Species: Mouse
Genes: PFN1
Mutations: PFN1 C71G
Modification: PFN1: Multi-transgene
Disease Relevance: Amyotrophic Lateral Sclerosis
Strain Name: FVB/N-Tg(Prnp-PFN1*C71G)22Zxu Tg(Thy1-PFN1*C71G)67Zxu/J
Genetic Background: FVB/NJ
Availability: Available as a triple transgenic through The Jackson Lab, Stock# 028608

Summary

Mutations in profilin, including C71G, are linked to rare familial cases of ALS. The profilin protein is best known for its role in polymerizing actin, but has also been shown to aggregate with RNA and proteins commonly associated with stress granules.

Two founder lines were created expressing mutant human profilin-1 with the C71G mutation. In one line transgene expression was driven by the human Thy1.2 promotor, whereas the other line used the mouse prion protein promotor (Prp). Both had an N-terminal V5 tag. These two lines were crossed to create the PFN1^C71G mouse which is homozygous for Thy1.2-PFN1^C71G and hemizygous for Prp-PFN1^C71G (Yang et al., 2016).

The Thy1.2-PFN1^C71G singly transgenic mice expressed profilin in motor neurons positive for Choline acetyltransferase (ChAT), but not in smaller neurons. The Prp-PFN1^C71G mice expressed the transgene in about 80 percent of neurons in the spinal cord including those that were ChAT positive and negative. Neither line expressed exogenous profilin in oligodendrocytes, astrocytes, or microglia. Expression ratios of exogenous to endogenous profilin were approximately 3x, 2x, and 5x for the Thy1.2-PFN1^C71G, Prp-PFN1^C71G, and the PFN1^C71G triple transgenic, respectively.

The PFN1^C71G mouse also exhibited transgene expression in the cortex, hippocampus, cerebellum, and brain stem. A line expressing wildtype profilin-1 had similar expression levels in the spinal cord to the PFN1^C71G mouse (see Related Strains below).

Gene-dosage and expression levels of PFN1^C71G protein  correlated with the severity and onset of weakness and paralysis. Of the two founder lines, the Prp-PFN1^C71G hemizygous mice did not develop muscle weakness even at 700 days old, while the Thy1.2-PFN1^C71G hemizygous mice developed weakness at an average age of 350 days and became paralyzed at 421 days. The PFN1^C71G triple transgenic mice developed weakness at an average age of 140 days and became paralyzed at 211 days. Thy1.2-PFN1^C71G homozygous mice and Thy1.2-PFN1^C71G/ Prp-PFN1^C71G double hemizygous mice displayed intermediate phenotypes between the founder lines and the PFN1^C71G line.

At 100 days PFN1^C71G mice preformed similarly on behavioral assays to nontransgenic mice and mice expressing wildtype PFN1. By 120 days, 10% of PFN1^C71G mice began showing minor gate changes and at 5-6 months they began demonstrating progressive deficits in Rotorod performance, vertical behaviors, grip strength. Body weight peaked at 4-6 months and then progressively decreased.  No phenotypic differences were observed between the genders.

At the paralysis stage (6-7 months), PFN1^C71G mice exhibit microgliosis, astrogliosis, and loss of motor neurons in the ventral horn. Axons in the ventral and dorsal roots were largely normal up to 100 days but by 120 days there was an increase in the number of degenerating axons and the number of axons decreased by 121 days and 171 days in the ventral and dorsal roots, respectively. In addition, PFN1^C71G mice showed atrophy and denervation of lower hind limb muscles by 171 days of age. The medulla showed signs of neurodegeneration and astrogliosis, while the cortex, hippocampus, and cerebellum appeared to be spared.

PFN1^C71G motor neurons had reduced neurofilament expression and diminished filament network. While PFN1^WT neurons expressed exogenous PFN1 evenly through the nuclei and cytoplasm PFN1^C71G neurons expression more punctate forming aggregates in the cytoplasm and processes and could be detected as early as 127 days. Additionally, PFN1^C71G mice also developed accumulations of ubiquitin and p62 in motor neurons. 

Related Strains

Prp-PFN1WT - In this line the mouse prion protein promoter drives the expression of wildtype human profilin-1 (with an N-terminal V5 tag). Available through The Jackson Laboratory Stock# 028607.

Phenotype Characterization

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References

Paper Citations

1. Yang C, Danielson EW, Qiao T, Metterville J, Brown RH Jr, Landers JE, Xu Z. Mutant PFN1 causes ALS phenotypes and progressive motor neuron degeneration in mice by a gain of toxicity. Proc Natl Acad Sci U S A. 2016 Oct 11;113(41):E6209-E6218. Epub 2016 Sep 28 PubMed.

External Citations

1. The Jackson Laboratory Stock# 028607.
2. The Jackson Lab, Stock# 028608

Further Reading