Publication Date

2019-04-30

Availability

Embargoed

Embargo Period

2021-04-29

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Biology (Arts and Sciences)

Date of Defense

2019-04-05

First Committee Member

Julia Dallman

Second Committee Member

Athula Wikramanayake

Third Committee Member

Akira Chiba

Fourth Committee Member

Lucina Uddin

Abstract

Sensory deficits have recently been added to the diagnostic criteria for autism spectrum disorder (ASD). Research suggests that between 65-90% of individuals with ASD have problems with sensory perception, reactivity, or have sensory fixations. These sensory deficits require animal modeling to determine the neuropathology underlying these sensory-motor behaviors. Zebrafish provide a unique animal model for studying neurodevelopmental disorders like ASD. For instance, zebrafish develop stereotyped embryonic behaviors that can be used to identify early critical periods impacted by neurodevelopmental gene mutations. Zebrafish embryos and larvae are also small, allowing for high-throughput behavioral screens, and optically transparent, providing in vivo visualization of anatomy and physiology. Together these attributes provide an integrative model that can be used to investigate behavioral deficits from the whole-brain to single neurons. This dissertation utilizes advances made in gene editing and physiological imaging to investigate what circuits in the brain underlie ASD sensory-motor deficits. The ASD gene SHANK3 is correlated with a diverse set of behavioral deficits, including sensory hyporeactivity. However SHANK3 is expressed as several unique isoforms and the position of the mutation may cause variability in phenotypic penetrance. In this study, mutations were generated in the zebrafish SHANK3 orthologues shank3a and shank3b (shank3ab; Chapter 2). To account for isoform expression, we generated mutations in the beginning and the end of shank3ab, termed shank3abN -/- and shank3abC -/-, respectively. These mutants were then screened for sensory hyporeactivity using the visual motor response (VMR) assay. A wildtype VMR includes hyperactivity following a sudden loss of illumination. shank3ab mutants exhibited a VMR, but were hyporeactive in reaching peak swimming velocity. To determine changes in brain activity, we used a phosphorylation event (pERK) that reaches peak expression within ~5 minutes of neuronal activity. Relative brain-wide pERK was then compared within genotypes between lights-on and lights-off, using the brain mapping program mitogen-activating protein (MAP)-mapping. While wildtype and shank3ab showed similar lights-on pERK intensity, wildtype exhibited a greater collection of forebrain and hindbrain regions with increased lights-off activity. Drug screening and hindbrain transplantation experiments were then used to identify deficits in hindbrain activity as the likely cause for lights-off hyporeactivity. This study is the first to functionally link shank3 mutations to sensory hyporeactivity, and provides a novel role for shank3 in hindbrain function.

Keywords

shank3; zebrafish; autism spectrum disorders; autism; hyporeactivity; hindbrain; neural circuits; intellectual disability; visual motor response; CRISPR; MAP-Mapping

Available for download on Thursday, April 29, 2021

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