Species: Mouse
Genes: FUS
Mutations: FUS R521C
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, including R521C, are linked to rare familial cases of ALS.

A transgene containing myc-tagged human FUS with the R521C mutation and an upstream Lox-P flanked stop sequence was inserted into the MAPT locus by homologous recombination to create the τ^OFFhFUS^R521C mouse. Expression of the transgene was then achieved by crossing τ^OFFhFUS^R521C mice to the Prm1-Cre line for germline recombination to remove the stop sequence, which created the heterozygous τ^ONhFUS^R521C 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^R521C 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^R521C 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 30 days, but motor neuron loss started at 60 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 τ^ONhFUS^R521C mice compared to controls.

Muscle fibers of the tibialis anterior and gastrocnemius muscles of the hind limb were progressively denervated starting by 40 and 90 days, respectively. In contrast, there was no significant denervation of the soleus muscle by 360 days. These three muscles showed no signs of denervation in heterozygous or homozygous τ^ONhFUS^WT control mice.

A τ^MNhFUS^R521C mouse was also created to restrict transgene expression to motor neurons by crossing τ^OFFhFUS^R521C mice to a line expressing Cre recombinase under control of the choline acetyltransferase promotor. Interestingly, τ^MNhFUS^R521C and τ^ONhFUS^R521C mice exhibited similar phenotypes for motor neuron loss and muscle denervation.

Modification Details

Transgene encoding myc-tagged human FUS-R521C with an upstream Lox-P flanked stop sequence was inserted into the MAPT locus by homologous recombination. These mice were crossed to the Prm1-Cre line for germline recombination to remove the stop sequence, allowing transgene expression.

Related Strains

FUS-R521C

hFUS^P525L

Phenotype Characterization

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References

Research Models Citations

1. FUS-R521C
2. hFUS-P525L

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