Modification: TARDBP: Transgenic
Disease Relevance: Amyotrophic Lateral Sclerosis, Frontotemporal Dementia
Strain Name: B6;SJL-Tg(Thy1-TARDBP)4Singh/J
Genetic Background: Transgene introduced into BL6/SJL oocytes. Founders crossed to C57BL6/J.
Availability: The Jackson Lab: Stock# 012836; Cryopreserved. The CRO QPS Austria offers research services with this model.
This mouse model of ALS overexpresses wild-type human TARDBP (TDP-43) in postnatal neurons. Mice in this line, called TAR4, develop ALS-related phenotypes, including severe motor impairment, loss of upper and lower motor neurons, and premature death. Homozygous mice (referred to as TAR4/4) become symptomatic very early and do not survive beyond one month of age. Hemizygous mice (referred to as TAR4) exhibit much milder phenotypes (Wils et al., 2010).
In this model the murine Thy-1 promoter drives transgene expression, resulting in preferential expression in neurons throughout the CNS. Because the Thy-1 promoter activates about one week after birth, transgene expression does not interfere with developmental processes in utero. Compared with other transgenic TDP-43 mice, TAR4/4 mice express relatively low amounts of transgene. TDP-43 mRNA levels in the brain are about twofold higher than endogenous levels. In hemizygotes, transgene expression is below endogenous levels.
Consistent with a gene dosage effect, homozygous mice are affected more severely than hemizygous animals and have more rapid disease progression. Although indistinguishable from non-Tg littermates at birth, TAR4/4 mice develop an abnormal motor reflex by postnatal day 14. When lifted by the tails, homozygotes pull in their hindlimbs rather than extending them. Early on, they also display a shortened stride, a wide stance, and frequent stumbling. By day 18 they are less adept on the accelerating Rotarod. Motor function continues to deteriorate rapidly, and complete paralysis of the hindlimbs occurs within about 10 days of symptom onset. The mice survive an average of just 24 days.
In contrast, hemizygous TAR4 do not develop an abnormal hindlimb reflex until about 14 months of age and do not show impairments on the Rotarod until about 15 months. These mice never develop frank paralysis but die at about 22–24 months of age.
Although the Thy-1 promoter drives expression in virtually all neurons of the brain and spinal cord, only specific neuronal subpopulations develop abnormal protein inclusions and neuronal loss. In terms of abnormal protein accumulation, diffuse ubiquitin staining occurs in cortical layer V of the anterior cortex, including primary motor cortex and somatosensory areas, as well as in the hippocampus, subiculum, brainstem, and cranial motor nuclei. Ubiquitin inclusions occur in both the cytoplasm and the nucleus. Nuclear inclusions were positive for TDP-43, whereas those in the cytoplasm variably co-labeled with TDP-43. Ubiquitinated proteins also accumulate in the spinal cord, in both cytoplasmic and nuclear compartments. Ubiquitin–negative cytoplasmic inclusions were also seen in spinal neurons of the anterior horn. Ultrastructural analysis revealed that these were abnormal accumulation of mitochondria (Janssens et al., 2013).
TAR 4/4 mice develop prominent astrogliosis and microgliosis in areas affected by ubiquitin pathology. In particular, cortical layer V of the anterior cortex, including motor and somatosensory cortices, are affected by numerous GFAP-positive astrocytes. Astrogliosis is also observed in the spinal cord, especially in areas affected by inclusion pathology.
Neuronal loss is prominent in both the brain and the spinal cord. In the brain, both superficial and deep cortical layers of the anterior cortex are affected. By day 24, loss occurs in the motor cortex of TAR4/4 mice. Hippocampal neurons are also affected. All regions of the spinal cord are affected, with prominent loss noted in the cervical and lumbar regions that innervate the extremities.
Transgene encodes wild-type human TARDBP, driven by the murine Thy-1 promoter. The transgene integrated at locus 6qB3 in the mouse genome and does not interrupt any known gene.
Wt-TAR6/6. These mice were generated in parallel with the TAR4/4 line and carry the same genetic construct (Wils et al., 2010). Wt-TAR6/6 mice express lower levels of wild-type transgenic TDP-43 protein (0.6 X the amount of the TAR4/4 line) and have a less aggressive phenotype. These mice exhibit neuropathological features of ALS, including elevated amounts of cytoplasmic and insoluble TDP-43, astrogliosis and microgliosis, and loss of motor neurons in the cortex and spinal cord; motor impairment; and early death (average survival is 6.7 months).
When visualized, these models will distributed over a 18 month timeline demarcated at the following intervals: 1mo, 3mo, 6mo, 9mo, 12mo, 15mo, 18mo+.
- NMJ Abnormalities
- Muscle Atrophy
Cortical Neuron Loss
In homozygous mice, quantitative loss of neurons occurs in the motor cortex compared with non-Tg littermates. Both superficial and deep cortical layers of the anterior cortex are affected.
Lower Motor Neuron Loss
By day 18, homozygous mice exhibited about 25 percent loss of motor neurons in the lumbar spinal cord compared with non-Tg littermates.
Homozygous mice developed cytoplasmic inclusions in the brain and spinal cord, many of which were ubiquitin-positive. A minority of inclusions co-labeled with TDP-43. Ultrastructural analysis revealed ubiquitin–negative cytoplasmic inclusions in anterior horn neurons to be abnormal accumulations of mitochondria.
Astrogliosis and microgliois especially in cortical layer V of the anterior cortex, including motor and somatosensory cortex, and in the spinal cord.
Homozygous mice exhibit an abnormal clasping reflex by postnatal day 14. Other early motor deficits include a shortened stride, a wide stance, and frequent stumbling. By day 18, reduced performance on the Rotarod. Complete paralysis occurs ~10 days after onset.
Size and weight of homozygous mice lag behind hemizygotes and non-Tg littermates.
Homozygous mice survive an average of just 24 days. In contrast, hemizygous mice survive to advanced age, although they die more prematurely than non-Tg mice, after 22 to 24 months.
Research Models Citations
- Wils H, Kleinberger G, Janssens J, Pereson S, Joris G, Cuijt I, Smits V, Ceuterick-de Groote C, Van Broeckhoven C, Kumar-Singh S. TDP-43 transgenic mice develop spastic paralysis and neuronal inclusions characteristic of ALS and frontotemporal lobar degeneration. Proc Natl Acad Sci U S A. 2010 Feb 23;107(8):3858-63. Epub 2010 Feb 3 PubMed.
- Janssens J, Wils H, Kleinberger G, Joris G, Cuijt I, Ceuterick-de Groote C, Van Broeckhoven C, Kumar-Singh S. Overexpression of ALS-associated p.M337V human TDP-43 in mice worsens disease features compared to wild-type human TDP-43 mice. Mol Neurobiol. 2013 Aug;48(1):22-35. Epub 2013 Mar 10 PubMed.