CblX disease is both an inborn error of cobalamin metabolism and a ribosomopathy

CblX is a recently described X-linked variant of combined methylmalonic acidemia and homocystinuria, cblC type, which is the most common inborn error of intracellular cobalamin metabolism. While cblC is due to mutations in MMACHC, which is in the cobalamin metabolic pathway, cblX is caused by mutations in the transcriptional cofactor HCFC1 and its obligate transcription factor partner RONIN . Since HCFC1 and RONIN jointly regulate MMACHC transcription, cblX patients suffer from low levels of MMACHC during development and thus develop a disease highly similar to cblC. Beyond this finding, there is little else known about the other genes de-regulated in cblX and the resulting pathophysiology. Therefore, we have generated the first mouse models of this disease (Hcfc1A115V/Y and RoninF80L/F80L). We show that our cblX models exhibit the expected metabolic perturbations, along with CNS, hematopoietic and cardiac developmental defects, typically observed in cblC patients. We also uncovered a large cohort of target genes that encode ribosome protein subunits as well as unexpected phenotypes that we ascribe to deregulation of ribosome biogenesis impacting normal translation during development. In addition to identifying RONIN and HCFC1 as new transcriptional regulators of ribosome biogenesis, we establish cblX as a complex syndrome exhibiting aspects of cblC and a ribosomopathy. RNA was extracted from the brains of control and mutant Ronin (F80L/F80L) animals for RNA-seq library preparation. And the brains of control animals were used as input for Ronin ChIP-seq.CblX是新近被报道的X连锁型复合型甲基丙二酸血症伴同型半胱氨酸尿症cblC型（combined methylmalonic acidemia and homocystinuria, cblC type）变异体，而cblC型是最常见的细胞内钴胺素代谢（intracellular cobalamin metabolism）先天异常疾病。cblC型由钴胺素代谢通路中的MMACHC基因突变所致，而cblX型则由转录辅因子HCFC1及其必需转录因子伴侣RONIN的突变引发。由于HCFC1与RONIN共同调控MMACHC的转录，cblX患者在发育过程中MMACHC水平低下，因此罹患与cblC型高度相似的疾病。除上述发现外，目前对cblX型中失调的其他基因及由此产生的病理生理学机制仍知之甚少。因此，本研究构建了该疾病的首个小鼠模型（Hcfc1A115V/Y与RoninF80L/F80L）。研究证实，我们构建的cblX模型出现了cblC患者中典型的代谢紊乱，以及中枢神经系统、造血系统与心脏发育缺陷。此外，我们还发现了一大批编码核糖体蛋白亚基的靶基因，以及可归因于发育过程中核糖体生物合成失调影响正常蛋白质翻译的意外表型。除确认RONIN与HCFC1为核糖体生物合成的新型转录调控因子外，本研究确立cblX型为兼具cblC型特征与核糖体病（ribosomopathy）特征的复杂综合征。研究人员从对照及突变型Ronin（F80L/F80L）模型动物的脑组织中提取RNA，用于RNA测序（RNA-seq）文库构建；同时以野生型对照小鼠的脑组织作为RONIN染色质免疫共沉淀测序（ChIP-seq）的输入样本。