The Hadassah Human Embryonic Stem Cell Research Center, The Goldyne Savad Institute of Gene Therapy, Hadassah Medical Center, Jerusalem, Israel.
Department of Neurology, University of Michigan Medical School, Ann Arbor, MI, United States of America.
PLoS Genet. 2021 Mar 29;17(3):e1009445. doi: 10.1371/journal.pgen.1009445. eCollection 2021 Mar.
Expansion of the hexanucleotide repeat (HR) in the first intron of the C9orf72 gene is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) in Caucasians. All C9orf72-ALS/FTD patients share a common risk (R) haplotype. To study C9orf72 expression and splicing from the mutant R allele compared to the complementary normal allele in ALS/FTD patients, we initially created a detailed molecular map of the single nucleotide polymorphism (SNP) signature and the HR length of the various C9orf72 haplotypes in Caucasians. We leveraged this map to determine the allelic origin of transcripts per patient, and decipher the effects of pathological and normal HR lengths on C9orf72 expression and splicing. In C9orf72 ALS patients' cells, the HR expanded allele, compared to non-R allele, was associated with decreased levels of a downstream initiated transcript variant and increased levels of transcripts initiated upstream of the HR. HR expanded R alleles correlated with high levels of unspliced intron 1 and activation of cryptic donor splice sites along intron 1. Retention of intron 1 was associated with sequential intron 2 retention. The SNP signature of C9orf72 haplotypes described here enables allele-specific analysis of transcriptional products and may pave the way to allele-specific therapeutic strategies.
六核苷酸重复序列（HR）在 C9orf72 基因的第一个内含子中的扩增是导致白种人肌萎缩侧索硬化症（ALS）和额颞叶痴呆（FTD）的最常见遗传原因。所有 C9orf72-ALS/FTD 患者均共享一个常见的风险（R）单倍型。为了研究 ALS/FTD 患者中突变的 R 等位基因与互补的正常等位基因相比，C9orf72 的表达和剪接情况，我们最初创建了一个详细的单核苷酸多态性（SNP）特征和各种 C9orf72 单倍型 HR 长度的分子图谱。我们利用该图谱确定了每个患者的等位基因来源，并解析了病理性和正常 HR 长度对 C9orf72 表达和剪接的影响。在 C9orf72 ALS 患者的细胞中，与非-R 等位基因相比，HR 扩增的等位基因与下游起始转录变体的水平降低以及 HR 上游起始的转录本水平升高相关。HR 扩增的 R 等位基因与高水平的未剪接内含子 1 以及内含子 1 中隐匿供体位点的激活相关。内含子 1 的保留与内含子 2 的连续保留相关。这里描述的 C9orf72 单倍型的 SNP 特征可实现对转录产物的等位基因特异性分析，并且可能为等位基因特异性治疗策略铺平道路。
