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FoxP influences the speed and accuracy of a perceptual decision in Drosophila
Gero Miesenböck
Biography
Gero Miesenböck studied medicine at the University of Innsbruck in his native Austria and did postdoctoral research at Memorial Sloan-Kettering Cancer Center in New York. He was on the faculty of Memorial Sloan-Kettering Cancer Center and Yale University before coming to Oxford in 2007. Gero is the founding director of the CNCB.
Gero has invented many of the optogenetic techniques used for visualizing and controlling nerve cells with light. He has also been a pioneer in the use of flies to study neural circuits.
As the current Waynflete Professor of Physiology do you feel that you are part of a tradition?
When I arrived in Oxford, my lab was housed in the Sherrington Building, named after perhaps the most famous Waynflete Professor of Physiology. In 1937, Charles Sherrington described the brain as ‘an enchanted loom where millions of flashing shuttles weave a dissolving pattern, always a meaningful pattern though never an abiding one; a shifting harmony of subpatterns.’ Despite the Victorian prose, Sherrington’s vision of flashes of light signalling the activity of nerve cells contains a modern idea: that the brain could reveal its inner workings optically. Many of the technical aspects of my work revolve around this idea.
It’s interesting that, as an avowed reductionist, you should start with the poetic.
Good poetry is also reductionist: it makes complex thought or sentiment elemental. I in fact wanted to become a writer for a very long time. My father was a classicist, and I was tempted to follow him into literature. But he was frustrated with his chosen profession, its subjective standards and its limited potential for discovery. He persuaded me, in strong terms, to choose science as the more exciting path. I started reading more and more science when I was at school and I became gripped by it. But I was gripped from an abstract point of view; I liked ideas and the way they were expressed and tested. I wasn’t tinkering around with a chemistry set.
Your father was clearly an early mentor. Were there others?
In 1989, I spent three months at the University of Umeå, near the Arctic Circle, to learn an experimental technique I needed for my dissertation. Unwisely, I had chosen winter for my visit. In the near-complete darkness of northern Sweden, our circadian clocks started to run free. People worked the strangest hours because it didn’t matter when you went to bed or got up: it was nearly always dark. The only event that brought everyone together was our journal club—a weekly discussion of the scientific literature that is a fixture in many labs. There I came across papers that blew me away with their boldness and the beauty of their ideas. The papers were the work of James Rothman. I made up my mind right there that I wanted a postdoctoral position with Rothman.
So how did you get yourself out of Austria and over to America?
I wrote to Rothman a year or two later when I was finishing medical school. It didn’t take long until a rejection letter arrived, in which my surname was spectacularly misspelled. Admittedly it is an unusual name, but 4 out of the 10 letters were incorrect. Come on! But I persisted. I visited Felix Wieland, a collaborator of Rothman’s in Heidelberg, and he must have put in a word for me, because a few days later I got a phone call at midnight, and it was Rothman saying that he might have made a mistake. In 1992 I moved to the USA for what I thought would be two or three years and ended up staying for 15. Rothman took a risk on a complete unknown. I try to remember this nowadays when I get applications that seem to come out of nowhere, but may in fact be the result of years of reflection and preparation.
What was your first project in the Rothman lab?
I initially worked on protein sorting in cells. But soon my work concentrated on what has become a recurring theme: the development of biological tools to illuminate biological problems. The first such tool used a light-emitting protein to make communication between nerve cells visible. To get the system to work, I had to isolate the DNA that encodes the protein from a particular species of shrimp found along the south coast of Japan. But getting my hands on these shrimp proved difficult. Late every evening in New York, I asked a Japanese colleague to make phone calls to universities, aquariums and natural history museums in Japan, but no luck. Finally, I just rang the Marine Biological Laboratory in Woods Hole, Massachusetts, and asked to speak to their bioluminescence expert, fully expecting to be told to get lost. But incredibly, the phone operator knew how to field my request. I was asked to hold on for a moment and then a voice came on the line. It was Osamu Shimomura. By chance I found myself talking to the one man who could help me.
Osamu Shimomura won the Nobel Prize in 2008 for his discovery of the green fluorescent protein (GFP), an essential reagent in biology. GFP glows greenly when exposed to blue light. It was first purified and studied by Shimomura in the 60s and 70s.
I explained the shrimp situation to him and he sent me a sample he had collected and sun-dried in Japan in 1944, along with a stack of reprints. One of these reprints had a stunning cover photograph: a manuscript page reporting the structure of the shrimp’s light-emitting chemical. The page was illuminated by the chemical reaction described on it—a little like Escher’s famous lithograph of hands drawing themselves.
Although Shimomura’s shrimp proved completely useless, they are one of my prized possessions. The light-generating system is still well enough preserved that you can see a beautiful, eerie blue glow when you crush a few shrimp and add water. The genetic material, of course, was degraded, but Shimomura directed me to a fresh supply of shrimp, from which I managed to isolate a piece of DNA encoding the glowing enzyme. It was this enzyme that produced the first images of synaptic transmission: Sherrington’s weaving shuttles. A later incarnation of the same principle, termed synapto-pHluorin, drew directly on Shimomura’s discovery of GFP. It used a pH-sensitive GFP mutant to provide an optical report of communication between neurons.
What was your first project in your own lab?
The initial aim was to image information flow in a neural circuit with synapto-pHluorin. But then very quickly, in the summer of 1999—it was one of those moments where I can even remember the time and the date and the room I was in—I had the idea of using light not only to observe but also to control. That then quickly became another focus of the lab.
When was that, and where were you?
It was the late afternoon of June 12, 1999, a Saturday. We were living on Union Square in Manhattan at the time. I had taken my daughter on the Staten Island Ferry across New York Harbor, come back home, and stretched out on the bed, ready to return to a book I was absorbed in, Independence Day by Richard Ford. As I was reaching for the book, drifting from the real world into Ford’s fictional New Jersey, there was the idea.
Where did the remote control idea come from?
I guess I had the advantage of being a newcomer to neurobiology. I was not too weighed down by received wisdom, maybe not too weighed down by neuroscience knowledge in general. But I had worked in a leading cell biology lab. I had seen that to establish causality and dissect a complex mechanism it’s essential to be able to control it. In neuroscience, I felt there was still way too much observation and not enough intervention. So I thought, wouldn’t it be wonderful if the two ingredients that I had relied on in my work with synapto-pHluorin—genetics and optics—could be combined again but this time for the opposite way of communicating with the neuron.
At first we were completely alone doing this work. Now, of course, many people have adopted and also improved the approach.
With optogenetic remote control you can say that neuron X is important for behaviour Y. What other questions can you address?
There is a whole range of questions we can ask when we have the ability to control specific groups of neurons. Optogenetics allows us to make non-invasive and physiological connections to brain tissue. We can use these techniques to work out the wiring diagrams of neural circuits. We can apply spatiotemporal patterns of input activity and measure what kinds of signals a target cell or a group of target cells is looking for. It means that rather than just finding the anatomical connections between neurons we can deduce the input/output characteristics of a circuit. A still higher level of analysis is to see what exact features of activity patterns are relevant for perception, action, cognition, memory and so forth.
Have you always been attracted to technological solutions and inventing new methods?
It was not a deliberate choice. I wanted to do certain types of experiment, and I couldn’t make any progress until I developed what was necessary. I wanted to work on networks of neurons and it was clear that there needed to be a new way of interacting with them.
Also, there is beauty in these development efforts in their own right. It’s really a pleasure to see something through from the conceptual stage, to trying to get it work, and then actually using it. Seeing the first images of a fruit fly smelling an odour as revealed by synapto-pHluorin and looking back over the entire arc that began with the engineering of the GFP mutant, or seeing the first remote-controlled fly take flight at the flash of a laser beam, I have to say these were very satisfying moments.
Why did you choose to work on the fly?
The nematode C. elegans has just 302 neurons and a correspondingly, shall we say, basic behavioural repertoire. Rodents are too complex. If you look at a mouse brain under a microscope you instantly realise that you are seeing only a small part of a much bigger structure. In contrast, if you look at a fly brain under a microscope you get the impression that you are seeing something self-contained. Most of the relevant parts are there, visible at once. The scale of the biological structure and that of our analytical methods, which operate at the resolution of individual cells, matches. Then there are the added benefits: a century of genetic work has been done on the fly, and its behaviour is rich.
But it is easy to underestimate the complexity of even the most simple-seeming organisms. In his late years Francis Crick, co-discoverer of the structure of DNA, became interested in consciousness. Crick once said to Seymour Benzer that he didn’t think the fly was very interesting from the point of view of consciousness, to which Benzer responded—I don’t recall the exact words, but it went something like ‘Francis, don’t underestimate flies; they can do more than you can do: For example, can you fly away and land upside down on the ceiling?’
What are your favourite papers?
There’s of course the one discussed in that fateful journal club in Umeå: ‘The rate of bulk flow from the endoplasmic reticulum to the cell surface’ by Felix Wieland, Michael Gleason, Tito Serafini, and Jim Rothman (Cell 1987: 50, 289-300).
Another eye-opener was ‘The statistical nature of the acetycholine potential and its molecular components’ by Bernard Katz and Ricardo Miledi (J. Physiol. 1972: 224, 665-699). This paper is a fine example of how much you can learn from your data if you have the courage to guess the underlying mechanism and the mathematical chops to formalise your guess. Chuck Stevens’s work is also an inspiration in this regard.
And which of your own papers are you particularly fond of?
Well, there’s the two that laid the foundations of optogenetic control: ‘Selective photostimulation of genetically chARGed neurons’ with Boris Zemelman, Georgia Lee and Minna Ng (Neuron 2002: 33, 15-22), and ‘Remote control of behavior through genetically targeted photostimulation of neurons’ with Susana Lima (Cell 2005: 121, 141-152).
Perhaps because I love literature, I tend to agonize over my own writing. I’m rather slow, managing at most 500 words a day even if I do nothing but write. But occasionally there is a paper that virtually writes itself. The most recent example is the fairy tale of Sandman: ‘Operation of a homeostatic sleep switch’ with Diogo Pimentel and Jeff Donlea (Nature 2016: 536, 333-337).
You take a top-down, reductionist approach in your work. Why?
Our goal is to understand the cellular basis of behaviour. There are two ways of approaching the problem: from the bottom up, or from the top down. If you start from the bottom up, by studying individual cells and their interactions, you quickly run into a problem: there is a horizon of predictability beyond which you cannot see. Even if you understand each individual component and each pairwise interaction in great detail, put just a few of these components together and you’ll discover that you can’t make any predictions at all about the behaviour of the resulting system. The problem is not particular to neuroscience or biology. A famous example is the three-body problem in celestial mechanics. Poincaré showed that the motion of a system of orbiting masses governed by precise Newtonian laws gives rise to deterministic chaos if there are more than two masses involved. So if someone tells me they are going to embark on a massive project in which they will analyse every neuron and every connection in the brain and then model the whole thing in a computer and find out how it works, well good luck but I won’t be closing down my lab just yet.
So what’s the alternative?
Given this horizon of predictability from the bottom up, the rational approach would seem to start from the top down. Find an interesting behaviour that taxes a particular circuit, and then take the system apart. Much of our work is predicated on the belief that brains do not employ an endless variety of circuits but rather a limited set. You need circuits that can compare signals, apply thresholds, or integrate information. You need oscillators to keep time, you need buffers that can hold the intermediates of your computations, you need memory you can write to and read from, and so on. If you understand any one of these circuits in any behavioural context, chances are you have learned something general.
What brought you to Oxford?
After New York I went to Yale. But after a couple of years I was approached by Oxford, and my first thought was, No way! I had spent a month in England as a boy, sent to Bournemouth for elocution lessons. As you can hear, they were not successful. I was bored and homesick and vowed I would never visit this country again. I kept to my promise for 30 years, but my wife persuaded me that I should at least consider the job. And surprisingly, I find that I love it here.
Heinrich Wieland Prize 2015
Gero Miesenböck will receive the Heinrich Wieland Prize 2015 for his conception and first experimental demonstration of optogenetics.
Named after the 1927 Chemistry Nobel Laureate Heinrich Wieland, the annual award recognises outstanding research on biologically active molecules and systems. It is among the most prestigious international science prizes awarded in Germany.
To find out more click here.
Gero Miesenböck elected as a Fellow of the Royal Society
The Royal Society is the national Academy of science in the UK. Its Fellowship is made up of the most eminent scientists, engineers, and technologists from or living and working in the UK and the Commonwealth.
The Society’s fundamental purpose, reflected in its founding Charters of the 1660s, is to recognise, promote, and support excellence in science and to encourage the development and use of science for the benefit of humanity.
The citation reads: “Gero Miesenböck pioneered the science of optogenetics. He established the principles of optogenetic control in 2002, using rhodopsin to activate normally light-insensitive neurons. He was the first to use optogenetics to control behaviour. These seminal experiments have provided a platform for an explosion in optogenetic applications. Recent honours testify to the significance of these findings. Miesenböck has exploited optogenetics in a succession of brilliant experiments illuminating synaptic connectivity, the neural basis of reward, mechanisms of sleep homeostasis and the control of sexually dimorphic circuitry. These incisive contributions to neuroscience have demonstrated the full potential of optogenetics beyond the proof-of-principle stage.”
Think before you act!
Fruit flies take time to deliberate when faced with difficult decisions. The process is linked to FoxP, a gene associated with cognitive development and language in humans.
Have you ever agonized over a difficult decision? Reflecting before committing to a choice is considered a hallmark of intelligence. In a study published in the journal Science, CNCB researchers report that fruit flies also ‘think’ before they act.
The insects were given choices between two concentrations of an odour. Before the experiment, the flies had been taught to avoid one concentration, which they had learned to associate with a negative outcome. When the odour concentrations were very different (and, therefore, easy to tell apart), the flies made quick decisions which were nearly always correct.
But when the odour concentrations were very close, making them difficult to distinguish, the flies mulled over their choices much longer, and they made more mistakes.
‘Psychologists and neuroscientists have studied these types of perceptual decision in humans and higher vertebrates since the 19th century,’ says Gero Miesenböck, in whose laboratory the new research was performed. ‘But people tended to think of insects as tiny robots that just respond reflexively to signals from the environment. Now we know that’s not true.’
Remarkably, the same mathematical models that describe the actions of a human decision-maker also accurately predict a fly’s behaviour.
The scientists discovered that flies carrying defective copies of a gene called FoxP were much slower to make up their minds. Defects in some human versions of theFoxP gene are associated with low intelligence, difficulties with language, and problems with fine movements.
Shamik DasGupta, the lead author of the study, illustrates the effect of FoxP by comparing the decision process to filling a bucket with water: ‘Before a decision is made, brain circuits collect information just like a bucket collects water. Once the amount of accumulated information has risen to a certain level, the decision is triggered. When FoxP is defective, either the flow of information into the bucket is reduced to a trickle, or the bucket has sprung a leak.’
In an experiment suggesting that the comparison with a leaky bucket is apt, the researchers were able to copy the genetic defect by introducing an electrical current leak into the 200 or so brain cells in which FoxP is active.
What role FoxP genes play in mental processes as diverse as decision-making, language, and motor control remains puzzling. One feature common to all of these processes is that they unfold over time. FoxP may thus be important for wiring into the brain a capacity for producing and processing temporal sequences.
FoxP influences the speed and accuracy of a perceptual decision in Drosophila by Shamik DasGupta, Clara Howcroft Ferreira and Gero Miesenböck. Science (2014) 344: 901–904.
Even Fruit Flies Need a Moment to Think It Over. The New York Times, May 22, 2014.
How the brain forms distinct memories
Sparse odour coding by the Kenyon cells of the mushroom body generates a large number of precisely addressable locations for the storage of odour-specific memories.
Anyone who associates the smell of freshly baked apple pie with happy childhood memories or the smell of disinfectant with a flu jab knows the power of associative memory, especially of associations with odours. But how do we attach distinct memories to the millions of possible odours we encounter?
In a study published in the journal Nature Neuroscience, CNCB scientists report that a key to forming distinct associative memories lies in how sensory information is encoded in the brain.
In many higher brain centres, sensory information is encoded ‘sparsely’, meaning that out of a large population of nerve cells, or neurons, only very few fire electrical impulses in response to any particular sensation.
‘This sparse coding means that neurons that respond to one odour don’t overlap much with neurons that respond to other odours, which makes it easier for the brain to tell odours apart even if they are very similar,’ says Andrew Lin, the lead author of the study.
The researchers discovered that if they ‘de-sparsened’ odour representations in the neurons that store associative memories, fruit flies lost the ability to form distinct memories for similar odours.
‘Fruit flies can learn that if one odour out of a pair is associated with a punishment, they should avoid the punished odour in favour of the unpunished odour,’ explains Lin.
Normally they can perform this task even if the two odours are very similar, because the neurons that store associative memories, called Kenyon cells, are inhibited by a negative feedback loop that prevents too many of them from firing for any particular odour.
However, if the negative feedback loop is blocked, the odour coding in Kenyon cells becomes less sparse and the flies attach the same memory to similar, yet different, odours.
‘We think the behavioural defect occurs because the odour responses in Kenyon cells overlap too much,’ says Andrew Lin. ‘If we use a dissimilar pair of odours, where the Kenyon cell responses are naturally well-separated, the flies don’t need the negative feedback to perform well.’
Although the research was carried out in fruit flies, the scientists say sparse coding is likely to play a similar role in human memory.
‘Sparse coding has been observed in the brains of other organisms, and there are compelling theoretical arguments for its importance*’, explains Gero Miesenböck, in whose laboratory the research was performed. ‘But until now it hasn’t been possible experimentally to link sparse coding with behaviour.’
Sparse, decorrelated odor coding in the mushroom body enhances learned odor discrimination by Andrew C Lin, Alexei M Bygrave, Alix de Calignon, Tzumin Lee and Gero Miesenböck. Nature Neuroscience (2014) doi:10.1038/nn.3660 (Published online February 23, 2014).
* Pentti Kanerva. Sparse Distributed Memory. MIT Press, 1988.
The switch that says it’s time to sleep
A small group of neurons put flies to sleep when they need to rest.
The body uses two mechanisms to regulate sleep. One is the body clock, which attunes humans and animals to the 24 hour cycle of day and night. The other mechanism is the sleep ‘homeostat’: a device in the brain that keeps track of your waking activity and puts you to sleep when you are tired and need to reset. This mechanism is purely internal. When it malfunctions, sleep deficits build up.
Over the past half-century, scientists have learned what precisely makes the circadian clock tick. The crucial insight came in 1971 with the discovery of mutant fruit flies whose clocks were abnormally fast or slow. In a study published in the journal Neuron, CNCB scientists now lift the curtain on the second master regulator of sleep: the homeostat.
Once again, fruit flies provided the critical clue, in the form of a molecular piece of the homeostatic sleep switch. ‘Mutating this gene leads to insomnia-like symptoms. Because of their inability to sleep normally, mutant flies have severe learning and memory deficits, much like people do after staying awake all night’ says Jeff Donlea, one of the lead authors of the study.
The switch works by regulating the activity of a handful of neurons in the brain that were previously found to promote sleep. The neurons become more responsive when we’re tired and need sleep, and then dampen down when we’re fully rested.
‘The sleep homeostat does something similar, in principle, to the thermostat in your home,’ says Gero Miesenböck, in whose lab the new research was performed. ‘A thermostat measures temperature and switches on the heating if it’s too cold. The sleep homeostat measures how long you have been awake and puts you to sleep if you exceed your limit.’
The sleep mechanism is likely to be relevant to humans. Donlea explains: ‘There is a similar group of neurons in a region of the human brain. These neurons are also electrically active during sleep and, like the flies’ cells, are the targets of general anaesthetics. It’s therefore likely that a molecular mechanism similar to the one we have discovered also operates in humans.’
The researchers say that pinpointing the sleep switch might help us identify new targets for novel drugs – potentially to improve treatments for sleep disorders.
But there is much still to find out, and further research could give insight into the mystery of why we need to sleep at all. ‘The big question now is to figure out what internal signal the sleep switch responds to,’ says Diogo Pimentel, the other lead author of the study. ‘What do these sleep-promoting cells monitor while we are awake?
‘If we knew what changes in the brain during waking that requires sleep to reset, we might get closer to understanding why all animals need to sleep.’
Neuronal Machinery of Sleep Homeostasis in Drosophilaby Jeffrey M. Donlea, Diogo Pimentel and Gero Miesenböck. Neuron 81: 860–872 (February 19, 2014).
Gabbay Award for optogenetics
Gero Miesenböck is one of this year’s recipients of the Jacob Heskel Gabbay Award in Biotechnology and Medicine. The award, presented by the Rosenstiel Center of Brandeis University in Massachusetts, is in recognition of the recipients’ ‘contributions to the discovery and applications of optogenetics’. In addition to Gero Miesenböck, Karl Deisseroth of Stanford University and Edward S. Boyden of the Massachusetts Institute of Technology are honoured.
Optogenetics is the technology which allows scientists to control the brain’s activity by genetically engineering neurons to fire in response to light. Gero Miesenböck laid the foundations of the field when he reported, in 2002, that he had genetically modified nerve cells to produce light-responsive pigments. By shining light on the pigment-producing cells he caused them to become electrically active; the function of the nerve cells could thus be influenced remotely instead of via intrusive electrical connections. Miesenböck was also the first to use optogenetics to remote-control the behaviour of an animal.
Hundreds of scientists across the world now use optogenetics to manipulate brain activity in animals, exploring the neurobiology of phenomena such as decision-making and neurodegenerative diseases.
The Gabbay Award was created by the Jacob and Louise Gabbay Foundation and recognises scientists in academia, medicine, or industry whose work has outstanding scientific content and significant practical consequences. Optogenetics joins a long list of innovations in biotechnology and medicine that have been recognised by the annual award, among them the DNA microarray, the human genome sequence, the gene knock-out mouse, human assisted reproduction, and novel types of pharmaceuticals.
On Thursday October 10 the recipients of the Gabbay Award 2013 will present lectures on their work at a symposium and presentation ceremony at Brandeis University. The symposium takes place at 3:30 p.m. in the Shapiro Campus Center Theater and the lectures are free and open to the public.
Two CNCB papers in Neuron
A CNCB double bill—papers from the Miesenböck and Waddell groups—appears in the September 4 issue of Neuron.
Click here to read Moshe Parnas, Andrew Lin, Wolf Huetteroth and Gero Miesenböck on ‘Odor discrimination in Drosophila: from neural population codes to behavior.’
Click here to read Emmanuel Perisse, Yan Yin, Andrew Lin, Suewei Lin, Wolf Huetteroth and Scott Waddell on ‘Different Kenyon cell populations drive learned approach and avoidance in Drosophila.’