Rijkers T, Deidda G, van Koningsbruggen S, van Geel M, Lemmers R J L F, van Deutekom J C T, Figlewicz D, Hewitt J E, Padberg G W, Frants R R, van der Maarel S M
Department of Human Genetics, Center for Human and Clinical Genetics, Leiden University Medical Center, Wassenaarseweg 72, 2333 AL Leiden, The Netherlands.
J Med Genet. 2004 Nov;41(11):826-36. doi: 10.1136/jmg.2004.019364.
Autosomal dominant facioscapulohumeral muscular dystrophy (FSHD) is associated with partial deletion of the subtelomeric D4Z4 repeat array on chromosome 4qter. This chromosomal rearrangement may result in regional chromatin relaxation and transcriptional deregulation of genes nearby.
Here we describe the isolation and characterisation of FRG2, a member of a chromosomally dispersed gene family, mapping only 37 kb proximal to the D4Z4 repeat array. Homology and motif searches yielded no clues to the function of the predicted protein. FRG2 expression is undetectable in all tissues tested except for differentiating myoblasts of FSHD patients, which display low, yet distinct levels of FRG2 expression, partly from chromosome 4 but predominantly originating from its homologue on chromosome 10. However, in non-FSHD myopathy patients only distantly related FRG2 homologues are transcribed, while differentiating myoblasts from healthy controls fail to express any member of this gene family. Moreover, fibroblasts of FSHD patients and control individuals undergoing forced Ad5-MyoD mediated myogenesis show expression of FRG2 mainly originating from chromosome 10. Luciferase reporter assays show that the FRG2 promoter region can direct high levels of expression but is inhibited by increasing numbers of D4Z4 repeat units. Transient transfection experiments with FRG2 fusion-protein constructs reveal nuclear localisation and apparently FRG2 overexpression causes a wide range of morphological changes.
The localisation of FRG2 genes close to the D4Z4 repeats on chromosome 4 and 10, their transcriptional upregulation specifically in FSHD myoblast cultures, potential involvement in myogenesis, and promoter properties qualify FRG2 as an attractive candidate for FSHD pathogenesis.
常染色体显性遗传面肩肱型肌营养不良症（FSHD）与4号染色体末端的亚端粒D4Z4重复序列部分缺失有关。这种染色体重排可能导致局部染色质松弛以及附近基因的转录失调。
在此，我们描述了FRG2的分离与特性，FRG2是一个染色体分散基因家族的成员，定位于距D4Z4重复序列仅37 kb的近端。同源性和基序搜索未提供有关预测蛋白功能的线索。除了FSHD患者正在分化的成肌细胞外，在所有测试组织中均未检测到FRG2表达，FSHD患者正在分化的成肌细胞显示出低水平但明显的FRG2表达，部分来自4号染色体，但主要源自其10号染色体上的同源物。然而，在非FSHD肌病患者中，仅转录出远缘相关的FRG2同源物，而来自健康对照的正在分化的成肌细胞则不表达该基因家族的任何成员。此外，FSHD患者的成纤维细胞和接受强制Ad5-MyoD介导的肌生成的对照个体显示FRG2的表达主要源自10号染色体。荧光素酶报告基因检测表明，FRG2启动子区域可指导高水平表达，但会受到D4Z4重复单元数量增加的抑制。用FRG2融合蛋白构建体进行的瞬时转染实验揭示了核定位，并且显然FRG2过表达会引起广泛的形态学变化。
FRG2基因定位于4号和10号染色体上的D4Z4重复序列附近，它们在FSHD成肌细胞培养物中特异性转录上调，可能参与肌生成以及启动子特性，使FRG2成为FSHD发病机制的有吸引力的候选基因。
