Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139.
Department of Brain and Cognitive Sciences, McGovern Institute for Brain Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139.
eNeuro. 2022 Sep 12;9(5). doi: 10.1523/ENEURO.0142-22.2022. Print 2022 Sep-Oct.
Fragile X syndrome (FXS) is a leading monogenic cause of intellectual disability and autism spectrum disorders, spurring decades of intense research and a multitude of mouse models. So far, these models do not recapitulate the genetic underpinning of classical FXS-CGG repeat-induced methylation of the locus-and their findings have failed to translate into the clinic. We sought to answer whether this disparity was because of low repeat length and generated a novel mouse line with 341 repeats, , which is the largest allele in mice reported to date. This repeat length is significantly longer than the 200 repeats generally required for methylation of the repeat tract and promoter region in FXS patients, which leads to silencing of the gene. Bisulfite sequencing fails to detect the robust methylation expected of FXS in mice. Quantitative real-time PCR and Western blotting results also do not resemble FXS and instead produce a biochemical profile consistent with the fragile X-associated premutation disorders. These findings suggest that repeat length is unlikely to be the core determinant preventing methylation in mice, and other organisms phylogenetically closer to humans may be required to effectively model FXS.
脆性 X 综合征 (FXS) 是智力障碍和自闭症谱系障碍的主要单基因病因，促使人们开展了数十年的深入研究，并产生了大量的小鼠模型。到目前为止，这些模型并没有再现经典 FXS-CGG 重复诱导的甲基化的遗传基础，而且它们的发现也未能转化为临床应用。我们试图回答这种差异是否是由于重复长度低造成的，并产生了一种新型的小鼠品系，其重复长度为 341 个，这是迄今为止在小鼠中报道的最大等位基因。这个重复长度明显长于 FXS 患者中重复片段和启动子区域甲基化通常所需的 200 个重复，这会导致 基因沉默。亚硫酸氢盐测序未能检测到 小鼠中预期的脆性 X 综合征的强烈甲基化。实时定量 PCR 和 Western blot 结果也不像 FXS，而是产生了与脆性 X 相关的前突变疾病一致的生化特征。这些发现表明，重复长度不太可能是阻止小鼠甲基化的核心决定因素，可能需要与人类在系统发生上更接近的其他生物体来有效地模拟 FXS。
