Species: Mouse
Genes: FUS
Mutations: FUS P525L
Modification: FUS: Knock-In
Disease Relevance: Amyotrophic Lateral Sclerosis
Strain Name: N/A
Genetic Background: C57Bl/6
Availability: Unknown.

Summary

FUS (Fused in Sarcoma) is a member of a family of RNA-binding proteins with roles in transcription, RNA processing, RNA transport, and translation. Mutations in FUS, many of which are clustered near the nuclear localization signal at the C-terminus, are linked to familial cases of ALS. The P525L mutation in FUS is associated with a rare and aggressive form of juvenile-onset ALS.

A transgene containing myc-tagged human FUS with the P525L mutation and an upstream Lox-P flanked stop sequence was inserted into the MAPT locus by homologous recombination to create the τ^OFFhFUS^P525L mouse. Expression of the transgene was then achieved by crossing τ^OFFhFUS^P525L mice to the Prm1-Cre line for germline recombination to remove the stop sequence, which created the heterozygous τ^ONhFUS^P525L mouse line. A control mouse line, τ^ONhFUS^WT, was created in the same manner using wild-type human FUS (Sharma et al., 2016).

Human FUS was expressed throughout the spinal cord in both neuronal and non-neuronal cells, consistent with the expression pattern of the MAPT locus. Protein levels of exogenous FUS were about four times greater in τ^ONhFUS^P525L mice due to decreased turnover compared to control τ^ONhFUS^WT mice. RNA levels of human FUS were similar between the two mouse lines.

In mutant mice, hFUS^P525L mislocalized to the cytoplasm and dendrites of lumbar spinal motor neurons, but no discrete aggregates were observed. Wild-type FUS, both exogenous and endogenous, remained nuclear and was not detected in the cytoplasm.

There was no loss of motor neurons in the lumbar spinal cord at 10 days, but motor neuron loss started at 30 days and progressed through 360 days. Mice expressing wild-type hFUS had no motor neuron loss even at 360 days. Sensory neurons in the dorsal root ganglia and motor neurons in the oculomotor nucleus were spared in both genotypes. Additionally, there was an increase in astrocytosis and microgliosis in the ventral horn of the lumbar spinal cord in t^ONhFUS^P525L mice compared with controls.

Muscle fibers of the tibialis anterior, gastrocnemius, and soleus muscles of the hind limb were progressively denervated starting by 20, 90, and 360 days, respectively. The tibialis anterior muscle also had decreased fiber diameter in mutant mice. These three muscles showed no signs of denervation in heterozygous or homozygous τ^ONhFUS^WT control mice.

Ultrastructural analysis of the neuromuscular junctions of the tibialis anterior muscle revealed a decrease in morphologically normal mitochondria, a decrease in synaptic vesicles, and no change in active zones numbers. Neuromuscular junctions of mice expressing hFUS^P525L also exhibited increased spontaneous activity and impaired response amplitude to mid- and high frequency stimulations.

Mice expressing hFUS^P525L showed signs of hind-limb weakness with impaired performance in the wire hang task at 360 days. Survival of τ^ONhFUS^P525L mice was not affected by 360 days of age.

A τ^MNhFUS^P525L mouse was also created to restrict transgene expression to motor neurons by crossing τ^OFFhFUS^P525L mice to a line expressing Cre recombinase under control of the choline acetyltransferase promotor. Interestingly, τ^MNhFUS^P525L and τ^ONhFUS^P525L mice exhibited similar phenotypes for motor neuron loss and muscle denervation. 

Related Strains

hFUS^R521C

Phenotype Characterization

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References

Research Models Citations

1. hFUS-R521C

Paper Citations

1. Sharma A, Lyashchenko AK, Lu L, Nasrabady SE, Elmaleh M, Mendelsohn M, Nemes A, Tapia JC, Mentis GZ, Shneider NA. ALS-associated mutant FUS induces selective motor neuron degeneration through toxic gain of function. Nat Commun. 2016 Feb 4;7:10465. PubMed.

Further Reading