title: A natural antisense transcript at the Huntington's disease repeat locus regulates HTT expression.
abstract: Huntington's disease (HD) is a progressive neurodegenerative disorder caused by a CAG repeat expansion in exon 1 of huntingtin (HTT). Relatively little attention has been directed to the genomic features of the antisense strand at the HD locus, though the presence of a transcript from this strand has been suggested by a survey of the entire transcriptome and the existence of several EST tags. In this study, we identified huntingtin antisense (HTTAS), a natural antisense transcript at the HD repeat locus that contain the repeat tract. HTTAS is 5' capped, poly (A) tailed and contains three exons, alternatively spliced into HTTAS_v1 (exons 1 and 3) and HTTAS_v2 (exons 2 and 3). Exon 1 includes the repeat. HTTAS_v1 has a weak promoter, and is expressed at low levels in multiple tissue types and throughout the brain. Reporter assays indicate that while efficient promoter activity requires a short repeat, repeat expansion reduces promoter efficiency. Consistent with the reporter assays, levels of HTTAS_v1 are reduced in human HD frontal cortex. In cell systems, overexpression of HTTAS_v1 specifically reduces endogenous HTT transcript levels, while siRNA knockdown of HTTAS_v1 increases HTT transcript levels. Minigene constructs of the HD locus confirm the regulatory effect of HTTAS_v1 on HTT, and demonstrate that the effect is dependent on repeat length and is at least partially Dicer dependent. Together, these findings provide strong evidence for the existence of a gene antisense to HTT, with properties that include regulation of HTT expression.
authors.affiliation: Department of Psychiatry, Division of Neurobiology, Laboratory of Genetic Neurobiology, Johns Hopkins University School of Medicine, CMSC 8-121, 600 N. Wolfe St., Baltimore, MD 21287, USA
authors.forename: Daniel W
authors.initials: DW
authors.lastname: Chung
authors.forename: Dobrila D
authors.initials: DD
authors.lastname: Rudnicki
authors.forename: Lan
authors.initials: L
authors.lastname: Yu
authors.forename: Russell L
authors.initials: RL
authors.lastname: Margolis
mesh_terms: D002460:Cell Line; D016373:DNA, Antisense / Q000235:genetics*; D005091:Exons / Q000235:genetics; D006801:Humans; D000071058:Huntingtin Protein; D006816:Huntington Disease / Q000235:genetics*; D009419:Nerve Tissue Proteins / Q000235:genetics*; D009687:Nuclear Proteins / Q000235:genetics*; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic / Q000235:genetics
chemical_list: D016373:DNA, Antisense; C086055:HTT protein, human; D000071058:Huntingtin Protein; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins