Section on Gene Structure and Disease Laboratory of Cell and Molecular Biology National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
Center for Molecular Modeling, Center for Information Technology, National Institutes of Health, Bethesda, MD 20892, USA.
Nucleic Acids Res. 2020 Aug 20;48(14):7856-7863. doi: 10.1093/nar/gkaa573.
The Fragile X-related disorders (FXDs) are Repeat Expansion Diseases, genetic disorders that result from the expansion of a disease-specific microsatellite. In those Repeat Expansion Disease models where it has been examined, expansion is dependent on functional mismatch repair (MMR) factors, including MutLγ, a heterodimer of MLH1/MLH3, one of the three MutL complexes found in mammals and a minor player in MMR. In contrast, MutLα, a much more abundant MutL complex that is the major contributor to MMR, is either not required for expansion or plays a limited role in expansion in many model systems. How MutLγ acts to generate expansions is unclear given its normal role in protecting against microsatellite instability and while MLH3 does have an associated endonuclease activity, whether that contributes to repeat expansion is uncertain. We show here, using a gene-editing approach, that a point mutation that eliminates the endonuclease activity of MLH3 eliminates expansions in an FXD mouse embryonic stem cell model. This restricts the number of possible models for repeat expansion and supports the idea that MutLγ may be a useful druggable target to reduce somatic expansion in those disorders where it contributes to disease pathology.
脆性 X 相关障碍 (FXD) 是重复扩展疾病，这是一种由特定微卫星扩展引起的遗传疾病。在那些已经检查过的重复扩展疾病模型中，扩展依赖于功能性错配修复 (MMR) 因子，包括 MutLγ，它是 MLH1/MLH3 的异二聚体，是哺乳动物中发现的三个 MutL 复合物之一，也是 MMR 的次要参与者。相比之下，MutLα 是一种丰度更高的 MutL 复合物，是 MMR 的主要贡献者，但在许多模型系统中，它要么对扩展不是必需的，要么在扩展中发挥的作用有限。鉴于 MutLγ 在防止微卫星不稳定性方面的正常作用，MutLγ 如何发挥作用导致扩展尚不清楚，尽管 MLH3 确实具有相关的内切酶活性，但该活性是否有助于重复扩展尚不确定。我们在这里使用基因编辑方法表明，消除 MLH3 内切酶活性的点突变消除了 FXD 小鼠胚胎干细胞模型中的扩展。这限制了重复扩展的可能模型数量，并支持这样一种观点，即 MutLγ 可能是一种有用的可用药靶，以减少那些与疾病病理相关的疾病中体细胞的扩展。
