title: Antisense transcripts of the expanded C9ORF72 hexanucleotide repeat form nuclear RNA foci and undergo repeat-associated non-ATG translation in c9FTD/ALS.
abstract: Frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) are devastating neurodegenerative disorders with clinical, genetic, and neuropathological overlap. A hexanucleotide (GGGGCC) repeat expansion in a non-coding region of C9ORF72 is the major genetic cause of both diseases. The mechanisms by which this repeat expansion causes "c9FTD/ALS" are not definitively known, but RNA-mediated toxicity is a likely culprit. RNA transcripts of the expanded GGGGCC repeat form nuclear foci in c9FTD/ALS, and also undergo repeat-associated non-ATG (RAN) translation resulting in the production of three aggregation-prone proteins. The goal of this study was to examine whether antisense transcripts resulting from bidirectional transcription of the expanded repeat behave in a similar manner. We show that ectopic expression of (CCCCGG)66 in cultured cells results in foci formation. Using novel polyclonal antibodies for the detection of possible (CCCCGG)exp RAN proteins [poly(PR), poly(GP) and poly(PA)], we validated that (CCCCGG)66 is also subject to RAN translation in transfected cells. Of importance, foci composed of antisense transcripts are observed in the frontal cortex, spinal cord and cerebellum of c9FTD/ALS cases, and neuronal inclusions of poly(PR), poly(GP) and poly(PA) are present in various brain tissues in c9FTD/ALS, but not in other neurodegenerative diseases, including CAG repeat disorders. Of note, RNA foci and poly(GP) inclusions infrequently co-occur in the same cell, suggesting these events represent two distinct ways in which the C9ORF72 repeat expansion may evoke neurotoxic effects. These findings provide mechanistic insight into the pathogenesis of c9FTD/ALS, and have significant implications for therapeutic strategies.
authors.affiliation: Department of Neuroscience, Mayo Clinic Florida, Jacksonville, FL, 32224, USA.
authors.forename: Tania F
authors.initials: TF
authors.lastname: Gendron
authors.forename: Kevin F
authors.initials: KF
authors.lastname: Bieniek
authors.forename: Yong-Jie
authors.initials: YJ
authors.lastname: Zhang
authors.forename: Karen
authors.initials: K
authors.lastname: Jansen-West
authors.forename: Peter E A
authors.initials: PE
authors.lastname: Ash
authors.forename: Thomas
authors.initials: T
authors.lastname: Caulfield
authors.forename: Lillian
authors.initials: L
authors.lastname: Daughrity
authors.forename: Judith H
authors.initials: JH
authors.lastname: Dunmore
authors.forename: Monica
authors.initials: M
authors.lastname: Castanedes-Casey
authors.forename: Jeannie
authors.initials: J
authors.lastname: Chew
authors.forename: Danielle M
authors.initials: DM
authors.lastname: Cosio
authors.forename: Marka
authors.initials: M
authors.lastname: van Blitterswijk
authors.forename: Wing C
authors.initials: WC
authors.lastname: Lee
authors.forename: Rosa
authors.initials: R
authors.lastname: Rademakers
authors.forename: Kevin B
authors.initials: KB
authors.lastname: Boylan
authors.forename: Dennis W
authors.initials: DW
authors.lastname: Dickson
authors.forename: Leonard
authors.initials: L
authors.lastname: Petrucelli
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000690:Amyotrophic Lateral Sclerosis / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D000073885:C9orf72 Protein; D002531:Cerebellum / Q000378:metabolism / Q000473:pathology; D042622:DNA Repeat Expansion; D005260:Female; D005625:Frontal Lobe / Q000378:metabolism* / Q000473:pathology; D057180:Frontotemporal Dementia / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D057809:HEK293 Cells; D006801:Humans; D008297:Male; D008875:Middle Aged; D017433:Protein Structure, Secondary; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D015138:RNA, Nuclear / Q000235:genetics / Q000378:metabolism*; D013116:Spinal Cord / Q000378:metabolism / Q000473:pathology
chemical_list: D000073885:C9orf72 Protein; C568651:C9orf72 protein, human; D011506:Proteins; D015138:RNA, Nuclear