Genetic background modulates behavioral impairments in R6/2 mice and suggests a role for dominant genetic modifiers in Huntington’s disease pathogenesis

Variability and modification of the symptoms of Huntington’s disease (HD) are commonly observed in both patient populations and animal models of the disease. Utilizing a stable line of the R6/2 HD mouse model, the present study investigated the role of genetic background in the onset and severity of HD symptoms in a transgenic mouse. R6/2 congenic C57BL/6J and C57BL/6J × DBA/2J F1 (B6D2F1) mice were evaluated for survival and a number of behavioral phenotypes. This study reports that the presence of the DBA/2J allele results in amelioration or exacerbation of several HD-like phenotypes characteristic of the R6/2 mouse model and indicates the presence of dominant genetic modifiers of HD symptoms. This study is the first step in identifying genes that confer natural genetic variation and modify the HD symptoms. This identification may lead to novel targets for treatment and help elucidate the molecular mechanisms of HD pathogenesis

Onset and Progression of Behavioral and Molecular Phenotypes in a Novel Congenic R6/2 Line Exhibiting Intergenerational CAG Repeat Stability

In the present study we report on the use of speed congenics to generate a C57BL/6J congenic line of HD-model R6/2 mice carrying 110 CAG repeats, which uniquely exhibits minimal intergenerational instability. We also report the first identification of the R6/2 transgene insertion site. The relatively stable line of 110 CAG R6/2 mice was characterized for the onset of behavioral impairments in motor, cognitive and psychiatric-related phenotypes as well as the progression of disease-related impairments from 4 to 10 weeks of age. 110Q mice exhibited many of the phenotypes commonly associated with the R6/2 model including reduced activity and impairments in rotarod performance. The onset of many of the phenotypes occurred around 6 weeks and was progressive across age. In addition, some phenotypes were observed in mice as early as 4 weeks of age. The present study also reports the onset and progression of changes in several molecular phenotypes in the novel R6/2 mice and the association of these changes with behavioral symptom onset and progression. Data from TR-FRET suggest an association of mutant protein state changes (soluble versus aggregated) in disease onset and progression

Retrospective evaluation of whole exome and genome mutation calls in 746 cancer samples

Funder: NCI U24CA211006Abstract: The Cancer Genome Atlas (TCGA) and International Cancer Genome Consortium (ICGC) curated consensus somatic mutation calls using whole exome sequencing (WES) and whole genome sequencing (WGS), respectively. Here, as part of the ICGC/TCGA Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium, which aggregated whole genome sequencing data from 2,658 cancers across 38 tumour types, we compare WES and WGS side-by-side from 746 TCGA samples, finding that ~80% of mutations overlap in covered exonic regions. We estimate that low variant allele fraction (VAF < 15%) and clonal heterogeneity contribute up to 68% of private WGS mutations and 71% of private WES mutations. We observe that ~30% of private WGS mutations trace to mutations identified by a single variant caller in WES consensus efforts. WGS captures both ~50% more variation in exonic regions and un-observed mutations in loci with variable GC-content. Together, our analysis highlights technological divergences between two reproducible somatic variant detection efforts

Congenicity across multiple generations of backcrossing R6/2 mice to C57BL/6J.

<p>Average percentage of homozygous B6 markers based on the 96-marker panel. Average percent B6 homozygosity was less than 50% after the first backcross but reached congenicity of 95% by the N4 generation.</p

Transcript expression across age in 110Q mice.

1<p>SEM represents the range of standard error of the means for statistical randomization tests.</p>2<p>p-values>0.05, <i>n.s.</i></p

Average repeat length of three R6/2 lines showing intergenerational stability or instability and the minimum and maximum repeat lengths identified in each generation.

<p>Average repeat length of three R6/2 lines showing intergenerational stability or instability and the minimum and maximum repeat lengths identified in each generation.</p

Mutant HTT protein progresses from soluble to aggregated forms with increasing age and disease progression.

<p>Relative levels of soluble and aggregated transgene protein across four ages. Soluble protein levels significantly decrease at every age. Aggregated protein levels increase at each age from 6 to 10 weeks. All p-values≤0.018 by one-way ANOVA.</p

Sensorimotor gating in B6 R6/2 mice across 4 ages.

<p>(<b>A</b>) Acoustic startle response measurements in male mice. Male R6/2 mice show reduced startle phenotypes at every age tested. The startle response in male R6/2 mice increased significantly from 4 to 6 and 6 to 8 weeks of age, but always remained below wildtype levels. (<b>B</b>) Acoustic startle response in female mice. Female R6/2 mice exhibit a significant reduction in startle response only at 4 weeks of age. A significant increase in startle was observed from 4 to 6 weeks in R6/2 females and at all later ages female R6/2 mice showed similar startle responses to wildtype mice. (<b>C</b>) Average percent PPI of wildtype and R6/2 mice (combined genders). Average PPI was normal in R6/2 mice at early ages but decreased inhibition was observed at 10 weeks of age. Follow-up analyses revealed that the inhibition deficits were present only in male R6/2 mice. (<b>D</b>) Percent PPI in male and female mice. Overall, male R6/2 mice show decreased inhibition compared to wildtype mice while female R6/2 mice performed comparably to controls. In all panels, ‘<i>a</i>’ reflects a decreased performance in R6/2 mice compared to wildtypes. All p-values≤0.012 by three-way ANOVA and simple effects analysis.</p

EM48 staining for aggregated mutant HTT appears to increase in amount and intensity with increasing age and disease progression.

<p>In 4 week old B6 110Q R6/2 mice, very few small, circular intranuclear inclusions characteristic of 110Q R6/2 mice can be identified. However, by 10 weeks of age such inclusions are readily observed neuronal nuclei. Intensity of EM48 staining appears increase from 4 and 10 weeks of age, further suggesting an increase in aggregate load.</p

Motor coordination and skill learning on the rotarod and body weights in R6/2 mice across 4 ages.

<p>(<b>A</b>) Latency to fall from the rotarod. (<b>B</b>) Bodyweight measurements from 4 to 10 weeks of age. In both <b>A</b> and <b>B</b>, ‘<i>a</i>’ represents that R6/2 were significantly different from wildtypes. In <b>A</b>, ‘<i>b</i>’ indicates R6/2 mice at 6 weeks had a longer latency to fall than R6/2 mice at 8 and 10 weeks of age and ‘<i>c</i>’ denotes a significant decrease in R6/2 mice at 6, 8 and 10 weeks relative to transgenic mice at 4 weeks old. In <b>B</b>, ‘<i>b</i>’ denotes an increase in body weight between R6/2 mice at 4 weeks of age and R6/2 mice at 6, 8 and 10 weeks. All p-values≤0.035 by three-way ANOVA and simple effects analysis.</p