Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Developmental Biology

Supervisor

Dr. Nathalie Berube

Abstract

Mutations in the ATRX gene cause alpha thalassaemia mental retardation, X linked, or can enable cancer progression. ATRX encodes a Swi2/Snf2 chromatin remodeling protein involved in deposition of the histone variant H3.3 at telomeres and pericentromeric heterochromatin. The aim of this study was to determine the role of ATRX in the regulation of gene expression. I identified the ancestral pseudoautosomal region (aPAR) genes as some of the most downregulated genes throughout forebrain development. The PARs are homologous regions located at the ends of the X and Y chromosomes, and are rich in repetitive sequences and GC content. However, mouse PAR homologs have translocated to autosomes and are called aPAR genes. The mouse aPAR genes regulated by ATRX are all located near telomeres. To determine how ATRX promotes aPAR gene expression, we focused on Dhrsx. I found that ATRX and H3.3 occupy the Dhrsx gene body in a guanine-rich segment predicted to form secondary structures called G-quadruplexes. In the absence of ATRX, I observed a decrease in H3.3 at Dhrsx and at other downregulated aPAR genes. Several other epigenetic marks are not altered in and around Dhrsx in the ATRX-null forebrain, and thus cannot provide an explanation for transcriptional dysregulation. However, increased RNA PolII occupancy at the ATRX/H3.3/G-rich region of Dhrsx indicates PolII stalling in the absence of ATRX, and suggests that ATRX promotes transcriptional elongation. I conclude that ATRX facilitates passage of the transcription machinery at G-quadruplex forming regions of a gene in a process that involves incorporation of H3.3.

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