Knock in of a hexanucleotide repeat expansion in the C9orf72 gene induces ALS in rats

Background:The GGGGCC(G4C2)repeat expansion in the human open reading frame 72 on chromosome 9,C9orf72,is the most common cause of amyotrophic lateral sclerosis(ALS).Studies in transgenic mouse models have linked the pathogenic mechanism of G4C2 repeat expansion to RNA foci or the accumulation of unnatural dipeptide repeats in neurons.However,only one of the existing transgenic mouse lines developed typical ALS.Methods:C9orf72 knockin rats were generated by knockin of 80 G4C2 repeats with human flanking fragments within exon1a and exon1b at the rat C9orf72 locus.Protein expression was detected by western blot.Motor coordination and grip force were measured using a Rotarod test and a grip strength test.Neurodegeneration was assessed by Nissl staining with cresyl violet.Results:C9orf72 haploinsufficiency reduced C9orf72 protein expression 40%in the cerebrum,cerebellum and spinal cords from knockin rats(P<.05).The knockin(KI)rats developed motor deficits from 4 months of age.Their falling latencies and grip force were decreased by 67%(P<.01)and 44%(P<.01),respectively,at 12 months of age compared to wild-type(WT)mice.The knockin of the hexanucleotide repeat expansion(HRE)caused a 47%loss of motor neurons in the spinal cord(P<.001)and 25%(5/20)of female KI rats developed hind limb paralysis at 13 to 24 months.Conclusion:Motor defects in KI rats may result from neurotoxicity caused by HRE and the resulting reduction in C9orf72 protein due to haploinsufficiency.These KI rats could be a useful model for investigating the contributions of loss-of-function to neurotoxicity in C9orf72-related ALS.

CGG repeat expansion in LOC642361/NUTM2B-AS1 typically presents as oculopharyngodistal myopathy

CGG repeat expansions in LOC642361/NUTM2B-AS1 have recently been identified as a cause of oculopharyngeal myopathy with leukoencephalopathy.However,since only three patients from a single family were reported,it remains unknown whether their clinicopathological features are typical for CGG repeat expansions in LOC642361/NUTM2B-AS1.Here,using repeat-primed-polymerase chain reaction and long-read sequencing,we identify 12 individuals from 3 unrelated families with CGG repeat expansions in LOC642361/NUTM2B-AS1,typically presenting with oculopharyngodistal myopathy.The CGG repeat expansions range from 161 to 669 repeat units.Most of the patients present with ptosis,restricted eye movements,dysphagia,dysarthria,and diffuse limb muscle weakness.Only one patient shows T2-weighted hyperintensity in the cerebellar white matter surrounding the deep cerebellar nuclei on brain magnetic resonance imaging.Muscle biopsies from three patients show a myopathic pattern and rimmed vacuoles.Analyses of muscle biopsies suggest that CGG repeat expansions in LOC642361/NUTM2B-AS1 may deleteriously affect aggrephagic capacity,suggesting that RNA toxicity and mitochondrial dysfunction may contribute to pathogenesis.Our study thus expands the phenotypic spectrum for the CGG repeat expansion of LOC642361/NUTM2B-AS1 and indicates that this genetic variant typically manifests as oculopharyngodistal myopathy with chronic myopathic changes with rimmed vacuoles and filamentous intranuclear inclusions in muscle fibers.

The parallel tetrameric DNA G-quadruplex formed by the two-repeat C9orf72 GGGGCC sequence in solution Dedicated to Professor Chaohui Ye on the occasion of his 80th birthday

The abnormal expansion of G-rich hexanucleotide repeat,GGGGCC(G4C2),in chromosome 9 open reading frame 72(C9orf72)is known to be the prevailing genetic cause of two fatal degenerative neurological diseases,amyotrophic lateral sclerosis(ALS)and frontotemporal dementia(FTD).It is well known that the DNA G4C2 repeat expansion with different lengths can form G-quadruplexes which affect gene transcription related to ALS/FTD,therefore it is crucial to understand DNA G4C2 G-quadruplex structures.Herein,by utilizing nuclear magnetic resonance(NMR)spectroscopy,we examined DNA G-quadruplex structure adopted by two G4C2 hexanucleotide repeats with an inosine substitution at position 4,d(G4C2)2-I4.We show that d(G4C2)2-I4 folds into an eight-layer parallel tetrameric G-quadruplex containing two parallel dimeric G-quadruplexes stacking together through p-p interaction via 50-to-50 mode in solution.Each dimeric G-quadruplex unit involves two propeller loops composed of two cytosine bases.This result is consistent with the observation in the crystal structure of d(G4C2)2.Our work not only sheds light on the structural diversity of G-quadruplexes adopted by d(G4C2)n but also provides a structural basis for drug design in treatment of ALS and FTD.

Clinical Characteristics, Radiological Features and Gene Mutation in 10 Chinese Families with Spinocerebellar Ataxias

Background： Spinocerebellar ata^ias （SCAs） are a group ofneurodegenerative disorders that primarily cause the degeneration in the cerebellum, spinal cord, and brainstem. We study the clinical characteristics, radiological features and gene mutation in Chinese families with SCAs. Methods： In this study, we investigated 10 SCAs Chinese families with SCAI, SCA3/Machado-Joseph disease （MJD}, SCA7, SCAB. There were 27 people who were genetically diagnosed as SCA, of which 21 people showed clinical symptoms, and 6 people had no clinical phenotype that we called them presymptomatic patients. In addition, 3 people with cerebellar ataxia and cataracts were diagnosed according to the Harding diagnostic criteria but tailed to be recognized as SCAs on genetic testing. Clinical characteristic analyses of each type of SCAs and radiological examinations were perlbrmed. Results： We found that SCA3/MJD was the most common subtype in Hart population in China, and the ratio of the pontine tegmentum and the posterior fossa area was negatively con＇elated with the number of cytosine-adenine-guanine （CAG） repeats： the disease duration was positively correlated with the International Cooperative Ataxia Rating Scale score; and the CAG repeats number of abnormal alleles was negatively correlated with the age of onset. Conchlsions： Collectively our study is a systematic research on SCAs in China, which may help for the clinical diagnosis and prenatal screening of this disease, and it may also aid toward better understanding of this disease.

Towards Understanding RNA-Mediated Neurological Disorders

RNA-mediated mechanisms of disease pathogenesis in neurological disorders have been recognized in the context of certain repeat expansion disorders. This RNA-initiated neurodegeneration may play a more pervasive role in disease pathology beyond the classic dynamic mutation disorders. Here, we review the mechanisms of RNA toxicity and aberrant RNA processing that have been implicated in ageing-related neurological disorders. We focus on diseases with aberrant sequestration of RNA-binding proteins, bi-directional tran- scription, aberrant translation of repeat expansion RNA transcripts （repeat-associated non-ATG （RAN） translation）, and the formation of pathological RNA：DNA secondary structure （R-loop）. It is likely that repeat expansion disorders arise from common mechanisms caused by the repeat expansion mutations. However, the context of the repeat expansion determines the specific molecular consequences, leading to clinically distinct disorders.