NOP56 is essential for mammalian generation and maintenance of multiple central nervous systems, associated with...

NOP56, a core nucleolar component involved in small nucleolar ribonucleoprotein assembly, has been genetically implicated in spinocerebellar ataxia type 36. However, the role of NOP56 in mammalian neurodevelopment and disease remains poorly defined. We investigated NOP56 pathobiology using both in vitro induced pluripotent stem cell-derived neurons and in vivo NOP56 knockout mouse models. NOP56 expression significantly decreased both in the spinocerebellar ataxia type 36 patients induced pluripotent cells and induced pluripotent cell-derived neurons, which suggests the possibility that the NOP56 loss of function is involved in the spinocerebellar ataxia type 36 phenotype. Therefore, we generated and validated the NOP56 knockout mouse phenotype. Homozygous NOP56 deletion resulted in total embryonic lethality; no NOP56^-/- progeny was viable at birth. Heterozygous knockouts showed clasping at 8 months of age and had a larger body size with aging, although there was no significant difference in survival between heterozygous and wild type. Heterozygous knockout mice showed deterioration in rotarod performance and a decrease in exploration behavior. Immunohistochemical analysis of the heterozygous knockouts revealed widespread, significant central nervous system abnormalities, particularly cerebellar degeneration, accompanied by motor cortex and spinal cord disturbances. Widespread ubiquitin-positive inclusions were detected in the cerebellum, motor cortex, and anterior spinal cord of the heterozygous knockout mice at the 12-month age, and it was positive from the 6-month age in the cerebellum. Colocalizations of TDP-43 and ubiquitin were observed in the motor cortex, spinal cord, and cerebellum. Along with findings from previous reports showing early downregulation of NOP56 in SOD1 G93A transgenic mice, this finding indicates that NOP56 might be involved in a wide range of motor neuron diseases. The pathological characteristics of the NOP56 heterozygous knockouts are like those of a patient with spinocerebellar ataxia type 36. Results reveal that NOP56 is indispensable for mammalian embryogenesis and central nervous system maintenance, and that its reduction contributes to molecular pathology in spinocerebellar ataxia type 36. These findings uncover a convergent neurodegenerative mechanism and identify NOP56 as a potential therapeutic target.Clinical trial registrationThis study was registered with the Japan Clinical Trials Registry (http//umin.ac.jp/ctr/index/htm), under the number UMIN000047097.