Thesis (Ph.D.) - Simon Fraser University, 2004. / Theses (Dept. of Biological Sciences) / Simon Fraser University. Bibliography : leaves 134-154.

Thesis (Ph. D.) in Biochemistry and Molecular Biology--University of Maine, 2001. / Includes vita. Includes bibliographical references (leaves 71-83).

Thesis (M. Phil.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Thesis (M. Phil.)--University of Hong Kong, 2006. / Also available online.

Thesis (Ph. D.)--Oregon State University, 2009. / Printout. Titles called 1 and 2. Includes bibliographical references (leaves 174-197). Also available on the World Wide Web.

No description available.

Recognition of non-self, pathogen-associated molecular patterns is a central component of host immune response to pathogens like viruses. Intracellular detection of viral nucleic acids leads to the production of type I interferons (IFN-I) and subsequent establishment of an antiviral state in infected and neighboring cells. Viruses have evolved multiple mechanisms to counteract IFN-I responses in infected cells, however, viral nucleic acids released from dying cells can stimulate IFN-I production in surrounding or distal uninfected cells. This thesis examines the mechanisms by which cells recognize extracellular viral nucleic acids and the subsequent downstream antiviral signaling. Class A scavenger receptors (SR-As) internalize extracellular viral double-stranded RNA (dsRNA) to mediate IFN-I responses, but little is known about extracellular viral DNA. We observed that extracellular DNA is recognized and internalized by SR-As in a manner like extracellular dsRNA. Furthermore, we established that SR-A1 is sufficient in mediating extracellular dsRNA-induced cellular responses and other nucleic acid receptors like SR-J1 and DEC-205 are dispensable. Finally, a direct interaction of RNA and DNA species was demonstrated with the coiled-coil collagenous domain of SR-A1, but not the scavenger receptor cysteine rich domain of SR-A6.We elaborated the role of SR-A1 by identifying the cellular processes activated through SR-A1 following uptake of extracellular dsRNA. Cytosolic sensors are essential in mediating an antiviral response to the endocytosed dsRNA, but the mechanism of endoplasmic release and cytoplasmic entry of dsRNA remains an enigma. We demonstrated that the lack of a dsRNA-channel, SIDT2, impaired the ability of the cells to mediate an antiviral response to extracellular dsRNA. Understanding host responses to extracellular viral nucleic acids will enable the development of novel vaccines and antiviral therapeutics against RNA and DNA viruses that efficiently counteract these responses in infected cells. / Thesis / Doctor of Philosophy (PhD) / Viral infections remain a threat to global health as new diseases continue to emerge. To develop effective vaccines and antivirals to combat viruses and alleviate human disease require a deeper understanding of virus-host interactions. Host cells identify virus-associated molecules to detect viruses and eliminate them whereas, viruses employ tactics to prevent the activation of the immune system. However, virus-induced cell lysis releases viral molecules that can stimulate immune responses in neighbouring uninfected cells. This thesis examines the mechanism by which cells respond to extracellular viral nucleic acids. We showed that a protein present at the cell surface called ‘class A scavenger receptor 1’ is sufficient to internalize extracellular viral nucleic acids, leading to immune responses. The response is impaired when a channel protein, SIDT2, is absent in the cells. Further work is necessary to understand how this knowledge can be harnessed to develop vaccines and antiviral therapeutics.

No description available.

published_or_final_version / abstract / Zoology / Master / Master of Philosophy

Homologous Recombination (HR) can promote genome stability through its capacity to faithfully repair DNA gouble 2trand !;!reak2 (DSBs) and preventing the demise of stalled replication forks in part by catalysing template switching to enable DNA polymerase to bypass lesions. Despite these beneficial roles, inappropriate or untimely HR events can have deleterious consequences. HR can cause genome instability by recombining "inappropriate" homologous sequences, especially if the recombination intermediates are resolved to form crossovers. Over the past few years, study of the rare inherited chromosome instability disorder, Eanconi Anaemia (FA), has uncovered a novel DNA damage response pathway. Although the FA pathway is required primarily for interstrand DNA cross link repair, its precise role in DNA repair reactions is still unclear. FA.Qomplementation group M (FANCM) is the sole component within the FA core complex which possesses a DNA helicase/ATPase domain and an endonuclease domain (albeit non-functional), suggesting that FANCM could translocate along DNA and target the FA core complex to blocked replication forks. To further elucidate the role of FANCM in HR, I have purified Fm11, the FANCM orthologue in the fission yeast Schizosaccharomyces pombe and tested its activity on a range of synthetic replication and recombination intermediates in vitro. Fml1 binds both replication forks and Holliday Junctions (HJs) which are key intermediates of HR.