Investigations of Neuronal Activity in a Novel Zebrafish Model of Angelman Syndrome

Abstract

Angelman Syndrome (AS) is a neurodevelopmental genetic disorder that presents with a happy demeanor, cognitive deficits, developmental delay, motor dysfunction, and sleep disturbances. The disorder is caused largely by a loss of maternal UBE3A, which encodes for a HECT domain E3 ubiquitin ligase that plays a critical role in targeting proteins for degradation. Various animal models, including Mus musculus and Drosophila melanogaster have provided insight into disease mechanisms from a loss of UBE3A including accumulation of Arc and Ephexin-5 at the synapse, deficits in synaptic plasticity, and abnormal dendritic spine morphology. Here, I add to the AS research toolbox by generating a Danio rerio model of Angelman Syndrome in an attempt to fill in the gaps in UBE3A research left open by limitations in other model organisms. As zebrafish are fertilized externally and develop translucently, this Ube3a knockdown model facilitates novel investigations of prenatal neuronal development over time in the living organism. Here, I demonstrate that splice-site morpholino injections resulted in Ube3a protein knockdown by a splicing exclusion of exon 2 in the ube3a mRNA transcript. My work indicates that Ube3a-knockdown phenotypes recapitulate some characteristics of AS individuals such as delayed development and motor difficulties.

Unlike, mouse and Drosophila models, my work indicates that zebrafish may require Ube3a function for embryonic development outside of the nervous system as knockdown is often fatal, and severe phenotypes correlate with reductions in protein levels. I find that Ube3a is localized to the entire neuronal body, including the soma and axons of mechanosensory neurons. Finally, I demonstrate that Ube3a-knockdown leads to abnormal Rohon-Beard morphology and deficits in neurite extension. Together these results provide a glimpse into possible role for UBE3A during embryogenesis and neuronal development and demonstrate that research using a Danio rerio model for Angelman Syndrome is feasible and effective.