Verheij C, Bakker C E, de Graaff E, Keulemans J, Willemsen R, Verkerk A J, Galjaard H, Reuser A J, Hoogeveen A T, Oostra B A
MGC Department of Clinical Genetics, Erasmus University, Rotterdam, The Netherlands.
Nature. 1993 Jun 24;363(6431):722-4. doi: 10.1038/363722a0.
The fragile X syndrome is the most frequent form of inherited mental retardation after Down's syndrome, having an incidence of one in 1,250 males. The fragile X syndrome results from amplification of the CGG repeat found in the FMR-1 gene. This CGG repeat shows length variation in normal individuals and is increased significantly in both carriers and patients; it is located 250 base pairs distal to a CpG island which is hypermethylated in fragile X patients. The methylation probably results in downregulation of FMR-1 gene expression. No information can be deduced about the function of the FMR-1 protein from its predicted sequence. Here we investigate the nature and function of the protein encoded by the FMR-1 gene using polyclonal antibodies raised against the predicted amino-acid sequences. Four different protein products, possibly resulting from alternative splicing, have been identified by immunoblotting in lymphoblastoid cell lines of healthy individuals. All these proteins were missing in cell lines from patients not expressing FMR-1 messenger RNA. The intracellular localization of the FMR-1 gene products was investigated by transient expression in COS-1 cells and found to be cytoplasmic. Localization was also predominantly cytoplasmic in the epithelium of the oesophagus, but in some cells was obviously nuclear.
脆性X综合征是继唐氏综合征之后最常见的遗传性智力障碍类型，在男性中的发病率为1/1250。脆性X综合征是由FMR-1基因中CGG重复序列的扩增引起的。这种CGG重复序列在正常个体中长度存在变异，在携带者和患者中显著增加；它位于一个CpG岛下游250个碱基对处，该CpG岛在脆性X患者中发生高度甲基化。这种甲基化可能导致FMR-1基因表达下调。从FMR-1蛋白的预测序列中无法推断出其功能信息。在这里，我们使用针对预测氨基酸序列产生的多克隆抗体来研究FMR-1基因编码的蛋白质的性质和功能。通过免疫印迹在健康个体的淋巴母细胞系中鉴定出四种可能由可变剪接产生的不同蛋白质产物。在不表达FMR-1信使RNA的患者细胞系中，所有这些蛋白质均缺失。通过在COS-1细胞中瞬时表达研究了FMR-1基因产物的细胞内定位，发现其定位于细胞质中。在食管上皮细胞中定位也主要在细胞质中，但在一些细胞中明显位于细胞核中。
