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Using C. elegans To Identify A Sex-Specific Behavior

Join us for episode 62 of 17 minutes of Science as we talk with Dr. Jagan Srinivasan from Worcester Polytechnic Institute about his recently published paper using C. elegans to identify a sex-specific behavior.

Dr. Srinivasan describes himself as an academic nomad! He did his undergraduate studies at the University of Chennai, majoring in Zoology and Chemistry, followed by a Master’s in Marine Biotechnology at the University of Goa.

He then worked as a research assistant in a Biophysics lab for a year at University of Pune before leaving the country to go to Germany for his PHD which he did in Animal Genetics at the Max Planck Institute of Developmental Biology in Tuebingen Germany. For his  postdoctoral research, Jagan worked at Caltech, Pasadena CA in Neurobiology. Today Jagan is an associate professor at Worcester Polytech Institute in Massachusetts. 

Transcript

Hannah Huston (Host): [00:00:10] Hi there and welcome to 17 Minutes of Science, our show that explores the world of science and how it affects both the starting academic and the seasoned professional. I am Hannah Huston and today I am joined by Dr. Jagan Srinivasan. Dr J, as he is lovingly called by his students, describes himself as an academic nomad. He did his undergraduate studies at the University of Chennai, majoring in Zoology and Chemistry, followed by a masters in Marine Biotechnology at the University of Goa. He then worked as a research assistant in a Biophysics lab for a year at the University of Puna, before leaving the country to go to Germany, where he did his PhD at the Max Planck Institute in Animal Genetics. For his postdoctoral research Jagan worked at Caltech Pasadena in neurobiology. Today, Jagan is an Associate Professor at Worchester Polytechnic Institute in Massachusetts. So welcome. We are very excited to have you joining us today on 17 Minutes of Science, um, and I was wondering if to start you could just tell us a little bit more about the research that you do.

 

Dr. Jagan Srinivasan (Guest): [00:01:23] Great. Thank you for having me. Hannah, it’s a pleasure. As I said, you know, one of the aspects of science that I really like is meeting new people and exploring new connections, and this is an excellent way to do that. So thank you so much for having me. So our research is what I like to call in a very fancy way ‘Systems Neuroscience,’ which is: we try to look at a problem from various angles. We start all the way from the 50,000 foot view of how the brain is functioning all the way down to how a single gene within a single neuron is functioning. So our interpretation of systems neuroscience is basically we are going through different levels of complexity within the organism to try and unravel the mysteries of the brain. I think, simply put, you know, we love to do everything that we can to address the problem in our wonderful model system.

 

Hannah Huston (Host): [00:02:16] And the model system that you use is one that we at InVivo Biosystems know and love as well – the C. elegans. So have you always used C. elegans in your research? And if not, what other models have you worked with?

 

Dr. Jagan Srinivasan (Guest): [00:02:32] So Hannah, my association with Worms goes back more than 21 years when I first came to Germany to do my Ph.D.. And originally I started in the neurobiology lab there, in the Max Planck Institute working on Axon Guidance. But within the first couple of years, my supervisor decided to explore options in the industrial arena, so I had to restart my Ph.D.. So my actual Ph.D. work started with another nematode -so I’m a wormy through and through – another nematode by the name of Pristionchus pacificus which is a satellite model system to understand the evolution of processes and evolution of behavior. So I worked in Professor Ralf Sommer’s lab at the Max Planck Institute of Developmental Biology. He is an evolutionary biologist by training, he worked on various organisms, including the beetle called tribolium, but for his own lab, he worked on this model system, which he also worked in Caltech, Pasadena and Professor Paul Steinberg’s lab. So we we were like F1 and F2 in terms of lineage within the worm field. And my first work was all about genomics. How do we establish a genomics perspective in this model system? Because little was known at the time when I started my Ph.D., so as one of the students was interested in how to marry technology with the biology of a model system, that genomics provided the excellent opportunity. And you know, it was really, I like to say it. It came together very well that we were able to describe what we wanted to do, and also achieve it, in my PhD thesis. Because normally what you state, you want to do in your PhD to what actually happens is like a huge big gap. But in my case, it was one of those cases where, and I feel very lucky and grateful both, for not only being able to – be a pioneer of genomics at that time in Pristionchus, but also having the opportunity and the infrastructure to be able to answer those questions. So that’s basically my background is I’ve only worked on worms, I’ve always wanted to work on other systems. But you know, something about worms keeps me back and I think I have no regrets.

 

Hannah Huston (Host): [00:04:55] That, tat’s wonderful. So you definitely had a little bit of a winding way to get to C. elegans, but you’ve stuck with them. And so why are C. elegans well-suited for the research that you do?

 

Dr. Jagan Srinivasan (Guest): [00:05:09] So, you know, to give you a very simplistic answer, they are very amenable to the question you are wanting to address, right? Whether it be a question on genetics – C. elegans has been a perfect model system for genetic screens, whether it be a question in neuroscience, where you really want to understand the biology – cell biology, the physiology of a neuron, you can address it, or you can just take the whole organism and study the behavior. So for our kind of systems level perspective that we kind of tried to envision for our lab, it serves all of these layers very nicely. We can do a genetic screen to find out a behavioral defect. We can then go ahead and clone the gene and then reintroduce the gene in the genetic background, mutated background, and rescue the phenotype. So. The breadth of questions that you can answer with C. elegans is just amazing, right? A new project that we are kind of delving into is the role of natural metabolites obtained from plants, and what we are trying to look at is just does the worm behave with – to these metabolites. And what we are finding is it’s the perfect testing platform for anything new. So I think C. elegans – I’m not saying other organisms are not as good, but the good amenability, this fast generation time, the ability to do multiple experiments at the same time really affords us to kind of, you know, be at the forefront of the research questions that we are asking.

 

Hannah Huston (Host): [00:06:48] Yeah, and we, we love C. elegans here at InVivo Biosystems for many of those same same reasons that you mentioned. So, you recently published a paper using C. elegans to identify a distinct neuropeptide-receptor molecule that regulates a sex specific behavior to pheromones. Can you tell us more about this study?

 

Dr. Jagan Srinivasan (Guest): [00:07:12] Yeah. Hannah, thank you for asking that question. I like to first try to give credit to the person who actually did the work. It’s my, it was my former graduate student, Douglas Reilly, who’s right now a Postdoc working on songbird behavior right now. So he jumped from worms to songbird learning. But the idea came about for this particular paper is a very interesting story, so I’m going to take a couple of minutes. So normally I don’t allow my students to work on weekends because I feel that there should be good work life balance. But there was this one experiment that I felt we were doing a completely different experiment, and I said to Doug, I said “Doug, this experiment is not going to work.” And he’s like, “I’ll bet you a beer it will work.” And the experiment was the basic essence of the paper that we published there, and he was the first one to have actually identified taking a neuropeptide gene which expresses multiple neuropeptides, took each and every individual neuropeptide, cloned it into a bacterial construct. And when he fed the worms – the mutant worms – with this phenotype, he was able to rescue some of the phenotype. Right. And its experiments like this that actually happened on the weekend or on times that you’ve never imagined that basically spawn a whole new area of research for the whole lab. So in this paper, what we came about from the labs big mission statement was we are looking at how is olfaction affecting sex specific behaviors in worms? So we’ve isolated a group of pheromones, as you told before, during my postdoctoral work. But in some of these pheromones, actually in males, but not in hermaphrodite or female worms, right? As we like to call – female worms are called hermaphrodites because they produce both the eggs as well as the sperm. So Doug had this mutation wherein he found that the male’s response to that particular pheromone, which is completely from attraction to aversion. In hermaphrodites, that queue is aversive, in males, the cue is attractive in the normal state. But when you mutate this gene, the attraction changes to a aversion. And he like this is a cool phenomenon because what is happening here is we are able – there seems to be a single switch that changes the attractive behavior to an aversive behavior. Now, science isn’t as simple as it looks, or it seems at the end of the experiment, so he’s like, I just want to understand which, which neuropeptide on this particular gene is required. So painstakingly, what he did for six months turned out to be this beautiful experiment wherein he had to clone this individual peptide in a bacterial construct. And when he fed one of the eight peptides, he found rescue of the attractive behavior. When he fed another peptide, he found attraction and aversion. Both were rescued. So his work showed that what we see at the behavioral level is a sum total of all the neuromodulatory events that happened before the actual behavior is enacted. So he actually gave us a circuit level glimpse of how peptidergic modulation happens. And that’s why this paper was accepted at Communications Biology, and it was very well received by the reviewers. So we are very lucky. But as I say, when I give a talk about this, I always say the talk is not about neuropeptide signaling, but how a PI lost a bet of a beer with his graduate student, and I’m very happy to have lost that bet.

 

Hannah Huston (Host): [00:10:57] That’s a great story, though, too. But that’s fascinating. So in this study, did the response that you found, did that align with what you were expecting to see?

 

Dr. Jagan Srinivasan (Guest): [00:11:11] No. The short answer is no, because you know, when you do a back of the envelope prediction on all of these things you want – there is a very streamlined way with which every scientist thinks, or at least I like to think that every scientist has their own mindset about it and the way I was looking at it was: it cannot be a single peptide switch. It can’t be as simplistic as that, right? But when you look at the result, and now what we are trying to do, we have a couple more graduate students who are kind of working on the project. You know, at the surface, it looks like a simple switch, but the switch is not on in every neuron. It’s only on in certain neurons at a certain developmental time stage. So what we are now trying to understand is – why is this timing happening? What is the mechanism of this timing? So the surprise was that it was a single neuropeptide. The beauty of that surprise is that it spawned a whole new area of work wherein we are now trying to look at how that peptide is acting over the developmental time course of the organism. And what all does it modulate? Does it only modulate this phenomenal response or does it modulate other things? So one critical experiment has spawned this whole new area of research wherein we like to call us like how is modulation of the nervous system happening over time? And very few labs outside of the worms have actually studied it, so we believe, like we are at the forefront of this particular area of research. And we hope to find some very interesting results as time goes by.

 

Hannah Huston (Host): [00:12:51] What an exciting area to be in.

 

Dr. Jagan Srinivasan (Guest): [00:12:53] Thank you.

 

Hannah Huston (Host): [00:12:54] So in this study, you are seeing a sex specific response, yet you use C. elegans, which, as you mentioned earlier, can be either males or hermaphrodites.

 

Dr. Jagan Srinivasan (Guest): [00:13:04] Yeah.

 

Hannah Huston (Host): [00:13:05] How can you accurately identify that this is a sex specific response without the use of a female model?

 

Dr. Jagan Srinivasan (Guest): [00:13:13] So the idea, and I think this is something that we face a lot of flak from reviewers of our grant applications is the hermaphrodite is not a female, right? And to a certain extent, that is a valid argument. But we now have tools within the worm community wherein what we can do is we can masculinities or feminized – we can change the genetic sex of each and every tissue involved. And we are currently collaborating with an amazing scientist from University of Rochester, Professor Doug Portman, who is basically one of the leaders in the field of the role of genetic sex in behavior and C. elegans, right? So. What – Doug’s experiment prompted him to give a talk at the International Board meeting that is held every other year and Doug Portman basically came to us after the meeting and says, “I have an experiment for you that a potential reviewer is going to ask.” And I’m like “Doug, it’s eight, eight p.m. You know, we’re all tired. It’s been a long day.” I was just heading to, you know, either my hotel room or to a bar. And he’s like, “No, let’s just sit down and talk about it.” So we got the experimental idea from Doug, Professor Portman, but when Doug did the experiment – it was really nice – so what he found out was, when he feminized the males, he didn’t lose the attractive response, because we thought, you know, it’s hermaphrodites do not have the active response, but when he masculinist the herms, he got the attractive response. So what it showed was that the sex of the nervous system dictates what kind of pheromonal response it should be. And that is something new. Now, that’s what we are trying to continue now, along with a new graduate student, is: why is it the sex of the nervous system that is determining this particular sex specific thing? So, in terms of answering the question about ‘is hermaphrodite a real female?’ No. But if you are able to change the genetic sex of the nervous system, we are able to get a completely opposite response. Therefore, we believe that the C. elegans hermaphrodite is a good model system or is good for us to be able to address those questions, right? Because it does produce the eggs before it produces the sperm.

 

Hannah Huston (Host): [00:15:36] Oh, wow, that is, that is so fascinating. So we have about two minutes left, and I wanted to ask, so in this study, you use a novel paradigm of neuropeptide rescue that you established. Can you tell us more about what this is and how you established it?

 

Dr. Jagan Srinivasan (Guest): [00:15:57] So and I think, as I said, this is the, this is where I give Doug Riley the credit for actually believing in this experiment because he was going through literature and he found this very nice paper from a group in China that basically said spider venom to C. elegans using bacteria in the bacteria that the worm eats. So he basically what they did was they transformed the bacteria with this particular spider venom and what they found out was that worms got paralyzed or worm egg laying behavior was affected. So when Doug presented this at a lab meeting and he’s like, I would like to pursue this, right? I’m like, Doug, there are too many different variables. So what he did was he contacted that lab, established a connection with that PI, got the construct, put in our neuropeptide in it and, just like the field of RNAi, what we really felt was the worm is basically eating the bacteria, processing that peptide through the intestine and then spreading it to the different tissues. So it’s kind of like an RNAi like technique, but for peptides now. And that is the new novel thing that we have currently actually applied for a patent. Our school is trying to apply for a patent and we are looking in for potential partners because this technology seems very similar to RNAi. But in RNAi there is knockout of gene function, wherein we are doing is rescue of gene function. So the effect is opposite, but the mechanism seems to be relatively mediated by RNA in both cases. So we would really like to know what is the mechanism, and I’m trying to write more grant applications to try and tease out that.

 

Hannah Huston (Host): [00:17:39] Well, that was perfect timing because our timer just went off. So –

 

Dr. Jagan Srinivasan (Guest): [00:17:44] Thank you.

 

Hannah Huston (Host): [00:17:47] Thank you for the wonderful answers and conversation that we had today. It was so lovely to have you join us on 17 Minutes of Science, and I look forward to following your research more and seeing where it goes in the future.

 

Dr. Jagan Srinivasan (Guest): [00:18:02] Thank you for the opportunity, and it was a pleasure meeting and talking with you.

 

Hannah Huston (Host): [00:18:06] Well, thank you, everyone, for tuning in today to 17 Minutes of Science. We will see you next time.

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