A disease-linked lncRNA mutation in RNase MRP inhibits ribosome synthesis [yeast]

Mutations in the human RMRP gene cause Cartilage Hair Hypoplasia (CHH), an autosomal recessive disorder characterized by skeletal abnormalities and impaired T-cell activation. RMRP encodes a non-coding RNA, which forms the core of the RNase MRP ribonucleoprotein complex. In budding yeast, RMRP cleaves a specific site in the pre-ribosomal RNA (pre-rRNA) during ribosome synthesis. CRISPR-mediated disruption of RMRP in human cells lines caused growth arrest, with pre-rRNA accumulation. Here, we analyzed disease-relevant primary cells, showing that mutations in RMRP impair mouse T cell activation and delay pre-rRNA processing. Analysis of pre-rRNA processing in patient-derived human fibroblasts with CHH-linked mutations showed a similar pattern of processing delay. Human cells engineered with the most common CHH mutation (70AG in RMRP) show specifically impaired pre-rRNA processing, resulting in reduced mature rRNA and a reduced ratio of cytosolic to mitochondrial ribosomes. Moreover, the 70AG mutation caused a reduction in intact RNase MRP complexes. Together, these results indicate that CHH is a ribosomopathy, and the first human disorder of rRNA processing to be described.人类RMRP基因的突变可引发软骨毛发发育不良综合征（Cartilage Hair Hypoplasia, CHH），这是一类以骨骼异常与T细胞活化受损为典型特征的常染色体隐性遗传病。RMRP编码一种非编码RNA，该RNA是RNase MRP核糖核蛋白复合物的核心组成部分。在出芽酵母中，RMRP可在核糖体合成过程中切割核糖体前体RNA（pre-ribosomal RNA, pre-rRNA）的特定位点。通过CRISPR介导的方式破坏人类细胞系中的RMRP，会引发细胞生长停滞，并伴随pre-rRNA的积累。本研究针对疾病相关的原代细胞展开分析，结果显示RMRP的突变会损伤小鼠T细胞的活化功能，并延迟pre-rRNA的加工进程。对携带CHH相关致病突变的患者来源人成纤维细胞进行pre-rRNA加工分析，也观测到了相似的加工延迟现象。经工程改造引入CHH最常见突变（RMRP基因的70AG）的人类细胞，其pre-rRNA加工过程出现特异性损伤，最终导致成熟rRNA水平降低，且胞质核糖体与线粒体核糖体的比值下降。此外，该70AG突变会导致完整RNase MRP复合物的丰度降低。综上，本研究结果证实CHH属于核糖体病（ribosomopathy），是目前已报道的首例人类rRNA加工异常相关遗传病。