Nature Podcast 9 November 2007
Introduction
This is a transcript of the 8th November edition of the weekly Nature Podcast. Audio files for the current show and archive episodes can be accessed from the Nature Podcast index page (http://www.nature.com/nature/podcast), which also contains details on how to subscribe to the Nature Podcast for FREE, and has troubleshooting top-tips. Send us your feedback to mailto:podcast@nature.com.
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Adam Rutherford: What animal is being described here?
Leslie B. Vosshall: And they also exhibit something that is very eerily similar to human sexual foreplay. The males are careful and deliberate in the ways they court females.
Adam Rutherford: You can find out in a minute which is the latest beast to have its surprising behaviour studied through its genome.Music
Adam Rutherford: This is the Nature Podcast and I'm Adam Rutherford. First this week, since 2003, the Cassini space probe has been carefully listening to radio waves from Saturn's Aurora. These signals were supposed to tell researchers about the gas giant's rotation, but things are not quite as simple as they seem. According to a paper in this week's Nature, charged particles from the sun maybe getting in the way. Geoff Brumfiel called lead author Philippe Zarka at the Paris Observatory and asked him what exactly they were measuring. Nature 450, 265–267 (8 November 2007)
Philippe Zarka: The main radio emission, the radio waves that we detect while Cassini is close to Saturn is a very strong radio emission that comes from the magnetic poles of Saturn and that are related to Saturn's Aurora.
Geoff Brumfiel: These radio waves are also related to the planet's rotation, is that right?
Philippe Zarka: Yeah, that's what we thought, actually for all the planets that had a magnetic field people used to think that the radio waves are emitted by electrons, this is for sure and these electrons move inside the planet's magnetic field. So, in some ways they are tied to the magnetic field and so the variations that you observe for the radio waves reflect the rotation of the planet.
Geoff Brumfiel: And so, why is it of interest to know exactly the details of Saturn's rotation?
Philippe Zarka: First, if you don't know the rotation of the interior of Saturn you cannot deduce the speed of the wind. So, you cannot study the dynamics of the atmosphere. There is a second thing, which is when you know with good accuracy the rotation of the planet, then you can define a system of longitude and you can use this as a reference when you want to compare measurements taken along Saturn. Some other interest for example is for the internal structure of Saturn. When spacecraft passed close to Saturn the detailed study of the trajectory, tells you how the mass is distributed inside the planet. Now, it also depends on the precise rotation rate of the planet. So, if you do not know the rotation rate, it is difficult to deduce the structure of the planet with some accuracy from the data you have on the trajectory.
Geoff Brumfiel: And why is it so difficult to figure out the rotation rate of Saturn's interior?
Philippe Zarka: Well, actually it was a surprise. When we did that at Jupiter, it turned out to be very straightforward and very accurate, but at Saturn the big surprise one that when you measure from the radio waves what you believe to be the rotation of the interior of Saturn at difference in time of two or three months, you get different value, but the value can be different as much as 1% and this is enormous because just to give a comparison 1% on the duration of the day on Earth is 15 minutes.
Geoff Brumfiel: So, what is going on here, why does the rotation keep changing?
Philippe Zarka: That is precisely the question that is addressed in the Nature paper. So actually, people up to now measured the variations of the rotation period only over intervals longer than two or three months. We decided that perhaps the short-term variation that could bear some more detailed information about what is going on and so we devised a method for measuring very accurately the rotation period not at a scale of three months, but at a scale of one week and the big surprise we got was that this period oscillates by plus or minus 1% or 2%, so even larger variation than on the long term at a time scale of 25 days.
Geoff Brumfiel: And so what do you think is causing that, that variation?
Philippe Zarka: When you are a space physicist and you see a phenomenon related to charged particles in magnetic field that is varying at a characteristic time of 25 days, you immediately think at the solar wind, which is a wind of electron and protons, which spreads over the whole Solar System and when you are at Saturn for example, when you are standing near Saturn, you see one full rotation of the solar wind in about 25 days. So, maybe the solar wind can play a role can act upon the apparent rotation of the planet.
Adam Rutherford: Philippe Zarka talking to Geoff Brumfiel. Now, here is a special report from Mike Hopkin on the latest set of species to get their genomes decoded.
Mike Hopkin: In what field of biology would you find several hedgehogs, a lunatic fringe and a load of damsels? The answer: fruit-fly genetics. Those are just some of the strange and creative names thought up over the years for mutant strains of Drosophila. This humble insect just a couple of millimetres long might not be much to look at, but it has arguably taught us more about genes in behaviour than any other species and in the age of genomics it is amazing research career shows no sign of slowing. I asked neurogeneticist, Leslie Vosshall of the Rockefeller University in New York, what made Drosophila such a favourite in the lab? Nature 450, 289–293 (8 November 2007)
Leslie B. Vosshall: What has always made fruit flies very popular amongst geneticists are practical things, you can grow enormous numbers of them, they go from birth to sexual maturity in a little under two weeks. So, you can get results very quickly and they exhibit this diversity of behaviours that translate really nicely to the kinds of behaviours we would like to understand in humans. So, they sleep, so you can make a case that flies do things that are quite similar to human sleep. Flies can experience jetlag. Flies when mutated can exhibit a homosexual behaviour and they also exhibit something that is very eerily similar to human sexual foreplay, the males are very careful and deliberate in the ways that they court females.
Mike Hopkin: This mix of complex behaviours and user-friendly genetics has made fruit flies a useful ally in studying a range of complex traits, including mating, the body clock, and even old age and death. They form a key staging pose between very simple organisms such as worms and very complex ones such as ourselves. As a result, fruit flies have shown us how simple genes can often influence complicated processes such as aging. I went down to the fruit fly labs at University College London to talk to geneticist Linda Partridge. Nature 450, 165–167 (8 November 2007)
Linda Partridge: They have some strengths where the worm and yeast have weaknesses. So, for instance, they have much better differentiated tissues, which are much more like those in mammals than do the worm we use. So, the fly has a very nice central nervous system, usually differentiated brain, and it has something that does not look much like a kidney, but functions just like one and in which the same genes those are active in mammalian kidneys are expressed. So, it is a good model for kidney disease. It has a heart and it can die of heart failure and the worm does not have heart at all and it has well-differentiated fat, intestine, a lot of the key systems that turn out to be important in aging in mammals. It also has skeletal muscles very like that of mammals. So, it is in many ways a better physiological model for mammalian aging. You can do more with it. First of all, people were not expecting to find single-gene mutations with a big effect on the rate of aging and they certainly were not expecting their effects to persist over large evolutionary distances and I think work with a fly really knocks out one in the head. The initial work with a worm showed that you can extend lifespan and work with a fly showed that the very same genes could be mutated in the flies do the same thing and I think that is really what has turned the field around, this discovery that you can manipulate the rate of aging.
Mike Hopkin: Groucho Marx once said that 'time flies like an arrow, but fruit flies like a banana' and time has flown for fruit fly researches. It is more than a century since Drosophila was first studied. Over that time, the main work course has been Drosophila melanogaster, literally meaning black-bellied sugar lover. Its genome was sequenced back in 2000 and research in this week's Nature unravels the genomes of a host of other Drosophila species bringing the total number up to 12. Comparing these dozen genomes will give scientists the chance to answer still more questions about fruit-fly genetics.
Chris Gunter: It is really fascinating to study how their genetics are shaped by their evolution.
Mike Hopkin: That is Nature's Genetics editor, Chris Gunter. Nature 450, 183 (8 November 2007)
Chris Gunter: So, now what we have are these 12 genomes and these organisms are called the same genus Drosophila, but really the distance between them genetically is similar to the distance between human and lizard. So, we are talking about the huge evolutionary snapshot that we have by comparing these 12 genomes, how do they compare to each other, how do their habitats compare to each other, etc., really fascinating questions that people have wanted to ask for a long time and finally now have the data to be able to ask.
Mike Hopkin: It is an enticing prospect for those studying fruit flies says Leslie Vosshall.
Leslie B. Vosshall: We are, I think, at the brink of something incredibly exciting with these other species because Drosophila melanogaster, which has been the species of fruit fly that has been studied the most in the last 100 years, it is something that has caught the generalist. So, they are cosmopolitan. You can find them in essentially every continent, except Antarctica. They live with humans; they eat almost anything that appeals to them. So, they are very human like. They associate with humans. They travel around the world on our fruits and we do not know much about what they would do in their normal environment, but these new species have very exotic and specialized behaviours, some like the sechellia strain, which lives exclusively on the Seychelles islands, off the coast of Africa, really eats only one thing that it eats the Noni fruit, Morinda citrifolia. That is the really exciting thing what happened in evolution from the ancestor of fruit fly to make this fly so incredibly specialized. How is it that it likes this fruit and only this fruit, and then, there are other kinds of flies that only like cactus fruit, so we can learn a lot about how animals adapt to their environment, how they select food sources and how they sort of get along in the part of the world where they live.
Mike Hopkin: Answering sweeping questions about animal evolution is a pretty impressive achievement for a tiny fly and it shows why over the years more and more scientists have turn to do Drosophila to help them address a wide range of questions. Chris Gunter sums it up.
Chris Gunter: They were first used, you know by one or two people in a lab grown very carefully and now flies have been sent up on a space shuttle to study the immune system. They have been a leader in genomics. Several Nobel Prizes have been given on flies. They have really come a long way in 100 years and having these 12 genomes is opening the way for the next 100 years.
Adam Rutherford: Chris Gunter ending that report from Mike Hopkin. All that Drosophila research is available on our website that is http://www.nature.com/nature along with all papers in this week's show, and sticking with the fruit fly theme, this week's Podium comes from Nature's senior editor Tanguy Chouard.
Tanguy Chouard: Today, we celebrate science at its best. Cooperation, fun, and generosity as the very best engines of discovery because today is the day of the fruit fly. With the publishing of 10 new fruit fly genomes, this little fellow's time has truly come. This comparative genomics will greatly help in spotting those two-thirds of genes that cannot be detected through mutation. It also paves the way to the bigger challenge of the finding what makes us humans, despite the scarcity of available DNA from Hominids and other primates. But a century of Drosophila research has not always been an easy ride. Based on the superficial morphological differences, compound eyes, body segments, legs, a long held prejudice has been that insects and humans cannot have much in common. Even today you can bet some eminent professors of medical neurology will chin up and go, 'to the best of my knowledge Drosophila does not have a cortex or does it?' Well, they need to get a clue. Drosophila research rocks. Today, it is more vibrant and relevant then ever. To answer the questions of just how relevant the fly has now become to medicine of the roughly 2.5 thousand human disease genes identified, 75% have a homologue in flies, and fly research has now provided groundbreaking discoveries in most areas of biology from classic genetics and embryology of course, which brought it Nobel Prizes in 1933, 1946, and 1995 to no less fundamental cell biology, ecology, evolution, and neuroscience. Fruit fly gene discoveries have made impacts in less expected parts of medicine from immunology to cancer research and they have recently become serious animal models for obesity, diabetes, Parkinson's disease, drug abuse, and sleep or learning disorders. There really are mutant flies of every creed, homosexual, bisexual, sex addicts, rovers, sitters, risk-averse flies, stress flies, aggressive flies, alcoholics, etc., etc., and there is many more cooking. Now, why such an amazing success? There was great scientific instinct from Thomas Hunt Morgan when he chose to study Drosophila in 1908. The fly simply is such a fabulous experimental system to do genetics with. Then came amazing luck; In 1984, when fly development genes were found in mammals, no body had ever predicted how much fly genes would turn out to be conserved in humans, but the main force behind the unmatched record of fly research has to do with the fantastic spirit of its community. All based on fun, generosity, and cooperation. Fly people over the ages have consistently been smart, humorous, hard working, and selfless. This has produced a snowball effect over the century. We have more cooperation producing more outstanding resources and great experimental tools, thus offering even more fun for even more young and smart people to join in the game. Now, if there is one other lesson I think to be drawn from the fantastic success of fly research, it is in the unmatched power of serendipity, the ability to discover what you did not set out to find in the first place. Serendipity happens when you love the game more then the gains. No one exemplifies the powers of sheer curiosity better than Seymour Benzer, 86 and kicking at Caltech. In the 60s, he single-handedly created the field of neurogenetics by setting out to find the genes controlling brain function and behaviour in Drosophila. At that time, many thought no such genes existed. In finding loads of them, he unleashed a chain reaction of groundbreaking discoveries with implications in areas of human biology as distant from neuroscience as cancer or cardiac research, which he could not have dreamed of. Speaking of unsung heroes, the humble fruit fly deserves more recognition for its unparallel contributions to biology. Perhaps, it is time for Seymour Benzer to get that long overdue call from Stockholm.
Adam Rutherford: Tanguy Chouard with this week's Podium. Remember you can write to us, mailto:podcast@nature.com is the address.
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Adam Rutherford: Now, surely nothing is worse than the funk of a rotting fish. We know that mice and other animals have an innate sense of smell when it comes to sniffing rotting food, but humans do not appear to have the mouse's ability to detect the odour of predators. They can literally smell danger. How this complex system works is not clear. The olfactory epithelium, which houses the smell receptors, was previously thought to be a screen which maps different smells into the olfactory bulb in the brain. A new study this week has shown that there are in fact distinct domains in the mouse's nose, which correspond to different types of smell response. Here is senior author, Hitoshi Sakano from University of Tokyo. Nature advance online publication 7 November 2007
Hitoshi Sakano: Unlike humans, the mice have a very weak eyesight. So, they have to rely on their smelling system. Using two different types of mutant animals, each having aberration over different areas, we were able to demonstrate that dorsal parts of the olfactory bulb is mainly for innate aversive responses and ventral areas are responsible for associative learning odour responses.
Adam Rutherford: Dr. Sakano explain to me, they created mice with smell receptors in the dorsal olfactory epithelium genetically wiped out and then tested them with various bad smells including rotting food and the scent of a snow leopard, the mice could still detect the smells, but were not repelled by them; however, over time they did learn to avoid these smells. So, the researchers concluded the dorsal area in the nasal epithelium appears to control an innate response and the ventral area controls the learn response. It parallels with a well-understood biological system are striking.
Hitoshi Sakano: The innate circuit was at first developed and established and later on the rest of the parts for the associative learning developed or evolved. So, this situation is very similar to the immune system like innate immune response and adaptive immune response so like the immune system it is also using those two separate pathways.
Adam Rutherford: Hitoshi Sakano telling me how the immune system and the mouse's sense of smell have two pathways, an innate response and an adaptive one.Music
Adam Rutherford: That is it for this week's show. Kerri will be back with me next week with a special report from the society for neuroscience conference in San Diego. So, listen out for that. Finally, it is sounds of science. Remember, you can send us your suggestions for this section, the address is mailto:podcast@nature.com. Now, in keeping with the 'hurrah' for the humble fruit fly this week, here is the mating song of Drosophila equinoxialis with thanks to evolutionary geneticist, Mike Ritchie of St Andrews University in Scotland. As you might expect from a species that lives in Brazil, it has got a great sense of rhythm. This is the Nature Podcast. Thanks for listening.
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