Anti-Fungal Innate Immunity in C. elegans – FUN-EL

The starting point for our studies is genetics: observing the effect of inactivating a gene on the capacity of the animal to mount an innate immune response. Today, we can individually inactivate each of the nematode’s 20,000 gene. We combine this approach with microscopy, cell biology, and the study of the factors that allow a pathogenic fungus to overcome host defences.

On the host side, we’ve discover a new way that infection is sensed. We will see whether this also works in humans. On the pathogen side, we’ve managed, for the first time, to make transgenic fungus. This is an important step forward for our future projects. As a consequence of this work, we’ve set up new collaborations in France (with an INRA lab and with bioinformatics experts) as well as abroad (with chemists at Cornell).

An important part of the project concerns the integration of biological data. This requires the development of novel methodologies that will be potentially useful in other areas of biological research. In the long term, underdstanding host-pathogen interactions may lead to new therapeutic approaches or the development of new antibiotics.

The FUN-EL project was presented in talks abroad (Innate Immunity 2012: from Evolution to Revolution, Sorrento, Italy; at the Karolinska Institute, Stockholm, Sweden) and in France (EFOR conference, Paris).

In layman's terms, this project addresses the question of what happens in an animal when it is infected by a pathogenic fungus: how can it resist succumbing to an infection, and what are the weak points in its defences? We work with a relatively simple animal, Caenorhabditis elegans, a nematode worm widely used by scientists to study the development and function of living organisms. In addition to being transparent, so we can follow what is happening inside, it is technically very easy to turn off or turn on a gene of C. elegans and to analyze the biological consequences of this manipulation. And on the pathogen side, we use fungi that naturally infect worms, against which worms have developed robust defences.
Up until now, we’ve focused most of our attention on identifying the different components, the genes and proteins that are called into play when a fungus invades the worm. As we want to understand how C. elegans defends itself, what we need to do now is put these pieces together, and we also need to look at different scales. So we want to look inside cells to see where and when different genes and proteins act. We’ll need to develop new tools to let us follow the progression of the infection. We can do this by putting a fluorescent protein (GFP) into the fungus. And we’ll tag the different organelles in the cells (such as the nucleus and the mitochondria), to see how they move when the fungus sends its hyphae into the worm. We will also look directly at the animals, measuring how fast they move, how well they eat, etc. Putting these pieces together will give us a complete picture of how the worm reacts to infection.
At the same time, we do need more knowledge on how the different proteins that we have already identified actually work, especially as some are only found in nematodes and have never been investigated functionally before. Again, this will contribute to a better understanding of what is important for defence.
Most of our work has been based on the investigation of one particular branch of defences in C. elegans, leading to the production of an antimicrobial peptide (NLP-29) that can kill fungus. We’ve found that another antimicrobial peptide (CNC-2) is controlled in a distinct manner, but for the time being we only have the outline of its regulation. We propose to conduct a thorough investigation of how CNC-2 is regulated, through large-scale forward and reverse genetic screens.
We’ve also discovered that when C. elegans is infected by different fungi, it doesn’t necessarily respond by making the same collection of antimicrobial peptides. We would like to investigate this in more detail, to understand what differentiates the signalling processes that are triggered by different pathogens.
By advancing on these fronts, we will build up a much more complete picture of how C. elegans defends itself against fungal pathogens. In doing so, we expect to identify key points in its defences. We think that in the long term, these could be exploited to find new ways to kill nematodes. That is important as there’s an urgent need to find novel drugs to counter the many parasitic worms that ruin crops or lead to debilitating disease in humans. And we also hope that this study will shed light on defence mechanisms that are also present in humans, so that this knowledge might ultimately be used to help fight fungal disease in man.