Biochemistry and Pharmacology - Theses
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ItemInvestigating features and interactions of the childhood respiratory microbiome( 2022)The human microbiome is closely linked with the health of an individual and is implicated in numerous complex diseases including diabetes, inflammatory bowel disease, cancer, cystic fibrosis (CF), and asthma. There is growing evidence to suggest the respiratory microbiome influences risk and trajectory of respiratory disease from an early age. Hence, unravelling the biology of the childhood respiratory microbiome is critical to gain a comprehensive understanding of respiratory disease, and requires characterisation of both the aggregate community and individual community members. This thesis strengthens our understanding of the childhood respiratory microbiome through i) investigation of specific community members, Haemophilus influenzae and Haemophilus parainfluenzae, in the context of CF, and ii) exploration of upper respiratory tract (URT) microbiome development during the first year of life with a particular focus on microbe-microbe interactions. While morbidity and mortality of CF principally result from repeated respiratory infections by Pseudomonas aeruginosa, there is emerging evidence that respiratory tract colonisation by Haemophilus species during childhood induces early disease progression. I describe the detection, antimicrobial resistance (AMR), and genome sequencing of H. influenzae and H. parainfluenzae isolated from airway samples of children enrolled in the AREST CF program. This work revealed H. influenzae and H. parainfluenzae carriage rates and strain persistence among participants. Haemophilus isolates were genetically diverse and commonly resistant to antimicrobials with several putative novel resistance determinants identified. Finally, genomic data identified transmission of Haemophilus strains between participants. The association between the respiratory microbiome and respiratory disease has been established in several cohort studies. However, no work has been undertaken to compare preservation of respiratory microbiome dynamics or to reconcile differences between cohort studies. This thesis explores 16S rRNA gene survey data from four longitudinal childhood cohorts, with a focus on microbe-microbe interactions. The URT microbiome composition dynamics during the first year of life are shown to be well preserved across cohorts, and the aggregate data set is leveraged to reveal associations between specific community members and symptoms of acute respiratory illness. A foundation for microbe-microbe interactions during the first year of life is established, which facilitated discovery of two communities that dominate the URT microbiome. For both areas of focus presented in this thesis I additionally developed two novel software tools to support and enhance analysis: hicap, a tool for robust inference of H. influenzae serotype and cap locus structure from WGS data, and FastSpar, a tool for rapid and scalable correlation estimation from compositional data. Collectively, this thesis contributes to our understanding of the childhood URT microbiome in the context of CF and normal development. The results in this thesis provide the first insights into the population dynamics and genomic AMR determinants of H. influenzae and H. parainfluenzae strains in a paediatric CF cohort. The presented findings further recapitulate the most complete overview of URT microbiome development during the first year of life and provide the first foundation for microbe-microbe interaction dynamics. The tools developed and the analyses performed in this thesis provide an important framework for future studies to investigate features and interactions of the respiratory microbiome.
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ItemMeasuring intolerance to missense variation within the human genome and proteome( 2021)This thesis summarises an experimental investigation of the measurement and application of intolerance to missense variation in the human genome, and its use in predicting the functional consequences of variants, as well as its ability to identify novel functionally relevant protein features. Using gnomAD, currently the largest publicly available dataset of sequenced human exomes, as well as UK Biobank and DiscovEHR population variation databases, I have systematically measured the proportion of missense variation across over 18,000 human genes and 80,000 gene transcripts over a sliding window of 31 codons, named the Missense Tolerance Ratio (MTR), and observed that known pathogenic variants in epilepsy patients preferentially exist in regions estimated as intolerant. We further validated the MTR using the set of known pathogenic variants in ClinVar and observed a significant difference in the MTR distribution between these and novel control missense variant datasets. Intolerant regions within a gene’s sequence have also been observed to cluster within the protein tertiary structure. We anticipate that the MTR therefore has extraordinary potential in identifying important functional domains within protein structures. Current methods of estimating the functional importance of regions within structures largely rely on conservation, however this is heavily dependent on the depth and appropriateness of the alignment where functionality is often not fully preserved between species. Missense intolerance within tertiary structures was measured using the MTR3D and shown to provide complementary information to the MTR. By combining the MTR and MTR3D with additional structural properties such as residue depth, we also developed the MTRX, a combined measure of intolerance that incorporates the predictions from the different scores. This was shown to have high predictive power towards known pathogenic variants. To assist in the prediction of variant consequences and inform on research in drug design, protein biochemistry and gene analyses, we are providing these intolerance estimates in their sequence-based and structure-based formulations to be freely available as user-friendly web-servers.
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ItemNo Preview AvailableInvestigation of alternative splicing in apicomplexan parasites( 2021)Alternative splicing is the phenomenon by which coding and non-coding regions of pre-mRNA molecules can be differentially spliced to yield multiple mRNA isoforms from a single gene. In metazoans, alternative splicing occurs to a substantial degree, contributing to protein diversity and the post-transcriptional regulation of gene expression. However, to what extent this occurs in apicomplexan parasites is much less understood. This thesis examines the landscape, regulators and function of alternative splicing in two apicomplexan parasites, T. gondii and P. falciparum. Technological advances in the short read sequencing of nucleic acids at unprecedented depths have enabled deep profiling of the transcriptome. However, the short reads present a limitation in the analysis of complex splicing events that span beyond the length of the reads. We evaluated the capability of a third generation long read sequencing technology, Oxford Nanopore Technologies (ONT) sequencing, in sequencing full-length native mRNA from T. gondii and P. falciparum, and established a method to analyse the alternative splicing landscape from the long reads. We successfully identified full-length transcripts spanning annotated and non-annotated junctions, implying a suitability in exploring complex splicing events. The analysis reveals an unusually high level of intron retained transcripts with premature terminating codons (PTCs). This suggests that most alternative splicing events in T. gondii and P. falciparum are unlikely to be productive. Alternative splicing in metazoans is modulated by alterative splicing factors, most notably the SR (serine-arginine–rich) protein family. We characterised the suite of SR proteins and two putative kinases/regulators of SR proteins in T. gondii. The proteins were found localised to sub-nuclear compartments characteristic of splicing factors. We demonstrated through genetic ablation and whole-transcriptome sequencing that the SR proteins modulate distinct but overlapping subsets of mostly non-productive alternative splicing events, as well as impacting transcript abundance. Alternatively spliced junctions were also enriched in characteristic SR binding motifs. The putative kinases of SR proteins were found to be essential to parasite survival and modulate extensive splicing events, but the events poorly mirrored that modulated by the SR proteins. This suggests a complex system of splicing regulation that do not conform to other eukaryotic models. The targeting of non-productive alternatively spliced transcripts for degradation through the nonsense mediated decay (NMD) pathway is one mechanism by which metazoans post-transcriptionally regulate gene expression. To explore if this was the case for T. gondii, we characterised the three core NDM proteins- UPF1, UPF2 and UPF3. The three proteins were found to co-immunoprecipitate with one another, implying a conservation of the core NMD complex. However, when we conditionally ablated the UPF proteins, parasite growth and survival was not impacted. We sequenced the parasite mRNA and found that only UPF2 impacted global intron retention rates. Moreover, a link between intron retention and gene expression regulation could not be established. Our results show that the fitness cost of mis- splicing determines intron retention rates, rather than targeted regulation. Hence, this thesis has shown that although non-productive alternative splicing is widespread and regulated in T. gondii, it is not a mechanism for post-transcriptional regulation of gene expression through the NMD pathway.