title: C9orf72 frontotemporal lobar degeneration is characterised by frequent neuronal sense and antisense RNA foci.
abstract: An expanded GGGGCC repeat in a non-coding region of the C9orf72 gene is a common cause of frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis. Non-coding repeat expansions may cause disease by reducing the expression level of the gene they reside in, by producing toxic aggregates of repeat RNA termed RNA foci, or by producing toxic proteins generated by repeat-associated non-ATG translation. We present the first definitive report of C9orf72 repeat sense and antisense RNA foci using a series of C9FTLD cases, and neurodegenerative disease and normal controls. A sensitive and specific fluorescence in situ hybridisation protocol was combined with protein immunostaining to show that both sense and antisense foci were frequent, specific to C9FTLD, and present in neurons of the frontal cortex, hippocampus and cerebellum. High-resolution imaging also allowed accurate analyses of foci number and subcellular localisation. RNA foci were most abundant in the frontal cortex, where 51 % of neurons contained foci. RNA foci also occurred in astrocytes, microglia and oligodendrocytes but to a lesser degree than in neurons. RNA foci were observed in both TDP-43- and p62-inclusion bearing neurons, but not at a greater frequency than expected by chance. RNA foci abundance in the frontal cortex showed a significant inverse correlation with age at onset of disease. These data establish that sense and antisense C9orf72 repeat RNA foci are a consistent and specific feature of C9FTLD, providing new insight into the pathogenesis of C9FTLD.
authors.affiliation: Department of Neurodegenerative Disease, UCL Institute of Neurology, Queen Square, London, WC1N 3BG, UK.
authors.forename: Sarah
authors.initials: S
authors.lastname: Mizielinska
authors.forename: Tammaryn
authors.initials: T
authors.lastname: Lashley
authors.forename: Frances E
authors.initials: FE
authors.lastname: Norona
authors.forename: Emma L
authors.initials: EL
authors.lastname: Clayton
authors.forename: Charlotte E
authors.initials: CE
authors.lastname: Ridler
authors.forename: Pietro
authors.initials: P
authors.lastname: Fratta
authors.forename: Adrian M
authors.initials: AM
authors.lastname: Isaacs
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000073885:C9orf72 Protein; D002531:Cerebellum / Q000378:metabolism / Q000473:pathology; D042622:DNA Repeat Expansion; D005260:Female; D005625:Frontal Lobe / Q000378:metabolism* / Q000473:pathology; D057174:Frontotemporal Lobar Degeneration / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D006624:Hippocampus / Q000378:metabolism / Q000473:pathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009474:Neurons / Q000378:metabolism* / Q000473:pathology; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D016372:RNA, Antisense
chemical_list: D000073885:C9orf72 Protein; C568651:C9orf72 protein, human; D011506:Proteins; D016372:RNA, Antisense