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Chromosome substitution strain assessment of a Huntington's disease modifier locus.

Ramos EM, Kovalenko M, Guide JR, St Claire J, Gillis T, Mysore JS, Sequeiros J, Wheeler VC, Alonso I, MacDonald ME - Mamm. Genome (2015)

Bottom Line: Crosses were performed to assess the possibility of dominantly acting chr10 AJ-B6J variants of strong effect that may modulate CAG-dependent Hdh(Q111/+) phenotypes.These findings in relatively small cohorts are suggestive of dominant chr10 AJ-B6 variants that may modify effects of the CAG expansion, and encourage a larger study with CSS10 and sub-strains.This cross-species approach may therefore be suited to functional in vivo prioritisation of genomic regions harbouring genes that can modify the early effects of the HD mutation.

View Article: PubMed Central - PubMed

Affiliation: Center for Human Genetic Research, Massachusetts General Hospital, Boston, MA, 02114, USA, esilvaramos@mgh.harvard.edu.

ABSTRACT
Huntington's disease (HD) is a dominant neurodegenerative disorder that is due to expansion of an unstable HTT CAG repeat for which genome-wide genetic scans are now revealing chromosome regions that contain disease-modifying genes. We have explored a novel human-mouse cross-species functional prioritisation approach, by evaluating the HD modifier 6q23-24 linkage interval. This unbiased strategy employs C57BL/6J (B6J) Hdh(Q111) knock-in mice, replicates of the HD mutation, and the C57BL/6J-chr10(A/J)/NaJ chromosome substitution strain (CSS10), in which only chromosome 10 (chr10), in synteny with the human 6q23-24 region, is derived from the A/J (AJ) strain. Crosses were performed to assess the possibility of dominantly acting chr10 AJ-B6J variants of strong effect that may modulate CAG-dependent Hdh(Q111/+) phenotypes. Testing of F1 progeny confirmed that a single AJ chromosome had a significant effect on the rate of body weight gain and in Hdh(Q111) mice the AJ chromosome was associated subtle alterations in somatic CAG instability in the liver and the formation of intra-nuclear inclusions, as well as DARPP-32 levels, in the striatum. These findings in relatively small cohorts are suggestive of dominant chr10 AJ-B6 variants that may modify effects of the CAG expansion, and encourage a larger study with CSS10 and sub-strains. This cross-species approach may therefore be suited to functional in vivo prioritisation of genomic regions harbouring genes that can modify the early effects of the HD mutation.

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HdhQ111/+ knock-in mice showed a dramatic decrease of DARPP-32 immunoreactivity when compared to wild type mice. a Micrographs of DARPP-32 positive cells in the striata and nucleus accumbens of representative 5 months mice with Hdh+/+B6J, HdhQ111/+B6J (142 CAGs), Hdh+/+B6J.AJ10 and HdhQ111/+B6J.AJ10 (140 CAGs) genotypes. b Quantification of DARPP-32 intensity (arbitrary values ranging from 0 to 255). The mice used for the DARPP32 analysis are as follows: Hdh+/+B6J (n = 8), HdhQ111/+B6J (n = 9), Hdh+/+B6J.AJ10 (n = 6) and HdhQ111/+B6J.AJ10 (n = 9). Each individual value represents the mean observed on three consecutive striatal sections for each mouse. Line represents mean of values for each genotype. ****p < 0.0001 and ***p < 0.001
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Fig7: HdhQ111/+ knock-in mice showed a dramatic decrease of DARPP-32 immunoreactivity when compared to wild type mice. a Micrographs of DARPP-32 positive cells in the striata and nucleus accumbens of representative 5 months mice with Hdh+/+B6J, HdhQ111/+B6J (142 CAGs), Hdh+/+B6J.AJ10 and HdhQ111/+B6J.AJ10 (140 CAGs) genotypes. b Quantification of DARPP-32 intensity (arbitrary values ranging from 0 to 255). The mice used for the DARPP32 analysis are as follows: Hdh+/+B6J (n = 8), HdhQ111/+B6J (n = 9), Hdh+/+B6J.AJ10 (n = 6) and HdhQ111/+B6J.AJ10 (n = 9). Each individual value represents the mean observed on three consecutive striatal sections for each mouse. Line represents mean of values for each genotype. ****p < 0.0001 and ***p < 0.001

Mentions: The striatum is critically affected in HD patients, where there is a selective and progressive loss of MSNs (Vonsattel and DiFiglia 1998; Vonsattel et al. 1985). DARPP-32, a dopamine D1 receptor-activated molecule that regulates phosphatase and kinase activity, is a marker of these striatal neurons. Levels of DARPP-32 were substantially reduced in the striatal MSNs of multiple HD mouse models (Bibb et al. 2000; Hickey et al. 2008; Slow et al. 2003; van Dellen et al. 2000). To assess whether the Htt CAG mutation may produce this abnormal DARPP-32 phenotype on a B6J background, we immunostained striatal sections of 5 months of age mice with DARPP-32 antibody (Fig. 7a). DARPP-32 immunoreactivity was significantly reduced (p < 0.0001) in the striatum (and nucleus accumbens) of HdhQ111/+B6J (134.2 ± 7.1) by 14 % when compared with Hdh+/+B6J control littermates (156.0 ± 3.7) (Fig. 7b). A similar, though milder, decrease was observed in mice carrying one copy of the AJ chr10, with HdhQ111/+B6J.AJ10 (137.4 ± 3.7) mice showing a 9 % reduction (p = 0.0003) when compared with control littermates (150.7 ± 7.0). However, we did not find any significant effect of the chr10 background in the levels of DARPP-32 when comparing B6J with B6J.10 mice, for both wild type (p = 0.0920) and mutant (p = 0.2521) Htt genotypes. It should be noted, however, that Hdh+/+B6J.AJ10 showed a 3.5 % decrease of DARPP-32 levels when compared with wild type B6J mice so that the similar DARPP-32 immunoreactivity signal in HdhQ111/+B6J.AJ10 and HdhQ111/+B6J striatal sections may reflect a slower rate of decrease in DARPP-32 staining in the former than the latter genotype.Fig. 7


Chromosome substitution strain assessment of a Huntington's disease modifier locus.

Ramos EM, Kovalenko M, Guide JR, St Claire J, Gillis T, Mysore JS, Sequeiros J, Wheeler VC, Alonso I, MacDonald ME - Mamm. Genome (2015)

HdhQ111/+ knock-in mice showed a dramatic decrease of DARPP-32 immunoreactivity when compared to wild type mice. a Micrographs of DARPP-32 positive cells in the striata and nucleus accumbens of representative 5 months mice with Hdh+/+B6J, HdhQ111/+B6J (142 CAGs), Hdh+/+B6J.AJ10 and HdhQ111/+B6J.AJ10 (140 CAGs) genotypes. b Quantification of DARPP-32 intensity (arbitrary values ranging from 0 to 255). The mice used for the DARPP32 analysis are as follows: Hdh+/+B6J (n = 8), HdhQ111/+B6J (n = 9), Hdh+/+B6J.AJ10 (n = 6) and HdhQ111/+B6J.AJ10 (n = 9). Each individual value represents the mean observed on three consecutive striatal sections for each mouse. Line represents mean of values for each genotype. ****p < 0.0001 and ***p < 0.001
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Related In: Results  -  Collection

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Fig7: HdhQ111/+ knock-in mice showed a dramatic decrease of DARPP-32 immunoreactivity when compared to wild type mice. a Micrographs of DARPP-32 positive cells in the striata and nucleus accumbens of representative 5 months mice with Hdh+/+B6J, HdhQ111/+B6J (142 CAGs), Hdh+/+B6J.AJ10 and HdhQ111/+B6J.AJ10 (140 CAGs) genotypes. b Quantification of DARPP-32 intensity (arbitrary values ranging from 0 to 255). The mice used for the DARPP32 analysis are as follows: Hdh+/+B6J (n = 8), HdhQ111/+B6J (n = 9), Hdh+/+B6J.AJ10 (n = 6) and HdhQ111/+B6J.AJ10 (n = 9). Each individual value represents the mean observed on three consecutive striatal sections for each mouse. Line represents mean of values for each genotype. ****p < 0.0001 and ***p < 0.001
Mentions: The striatum is critically affected in HD patients, where there is a selective and progressive loss of MSNs (Vonsattel and DiFiglia 1998; Vonsattel et al. 1985). DARPP-32, a dopamine D1 receptor-activated molecule that regulates phosphatase and kinase activity, is a marker of these striatal neurons. Levels of DARPP-32 were substantially reduced in the striatal MSNs of multiple HD mouse models (Bibb et al. 2000; Hickey et al. 2008; Slow et al. 2003; van Dellen et al. 2000). To assess whether the Htt CAG mutation may produce this abnormal DARPP-32 phenotype on a B6J background, we immunostained striatal sections of 5 months of age mice with DARPP-32 antibody (Fig. 7a). DARPP-32 immunoreactivity was significantly reduced (p < 0.0001) in the striatum (and nucleus accumbens) of HdhQ111/+B6J (134.2 ± 7.1) by 14 % when compared with Hdh+/+B6J control littermates (156.0 ± 3.7) (Fig. 7b). A similar, though milder, decrease was observed in mice carrying one copy of the AJ chr10, with HdhQ111/+B6J.AJ10 (137.4 ± 3.7) mice showing a 9 % reduction (p = 0.0003) when compared with control littermates (150.7 ± 7.0). However, we did not find any significant effect of the chr10 background in the levels of DARPP-32 when comparing B6J with B6J.10 mice, for both wild type (p = 0.0920) and mutant (p = 0.2521) Htt genotypes. It should be noted, however, that Hdh+/+B6J.AJ10 showed a 3.5 % decrease of DARPP-32 levels when compared with wild type B6J mice so that the similar DARPP-32 immunoreactivity signal in HdhQ111/+B6J.AJ10 and HdhQ111/+B6J striatal sections may reflect a slower rate of decrease in DARPP-32 staining in the former than the latter genotype.Fig. 7

Bottom Line: Crosses were performed to assess the possibility of dominantly acting chr10 AJ-B6J variants of strong effect that may modulate CAG-dependent Hdh(Q111/+) phenotypes.These findings in relatively small cohorts are suggestive of dominant chr10 AJ-B6 variants that may modify effects of the CAG expansion, and encourage a larger study with CSS10 and sub-strains.This cross-species approach may therefore be suited to functional in vivo prioritisation of genomic regions harbouring genes that can modify the early effects of the HD mutation.

View Article: PubMed Central - PubMed

Affiliation: Center for Human Genetic Research, Massachusetts General Hospital, Boston, MA, 02114, USA, esilvaramos@mgh.harvard.edu.

ABSTRACT
Huntington's disease (HD) is a dominant neurodegenerative disorder that is due to expansion of an unstable HTT CAG repeat for which genome-wide genetic scans are now revealing chromosome regions that contain disease-modifying genes. We have explored a novel human-mouse cross-species functional prioritisation approach, by evaluating the HD modifier 6q23-24 linkage interval. This unbiased strategy employs C57BL/6J (B6J) Hdh(Q111) knock-in mice, replicates of the HD mutation, and the C57BL/6J-chr10(A/J)/NaJ chromosome substitution strain (CSS10), in which only chromosome 10 (chr10), in synteny with the human 6q23-24 region, is derived from the A/J (AJ) strain. Crosses were performed to assess the possibility of dominantly acting chr10 AJ-B6J variants of strong effect that may modulate CAG-dependent Hdh(Q111/+) phenotypes. Testing of F1 progeny confirmed that a single AJ chromosome had a significant effect on the rate of body weight gain and in Hdh(Q111) mice the AJ chromosome was associated subtle alterations in somatic CAG instability in the liver and the formation of intra-nuclear inclusions, as well as DARPP-32 levels, in the striatum. These findings in relatively small cohorts are suggestive of dominant chr10 AJ-B6 variants that may modify effects of the CAG expansion, and encourage a larger study with CSS10 and sub-strains. This cross-species approach may therefore be suited to functional in vivo prioritisation of genomic regions harbouring genes that can modify the early effects of the HD mutation.

Show MeSH
Related in: MedlinePlus