Angelman syndrome results when maternally-inherited 15q11-13 is deleted or imprinted 15q11-13 gene Ube3a is mutated. Autism results when maternal 15q11-13 is triplicated. The parental inheritance patterns are explained by Ube3a the only 15q11-13 gene expressed solely from the maternal allele in neurons. The countervalent 15q disorders display some contrasting behavioral changes. Angelman syndrome presents with intellectual and motor deficits, but also a hypersocial demeanor, while 15q triplication displays impaired social behavior. Interestingly, in additional to the other previousl characterized deficits, we recently established the Angelman syndrome mice display increased social interaction and ultrasonic vocalization. By contrast, tripling Ube3a gene dosage reduced social interaction and vocalization providing a model of autism. The results establish a Goldilock effect for Ube3a gene dosage and social behavior. Reciprocal gene dose-dependent effects also argue some Ube3a effects could arise from ongoing regulatory rather than remote developmental defects. Ube3a acts as an E3 ubiquitin protein ligase to promote protein degradation and as a nuclear receptor co-activator. To test the hypothesis that Ube3a deficiency in Angelman syndrome causes deficits in behavior and circuit function via ongoing regulatory rather than developmental defects, we will test for reversal of the behavioral and circuit deficits when Ube3a is genetically reactivated in adulthood. To achieve this goal, we generated mice carrying a single extra copy of Ube3a-ON transgene that is silenced by a loxP-flanked STOP cassette. The Ube3a-ON transgene is inactive until the loxP-flanked STOP cassette is deleted by Cre recombinase. Crossing Ube3a-ON transgenic to Cre-ER"""""""" fusion protein transgenic mice enables tamoxifen- induced Ube3a gene expression. ERTM is mutated, responding to tamoxifen but not estrogen. Cre recombinase is tethered to heat shock proteins in the cytoplasm by ERTM. Tamoxifen penetrates the CNS and binds ERTM, permitting Cre to enter the nucleus and delete the loxP-flanked STOP cassette. If adult rescue is not achieved, we will perform temporal mapping to postnatal or embryonic developmental periods. We also created an Ube3a-OFF transgene where loxP sequences flank Ube3a exon 2 so tamoxifen causes Cre-ERTM to inactivate Ube3a. Crossing Ube3a-OFF/Cre-ERTM into the Angelman model, we will determine if inactivating Ube3a in adulthood or at specific developmental times recreates the disorder. The result will establish the feasibility of rescuing Angelman syndrome and provide insights into the pathophysiological basis and treatment options for the disorder.
The study will determine whether the behavioral and circuit defects present in a mouse model of Angelman syndrome are reversible if a normal copy of the Ube3a gene is restored in adulthood. If not, the study will restore the normal Ube3a gene at various developmental ages to precisely map the timing when disease reversibility can be achieved. These studies are critical to guide future studies aimed at developing therapies to treat the disorder.