Integrated analysis of antifungal innate immunity in C. elegans – ELEGINN

In recent years, the nematode C. elegans has been increasingly used as a genetically tractable model for the dissection of host-pathogen relationships. We have focused on the interaction between C. elegans and the obligate fungal pathogen Drechmeria coniospora to address the question, “How does an animal without an adaptive immune system respond to infection”? Our work has been divided into 2 complementary areas, focused genetic and cell-biological dissection of specific signalling modules, and functional genomic and computational approaches to reconstruct a global innate immune network.
Spores of D. coniospora attach to the nematode cuticle and infect C. elegans through its epidermis. The host innate immune response is characterised by the rapid induction of antimicrobial peptide gene expression in the epidermis. We have identified a trigger for this response: infection leads to an increase in the amount of a specific tyrosine derivative that activates a receptor expressed on the epidermal cell-surface. How pathogen invasion provokes this increase is currently unknown. Here, we propose to undertake a focused genetic investigation of this question, to decipher the very first steps in the innate immune response.
Our previous studies have revealed a large number of genes that participate in transducing the signal from the cell surface and mediating the expression of defence genes. While most of the corresponding proteins are conserved in other species and have well characterised functions, for many we have little or no idea of how they modulate the immune response. To deepen our understanding of this process, we propose to undertake biochemical and structural studies of these signalling proteins of unknown function, selected primarily on the basis of their conservation in parasitic nematodes.
In addition to the signalling that occurs within the epidermis, we recently found an important role for cross-tissue signalling in the immune response that we wish to investigate. Disruption of mitochondrial homeostasis in the nematode intestine suppresses the capacity of the epidermis to express antimicrobial peptide genes. The underlying mechanism is currently completely obscure. We propose to conduct a genetic suppressor screen to identify the genes involved in this coordinated response to stress.
There are numerous examples of pathogens subverting host innate immunity. Studying these virulence strategies has proven to be a powerful way to understand key points in defences. We have now developed D. coniospora as a genetically tractable model. We have a high-quality annotated genome and tools for editing its genome. This allows us to propose to initiate a new research direction, the characterization of fungal virulence mechanisms. We aim to take complementary biochemical and genetic approaches to uncover examples of how the fungus overcomes specific host defence mechanisms. We have already uncovered one case of a fungal protein that is potentially capable of interfering with an innate immune effector. It will serve as a test case for our work. Again, here, we wish to extend our analysis to the structural level, and propose to determine the precise molecular nature of the interference for a limited number of pathogen-host protein interactions.
By pursuing these aims, we will build a more complete picture of C. elegans immunity and identify key points in its defences. In the long term, these could be exploited to find new ways to kill parasitic nematodes that represent a heavy burden to human health. The project also promises to give insight into mechanisms of fungal virulence and might ultimately be used to help fight fungal disease in man.