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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/+B6J.AJ10 mice showed a mild increase of liver somatic repeat instability when compared to HdhQ111/+B6J mice. a GeneMapper traces of PCR-amplified Htt CAG repeats from tail, striatum and liver of representative 5 months HdhQ111/+B6J (144 CAGs) and HdhQ111/+B6J.AJ10 (141 CAGs) mice. b Somatic repeat instability was quantified from GeneMapper traces by determining an instability index for tail, striatum and liver of each mouse. Additionally, to capture the different patterns of repeat instability in liver and striatum, we measured c the distance between the constitutive repeat mode and the longest repeat after background correction and d the distance between the modes of the constitutive and somatically expanded repeats. HdhQ111/+B6J (n = 8) mice are represented in squares and HdhQ111/+B6J.AJ10 (n = 8) mice in triangles
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Fig5: HdhQ111/+B6J.AJ10 mice showed a mild increase of liver somatic repeat instability when compared to HdhQ111/+B6J mice. a GeneMapper traces of PCR-amplified Htt CAG repeats from tail, striatum and liver of representative 5 months HdhQ111/+B6J (144 CAGs) and HdhQ111/+B6J.AJ10 (141 CAGs) mice. b Somatic repeat instability was quantified from GeneMapper traces by determining an instability index for tail, striatum and liver of each mouse. Additionally, to capture the different patterns of repeat instability in liver and striatum, we measured c the distance between the constitutive repeat mode and the longest repeat after background correction and d the distance between the modes of the constitutive and somatically expanded repeats. HdhQ111/+B6J (n = 8) mice are represented in squares and HdhQ111/+B6J.AJ10 (n = 8) mice in triangles

Mentions: HdhQ111/+ knock-in mice also exhibit CAG length, age dependent and tissue specific somatic instability, with significant accumulation of expansions in striatum and liver that becomes apparent by 5 months of age (Lee et al. 2010, 2011; Wheeler et al. 1999). In order to evaluate the potential effect of AJ-B6J genetic variants at chr10 in somatic instability, we extracted genomic DNA from one stable (tail) and two unstable (liver and striatum) tissues from HdhQ111/+B6J and HdhQ111/+B6J.AJ10 mice at 5 months of age. As shown in Fig. 5a, the Htt CAG repeats in tail were very stable in contrast to striatum and liver that showed significant levels of instability, irrespective of chr10 background. Next we quantified the levels of repeat instability for each tissue using a conservative threshold (20 % of the highest peak). As shown in Fig. 5b, the highest instability indices were observed in the liver (+11.95 ± 0.81 for HdhQ111/+B6J and +12.71 ± 1.03 for HdhQ111/+B6J.AJ10) followed by the striatum (+8.15 ± 1.51 for HdhQ111/+B6J and +8.40 ± 1.27 for HdhQ111/+B6J.AJ10). There was no significant difference for the instability indices, or for the expansion and contraction indices (data not shown) when comparing the two groups of HdhQ111 mice. As previously described (Lee et al. 2011), the patterns of repeat instability differed between liver and striatum: while in the liver a distinct population of unstable CAG repeats was evident, in the striatum these repeats were more broadly distributed. To qualitatively characterise these different patterns of repeat instability, two additional measurements were made: the distance to the longest repeat (striatum and liver, Fig. 5c) and the distance between the two modes (liver, Fig. 5d). There was no significant difference in the patterns of repeat instability when comparing HdhQ111/+B6J and HdhQ111/+B6J.AJ10. However, as for the instability index, we did observe a numerically larger distribution of the unstable repeats in the liver of HdhQ111/+B6J.AJ10 mice.Fig. 5


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/+B6J.AJ10 mice showed a mild increase of liver somatic repeat instability when compared to HdhQ111/+B6J mice. a GeneMapper traces of PCR-amplified Htt CAG repeats from tail, striatum and liver of representative 5 months HdhQ111/+B6J (144 CAGs) and HdhQ111/+B6J.AJ10 (141 CAGs) mice. b Somatic repeat instability was quantified from GeneMapper traces by determining an instability index for tail, striatum and liver of each mouse. Additionally, to capture the different patterns of repeat instability in liver and striatum, we measured c the distance between the constitutive repeat mode and the longest repeat after background correction and d the distance between the modes of the constitutive and somatically expanded repeats. HdhQ111/+B6J (n = 8) mice are represented in squares and HdhQ111/+B6J.AJ10 (n = 8) mice in triangles
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Fig5: HdhQ111/+B6J.AJ10 mice showed a mild increase of liver somatic repeat instability when compared to HdhQ111/+B6J mice. a GeneMapper traces of PCR-amplified Htt CAG repeats from tail, striatum and liver of representative 5 months HdhQ111/+B6J (144 CAGs) and HdhQ111/+B6J.AJ10 (141 CAGs) mice. b Somatic repeat instability was quantified from GeneMapper traces by determining an instability index for tail, striatum and liver of each mouse. Additionally, to capture the different patterns of repeat instability in liver and striatum, we measured c the distance between the constitutive repeat mode and the longest repeat after background correction and d the distance between the modes of the constitutive and somatically expanded repeats. HdhQ111/+B6J (n = 8) mice are represented in squares and HdhQ111/+B6J.AJ10 (n = 8) mice in triangles
Mentions: HdhQ111/+ knock-in mice also exhibit CAG length, age dependent and tissue specific somatic instability, with significant accumulation of expansions in striatum and liver that becomes apparent by 5 months of age (Lee et al. 2010, 2011; Wheeler et al. 1999). In order to evaluate the potential effect of AJ-B6J genetic variants at chr10 in somatic instability, we extracted genomic DNA from one stable (tail) and two unstable (liver and striatum) tissues from HdhQ111/+B6J and HdhQ111/+B6J.AJ10 mice at 5 months of age. As shown in Fig. 5a, the Htt CAG repeats in tail were very stable in contrast to striatum and liver that showed significant levels of instability, irrespective of chr10 background. Next we quantified the levels of repeat instability for each tissue using a conservative threshold (20 % of the highest peak). As shown in Fig. 5b, the highest instability indices were observed in the liver (+11.95 ± 0.81 for HdhQ111/+B6J and +12.71 ± 1.03 for HdhQ111/+B6J.AJ10) followed by the striatum (+8.15 ± 1.51 for HdhQ111/+B6J and +8.40 ± 1.27 for HdhQ111/+B6J.AJ10). There was no significant difference for the instability indices, or for the expansion and contraction indices (data not shown) when comparing the two groups of HdhQ111 mice. As previously described (Lee et al. 2011), the patterns of repeat instability differed between liver and striatum: while in the liver a distinct population of unstable CAG repeats was evident, in the striatum these repeats were more broadly distributed. To qualitatively characterise these different patterns of repeat instability, two additional measurements were made: the distance to the longest repeat (striatum and liver, Fig. 5c) and the distance between the two modes (liver, Fig. 5d). There was no significant difference in the patterns of repeat instability when comparing HdhQ111/+B6J and HdhQ111/+B6J.AJ10. However, as for the instability index, we did observe a numerically larger distribution of the unstable repeats in the liver of HdhQ111/+B6J.AJ10 mice.Fig. 5

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