Modification: FUS: Transgenic
Disease Relevance: Amyotrophic Lateral Sclerosis, Frontotemporal Dementia
Strain Name: Tg (Prnp-FUS)WT3Cshw/J
Genetic Background: C57Bl/6/SJL founder mice backcrossed to C57Bl/6
Availability: The Jackson Lab: Stock# 017916; Cryopreserved
This transgenic mouse model of ALS overexpresses wild-type human FUS. Motor symptoms appear at a young age, accompanied by degeneration of spinal motor neurons. End-stage disease occurs by 12 weeks of age in homozygous mice, and is characterized by severe motor dysfunction that includes hindlimb paralysis (Mitchell et al., 2013).
In this model, the mouse prion protein promoter (PrP) regulates transgene expression, driving expression preferentially in the brain and spinal cord, with much lower levels elsewhere. Even in the CNS, transgenic protein levels were relatively low. Compared to levels in non-Tg mice, total FUS protein was elevated in hemizygous and homozygous mice by 1.4- and 1.7–fold, respectively. Homozygous mice are the focus of this entry because hemizygous mice were fairly normal. They gained weight normally, displayed no significant motor dysfunction or signs of ill health, and appeared to have a normal lifespan (>104 weeks).
Homozygous mice, on the other hand, rapidly develop severe motor neuron disease. Although indistinguishable from littermates at birth, they develop tremor by about four weeks of age and a stilted gait. At that time, their growth tapers off and they have difficulties maneuvering on the Rotarod. By eight weeks, they have reduced locomotion and progressive hindlimb weakening, manifested by an inability to raise the pelvis off the ground. Homozygous mice were euthanized by 10 to 13 weeks of age due to hindlimb paralysis and/or a 25 percent weight loss. Specifically, the average survival was 82 ± 12 days.
The severe motor impairment manifested by these mice is accompanied by significant motor neuron pathology and degeneration. Despite relatively mild over-expression, transgenic FUS protein accumulates in the cytoplasm of homozygous mice. Furthermore, some cytoplasmic FUS accumulates into neuronal inclusions in both the brain and spinal cord. Inclusions in the spinal cord were described as “globular” and “granular.” No apparent loss of nuclear FUS was observed. Ubiquitin-positive inclusions were also observed, but did not co-localize with FUS immunoreactivity.
Although the human FUS transgene was expressed in both the brain and spinal cord, neuronal degeneration appears specific to the spinal cord in this model. By end stage, about 60 percent of lumbar spinal neurons were lost in the anterior horn. Neuronal degeneration was accompanied by astrogliosis and microgliosis as well as denervation of hindlimb muscles and focal muscle atrophy.
In this model there is no indication of gender differences in phenotype onset or progression. The mice do not appear to be affected by gastrointestinal dysfunction even by end-stage, although pathological assessment of the myenteric plexus has not been carried out (personal communication, Jacqueline Mitchell, Nov 2015).
The transgene in this model expresses wild-type human FUS with an N-terminal HA-tag. The mouse prion protein promoter (PrP) drives transgene expression.
When visualized, these models will distributed over a 18 month timeline demarcated at the following intervals: 1mo, 3mo, 6mo, 9mo, 12mo, 15mo, 18mo+.
- Cortical Neuron Loss
Cortical Neuron Loss
In the brain, overt neuronal loss was absent at end stage (~11 weeks).
Lower Motor Neuron Loss
By end stage (~11 weeks), homozygous mice had lost about 60 percent of α-motor neurons in the anterior horn of the lumbar spinal cord.
By end stage, cytoplasmic FUS inclusions, described as “granular” and “globular,” develop in the spinal cord of homozygous mice. Ubiquitin-positive inclusions also develop, but do not co-localize with FUS inclusions. Neurons in the brain also develop “granular” and “skein-like” FUS inclusions.
By end stage (~11 weeks), homozygous mice had microgliosis and astrogliosis in the anterior horn of the spinal cord and in the white matter of the dorsal columns. Reactive gliosis was absent in the brain, despite cytoplasmic inclusions of FUS in some neurons.
Homozygous mice had about 20 percent fewer functional motor units in the extensor digitorum longus muscle as estimated by neurophysiological assessment.
Muscle histology from end stage (~11 weeks) homozygous mice showed focal muscle atrophy in hindlimb muscles.
Homozygous mice exhibited motor symptoms at four weeks of age, starting with a tremor and mild signs of hindlimb dysfunction, including gait abnormalities. Motor symptoms progressed quickly, ultimately developing into hindlimb paralysis.
Homozygous mice fail to gain weight normally starting about four weeks of age. Their body weight declines in subsequent weeks, often precipitating euthanasia.
Homozygous mice were euthanized between 10 and 13 weeks of age when they developed severe motor impairment or lost 25 percent of their body weight. Average survival was 82 ± 12 days.
- Mitchell JC, McGoldrick P, Vance C, Hortobagyi T, Sreedharan J, Rogelj B, Tudor EL, Smith BN, Klasen C, Miller CC, Cooper JD, Greensmith L, Shaw CE. Overexpression of human wild-type FUS causes progressive motor neuron degeneration in an age- and dose-dependent fashion. Acta Neuropathol. 2012 Sep 9; PubMed.