[
International Worm Meeting,
2021]
Animals have evolved extensive immune pathways to combat the myriad of pathogenic microbes they encounter. Conversely, pathogens have evolved many mechanisms to exploit their hosts. To understand how Nematocida parisii, a natural microsporidian pathogen of C. elegans, infects its host, we performed a forward genetic screen to identify mutant animals that had a Fitness Advantage with Nematocida (fawn). All three fawn isolates produce progeny at high levels, are less infected than wild-type animals, and contain mutations in T14E8.4. This signal peptide containing gene is expressed in the pharynx and intestine. Expression of T14E8.4 in the intestine of T14E8.4 animals restores N. parisii infectivity, which is dependant upon secretion. Resistance to N. parisii infection in T14E8.4 mutants is developmentally restricted to the L1 stage and results in decreased parasite invasion. N. parisii spores in T14E8.4 animals display improper orientation in the intestinal lumen, indicating spores are firing incorrectly. Interestingly, T14E8.4 expression is upregulated by both N. parisii and Pseudomonas aeruginosa infection. T14E8.4 mutants display both increased susceptibility and colonization from P. aeruginosa and over expression of T14E8.4 reduces P. aeruginosa colonization. Competitive fitness assays show that T14E8.4 mutants are favoured in the presence of N. parisii but disadvantaged on P. aeruginosa. Furthermore, C. elegans wild isolates don't possess predicted loss of function mutations in T14E8.4. Together, this work demonstrates how microsporidia exploits an antibacterial immune protein to facilitate host invasion. The opposing fates of T14E8.4 mutants on different pathogens highlights a central role in infection and immunity.
[
International Worm Meeting,
2019]
The evolutionary arms race between pathogen and host has been a topic of inquiry for many years. Of particular interest, is that between microsporidia and their wide variety of hosts. Microsporidia are rapidly evolving, obligate intracellular fungal-like parasites with the smallest known eukaryotic genomes and remarkable host specificity. They have detrimental effects on many commercially and ecologically important species and have been associated with lethality in immunocompromised individuals, placing them on the NIH's list of priority pathogens. However, the mechanisms by which these parasites cause disease in their hosts is still widely unknown. Due to the lack of available tools to study microsporidia, the genetically tractable model organism Caenorhabditis elegans provides an excellent opportunity to study a nematode-infecting species of microsporidia, Nematocida parisii. To identify mechanisms by which C. elegans can prevent infection, we performed a forward genetic screen to identify mutant animals that had a Fitness Advantage With Nematocida (fawn). All three fawn isolates produce progeny at high levels and are less infected than wild-type animals. To identify the causative gene we performed whole genome sequencing and mapping using Molecular inversion probes (MIPs) and saw that all three fawn mutants contain different loss of function alleles in the same gene, T14E8.4, on the X chromosome. To understand how loss of this gene provides resistance against N. parisii, we tested infection on different stages of animals, determining that resistance is developmentally restricted to the first larval stage (L1) of growth. In addition, through a pulse infection assay we determined that these mutants are initially less infected than wild-type leading us to hypothesize that there may be an invasion defect, compromising the ability of N. parisii spores to invade their host. Work is currently underway to investigate the expression pattern of this gene, and uncover the molecular mechanism of how it is involved in microsporidia infection. Through this project, we expect to uncover novel strategies by which these fascinating parasites are able to successfully invade and propagate inside their hosts, and how hosts in turn are able to prevent infection.