Episode 14: Susana Lima, PhD

The following interview was conducted in-class, during the Fall 2021 session of Hidden Figures: Brain Science through Diversity, taught by Dr. Adema Ribic at the University of Virginia. What follows is an edited transcript of the interview, transcribed by Cornelius Smith, Delaney Sears-Webb, Jamil Abed, Julia Miao, Catherine Johnson, Evalyn Kim, and Sarah Lee, who also drafted Dr. Lima’s biography. The final editing was by Dr. Adema Ribic. The original recordings are available in Podcasts.

              Dr. Susana Lima is at the Champalimaud Center for the Unknown in Lisbon, Portugal. During her Ph.D. in Giero Miesenbock’s lab, she developed the first optogenetic method for the control of behavior in a freely moving organism. She completed her postdoctoral training in Tony Zador’s lab at Cold Spring Harbor Laboratory, where she developed an optogenetic tool for identifying neuronal subtypes in vivo. Dr. Lima moved to the Champalimaud Center in 2008 and continues to explore neural circuits that drive different behavior, with a focus on sexual behavior and mate choice.

Dr. Lima, what was your childhood like?

I was born in the Azores Islands, a small group of islands in the mid-Atlantic; it's almost the only group between Europe and the United States. When I was very young, I moved to Northern Portugal and was raised near Porto City, Portugal’s second city and where I spent most of my life. I come from a very traditional Portuguese family; I lived in my parents’ house that was close to my grandparents’ house and my uncle's, so we had this very close family connection. I went to school there, near my place -- both middle school and high school. I stayed in Porto afterward, so I continued living with my parents until my last year of college.

What got you interested in science?

To be honest, I was always a very good student and really liked that. It's nice when you're a good student and all your family's especially happy; you get a lot of positive reinforcement from that. I always liked learning, but there was nothing in particular that I was actually very fond of. Back then, I guess I always liked biology and science. Many people asked me, “Did you want to be a scientist from the beginning?”, and I said “No.” I think I only really decided that I wanted to be a scientist in the last decade or so, and for me, it's been kind of an interesting process. The reality is that it isn’t always that straightforward. Even once I got older, especially when I moved from high school to college, I still had no idea what I wanted to do. So, I tried to go with what gave me the most flexibility. My interest was always related to the natural sciences: I could be a doctor; I could be a veterinarian; I could be a biologist; I could be a bunch of things. I ended up going for a biochemistry degree, which was new in Portugal. I found research, in particular, to be vague enough yet still exciting. So that’s me now; I am a biochemist.

What made you decide to pursue a Ph.D. program?

When I was 22, I had a boyfriend at the time and really wanted to stay in Porto because we had an idea to get married and have kids, so everything was kind of laid out for me. Then my father forced me to apply to a project abroad during the last six months of my college, even though I really didn't want to go abroad. I was super shy and had my life there; I didn't want to go. I was so scared that my parents drove me all the way to Amsterdam, so I moved to Holland and never came back. It was very intense and not always pleasant in the beginning, but I understood that there was an outside world and I had never experienced it; I guess I was just a little scared of it. I ended up staying there for nine months -- my projects got extended for a couple of months and I was doing heat shock in yeast. We were trying to understand what kind of genetic program is activated when yeast is exposed to heat shock and how it responds. I got very nice results, and once I finished that I was like “Okay, I want to continue,” and I decided to. I had just really loved the life in the lab discussing science all the time.

Can you describe your application process and how you chose your Ph.D. lab?

Again, I didn’t care so much about what I was going to do. I know this might be shocking for some people because our students get here now and have very strong ideas about what they want to do. I always keep on saying to relax; some people are like that while some are like me, and there's everybody in between. I applied to 3 Ph.D. programs: two in Holland, one in Portugal. I was going to do something related to biochemistry and this program in Portugal was kind of a dream come true for me. Portugal had a dictatorship until 1974 and it took us many years to come to the level of development that we have today. Especially science-wise, there was not much going on; in neuroscience, there were not many labs or research going on. In the early 90s, a Portuguese immunologist who made many important discoveries in the field of immunology abroad returned to Portugal and wanted to shake things up. He started his first Ph.D. program in Portugal and I was a part of it.

What was that new program like?

I started in 1999, with 16 other students. For one year, we had classes on everything that you can imagine. I remember we started with bioinformatics, then onto protein crystallography, and evolution and development. For every course, there would be people from abroad that would come and teach; it was amazing. In our class, there was an economist, a mathematician, a bunch of biologists, and some biochemists, like me. We were exposed to some of the most famous scientists: we had Nobel Prize winners come to teach us. At that point, when we started, they didn’t want anybody that knew exactly what they wanted to do in the beginning. They wanted people to be open-minded. In the end, we had to come up with a scientific question we wanted to address, find wherever in the world that was working on the question we were interested in researching, and then move there. We had 4-year funding to work in any lab abroad. The main goal was to send Portuguese students abroad, do their postdocs, and then one day have them come back home and start their own labs. The Ph.D. program ended up being very successful, not just because people were trained, but because we established a lot of networking that didn’t exist.

How did this program help you decide what you wanted to research?

At the time, there was no neuroscience being taught in this course. There was one person from the program that thought it should be taught so they started the first course, but it was optional. I decided to take it because when would I have neuroscience in my life again? For two weeks, I had an amazing time. We were learning about the development of the nervous system, motor control, and plasticity. Because of this, I searched labs that researched evolution and development. Again, there was no real direct route that took me to where I am, but this is how I got excited about these two fields.

Why New York?

I really, really loved science but wanted to go to an exciting place as well. I ended up taking a neuroscience class with a neuroscientist named Erich Jarvis. The week before he came, I was watching a movie with my roommate that was filmed in New York and thought of how cool it would be to live there. Jarvis used to be a dancer at the school where this movie was filmed. We had a party at our place and he came, and I was really amazed by his dancing. We started talking and he explained how he was a scientist and a dancer, and I decided that I was going to go to New York. I interviewed in New York with three labs working in evolution and development, and I ended up at Memorial Sloan Kettering.

What made you decide to work with Gero Miesenboeck?

Gero’s ideas were some of the smartest ever. For example, we know that when neurons are activated, the action potential travels down the axon. When you go to the axon terminal, you have vesicles fusing and releasing the contents into the synapse. So the pHs of the vesicles, when the vesicles are closed and inside the neuron versus when they’re open and fuse with the membrane, are different. What he did was he put the GFP that was pH-sensitive inside the vesicles, so that it’s not very fluorescent before the neurotransmitter is released. When the vesicles fuse and open, it becomes bright green. This means that you could now look at neurons being active and releasing neurotransmitters onto the postsynaptic target. It’s so cool because now you can put this as a genetic element into the DNA of a fly, for example, and you can see all the neurons that respond, how they respond, and what is released to the downstream target. So I was super excited to be able to follow how information is transmitted from station to station, and that’s what I came to Gero’s lab to do. I did a lot of work with genetics and photon imaging.

How did you choose your topics to research?

When I joined the lab, it was his other that got me even more excited. His idea is what nowadays is called optogenetics. He thought that it’d be cool if you were able to control the activity of some neurons and follow what comes after, due to the activation of a single neuron, for example. We figured that because an action potential can be triggered in a millisecond, we would need something very fast in order to activate a single neuron. He proposed that we should use light in order to trigger neuronal activity. We have receptors that naturally receive light in our eyes: opsins. We thought, let’s take the machinery from our eyes and put it into neurons that normally do not respond to light. In this case, what they decided was to take the rhodopsin, G protein in a resting state, and put it into “hippocampal neurons” -- this was the first paper he published. Now essentially, you shine a light, and neurons start firing.

So what did you end up doing?

For years, I tried to do the same, but in a fruit fly. After creating 50 different transgenic lines, I thought of trying something else. There’s a bunch of receptors in our brain that respond to ATP called P2X2 receptors. The fly doesn’t have these receptors, so we introduced them into the fly through genetics and used ATP to activate them. We used a photo-sensitive form of ATP to control the neuron activity with light (optogenetics).

Can you tell us more about your research?

Have you ever tried to catch a fly? Even if there’s no air displacement, there are differences in light that they can detect. These things are usually activated by a giant fiber which is an escape system activated by really strong stimuli, like strobe lights. Essentially, there are scary stimuli and the fly responds by jumping, extending the legs, and flying. It’s caused by two neurons in the head of the fly, one on each hemisphere, which are really big neurons that send synapses to other neurons in the thorax. What I did was to start targeting each one of these components with my P2X2, with my ATP channel, and try to artificially stimulate them. So I have flies that are completely normal, except these two neurons in the fly brain are now expressing this receptor from the mouse. I can control the release of ATP by shining light onto this prep, but flies usually run away from light, so I had to use blind flies that didn't see any light.

Did it work? What were the results?

I injected hundreds of flies one by one into the head with this cage compound. Every time I would shine the light, the fly would do a jump. It occurred to me that I should be able to take the head of the flies and activate the thoracic cells directly, without the need of a head, to cause the flies to jump. The inspiration for this prep grooming in flies. Once you remove the head from the flies, they don't move. They stay still for days until they are completely dried. But you can put the grass on top of the wings, and they will clean the wings. In my experiment, I cut the head of the flies and asked can they still jump if I activate their thorax with optogenetics? I wasn’t expecting them to fly away, so I didn't put the lid on this experiment. But to my surprise, I had decapitated flies that could jump and run away.

This seems like a really important finding. What did it mean for you and how did you feel about it?

Seeing it from far away, it was very cool. It was very stressful because when I started this, I was incredibly naive. I had no idea what I was getting into, but it was so exciting. There was a lot of competition going on which I didn't understand at the time. I ended up being very lucky because the paper was published in April, and then in August that year, Deisseroth and Boyden published the first paper with the optogenetics that almost everybody uses nowadays. If it'd been the other way around, if his paper had been published first, I guess I don't think I would have published my findings in Cell. We also got a lot of attention, which was kind of crazy. The first few weeks after the paper came out was really insane, people were calling us to ask if you could use this technology to control armies of insects to invade other countries -- all sorts of crazy stuff. At the same time, it was almost four years of nothing working, and then suddenly something works and you see a lot of people interested in your work, and it's really cool.

What did you do after this?

After my Ph.D., I worked at Cold Spring Harbor Laboratory with Anthony Zador. I did something completely different and worked on the rodent auditory cortex. The idea was to tag neurons with optogenetics. When doing electrophysiological recordings, it’s hard to know which area is being recorded; you place your electrodes with a stereotactic device but the electrode is kind of blind to the cells that are being recorded. You don’t really know if this is a dopamine neuron or GABA neuron or whatever it may be. But, if you can shine a light on the neuron to activate it, and then look at the spike waveform, you can identify what type of neuron it is. This is a technique called optotagging.

How did you end up back in Portugal working in the Champalimaud Neuroscience Program?

When I was at Cold Spring Harbor, I met my future husband who was a young scientist there. At the time of our marriage, the richest guy in Portugal died: Antony Champalimaud. He left ⅓ of his fortune for which he didn’t specify exactly what he wanted, but for something that would help the health of humankind. His wife was on his will and she took over that ⅓ of his fortune to start his foundation. She went around trying to understand what to do and getting opinions from several people. Somehow, for reasons we still don’t fully understand, they (the foundation) reached my husband, Zach (Meinen). They wanted to work on two fields: cancer and neuroscience and wanted somebody young who would come to Portugal for this reason. We had just gotten married and my husband was willing to go to Portugal and start the neuroscience department, so I followed him. There, I became part of the initial group that created the Champalimaud Neuroscience Program.

Could you expand upon the origins of your current research?

I went through a lot of pain in order to understand what I really liked and where my heart was directed. That's how I ended up studying sexual behavior in rodents, using them as a model system. There are several reasons why I got into this, but one of them is the concept of choice and the fact that animals choose their partners. It wasn’t easy because mate selection implies that there is diversity in the population, and I wanted to study this in the lab and reduce the variability so I can study the process. We were essentially spending days and days looking at female mice and male mice having sex. Just by observing them, we started becoming fascinated by a bunch of things that were happening. All of my research now stems from these initial observations.

What is something you find interesting about the observations you made regarding the mating patterns of mice?

We all know that sex is rewarding and pleasurable for many species and for most humans, but the time that animals do exhibit sexual behavior is very tightly controlled. In many species, it's controlled by the female reproductive cycle. In contrast to humans, most females [of other species] only have sex in very restricted epochs of their reproductive cycle. They are not sexually receptive all the time. Female mice are fertile and sexually receptive every five days. During that period, the probability of them engaging in sexual behavior is really, really high, but outside of that period is impossible. The male can try as much as he wants, and he will never be able to have sex with her.

Do you have an example of how mating patterns change in mice at different parts of their cycle?

One example is the same mouse couple we examined two times, just three days apart. In the beginning, the female was receptive so the male tried to mate with her and she accepted. But three days later, that same female was unreceptive: the male was trying to get close to her but she was screaming, upright, in a defensive posture, and was not accepting him at all. And I thought, “This is insane! How is it that the same exact stimulus, a male, drives such different behavior in a female?”

What have you studied most recently in your lab?

For the last nine years, we've been studying how the ventromedial hypothalamus controls mating behavior. This part of the hypothalamus was known for many years to control lordosis. The female mice, like many other animals, will arch their back in order for the male to be able to copulate with them. And if they are not receptive, they will do the opposite: they curl their back so that the male cannot penetrate, and then they walk away. This area that we are studying was thought to only be involved in lordosis on the receptive posture. However, we now have pretty convincing data that the ventromedial hypothalamus is divided into at least two different components. One is important for the receptivity, and the other one is important for the rejection behavior. What we see is the “Yin and Yang.” When the female is unreceptive, the rejection behavior part is active and the other is inhibited. When the female becomes sexually receptive, it goes the other way around; the rejection behavior is inhibited and the other one can now be expressed. This is a big component of the lab: understanding the control of how to start and terminate mating behaviors of mice. For example, upon ejaculation, a male mouse drops to the side and remains there for a long time-days even-not wanting to have sex again. My lab investigates what goes on during this refractory period.

How did you get through periods of time where you didn’t get many results or didn’t get exactly what you were looking for?

As a Ph.D. student, I worked every weekend that I was in the U.S. I’d come home once a year, or maybe two weeks a year, but I worked a lot. I am very stubborn, so when I want something, I really work until I break or until this thing breaks. During my postdoc work, I was trying to make my own viruses and put them in the auditory cortex. In the first experiment, I managed to find a cell that was labeled with channelrhodopsin. I went to a meeting with a poster that had one cell and showed everybody. So, I went back to the lab and spent three months injecting rats every day, and I never got anything. However, I was sure that it was going to work because I saw it once. I think this is a characteristic that is important to succeed in science. I’ve always had a very nice social structure. I always had friends and even if I was destroyed, I’d go and be with my friends. I’m 45 now and because of this pandemic I had to come down a little bit on that, but I’d go dancing once a week. My social life is the thing that kept me going through all those years, even if I was working like crazy.

Looking back now, are you happy with your decision to pursue research and become a scientist?

One of the things I realized is that I really, really love being in the middle of this field. I live in a bubble -- my husband is a scientist, most of my friends are scientists, and many of them are also married or partners with scientists. I know it's a reduced view of life in a way, but it's really nice to be in this position and have this close connection with the way we deal with life. The way we go on with our basic activities is very influenced by science, and being in this environment made me love it even more -- I can’t imagine my life outside of science nowadays. This is what I hope to do for the next 20 years straight: to understand how sexual behavior is organized.

 This interview was conducted during the Fall Session of UVA’s Hidden Figures class in 2021. 

Class roster: Brink, Julia Elizabeth; Abraham, Carly Elizabeth; Rose, Odell Bayou; Kang, Elizabeth; Posner, Chloe Grace; Luscko, Caroline Ann; Pappagallo, Julia Dominique; Ware, Liza Elizabeth; Murphy, Ryan Martin; Faisal, Zainab; Fastow, Elizabeth; Walker, Mary-Catherine; Petz, Kaitlyn Dorothy; Terblanche, Alexandra Savenye; Nguyen, Katie; Guttilla, Gianna Marie; Hoang, Chloe Nam; Grace, Ann Brown; Smith, Charles Cornelius; Sears-Webb, Delaney Jean; Abed, Jamil; Miao, Julia Stephanie; Johnson, Catherine Anne; Kim, Evalyn; Lee, Sarah; Pietsch, Maggie Malia; Cheng, Kaitlyn Jiaying; Freud, Jordan Maria; Patel, Sonia; Silbermann, Katherine Elizabeth; Lumpkin, Justin; Lemley, Rachel Ann; Hall, Maria Elizabeth; Nugent, Elise Genevieve; Limon, Safiye; Mangan, Erva; Ali, Sophie; Muse, Morgan Noelle; Miley, Sareena Elizabeth; Bennett, Bailey Grace; Mollin, Hannah Beth; Nguyen, Daniel Van; Englander-Fuentes, Emilu Maria; Pest, Marshall Sinclair; Mahuli, Rhea Mina; Chindepalli, Jahnavi; Malyala, Meghana; Weldon, Nathaniel Andreas; Aschmies, Lindsay Elizabeth; Chakrapani, Krithi; Heintges, Bella Grace; Baker, Gabriella Christine; Bonsu, Tenneh Ina; Hall, Ann M; Rodriguez, Kaitlyn; Simmons, Emma Isabela; Davenport, Julia Barrett; Andrews, Tara; Ramirez, Alexa Hidalgo; Petrus, Sarah Anne; Singh, Aanika; Wilson, Sydney Paige; Younan, Krestina. 

TA: Kipcak, Arda. Instructor: Ribic, Adema, PhD.