Species: Mouse
Genes: LRRK2
Mutations: LRRK2 R1441C
Modification: LRRK2: Transgenic
Disease Relevance: Parkinson's Disease
Strain Name: STOCK Gt(ROSA)26Sortm1(LRRK2*R1441C)Djmo/J
Genetic Background: R26-LRRK2 mice were generated from 129/SvJ ES cells microinjected into C57Bl/6J mouse blastocysts. Chimeras were bred with C57Bl/6J mice and maintained on a mixed genetic background (129/SvJ and C57Bl/6J). BAC-DAT-iCRE mice were maintained on a C57Bl/6J background.
Availability: Available through The Jackson Laboratory, Stock# 022793, Cryopreserved or frozen embryo.

Summary

R26-LRRK2^+/+ mice harbor a transgene containing a full-length mutant human LRRK2 preceded by a floxed stop cassette, inserted into the ROSA26 locus; these mice allow for conditional expression of human LRRK2 R1441C when crossed with mice carrying a transgene for Cre recombinase. 

These transgenic mice were designed to selectively express human LRRK2 with the R1441C mutation in dopaminergic neurons of the brain. R26-LRRK2^+/+ mice were crossed with BAC-DAT-iCre mice, which express Cre-recombinase driven by the promoter for the dopamine transporter (DAT). The progeny of this cross, hereafter referred to as DAT-LRRK2, express near-endogenous levels of full-length mutant LRRK2, predominantly in the ventral midbrain due to Cre-dependent expression. DAT-LRRK2 mice are viable, fertile, and exhibit no overt behavioral abnormalities. They live a normal lifespan without significant neurobehavioral deficits or neuropathology, with the exception of subtle abnormalities in nuclear morphology (Tsika et al., 2014).

The transgene regulation provided by the combination of DAT-Cre and the endogenous mouse ROSA26 promoter results in expression of transgene mRNA in the olfactory bulb and ventral midbrain. Human LRRK2 protein was detected predominantly in the ventral midbrain, olfactory bulb, and spinal cord, with lower levels in the cerebral cortex and cerebellum, perhaps due to ectopic Cre recombinase activity. Levels of mouse LRRK2 protein were at or near physiological levels.

DAT-LRRK2 mice behaved normally into advanced age. In open-field tests out to 20 months of age, they exhibited comparable locomotor activity to mice expressing just the R26-LRRK2 transgene with no exogenous Cre. Likewise, at 6 and 19 months, motor coordination on the Rotarod was comparable to controls. Furthermore, gait was normal up to 20 months (measured on the CatWalk system), as was olfactory function as assessed by the ability to locate buried food. There were no significant differences in body weight between R26-LRRK2 controls and DAT-LRRK2 mice.

Neuropathologically, DAT-LRRK2 mice were largely normal. Expression of the mutant LRRK2 did not affect the number of tyrosine hydroxylase(TH)-positive neurons or the total number of Nissl-positive neurons in the substantia nigra pars compacta at 12 and 22 months. The dopaminergic neurons were of normal size and morphology, and the density of TH-positive nerve terminals in the striatum was likewise comparable to controls. Immunohistochemical analysis of the brain at 22 months did not reveal abnormalities in α-synuclein, ubiquitin, or tau. Moreover, GFAP and Iba1 immunoreactivity was comparable to controls, indicating lack of astrocytosis and microgliosis, respectively. Autophagy markers (LC3 and p62) were unchanged.

Dopamine levels in the striatum were comparable to controls as assessed at 10 months of age. Likewise, levels of the primary dopamine metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), were not significantly altered.

Although lacking the usual Parkinson's disease-like features of neuropathology, DAT-LRRK2 mice do develop subtle abnormalities in in dopaminergic and non-dopaminergic neuronal nuclei as they age, namely irregularly shaped nuclei and increased invaginations of the nuclear envelope. These abnormalities are not observed at 5 months of age, but are detectable by 20 to 22 months of age.

Modification Details

A cassette containing the sequence for full-length human LRRK2 with the R1441C mutation was targeted to the endogenous mouse ROSA26 locus by homologous recombination in embryonic stem cells. Cre-mediated excision of the transcriptional termination sequence in the cassette allowed for transgene expression. In this case, the Cre line expressed Cre-recombinase driven by the promoter for the dopamine transporter (DAT) gene derived from a BAC construct containing the entire mouse DAT (slc6a3) gene.

Related Strains

B6.Cg-Gt(ROSA)26Sortm1(LRRK2*R1441C)Djmo/J -  congenic B6 background. Available through The Jackson Laboratory Stock# 026293.

Phenotype Characterization

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References

Paper Citations

1. Tsika E, Kannan M, Foo CS, Dikeman D, Glauser L, Gellhaar S, Galter D, Knott GW, Dawson TM, Dawson VL, Moore DJ. Conditional expression of Parkinson's disease-related R1441C LRRK2 in midbrain dopaminergic neurons of mice causes nuclear abnormalities without neurodegeneration. Neurobiol Dis. 2014 Nov;71:345-58. Epub 2014 Aug 29 PubMed.

External Citations

1. The Jackson Laboratory Stock# 026293
2. The Jackson Laboratory, Stock# 022793

Further Reading

No Available Further Reading