Date of Completion

2-6-2018

Embargo Period

8-31-2018

Keywords

Neuroscience, Neurodevelopment, Electrophysiology, Autism, Synaptic Plasticity

Major Advisor

Eric S. Levine

Associate Advisor

Stormy Chamberlain

Associate Advisor

Richard Mains

Associate Advisor

Stephen Crocker

Field of Study

Biomedical Science

Degree

Doctor of Philosophy

Open Access

Campus Access

Abstract

Maternal deletion of chromosome 15q11-q13 results in a neurodevelopmental disorder known as Angelman syndrome (AS). Interestingly, individuals with a duplication of this region have a related neurodevelopmental disorder called chromosome 15q duplication syndrome (Dup15q). Despite opposite genetic causes, these syndromes have overlapping phenotypes including intellectual disability and seizures. The gene believed to be responsible for AS encodes the ubiquitin ligase UBE3A, which also plays an important role in Dup15q. In both syndromes, alterations in synaptic signaling and excitability appear to contribute to the disease phenotype, at least in mouse models, but the downstream targets of UBE3A and their functional roles are unknown. The recent discovery of genomic reprogramming of human somatic cells into induced pluripotent stem cells (iPSCs) provides a novel way to model human diseases with complex genetics, as animal models of such disorders often fail to encompass the full range of disease phenotypes. In this thesis we use iPSC-derived neurons from Angelman syndrome and Dup15q patients to study the underlying pathophysiology using both electrophysiological and calcium imaging techniques. This study has established that control and Dup15q neurons are capable of significant maturation across 20-weeks in culture, which is dramatically impaired in AS-derived neurons. This AS phenotype can be recapitulated by knockdown or knockout of UBE3A in control neurons. We have also established that impairments in synaptic activity and action potential firing are downstream of an altered resting membrane potential in early development and that BDNF signaling is disrupted. Despite a largely normal maturation, Dup15q neurons display exaggerated spontaneous action potential firing and synchronous activity at 20+ weeks, which are due to disruptions to the seizure-associated KCNQ2 channel. We have also induced synaptic plasticity in iPSC-derived control neurons, which is disrupted in both AS and Dup15q neurons. Overall, this study points to two very distinct cellular phenotypes in AS- and Dup15q-derived neurons. This provides an important starting point for understanding the signaling mechanisms involved in these robust phenotypes with the goal of using these measures for screening pharmacological treatments for the seizures, motor impairments, and other symptoms associated with these rare neurodevelopmental disorders.

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