ABSTRACT
"Fierce" mice, homozygous for the deletion of nuclear receptor 2E1 (NR2E1), show abnormal brain-eye development and pathological aggression. To evaluate functional equivalency between mouse and human NR2E1, we generated mice transgenic for a genomic clone spanning the human NR2E1 locus and bred these animals to fierce mice deleted for the corresponding mouse gene. In fierce mutants carrying human NR2E1, structural brain defects were eliminated and eye abnormalities ameliorated. Excitingly, behavior in these "rescue" mice was indistinguishable from controls. Because no artificial promoter was used to drive transgene expression, promoter and regulatory elements within the human NR2E1 clone are functional in mouse. Normal behavior in rescue animals suggests that mechanisms underlying the behavioral abnormalities in fierce mice may also be conserved in humans. Our data support the hypothesis that variation at NR2E1 may contribute to human behavioral disorders. Use of this rescue paradigm with other genes will permit the direct evaluation of human genes hypothesized to play a causal role in psychiatric disease but for which evidence is lacking or equivocal.
Subject(s)
Aggression/physiology , Brain/abnormalities , Eye Abnormalities/genetics , Receptors, Cytoplasmic and Nuclear/deficiency , Receptors, Cytoplasmic and Nuclear/physiology , Agonistic Behavior/physiology , Animals , Brain/embryology , Cerebral Cortex/abnormalities , Congenital Abnormalities/embryology , Congenital Abnormalities/genetics , Congenital Abnormalities/therapy , Crosses, Genetic , Exploratory Behavior/physiology , Eye Abnormalities/embryology , Eye Abnormalities/therapy , Female , Genotype , Humans , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Mice, Transgenic , Olfactory Bulb/abnormalities , Orphan Nuclear Receptors , Phenotype , Promoter Regions, Genetic , Receptors, Cytoplasmic and Nuclear/chemistry , Receptors, Cytoplasmic and Nuclear/genetics , Regulatory Sequences, Nucleic Acid , Retina/abnormalities , Reverse Transcriptase Polymerase Chain Reaction , Species Specificity , TerritorialityABSTRACT
Huntington's disease (HD) is an adult-onset neurodegenerative disorder involving motor dysfunction, cognitive deficits, and psychiatric disturbances that result from underlying striatal and cortical dysfunction and neuropathology. The YAC128 mouse model of HD reproduces both the motor deficits and selective degeneration observed in the human disease. However, the presence of cognitive impairment in this model has not been determined. Here, we report mild cognitive deficits in YAC128 mice that precede motor onset and progressively worsen with age. Rotarod testing revealed a motor learning deficit at 2 months of age that progresses such that by 12 months of age, untrained YAC128 mice are unable to learn the rotarod task. Additional support for cognitive dysfunction is evident in a simple swimming test in which YAC128 mice take longer to find the platform than wild-type (WT) controls beginning at 8 months of age. YAC128 mice also have deficits in open-field habituation and in a swimming T-maze test at this age. Strikingly, in the reversal phase of the swimming T-maze test, YAC128 mice take twice as long as WT mice to locate the platform, indicating a difficulty in changing strategy. At 12 months of age, YAC128 mice show decreased prepulse inhibition and habituation to acoustic startle. The clear pattern of cognitive dysfunction in YAC128 mice is similar to the symptoms and progression of cognitive deficits in human HD and provides both the opportunity to examine the relationship between cognitive dysfunction, motor impairment, and neuropathology in HD and to assess whether potential therapies for HD can restore cognitive function.
Subject(s)
Cognition Disorders/etiology , Huntington Disease/pathology , Huntington Disease/physiopathology , Movement Disorders/etiology , Acoustic Stimulation/adverse effects , Age Factors , Analysis of Variance , Animals , Behavior, Animal , Disease Models, Animal , Dose-Response Relationship, Radiation , Exploratory Behavior/physiology , Habituation, Psychophysiologic , Huntington Disease/genetics , Inhibition, Psychological , Maze Learning/physiology , Memory/physiology , Mice , Motor Activity/genetics , Motor Activity/physiology , Psychomotor Performance/physiology , Reflex, Acoustic/physiology , Rotarod Performance Test/methods , Swimming/physiology , Time FactorsABSTRACT
An expanded CAG repeat is the underlying genetic defect in Huntington disease, a disorder characterized by motor, psychiatric and cognitive deficits and striatal atrophy associated with neuronal loss. An accurate animal model of this disease is crucial for elucidation of the underlying natural history of the illness and also for testing experimental therapeutics. We established a new yeast artificial chromosome (YAC) mouse model of HD with the entire human HD gene containing 128 CAG repeats (YAC128) which develops motor abnormalities and age-dependent brain atrophy including cortical and striatal atrophy associated with striatal neuronal loss. YAC128 mice exhibit initial hyperactivity, followed by the onset of a motor deficit and finally hypokinesis. The motor deficit in the YAC128 mice is highly correlated with striatal neuronal loss, providing a structural correlate for the behavioral changes. The natural history of HD-related changes in the YAC128 mice has been defined, demonstrating the presence of huntingtin inclusions after the onset of behavior and neuropathological changes. The HD-related phenotypes of the YAC128 mice show phenotypic uniformity with low inter-animal variability present, which together with the age-dependent striatal neurodegeneration make it an ideal mouse model for the assessment of neuroprotective and other therapeutic interventions.