FSHD Syndrome: DNA Repeats, Methylation, & Chromatin

描述（由申请人提供）：肩肱型肌营养不良症 （FSHD）是一种不寻常的常染色体显性遗传综合征， 一个染色体的亚端粒区（4q35）中的复杂重复序列（D4Z4）的拷贝数 4号染色体同源物。在4q35的这个3.3kb重复序列的拷贝数是 多态的未受影响的个体在每个等位基因上有11至约95个拷贝 4q35。相比之下，超过90%的FSHD患者在24小时内的拷贝数少于10个。 这些等位基因4q亚端粒区之一。许多人提出， 研究人员认为，通常这一地区是异染色质，但当 如果D4Z4的串联拷贝数小于10，则该区域失去其浓缩的 染色质结构，异染色质化的丧失反过来又是 假设诱导受影响肌肉中不适当的基因表达 细胞然而，目前还没有关于染色质的研究报道 在正常或FSHD细胞的这个区域中的结构。 在计划的研究中，免疫化学，细胞化学和免疫细胞化学 方法将被用来检查这个区域是否确实是异染色质的 以及当它含有FSHD时，它是否失去了异染色质结构 删除。来自正常人的成肌细胞培养物和淋巴母细胞样细胞系 将研究个体和FSHD患者。这些实验将包括 组蛋白乙酰化和异染色质1 β蛋白结合的分析 D4Z4染色质区域。此外，我们将确定该地区是否是 在正常细胞中晚期复制，就像异染色质一样。 与该区域的异色性一致， 最近的研究表明，这个重复序列是高度甲基化的。初步 D4Z4重复序列甲基化的研究将被扩展，以检查是否 在含有缺失的染色体中，该重复序列不再高度甲基化 FSHD细胞中4个。最近的研究表明，来自另一种基因的细胞 ICF综合征（DNA甲基转移酶缺乏和染色体不稳定 综合征），在这个重复中甲基化不足。因为异常的低甲基化 可以有利于染色体重排，ICF和正常细胞系将进行比较 这一区域基因重组的频率。拟议研究 应该有助于阐明神秘的FSHD综合征的分子病因。

DESCRIPTION (provided by applicant): Fascioscapulohumeral muscular dystrophy (FSHD) is an unusual autosomal dominant syndrome caused by the loss of some copies of a complex repeat (D4Z4) in a subtelomeric region (4q35) of one chromosome 4 homologue. The number of copies of this 3.3-kb repeat at 4q35 is polymorphic. Unaffected individuals have 11 to about 95 copies on each allelic 4q35. In contrast, more than 90% of FSHD patients have less than 10 copies at one of these allelic 4q subtelomeric regions. It has been proposed by many investigators that normally this region is heterochromatic but that when the number of tandem copies of D4Z4 is less than 10, the region loses its condensed chromatin structure, This loss of heterochroma-tinization, in turn, is hypothesized to induce inappropriate gene expression in the affected muscle cells. However, there have been no reports about studies of the chromatin structure in this region for normal or FSHD cells. In the planned research, immunochemical, cytochemical, and immunocytochemical methods will be used to examine whether this region is indeed heterochromatic and whether it loses the heterochromatic structure when it contains the FSHD deletion. Myoblast cultures and lymphoblastoid cell lines from normal individuals and FSHD patients will be studied. These experiments will include analysis of histone acetylation and binding of heterochromatin 1 beta protein to the D4Z4 chromatin region. Also, we will determine whether this region is late-replicating in normal cells, as is the case for heterochromatin. Consistent with the proposed heterochromatic nature of this region, it has recently been shown that this repeat is highly methylated. The preliminary study of methylation of the D4Z4 repeat will be expanded to examine whether this repeat is no longer hypermethylated in the deletion-containing chromosome 4 in FSHD cells. It has recently been shown that cells from another genetic syndrome, ICF (a DNA methyltransferase-deficiency and chromosome instability syndrome), are undermethylated in this repeat. Because abnormal hypomethylation can favor chromosome rearrangements, ICF and normal cell lines will be compared for the frequency of rearrangements in this region. The proposed research should help elucidate the molecular etiology of the enigmatic FSHD syndrome.