Characterising microsporidian host-parasite interactions

Abstract

Microsporidia are an enormously successful group of obligate intracellular fungal parasites that infect most eukaryotes including humans. In my thesis I have analysed and compared microsporidian genomes to identify which genes have been conserved, and which lost, during the transition of the group to parasitism, sequenced the transcriptome of a mixed infection of Trachipleistophora hominis in a rabbit kidney cell line, and provided a description of the T. hominis intracellular lifecycle. My results demonstrate that microsporidian genome evolution is extremely dynamic; with huge loss of genes in the microsporidian common ancestor balanced by group and lineage-specific gene family expansion and innovation. Genes that are conserved among microsporidians are generally expressed at higher than average levels in the transcriptome of T. hominis. Lineage-specific genes show greater variation in expression, but some are very highly expressed suggesting that they play important roles in T. hominis biology. The transcriptomics data for T. hominis confirmed that it contains one of the largest microsporidian genomes in terms of gene content and also identified previously unannotated genes, some of which may have important roles in the parasite. Detailed analysis of my gene expression data demonstrated that differential expression of duplicate genes is a general feature of T. hominis gene families, including nucleotide transport proteins that are already known to have important roles in the microsporidian lifestyle. A method for partially synchronising the T. hominis infection was established and used to investigate the development of the infectious cycle using light microscopy and antibodies to T. hominis proteins. My observations suggest that the infection proceeds in a reproducible and predictable pattern under the experimental conditions used; providing a tool for future detailed study of how T. hominis infects and exploits eukaryotic host cells.