Neurobiological Mechanism of 15q11-13 Duplication Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a heterogeneous group of related behavioral disorders, characterized by deficits in three core domains: communication and social interaction, and repetitive behaviors. This project seeks to learn how Ube3a, a gene within the most common genetic copy number variant found in human autism (maternal 15q11-13 duplication) affects the expression of other genes and their proteins to alter brain circuit functions underlying these behavioral disturbances. These proteins will become therapeutic targets to treat the disease.The long-term objective of this project is to compare and contrast the defects in neuronal mRNA expression and circuit functions produced by altered Ube3a gene dosage that may underlie the behavioral phenotypes of Autism Spectrum Disorder (ASD) with maternal 15q11-13 duplication and Angelman's Syndrome (AS). Cells from 15q11-13 ASD and AS patients have excess and deficient E3 ubiquitin ligase, Ube3a, respectively. Ube3a is the sole gene expressed selectively from the maternal allele in brain. The majority of children who inherit 15q11-13 duplications from their mothers develop ASD and the more copies inherited, the more severe the impairment. Recently, we established that increasing Ube3a gene dosage alone reconstitutes the triad of autism-related behavioral deficits in mice. Angelman's Syndrome (AS), by contrast, results when children inherit maternal Ube3a gene mutations. Importantly, Ube3a also acts as a nuclear receptor co-activator regulating gene expression independent of ligase activity. Thus we hypothesized that excess Ube3a (15q dup model) acts in the nucleus to perturb the normal expression of specific neuronal genes and encoded proteins to alter circuit function and thereby generate autism-related behavioral deficits. The logical corollary is that deficiencies of nuclear Ube3a may alter gene expression to change circuit function and produce Angelman-related behavioral deficits through the same, but opposite mechanisms. Because the brain's circuitries are designed for quantitative assessment of sensory information and quantitative motor responses, it is likely that many molecules controlling circuit functions can cause graded changes in behavior when their quantities are altered. We propose Ube3a do so through a dose-dependent regulation of neuronal gene expression. Such molecular quantity variations likely underlie the intrinsic heterogeneity of behavioral disorders like ASD. The specific aims of this R01 grant follow: (1 and 2) determine if Ube3a gene dosage causes ASD (excess Ube3a) and AS (deficient Ube3a) related behavioral deficits through its actions within the nucleus; (3) identify the cortical neuron mRNAs quantitatively regulated by excesses or deficiencies of Ube3a; and (4) identify the cortical circuit dysfunctions quantitatively induced by excesses and deficiencies of Ube3a. Our methods include a novel nuclear-targeted Ube3a transgene, a neuron cell-type specific expression of Ube3a, genome wide analysis of transcripts, and identification of consensus Ube3a-gene promoter binding sites. Slice electrophysiology and neuronal morphology will examine the effects of global and cell-type specific changes and nuclear targeted changes of Ube3a gene dosage on cortical circuit function in living brain slices. This analysis will facilitate our effors to bridge from genes to circuits to behavior in the two contrasting human neurological diseases. The project promotes the agency's mission to further a deeper understanding of the neuronal cells, circuits, and genes involved in ASD and AS via genetic models. The novel molecular insights and genetic tools will facilitate development of treatments