A case of fatal attraction now, and a gene that enables a nematode to track down a species of oriental beetle using the beetle's sex pheromone. Intriguingly, the gene that the nematode uses also protects it from what is otherwise a toxic effect of the pheromone. Jessica Cinkornpumin is at California State University, Northridge.
Jessicca - The nematode we study is Pristionchus pacificus, and it's specifically attracted to a sex pheromone released by the beetle called, ZDTO. We wanted to study how this interaction actually occurs in a genetic level. We know that the chemical is released by the beetle and the nematode senses it with these neurons that are in their head, and when they sense this pheromone they actually stand up and they are able to actually hop on to the beetle and live on the beetle until the beetle dies. And this is when they actually emerge again and are able to reproduce.
Chris - The big question then is - Well. How are they actually doing that sensing?
Jessica - We don't know. So, we try to identify this gene and how we did it was, since we know that the nematode is very attracted to the pheromone ZDTO, there's a screen to identify Pristionchus pacificus nematode that doesn't sense ZDTO specifically.
Chris - How clever. I'm anticipating then what you're going to say to me is that by looking for a nematode that doesn't do the sensing, you're assuming there must be something missing genetically from that nematode strain. And if you can find out what's missing, that tells you what the gene is that does the sensing normally.
Jessica - Yes. And I think I want to emphasize that the reason why we did the screen this way is because we want to find a gene that's really responsible for seeking hosts and not a gene responsible for just sensing in general, so that we can study this relationship.
Chris - And how did you know that that's what you were going to get when you did this study and you weren't just exploring genes that might abolish the behaviour in some other way?
Jessica - So, we did take the nematode that we study that is missing the attraction to ZDTO and then tested it with all these other pheromones or signals that it's also attracted to, and we found that it's really, really specific to ZDTO.
Chris - Which tells you that gene must be responsible for picking up that signal?
Jessica - Yes.
Chris - Did you then do the obvious experiment which is to take the missing gene from the nematodes that have it or the gene product and put it into the one that doesn't, and prove that you can restore that behaviour?
Jessica - That's exactly what we did. We made a functional copy of the gene and this working copy was then injected into the nematode that lacked it. After it grows and produces its eggs, these eggs actually had the gene rescued.
Chris - Thus, proving that it really does work?
Jessica - Yes.
Chris - Why is this important? Because, yes, it's nice you've got this gene; you've identified how these nematodes track down this beetle target using one of its own pheromones. But what are the implications of this finding, apart from its academic interest?
Jessica - Well, I think, especially since we identified this one gene to do two things. One, sense; and one, protect it from the same attractant, this pheromone ZDTO. This indicates to us that there are many genes and interactions we still don't even know, and when we understand this interaction much better, we can actually use this information that we know to study how parasites also find their host and use that in a, maybe, agricultural sense and use it to protect agriculture from the harmful effects of these pests.
Chris - When you say that the gene can protect the nematode from the beetle, explain how that works a bit. Would the pheromone normally be poisonous, or in some way destructive to the nematode then?
Jessica - Actually, this is very new to us. We actually didn't expect to find this so we are really interested into looking into this more, but as we know so far, nematode that doesn't have ZDTO and is exposed to the pheromone, gets paralyzed by the pheromone.
Chris - Do you have any idea how the gene is doing the protection?
Jessica - We think it's a lipid binding protein that actually responds to the pheromone. So, we either think it actually carries a pheromone to a receptor that does some downstream effects - either protecting or sensing since it does two things, or that it actually works in a function of removing the pheromone from the receptor so that it can continually have another pheromone bind the receptor. And we think somehow, this binding and the downstream effects is how it will protect or sense the ZDTO.