质区域存在于家鼠的许多天然群体（小家鼠家鼠）。HSR由远程重复簇Sp100-rs组成，重复长度为100 kb。为了了解HSR在减数分裂染色体中的组织和功能，我们使用FISH与HSR特异性DNA探针和关键减数分裂蛋白的免疫定位检查了携带HSR的雄性小鼠杂合和纯合的突触和重组。在所有纯合子和杂合子的粗线核中，我们观察到了由HSR FISH探针标记的完全突触的线性同型二价1。杂合子的突触调节是双向的：携带HSR的同源物缩短，而野生型同源物延长。调节是可逆的：在二戊烯处的突触伴随着高铁的延长。H3K9me2 / 3的免疫定位表明，减数分裂染色体中的HSR保留了体细胞中C-异染色质的典型表观遗传修饰。在杂合子的近端HSR带和纯合子的两个HSR带中均检测到标记成熟重组结节的MLH1病灶。在长距离重复簇内不相等的交叉会导致HSR的大小发生变化，这已在家鼠的自然种群中被检测到。
细胞遗传学基因组研究