The Functional Significance of Allelic Diversity in Candida Albicans
Thesis or dissertation
University of Exeter
Allelic expression imbalance, or AEI, is the term given to differences in the expression levels of the two alleles of a gene. AEI has been previously identified in a number of species using various techniques. Here, the genome-wide extent of allelic expression imbalance in the pathogenic yeast species, Candida albicans, was examined through use of RNA sequencing in combination with a novel computational pipeline based around the diploid reference genome. Techniques for validating these results were investigated, and the difficulties surrounding specificity and quantification are discussed. As C. albicans is a highly heterozygous species, it was hypothesised that polymorphisms within alleles lead to differences in allele expression, which are further linked to differences in allele function. The functional consequences of AEI were therefore interrogated through investigation of Gene Ontology, identification of condition specific responses in AEI, and targeted construction and phenotypic screening of heterozygous knockout strains. Together, these results strongly suggest that divergence in allele expression is not linked to differences in allele function. Investigations of the possible control mechanisms behind the differences in allele expression were considered, with a focus upon structural factors such as chromosomal location, GC content, allele length and codon usage. However, issues with establishing causality are present, and difficulties lie in distinguishing between functional differences and consequences of bias in sequencing technologies. This piece of research has advanced the understanding of gene expression mechanisms within a medically important pathogen, paving the way for further investigations into the functional consequences of allelic expression imbalance in Candida albicans.
PhD Biological Sciences