Our results suggest that E6-AP functions as a cellular quality control ubiquitin ligase and, therefore, can be implicated not only in the pathogenesis of Angelman syndrome but also in the biology of neurodegenerative disorders involving protein aggregation.
Patients with AS had a much higher incidence of seizures with characteristic EEG findings, similar to those seen in mice that are deficient in a single gene (UBE3A) that displays regional brain-specific imprinting in humans and mice.
These results indicate sociability is repressed by social experience and the endogenous levels of UBE3A protein and suggest some social behavioral features observed in Angelman syndrome may reflect an increased social motivation.
Since the initial recognition that Angelman syndrome is caused by maternal deficiency of the E6-AP ubiquitin E3 ligase (gene symbol UBE3A), several. other disorders of E3 ligases have been identified, including autosomal recessive juvenile Parkinson disease, the APECED form of autoimmune polyendocrinopathy syndrome, von Hippel-Lindau syndrome, and congenital polycythemia.
Angelman syndrome (AS) is a congenital neuro-developmental disorder typically occurring due to functional defects of the UBE3A gene caused by uniparental disomy (UPD), translocation or single gene mutation.
Here, we report that ganaxolone, a synthetic neurosteroid that acts as a positive allosteric modulator of synaptic and extrasynaptic GABA<sub>A</sub> receptors, was anxiolytic, anticonvulsant, and improved motor deficits in the Ube3a-deficient mouse model of AS when administered by implanted mini-pump for 3 days or 4 weeks.
The present study is the first to determine that the Ube3a protein ablation seen in the AS mouse model is also characteristic of AS patients and the silencing of the paternal UBE3A allele appears to be lifelong.
Here we used Drosophila melanogaster to screen for the targets of this ubiquitin ligase under conditions of both decreased (as in AS) or increased (as in dup(15)) levels of the fly Dube3a or human UBE3A proteins.
At least one other gene, the E6-associated protein ubiquitin-protein ligase (UBE3A) gene, has been implicated in AS, so the relative contribution of the GABRB3 gene alone or in combination with other genes remains to be established.
Interestingly, HDAC inhibitor also significantly increased the expression of Ube3a in cultured neuronal cells and in the brain of wild type mice but not in AS mice.
We have found that a 15q inversion inherited by an AS child from her normal mother disrupts the 5' end of the UBE3A (E6-AP) gene, the product of which functions in protein ubiquitination.
Although de novo genetic and epigenetic imprinting defects of UBE3A genomic locus account for majority of Angelman diagnoses, approximately 10% of individuals affected with Angelman syndrome are a result of UBE3A loss-of-function mutations occurring on the expressed maternal chromosome.
Exome sequencing revealed a previously unreported mutation of Ubiquitin Protein Ligase E3A (UBE3A) gene, confirming the diagnosis of Angelman syndrome.
By combining our data with those of the literature, we demonstrate statistically that the frequency of UBE3A mutations is significantly higher in the familial than sporadic subsets of AS.