A molecular investigation of true dominance in Huntington's disease

Abstract

Huntington's disease (HD) is thought to show true dominance, since subjects with two mutant alleles have been reported to have similar ages at onset of disease compared to heterozygous sibs. We have investigated this phenomenon using a cell culture model. Protein aggregate formation was used as an indicator for pathology, as intraneuronal huntingtin inclusions are associated with pathology in vitro and in vivo. We showed that cytoplasmic and nuclear aggregates are formed by constructs comprising part of exon 1 of huntingtin with 41, 51, 66, or 72 CAG repeats, in a rate that correlates with repeat number. No inclusions were seen with 21 CAG repeat constructs. Mutant and wild type huntingtin fragments can be sequestered into inclusions seeded by a mutant huntingtin. Wild type huntingtin did not enhance or interfere with protein aggregation. The rate of protein aggregation was dose dependent for all mutant constructs tested. These experiments suggested a model for the dominance observed in HD; the decrease in the age at onset of a mutant homozygote may be small compared to the variance in the age at onset for that specific repeat number in heterozygotes. Our experiments also provide a model, which may explain the diVerent repeat size ranges seen in patients and healthy controls for the diVerent polyglutamine diseases. (J Med Genet 1999;36:739-746)

Autophagic substrate clearance requires activity of the syntaxin-5 SNARE complex

“…1D). The percentage of cells with such mutant huntingtin aggregates increases linearly with its expression levels (Narain et al, 1999) and this is also seen when autophagy is blocked (Ravikumar et al, 2002) (Fig. 1D).…”

“…HD gene exon 1 fragment with 74 poly-Q repeats in pEGFP-C1 (Clontech) (EGFP-HDQ74) construct was characterised previously (Narain et al, 1999); the EGFP-LC3 (gift from Tamotsu Yoshimori, Osaka University, Osaka, Japan) and the mCherry-LC3 expression vectors have been already described (Jahreiss et al, 2008). The cloning of the luciferase reporter vector bearing the human Bip/grp78 promoter region has been described elsewhere (Renna et al, 2007).…”

Inactivation of Drosophila Huntingtin affects long-term adult functioning and the pathogenesis of a Huntington’s disease model

“…Further, existing evidence suggests that normal Htt activity can be inactivated by mechanisms such as abnormal sequestration into insoluble aggregates (Huang et al, 1998;Kazantsev et al, 1999;Narain et al, 1999;Preisinger et al, 1999;Wheeler et al, 2000). These and other observations have lead to the hypothesis that the perturbation of endogenous Htt function, such as by late-onset inactivation of endogenous Htt, contributes to HD pathogenesis (Cattaneo et al, 2001).…”

α-Synuclein Is Degraded by Both Autophagy and the Proteasome

“…Ref. 26) for either wild-type, A30P, or A53T, even after expression of ␣-synuclein for 10 days. The staining for ␣-synuclein in uninduced cells was below the level of detection when analyzed with confocal microscopy using the same settings that gave clear signals for induced cells (Fig.…”