Date of Award

1-1-2020

Language

English

Document Type

Master's Thesis

Degree Name

Master of Science (MS)

College/School/Department

Department of Biomedical Sciences

Content Description

1 online resource (iii, 89 pages) : color illustrations.

Dissertation/Thesis Chair

Valerie J Bolivar

Committee Members

Bruce J Herron, Richard W Cole

Keywords

Autism spectrum disorders, Corpus callosum, Axons, Mice as laboratory animals

Subject Categories

Biology | Neuroscience and Neurobiology | Social and Behavioral Sciences

Abstract

Autism Spectrum Disorder (ASD) is known for distinct behavioral phenotypes such as a preference for repetitive activities and difficulty in socialization. However, little is known about what might cause ASD. Current evidence implicates genetics as playing a substantial role in ASD. Mouse models, such as BTBR T+ Itpr3tf/J (BTBR) inbred mice, are an invaluable resource for ASD research, as they allow the investigation of both genetics and behavior in parallel. BTBR mice are of interest due to their reduced hippocampal commissure (HC) and absent corpus callosum (CC), along with increased exploratory activity, decreased anxiety, reduced sociability, and increased repetitive self-grooming relative to other inbred strains. Investigation of BTBR’s genome revealed Draxin, a gene known to play a role in axon guidance during early development, as one of BTBR’s most unique mutations. The present study assesses the forebrain commissures and several behaviors of BTBR mice expressing a homozygous CRISPR/Cas9-corrected wild-type Draxin (DraxinWT/WT), and compares them to those of BTBR mice expressing a homozygous mutant Draxin (DraxinMut/Mut), and heterozygous mice expressing one copy of each Draxin variant (DraxinWT/Mut). Both male and female mice were tested. Postmortem brain staining reveals DraxinWT/WT mice to have fully-repaired forebrain commissures, while DraxinWT/Mut mice show variability from partial to complete repairment, and DraxinMut/Mut mice consistently show the forebrain commissure impairment characteristic of the BTBR inbred strain. Exploratory and anxiety-related behaviors were investigated in the open field and elevated zero maze tests, which show few significant differences between sexes or genotypes. Sociability assay testing reveals Draxin repair to have little effect on social interaction time, regardless of sex or genotype. Furthermore, examining stereotypic behaviors in the marble burying and self-grooming tests also shows little effect of Draxin genotype on the behaviors of interest. We found four sex differences, and female mice were found to be overall more impacted by Draxin than were male mice. The present results may have implications in ASD theories driven by sex differences. However, a more precise genetic basis for BTBR’s behavioral differences and the limitations of our behavioral testing pose questions for future studies.

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