Enabling systems-level analyses of the host response to infectious diseases in bovine and other mammalian species

The innate immune response is a critical branch of immunity, providing a first line of defense against pathogens and shaping subsequent adaptive immune responses. The complexity of this system necessitates the application of systems-level approaches. InnateDB is an integrated web-accessible database and systems biology platform being developed to facilitate the systems level analysis of innate immunity pathways and networks. One of the aims of this thesis was to enhance InnateDB with bovine data, thereby providing a resource for investigation of this agriculturally important model organism. Using an orthology based approach, over 70% of InnateDB’s human protein-protein interactions (PPIs), and a similar fraction of human pathways were reconstructed in cow and integrated into InnateDB. Pathway analysis, the statistical association of observations at the molecular level with processes at a more systems level, plays a crucial role in the interpretation of high-throughput experimental datasets. A widely neglected challenge in pathway analysis relates to the handling of multifunctional genes. I therefore developed SIGORA, a novel pathway analysis method that identifies genes and gene-pairs that are unique signatures of a pathway and examines their over-representation in a given list of genes of interest (e.g. the list of differentially expressed genes in an infectious condition). With several biological datasets, SIGORA outperformed traditional methods, delivering biologically more plausible and relevant results. This was also reflected in significantly lower false positive rates for simulated datasets. An additional challenge in high-throughput dataset interpretation concerns the lack of functional annotation for many genes. The guilt by association (GBA) principle was applied in a conservative manner to a large tissue expression dataset (105 Tissues, 13000 genes) to infer gene functions from co-expression data. Overall, 180 previously un-annotated bovine genes were assigned a putative function by this approach. In 20% of the cases, the inferred function was additionally supported by literature in other species. microRNAs are emerging as important innate immune response regulators and as biomarkers of disease. Determining microRNA functions requires the identification of their targets, yet computational prediction of such targets is challenging. As part of a group investigating microRNA roles in bovine mastitis, I used a combination of prediction tools to compile a list of likely targets. Here, the overall emerging picture (including pathway enrichment) is consistent with our current understanding of this condition. Collectively this work provides new tools and insights that may more broadly be used to improve systems-based analysis of bovine and other mammalian responses.