Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Physiology and Pharmacology

Supervisor

Kramer, Jamie M

Affiliation

Dalhousie University

Abstract

Intellectual disability (ID) is a neurodevelopmental disorder associated with many epigenetic regulators and chromatin modifying enzymes like histone lysine methyltransferases (KMTs) and demethylases (KDMs). Here, I systematically investigate the role of 7 KDMs: Su(var)3-3, KDM2, Lid, CG2982, UTX, KDM4B, JHDM2, and 1 KMT: trr in the context of learning and memory using Drosophila melanogaster. Genetic knockdown of each gene in the mushroom body (MB) of flies are tested for short- and long-term memory impairment using courtship conditioning. Knockdown of 6 KDMs and trr resulted in memory loss. MB morphology was analyzed to determine potential cause of memory loss. However, no gross morphological defects were observed following knockdown. This suggests the cause of memory loss is not due to structural deformities to the MB but may be due to defects in memory-dependent transcriptional activation or cell identity. These findings will help uncover the roles of KDMs in regulated neuronal processes and Drosophila memory.

Summary for Lay Audience

Intellectual disability (ID) is a neurodevelopmental disorder characterized by limited intellectual function and adaptive behaviour before the age of 18. ID is associated with many enzymes that regulate gene transcription. Currently, there are over 350 known dominant ID genes with many of these associated with post-translational histone modifications (PTMs). These modifications alter the physical structure of DNA to determine how cells “read” genes. These PTMs have roles in defining gene expression patterns in different cell types and have also been strongly implicated in the regulation of higher brain functions, like learning and memory. There are many types of PTMs, one being histone methylation which is known to be dynamically regulated in the context of learning and memory but the function of histone demethylases in the brain is not well described. Here, I will systematically investigate the roles of several histone lysine demethylases in the context of learning and memory using the model organism, Drosophila melanogaster. Genetic knockdown of these genes in the memory center of the fly brain called the mushroom body (MB), were tested for short- and long-term memory defects using courtship conditioning. This memory assay utilizes the innate mating behaviour exhibited by males in an attempt to copulate with an unresponsive female. A learning defect is determined if males fail to respond to the rejection by reducing the amount of courting or a reduced memory index compared to the corresponding control. Knockdown of several of these KDMs resulted in loss of both short- and long-term memory suggesting that these genes may play a role regulating memory dependent pathways in the memory center of fly brains. To determine if these defects are caused by MB defects, we also analyzed MB morphological defects following knockdown of these genes and observed no obvious defects. Therefore, these genes do not cause a structural defect but rather may affect neuronal – cell identity or transcriptional activation.

Available for download on Friday, April 02, 2021

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