Unlike RNA viruses, which typically encode their own RNA-dependent RNA polymerases, DNA viruses typically utilize host RNA Polymerase II (RNAPII) to transcribe their genes. Therefore, host factors that interact with RNAPII often maintain important regulatory roles during DNA virus infections. Senataxin (SETX) is a ubiquitously expressed 303 kDa RNA:DNA helicase that associates with RNAPII. It is involved in the resolution of R-loops and plays a role during the DNA damage response. Mutations in SETX are implicated in the neurodegenerative diseases Type 2 Ataxia with Oculomotor Apraxia (AOA2) and juvenile Amyotrophic Lateral Sclerosis (ALS4). Recent work from our group has demonstrated that SETX also acts as an antagonist of the antiviral response during RNA virus infections. Infections, including those caused by Herpes Simplex Virus type I (HSV-1), have been identified as potential environmental triggers of neurodegenerative diseases. Therefore, we elected to study the role of SETX during DNA virus infections since, in addition to regulating host genes, it may also play a role in viral transcription and/or DNA replication. Our data suggests that SETX is involved in the regulation of viral gene expression, and that SETX facilitates DNA replication and contributes to viral biogenesis. SETX attenuates the antiviral response, and in mouse models of infection, is protective against HSV-1 disease pathogenesis. These studies have enhanced our understanding of the role played by SETX during viral infection and may shed light on the mechanism(s) through which SETX dysfunction results in neurodegenerative diseases. / Thesis / Master of Health Sciences (MSc) / DNA viruses utilize host proteins in gene expression, therefore, associated factors play roles during DNA virus infections. Senataxin (SETX) is a RNA:DNA helicase associated with these proteins. SETX mutations are implicated in the neurodegenerative diseases Type 2 Ataxia with Oculomotor Apraxia (AOA2) and juvenile Amyotrophic Lateral Sclerosis (ALS4). Recently, our group demonstrated SETX antagonizes antiviral responses to RNA virus infections. Infections, including those caused by Herpes Simplex Virus type I (HSV-1), are identified as potential triggers of neurodegenerative diseases. We elected to study the role of SETX during DNA virus infections. Our data suggests that SETX is involved in the regulation of viral gene expression, facilitates HSV-1 DNA replication, attenuates the antiviral response, and in mouse models of infection, is protective against HSV-1 disease pathogenesis. These studies enhance understanding of the role of SETX during viral infection and may shed light on the mechanism(s) of SETX role in neurodegenerative disease.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Le complexe condensine est le moteur de la condensation mitotique des chromosomes, un processus essentiel à la stabilité du génome au cours de la division cellulaire. De nombreuses données publiées indiquent qu’il existe des liens fonctionnels étroits entre le processus de transcription des gènes et le processus d’organisation des chromosomes par condensine. Ces données sont toutefois souvent contradictoires et aucun modèle ne fait actuellement consensus pour expliquer les liens entre transcription et condensine. Au cours de cette thèse, nous avons montré chez la levure Schizosaccharomyces pombe qu’en l’absence de l’hélicase à ADN/ARN Sen1, condensine s’accumule spécifiquement à proximité des gènes transcrits par l’ARN Polymérase III. Nous avons utilisé ces observations pour mieux comprendre les liens entre transcription par l’ARN polymérase III et le positionnement de condensine. Nos données montrent que Sen1 est un cofacteur de l’ARN Polymérase III impliqué dans la terminaison de la transcription. Ce résultat est important car il démontre que les modèles existants qui affirment que l’ARN polymérase III termine de transcrire de façon autonome sont erronés. Nous avons ensuite démontré que les défauts de terminaison de l’ARN polymérase III observés en l’absence de Sen1 suffisent entièrement à expliquer l’accumulation de condensine en ces sites. Cette observation importante démontre que le contrôle de qualité de la transcription est directement impliqué dans le positionnement de condensine sur les chromosomes en mitose. Nos résultats nous permettent de proposer qu’au-delà d’un certain seuil, la densité en ARN polymérases est un obstacle à la translocation de condensine sur les chromosomes. / The condensin complex is a key driver of chromosome condensation in mitosis. The condensin-dependent assembly of highly compacted chromosomes is essential for the faithful transmission of the genome during cell division. Many independent studies have established that gene transcription impacts the association of condensin with chromosomes, but the molecular mechanisms involved are still unclear. This is especially true as a number of sometimes contradictory mechanisms have been proposed so far. Here, we show in Schizosaccharomyces pombe that condensin accumulates specifically in the vicinity of a subset of RNA polymerase III-transcribed genes in the absence of the conserved DNA/RNA helicase Sen1. We demonstrate that Sen1 is a cofactor of RNA polymerase III (RNAPIII) required for efficient transcription termination. These results are important because they fundamentally challenge the pre-existing view that RNAPIII terminates transcription autonomously. Strikingly, we show that the RNAPIII transcription termination defects are directly responsible for the accumulation of condensin in the absence of Sen1. This indicates that the quality control of transcription impacts the distribution of condensin on mitotic chromosomes. We propose that above a certain density threshold, the accumulation of RNAPIII constitutes a barrier for the translocation of condensin on chromosomes.