Species: Mouse
Disease Relevance: Amyotrophic Lateral Sclerosis, Frontotemporal Dementia
Strain Name: N/A
Genetic Background: C57BL/6J
Availability: Viral construct available through Leonard Petrucelli.

Summary

The six-nucleotide (GGGGCC) repeat expansion in C9ORF72 encodes five dipeptide-repeat proteins that accumulate in ALS/FTD: glycine-arginine (GR), proline-arginine (PR), glycine-alanine (GA), proline-alanine (PA), and glycine-proline (GP). The GFP-(GA)₅₀ mouse allows researchers to specifically study the pathogenicity of poly(GA) in vivo in a vertebrate model. To create this model, an adeno-associated viral (AAV) vector encoding 50 GA repeats tagged with green fluorescent protein was injected into the ventricles of neonatal mice. GFP-(GA)₅₀ mice exhibit ubiquitin-positive poly(GA) inclusions, progressive neuron loss, and motor and cognitive impairments.

In order to study the effects of protein aggregation on the pathogenicity of poly(GA) peptides, a second model, GFP-(GA)_50-mut, was also generated, in which mice were injected intracerebroventricularly with an AAV expression vector in which a proline was inserted after every fifth GA repeat to disrupt the conformation of the peptide and inhibit its aggregation. Finally, control mice were injected with an AAV vector encoding GFP. Levels of transgene expression in the cortices and hippocampi were similar in GFP-(GA)₅₀ and GFP-(GA)_50-mut mice, but were higher in GFP mice.

Poly(GA)- and ubiquitin-positive inclusions were already present in neurons of 4- to 6-week-old GFP-(GA)₅₀ mice but not GFP or GFP-(GA)_50-mut mice. In the brains of 6-month GFP-(GA)₅₀ mice, most poly(GA) inclusions were ubiquitin-positive. In addition, HR23A and HR23B, proteins involved in DNA repair and ubiquitin-dependent protein degradation (Yokoi and Hanaoka, 2017), and the nuclear pore complex proteins RanGAP1 and Pom121 co-localized with poly(GA) inclusions. Rare inclusions of phosphorylated TDP-43 were also observed. Inclusions were primarily cytoplasmic, but occasional nuclear inclusions occurred. Inclusions were found in cortex, hippocampus, olfactory bulb, cerebellum and thalamus. Poly(GA) proteins were only rarely seen in spinal cord.

GFP-(GA)₅₀ mice lose neurons in the cortex and hippocampus as they age. At 4 to 6 weeks of age, brain weights and neuron numbers are similar among GFP-(GA)₅₀, GFP-(GA)_50-mut, and GFP mice, but at 6 months, the brains of GFP-(GA)₅₀ mice weigh only about two-thirds of the GFP-(GA)_50-mut and GFP animals’, with neuron loss occurring in cortex — including layer V of motor cortex — and the CA3 region of the hippocampus. Purkinje cell numbers also decline in GFP-(GA)₅₀ mice.

Astrogliosis was present in the cortices and hippocampi of 6-month-old GFP-(GA)₅₀ mice, but microgliosis was not observed. Neither astrogliosis nor microgliosis were seen in GFP-(GA)_50-mut or GFP mice.

Compared with GFP-(GA)_50-mut and GFP mice, at 6 months of age, GFP-(GA)₅₀ mice exhibited motor deficits (failure to extend hindlimbs and clasped forelimbs in a tail-suspension test), impaired coordination in the rotarod test, hyperactivity and increased anxiety in the open field, and deficits in contextual and cued fear conditioning.

The body weights of male GFP-(GA)₅₀ mice are less than those of GFP-(GA)_50-mut or GFP control mice, again measured at 6 months of age; however, the body weights of females do not differ between the three groups.

Modification Details

An adeno-associated viral (AAV) vector encoding 50 glycine-alanine (GA) repeats tagged with green fluorescent protein was injected into the ventricles of neonatal mice.

Phenotype Characterization

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References

Paper Citations

Other Citations

1. Leonard Petrucelli

Further Reading

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