The ubiquitin E3 ligase Ube3a has been implicated in two severe neurological disorders, Angelman's syndrome (AS) and autism spectrum disorder caused by maternal 15q 11-13 duplication (15qASD). Cells from 15qASD and AS patients have excess and deficient UBE3A, respectively. Several lines of evidence indicate that this alteration in Ube3a dosage mediates the behavioral disturbances in 15q11-13 ASD and AS. Ube3a is the sole gene consistently shown to express selectively from the maternal allele in the brains of mice and men. The majority of children who inherit 15q11-13 duplications from their mothers develop ASD;the more copies inherited, the more severe the impairment. Angelman's Syndrome (AS), by contrast, results when children fail to inherit maternal 15q11-13 or a functional maternal UBE3A gene product. We hypothesize that excess Ube3a (created by extra copies of 15q11-13) contributes to ASD by increasing the ubiquitination and degradation of key brain proteins needed to preserve normal neuronal circuit function, and that deficient Ube3a contributes to Angelman's Syndrome through the same, but opposite mechanisms. Since the brain's circuitries are designed to quantitatively evaluate sensory information and to generate quantitative motor responses, there are likely many regulatory molecules within the neuronal circuitry that can cause graded changes in behavior when their quantities are varied. Such molecular quantity variation might underlie the intrinsic heterogeneity of psychiatric disorders like autism spectrum disorder. We propose Ube3a will become the first well-described example of this mechanism.
The specific aims of this R21 grant follow: (1) identify the hippocampal CA1 pyramidal neuron proteins quantitatively regulated by varying excesses and deficiencies of Ube3a;and (2) identify the hippocampal CA1 circuit functions quantitatively regulated by varying excesses and deficiencies of Ube3a. Our methods will include using the 3xFLAG epitope tag to immunoprecipitate native hippocampal CA1 region proteins physically associated with Ube3a, and using mass- spectrometry to identify the protein interactors and potential targets. Targets will be directly assessed by comparing the level of proteins on 1-D or 2-D PAGE and identification of those showing bidirectional alterations. Slice electrophysiology and neuronal morphology will be used in our new Ube3a transgenic and existing Ube3a knockout mice to examine the effects of gene dosage on postnatal development and adult function of CA1 pyramidal neuron excitability and synaptic function (excitatory and inhibitory) in living brain tissues. Our seven (7) mouse lines with extra 15q11-13 gene copies and varying gene dosage permit us to evaluate the impact of gene copy number on circuit function. This project promotes the agency's mission to deepen the understanding of the neuronal cells and circuits involved in ASD via genetic models. By examining these model systems, we will glean information about the defects in molecular, cellular, and circuit function that underlie these debilitating mental disorders.
Autism spectrum disorder (ASD) is a heterogeneous group of related behavioral disorders, characterized by deficits in three core domains: communication, social interaction, and rigid behavior. This project seeks to learn how certain autism-related genes may affect proteins in the brain and the function of brain circuits that underlie these behavioral disturbances. This understanding may lead to the development of new drugs and behavioral interventions.
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| Smith, Stephen E P; Zhou, Yu-Dong; Zhang, Guangping et al. (2011) Increased gene dosage of Ube3a results in autism traits and decreased glutamate synaptic transmission in mice. Sci Transl Med 3:103ra97 |
