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.
These transgenic mice were designed to selectively express mutant human LRRK2 in dopaminergic neurons of the brain. The mutation carried is the R1441C mutation. The experimental approach involved mating mice harboring the mutant LRRK2 transgene driven by ROSA26 promoter to mice expressing Cre-recombinase driven by the promoter for the dopamine transporter (DAT). The progeny of this cross, referred to as R26-LRRK2, express near-endogenous levels of full-length mutant LRRK2, predominantly in the ventral midbrain thanks to Cre-dependent expression. R26-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 produce transgene mRNA in the olfactory bulb, ventral midbrain, and cerebellum. 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 some ectopic Cre recombinase activity. Lrrk2 protein levels were at or near physiological levels.
R26-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 six and 19 months, motor coordination on the Rotarod was comparable to controls. Furthermore, gait was normal out to 20 months, as was olfactory function as assessed by the ability to locate buried food. There were no significant differences in body weight.
Neuropathologically, R26-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. Likewise, GFAP and Iba1 immunoreactivity was comparable to controls, indicating lack of astrocytosis and microgliosis, respectively. Autophagy markers 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 measures of neuropathology, R26-LRRK2 mice do develop subtle abnormalities in neuronal nuclei as they age, namely irregularly shaped nuclei and increased invaginations of the nuclear envelope. These abnormalities are not observed at five months, but are detectable by 20-22 months of age.
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 ES 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) derived from a BAC construct containing the entire mouse DAT (slc6) gene.
B6.Cg-Gt(ROSA)26Sortm1(LRRK2*R1441C)Djmo/J - congenic B6 background. Available through The Jackson Laboratory Stock# 026293.
When visualized, these models will distributed over a 18 month timeline demarcated at the following intervals: 1mo, 3mo, 6mo, 9mo, 12mo, 15mo, 18mo+.
- Dopamine Deficiency
- α-synuclein Inclusions
- Motor Impairment
- Neuronal Loss
- Mitochondrial Abnormalities
- Cognitive Dysfunction
Immunohistochemical analysis of the brain at 22 months did not reveal abnormalities in α-synuclein, and no proteinaceous inclusions were seen.
Immunohistochemical analysis of the brain at 22 months found GFAP and Iba1 immunoreactivity comparable to control levels.
HPLC analysis of striata from 10-month-old mice revealed no significant differences in the levels of dopamine or its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA).
Around 20 months of age, R26-LRRK2 mice behaved normally, exhibiting no deficits in locomotor activity (open-field test), motor coordination (Rotarod), or gait (digital catwalk system).
In the substantia nigra pars compacta, there was no difference in the number of tyrosine hydroxylase(TH)-positive neurons or the total number of Nissl-positive neurons at 12 and 22 months.
- 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.
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