Research Models

SOD1-G93A (hybrid) (G1H)

Synonyms: High-copy SOD1-G93A, B6SJL SOD1-G93A, Tg(hSOD1-G93A)1GUR mice, Gurney mice

Species: Mouse
Genes: SOD1
Mutations: SOD1 G93A
Modification: SOD1: Transgenic
Disease Relevance: Amyotrophic Lateral Sclerosis
Strain Name: B6SJL-Tg(G93A-SOD1)1Gur/J
Genetic Background: C57Bl/6/SJL.
Availability: The Jackson Lab: Stock# 002726; Live

Summary

First reported in 1994, SOD1-G93A mice ushered in a new era of ALS research. This transgenic model, which expresses large amounts of mutant SOD1, develops adult-onset neurodegeneration of spinal motor neurons and progressive motor deficits leading to paralysis. The original SOD1-G93A line (Gurney et al., 1994) has since diverged into a family of strains with different genetic backgrounds and transgene expression levels. These factors—genetic background and copy number—significantly affect the onset and severity of symptoms (Heiman-Patterson et al., 2011; Mancuso et al., 2012). As a group, the G93A models have amassed an extensive body of literature, and they remain a cornerstone of preclinical ALS research. This entry focuses on the G1H line, which has high transgene expression, and was originally developed on a mixed SJL and C57BL/6J background.

As reported in 1994, the original SOD1-G93A strain, designated G1, expressed approximately 18 copies of human SOD1, randomly inserted into the genome (Gurney et al., 1994). An unequal crossover event in a breeding pair of G1 mice produced progeny with about 25 copies of the transgene. These mice, designated G1H (“H” for high copy number), have a more aggressive disease course than the founder line. Signs of motor impairment appear around 91 days of age in G1H mice (Tu et al., 1996), compared with about 121 days in G1 mice (Gurney et al., 1994). G1H mice reach end-stage disease at about 139 days (Chiu et al., 1995), compared with about 170 days in G1 mice (Gurney et al., 1994).

One of the first signs of illness in G1H mice is plateauing of growth and body weight at about three months of age. This is followed by the appearance of motor symptoms, including a shaking tremor in one or more limbs. As the disease progresses, the tremor becomes more pronounced and involves all limbs. Proximal muscle weakness develops along with muscle atrophy and denervation of neuromuscular junctions, eventually leading to paralysis and premature death (Chiu et al., 1995).

In this model, age at symptom onset and survival are affected by gender, with females typically surviving four to seven days longer than males. For example, in one colony, females survived 132 ± 12.4 days, whereas males survived just 127.9 ± 9.5 days, despite an equal copy number (Heiman-Patterson et al., 2005). A similar gender difference in survival was seen in G93A mice on a congenic SJL background, but not on a C57BL/6J background (Heiman-Patterson et al., 2005).

The mutant SOD1 retains enzymatic activity (Gurney et al., 1994), although it does not bind copper ions as effectively as wild-type SOD1 (Pratt et al., 2014).

Neuropathology

Although the SOD1 G93A transgene is expressed widely, pathology in this model is largely restricted to the spinal cord (especially the lumbar cord), brainstem, descending spinal tracts, and neuromuscular junctions. A variety of pathological hallmarks develop in the spinal cord prior to the onset of clinical symptoms, including mitochondrial vacuolization (Dal Canto and Gurney, 1995), Gogli fragmentation (Mourelatos et al., 1996), neurofilament-positive inclusions (Tu et al., 1996), Lewy body-like inclusions (Dal Canto and Gurney, 1995), and cytoplasmic SOD1 aggregates (Johnston et al., 2000). Neuromuscular junctions degenerate around 47 days of age; fast-fatiguable motor neurons are affected first (Frey et al., 2000; Pun et al., 2006). Spinal motor neurons then die off, with about a 50 percent reduction in the cervical and lumbar segments by end-stage (Chiu et al., 1995).

Neuropathology is not restricted to lower motor neurons. In upper motor neurons, signs of degeneration include swollen neurites, Gallyas silver-positive aggregates, vacuoles, and neuritic spheroids. These changes occur at about five months of age, after degeneration in the spinal cord is underway, and generally do not progress to outright neuronal loss (Leichsenring et al., 2006). Degeneration of cranial nuclei, such as the trigeminal, facial, and hypoglossal nerves, has been observed (Angenstein et al., 2004; Zang et al., 2004) and there is age-dependent regression of descending corticospinal, bulbospinal, and rubrospinal tracts (Zang and Cheema, 2002).

Gliosis, including the proliferation of reactive microglia and astrocytes, develops in parallel with motor neuron degeneration in the spinal cord. GFAP and MAC1 immunoreactivity indicate an increase in reactive glia by 117 days of age (Almer et al., 1999; Hall et al., 1998).

Usage

These mice have been studied extensively over many years, and this research laid the groundwork for updated guidelines about preclinical research in ALS (Ludolph et al., 2010; see also Scott et al., 2008).  Recommendations for experimental design include using enough mice to sufficiently power experiments, using experimental cohorts balanced for gender and littermates, and reporting this information in all manuscripts. Given the importance of copy number, quantitative genotyping should be used to ensure that all experimental animals have the expected copy number (Alexander et al., 2004).

One potential caveat to this model is that because of the high copy number, they produce a large excess of SOD1 protein. This may affect the interpretation of results given that ALS patients with SOD1 mutations have just one mutant allele.

The Jackson Lab notes that male mice from this line are particularly aggressive. They recommend limiting numbers to no more than four males per cage.

Modification Details

These transgenic mice express multiple copies of human SOD1 bearing the missense mutation G93A randomly integrated into chromosome 12 of the mouse.

Related Strains

There are a variety of SOD1-G93A strains available, including:

SOD1-G93A (congenic): This congenic line is derived from the original hybrid line by backcrossing to C57BL/6J mice. It is available through The Jackson Laboratory, Stock #004435. Mice on a C57BL/6J background have a milder phenotype (i.e., later onset, longer lifespan) than hybrid B6SJL mice or those on an SJL background (Pfohl et al., 2015; Heiman-Patterson et al., 2005). Note, substrains of C57BL6, such as C57BL/6JOlaHsd, may have additional phenotypic differences (Nardo et al., 2016).

SOD1-G93A (congenic) low expresser: This congenic line is derived from the original mixed B6 SJL line. It has fewer transgene copies than the SOD1-G93A (congenic) described above and develops disease phenotypes later. It is available through The Jackson Laboratory, Stock #002299.

Phenotype Characterization

Cortical Neuron Loss

Although outright upper motor neuron loss is absent or rare, degenerative signs (e.g., swollen neurites, Gallyas-positive aggregates, vacuoles, and neuritic spheroids) have been shown in motor regions of the cerebral cortex by five months of age.

Lower Motor Neuron Loss

Up to 50% loss of motor neurons in the cervical and lumbar segments of the spinal cord at end stage.

Cytoplasmic Inclusions

Inclusions accumulate in spinal motor neurons starting around 82 days of age. Inclusions generally take the form of spheroids or Lewy-body-like inclusions and commonly include a variety of neuronal intermediate filament proteins. TDP-43-positive inclusions are not present.

Gliosis

Gliosis, including the proliferation of reactive microglia and astrocytes, develops in parallel with motor neuron degeneration in the spinal cord.

NMJ Abnormalities

Neuromuscular junctions degenerate around 47 days of age; fast-fatiguable motor neurons are affected first.

Muscle Atrophy

Longitudinal MRI has shown reduced muscle volume as early as 8 weeks of age. Atrophy is progressive. Skeletal muscle is affected, including limb and diaphragm.

Motor Impairment

Signs of motor impairment begin at about 3 months of age with a shaking tremor that leads to paralysis.

Body Weight

One of the first signs of illness is a slowing of growth and a plateauing of weight.

Premature Death

G1H mice reach end-stage disease by 5 months of age. Females typically survive longer than males.

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References

Paper Citations

  1. . Motor neuron degeneration in mice that express a human Cu,Zn superoxide dismutase mutation. Science. 1994 Jun 17;264(5166):1772-5. PubMed.
  2. . Effect of genetic background on phenotype variability in transgenic mouse models of amyotrophic lateral sclerosis: a window of opportunity in the search for genetic modifiers. Amyotroph Lateral Scler. 2011 Mar;12(2):79-86. Epub 2011 Jan 17 PubMed.
  3. . Effect of genetic background on onset and disease progression in the SOD1-G93A model of amyotrophic lateral sclerosis. Amyotroph Lateral Scler. 2012 May;13(3):302-10. PubMed.
  4. . Transgenic mice carrying a human mutant superoxide dismutase transgene develop neuronal cytoskeletal pathology resembling human amyotrophic lateral sclerosis lesions. Proc Natl Acad Sci U S A. 1996 Apr 2;93(7):3155-60. PubMed.
  5. . Age-dependent penetrance of disease in a transgenic mouse model of familial amyotrophic lateral sclerosis. Mol Cell Neurosci. 1995 Aug;6(4):349-62. PubMed.
  6. . Background and gender effects on survival in the TgN(SOD1-G93A)1Gur mouse model of ALS. J Neurol Sci. 2005 Sep 15;236(1-2):1-7. PubMed.
  7. . Aggregation propensities of superoxide dismutase G93 hotspot mutants mirror ALS clinical phenotypes. Proc Natl Acad Sci U S A. 2014 Oct 28;111(43):E4568-76. Epub 2014 Oct 14 PubMed.
  8. . Neuropathological changes in two lines of mice carrying a transgene for mutant human Cu,Zn SOD, and in mice overexpressing wild type human SOD: a model of familial amyotrophic lateral sclerosis (FALS). Brain Res. 1995 Apr 3;676(1):25-40. PubMed.
  9. . The Golgi apparatus of spinal cord motor neurons in transgenic mice expressing mutant Cu,Zn superoxide dismutase becomes fragmented in early, preclinical stages of the disease. Proc Natl Acad Sci U S A. 1996 May 28;93(11):5472-7. PubMed.
  10. . Formation of high molecular weight complexes of mutant Cu, Zn-superoxide dismutase in a mouse model for familial amyotrophic lateral sclerosis. Proc Natl Acad Sci U S A. 2000 Nov 7;97(23):12571-6. PubMed.
  11. . Early and selective loss of neuromuscular synapse subtypes with low sprouting competence in motoneuron diseases. J Neurosci. 2000 Apr 1;20(7):2534-42. PubMed.
  12. . Selective vulnerability and pruning of phasic motoneuron axons in motoneuron disease alleviated by CNTF. Nat Neurosci. 2006 Mar;9(3):408-19. PubMed.
  13. . Ascending neuropathology in the CNS of a mutant SOD1 mouse model of amyotrophic lateral sclerosis. Brain Res. 2006 Jun 22;1096(1):180-95. PubMed.
  14. . Age-dependent changes in MRI of motor brain stem nuclei in a mouse model of ALS. Neuroreport. 2004 Oct 5;15(14):2271-4. PubMed.
  15. . Magnetic resonance imaging reveals neuronal degeneration in the brainstem of the superoxide dismutase 1 transgenic mouse model of amyotrophic lateral sclerosis. Eur J Neurosci. 2004 Oct;20(7):1745-51. PubMed.
  16. . Degeneration of corticospinal and bulbospinal systems in the superoxide dismutase 1(G93A G1H) transgenic mouse model of familial amyotrophic lateral sclerosis. Neurosci Lett. 2002 Oct 31;332(2):99-102. PubMed.
  17. . Inducible nitric oxide synthase up-regulation in a transgenic mouse model of familial amyotrophic lateral sclerosis. J Neurochem. 1999 Jun;72(6):2415-25. PubMed.
  18. . Relationship of microglial and astrocytic activation to disease onset and progression in a transgenic model of familial ALS. Glia. 1998 Jul;23(3):249-56. PubMed.
  19. . Guidelines for preclinical animal research in ALS/MND: A consensus meeting. Amyotroph Lateral Scler. 2010;11(1-2):38-45. PubMed.
  20. . Design, power, and interpretation of studies in the standard murine model of ALS. Amyotroph Lateral Scler. 2008;9(1):4-15. PubMed.
  21. . Effect of transgene copy number on survival in the G93A SOD1 transgenic mouse model of ALS. Brain Res Mol Brain Res. 2004 Nov 4;130(1-2):7-15. PubMed.
  22. . Characterization of the Contribution of Genetic Background and Gender to Disease Progression in the SOD1 G93A Mouse Model of Amyotrophic Lateral Sclerosis: A Meta-Analysis. J Neuromuscul Dis. 2015;2(2):137-150. Epub 2015 Jun 4 PubMed.
  23. . New Insights on the Mechanisms of Disease Course Variability in ALS from Mutant SOD1 Mouse Models. Brain Pathol. 2016 Mar;26(2):237-47. PubMed.

External Citations

  1. The Jackson Laboratory, Stock #004435
  2. The Jackson Laboratory, Stock #002299
  3. The Jackson Lab: Stock# 002726

Further Reading

Papers

  1. . Design, power, and interpretation of studies in the standard murine model of ALS. Amyotroph Lateral Scler. 2008;9(1):4-15. PubMed.
  2. . Guidelines for preclinical animal research in ALS/MND: A consensus meeting. Amyotroph Lateral Scler. 2010;11(1-2):38-45. PubMed.
  3. . New Insights on the Mechanisms of Disease Course Variability in ALS from Mutant SOD1 Mouse Models. Brain Pathol. 2016 Mar;26(2):237-47. PubMed.
  4. . Early and gender-specific differences in spinal cord mitochondrial function and oxidative stress markers in a mouse model of ALS. Acta Neuropathol Commun. 2016 Jan 13;4:3. PubMed.
  5. . Transgenics, toxicity and therapeutics in rodent models of mutant SOD1-mediated familial ALS. Prog Neurobiol. 2008 May;85(1):94-134. PubMed.
  6. . Identification of B6SJL mSOD1(G93A) mouse subgroups with different disease progression rates. J Comp Neurol. 2015 Dec 15;523(18):2752-68. Epub 2015 Jun 22 PubMed.