Nature Podcast 13 April 2006
Introduction
This is a transcript of the 13 April 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.
This week, using yeast to make anti-malarials, the world's most efficient light bulb, how scientists are pushing up the power of the light microscope to see things on a molecular scale and where we came from, another piece of the fossil jigsaw of human evolution has fallen into place. Hello, I'm Chris Smith, welcome to the 13th April edition Nature's Podcast. Now malaria is one of the most significant health problems worldwide, it caused 300 million infections every single year and could kill up to 3 million people. In the case of one strain, Plasmodium falciparum, the problem is magnified further by the emergence of multi-drug resistant strains of the parasite. But there is one very effective agent to treat the problem. Artemisinin which comes from the Artemisia annua plant which is also as Sweet Wormwood. The problem is, though, that the drug is in very short supply and it's therefore often too costly for the people who need it most. Thankfully there's a solution. Jay Keasling from the University of California at Berkley, has transferred the enzymes that make the drug in the Artemisia plant into yeast, enabling large amounts of the raw material needed to make the drug, to be produced in the lab. (Nature 440, 940-943 (2006) ).
Jay Keasling: In our paper we've shown, for the first time, that one can produce a pre-cursor to the anti malarial drug, artemisinin, in microbes. This is important because the pre-cursor can be easily modified to make any one of the artemisinin derivatives that are very effective in curing malaria. This will give us a low cost solution and production process for artemisinin and it's derivatives.
Chris Smith: You've used yeast, why yeast and not, say, E.coli?
Jay Keasling: We've used both yeast and E.coli. In this paper we report on yeast. The E.coli process is not yet functional. The yeast process is functional and it is very effective. Part of the reason is because yeast contains the underlying machinery, much like the plant would have, for making these enzymes functional. So we were able to clone out the genes from the plant, transplant them into the yeast and, actually, get them functional in the yeast to product this drug.
Chris Smith: Is it not toxic to the yeast?
Jay Keasling: There's this interesting phenomenon, which we're now investigating, that the yeast actually pumps it outside the cell, so the drug that we actually found was on the outside of the cell and not inside the cell and this maybe a mechanism that yeast uses naturally to detoxify drugs or other molecules that might be harmful to it.
Chris Smith: So this stuff accumulates on the outside of the yeast. How do you get it away from the yeast and all of the other metabolites they produce, how do you purify it, is it simple?
Jay Keasling: That was actually another really nice discovery that we report in this paper. The molecule was actually sensitive to pH and so, by simply changing the pH we could get it off of the cells in relatively pure form and that's really important because we didn't have to go to harsh processing conditions like lysing the cells to get it out, which reduces the cost further for potentially producing this drug.
Chris Smith: And there's no danger that, by adding these genes to the yeast, they're going to also product side reactions or side products that might co-purify with the active agent, the thing you want, and actually have a nasty effect?
Jay Keasling: There's always that possibility, but that's why, when you do this on a large scale, you go through very rigorous quantitative analysis of the product. Now I should mention that the way the drug is currently gotten from Artemisia annua,the plant that produces it, is using diesel fuel to extract it and that is not a particularly pure process. What's more, the plant makes other molecules that are similar to artemisinin, so in fact, you might have more danger of having contamination from other molecules like artemisinin when it's coming from the plant, that you would from a microbe.
Chris Smith: It is actually produced in appreciably reasonable amounts, in other words, is this likely to be an economic viable way of doing it?
Jay Keasling: It certainly will be once we get the yields up. Now the paper reports producing between 100 and 200 milligrams per litre. If we can get it up to the 25 to 50 gram per litre range, then using, say, 100,000 to 200,000 litre fermenter, if you use that tank continuously, you could actually produce enough of the drug for the worlds supply. So, actually, in terms of a process, it's certainly within reach and we think it's going to be within reach in a very short period of time.
Another reason to view Brewer's Yeast as one of our best friends: the University of California, Berkley's, Jay Keasling. Now how many scientists does it take to change a light bulb? Well, one it seems because the University of Michigan's Steve Forrest has come up with the most power efficient mechanism yet discovered to product white light. And that means that the humble household incandescent light bulb could be about to become a whole lot brighter and more cost effective. (Nature 440, 908-912 (2006) ).
Stephen Forrest: What we have is a method of using very thin film organic materials, that is basically carbon-containing materials, to generate very bright and very pure colour white, which could be used for indoor illumination sources.
Chris Smith: Presumably this is more efficient than standard incandescent lights?
Stephen Forrest: Yes it is. It's about one and a half times more efficient. Now there are very efficient light sources, fluorescent bulbs, but households still prefer incandescents for it's colour and for the fact that you can dim it easily and that the bulb itself is very cheap. However, the cost of ownership of that bulb, how often you have to replace it and how much energy it uses, it turns out to be a very expensive piece of equipment.
Chris Smith: So how have you got round the problem, Steve?
Stephen Forrest: Well we're using these organic thin films and by putting electric current through them we can light up the material so that it is quite white and very bright.
Chris Smith: What's new about this, because I've seen, obviously, people have managed to make quantum dots and things before that have given off white light, but why is yours better than theirs?
Stephen Forrest: What is interesting is that we have managed to manage the distribution of molecular excited states within the device. When you inject electrons into inorganic material it forms a molecular excited state. When the molecule becomes unexcited it gives off a photon and the colour of the photon, whether it's red, green or blue, depends exactly on the structure of the molecule. Now we recognize that one out of four electrons that are injected go into a quantum mechanical state called the singlet state and those are only radiative through, what we call, fluorescent materials and through the process of fluorescence. And three out of the four electrons enter what's called the triplet state, those are non-radiative states but by using a molecule with a heavy metal atom in it, such as iridium, that triplet state now become radiative. And what we've done in our device is we have all of the singlet states that one quarter generate blue light through fluorescence and the three quarters of the excited states generate red and green light through phosphorescence. And by the mixture of blue, red and green, we get white.
Chris Smith: And it's cold light, which means it's got numerous applications where the generation of heat is a bad thing?
Stephen Forrest: Oh, absolutely and it's a very efficient process, we loose, in principle, no electrons to, let's say heat or some other parasitic process. As a matter of fact, some of the building consumption of electricity in lighting comes from the fact that you have to cool the building because you are generating so much heat. These devices will give off abundant light at about five or six volts and if you put your hand on the bulb it would feel room temperature.
Chris Smith: And is this actually commercially exploitable at the moment? In other words can you make these phosphors in a reasonable amount of time and in a reasonable amount of weight, in order to use them?
Stephen Forrest: Yes, I know this for a fact because a lot of these materials are currently used in displays that are now commercially available, but you have to realize that lighting is one of the cheapest commodities out there. And to meet those sorts of cost targets today it will take a lot more manufacturing development before it really becomes a practical solution for lighting.
The University of Michigan's Steve Forrest. Coming up next, pushing up the power of the light microscope and another of the missing links in the evolution of humankind. But first with this week's news and talking to Anna Lacey, here's Nature's Jo Marchant.
Jo Marchant: Thanks. The first story I'm going to talk about today regards bird flu and a question that a lot of people are asking this week, can people catch the H5N1 avian flu virus from eating infected poultry? This is something that people are particularly worried about in Europe at the moment, with the virus spreading from country to country and the UK actually had its first case in a wild bird, reported last week. For Colin Blakemore, he's the executive of the UK Medical Research Council, the public don't need to worry. He said last week there is no evidence of transmission to people by eating cooked eggs or chicken, adding that that the only food risk he could see was from drinking swans' blood. (Nature 440, 850 (2006) ).
Anna Lacey: So the official advice is obviously that chicken and eggs are safe but how have they actually come to this conclusion?
Jo Marchant: Well, they've looked at the scientific evidence that's out there, reports that are published so far of what we know about the human cases that have happened so far. And, although we know that H5N1 is present in meat and eggs of infected birds and that animals have been infected by eating diseased birds, they are right to say that there is no evidence proving that humans can catch H5N1 from eating infected poultry, the problem is that yes, there is no evidence that humans can catch it in that way, but equally we don't have the evidence to show that they can't, so although the risk is low, particularly compared to coming into contact with diseased birds themselves, for example, it's a little bit of an overstatement to say that we know that poultry would be safe to eat.
Anna Lacey: Is it not a risky strategy by the government to say that it's okay to eat chicken and eggs, especially when you consider things like the BSE crisis?
Jo Marchant: Well, you can see that it's a very sensitive subject and you've also got to take into account the fact that the virus would have to get into the human food chain first, and that is quite unlikely, although some scientists do point out that you could have a window of opportunity, for example, if the virus got into poultry a few days before the symptoms showed up. There's also the argument that cooking would destroy the virus, but then on the other hand we know that a lot of people don't follow really strict hygiene guidelines when they're cooking their chicken, so it's definitely a very difficult line to draw. You don't want to cause public panic when you haven't got any clear evidence of a risk, you don't want to cause economic damage to the poultry industry, but on the other hand scientist are saying to us that, possibly, it would be better to be honest, that we just don't know what the risk would be if the virus got into the human food chain.
Anna Lacey: While we wait to see what flies in on the bird flu front, it looks as thought some super antibody treatments are on their way out?
Jo Marchant: Well, yes, we've got a special report this week on antibody therapy. This is the kind of drug which became infamous a few weeks ago in this clinical trail in the UK, an experimental drug called TGN 1412 that put six British men into intensive care. Initially we weren't sure whether there was a problem with contamination, with the dose, with the way the trial was carried out? But last week an initial report suggests that there wasn't a problem there. (Nature 440, 855 (2006) ).
Anna Lacey: So, how was this drug supposed to work?
Jo Marchant: Basically, one group of cells in the immune system is called T-cells. Normally to activate T-cells you need two different signals and what this drug is doing is overriding those things, so you just need this one particular antibody and that will activate T-cells across the board because they all have this receptor. When the company tested this drug in animals and in primates they saw that only the regulatory T-cells, so these calming down cells, were being activated. That implied that this could be, actually, a very useful drug for calming down the immune system in things like rheumatoid arthritis, type 1 diabetes and nerve inflammation.
Anna Lacey: So what went wrong in humans then?
Jo Marchant: We don't know for sure, I mean people are still looking into that, but it seems that the most likely thing was that it wasn't just the regulatory T-cells that got activated and that, perhaps, the helper T-cells got activated as well. If it was activating the helper T-cells they would have all released cytokine molecules and, basically, just hugely activated the immune system across the board in a very uncontrolled way.
Anna Lacey: So what's the future for this method? Are people going to continue using drugs that bypass the cells natural, sort of, safety net, so to speak?
Jo Marchant: Well that's a very interesting question and a difficult question to answer and the experts that we've been speaking to, some of them are saying this was tragic but this basically highlights the potential of this field. Other people are saying we can't believe they were allowed to do this in the first place, so you've got a huge spectrum of opinion in the field. What's likely to happen in practice is that individual studies are looked at very carefully on a case-by-case basis before going into human clinical trials.
Anna Lacey: But this isn't the only therapeutic method coming under fire this week, is it?
Jo Marchant: No, that's right, we've got another piece on spinal chord treatments. A particular study that we're looking at his week if from a Beijing neurosurgeon called Hongyun Huang, not to be confused with the stem cell researcher who's been in the news recently, Woo Suk Hwang. His particular technique is based on the theory that cells called olfactory and sheathing cells can actually help regenerate nerve cells at the sight of an injury by implanting these cells into the spinal chord. He's got a lot of anecdotal evidence to say that it works but what some researchers are concerned about is the fact that proper clinical trials haven't been carried out and, actually, three experts have gone as far as publishing a critique of his methods and they are concerned that they didn't see any improvement in the people that they looked at. They did see significant side effects that weren't reported initially by Huang. (Nature 440, 850 (2006) )
Anna Lacey: The people critiquing this technique, they only looked at less than, say, 1% off all the patients that Huang has treated, can we really be using their data?
Jo Marchant: They're not trying to say anything definitive. I mean what they're really trying to highlight is the importance of clinical trials and unless you carry out those trials you cannot say, for sure, whether a technique is working or not. One issue that they would like to be considered is the fact that, if you're looking at anecdotal evidence from patients, often these people were desperate for the treatment, they've shelled out large amounts of money to do it, they really want to believe that it's worked so, in some cases, they may believe that they've got better, even it they haven't.
Anna Lacey: So, if people with spinal chord injuries are looking for treatment, what do they recommend?
Jo Marchant: Well, some researchers are putting together some guidelines at the moment that they hope will help patients and clinicians kind of judge what the evidence out there is and whether there's good reason to go for a particular treatment. But I think part of it is just explaining to patients how to judge different trials, whether a clinical trial has been properly carried out and also including data such as the fact that, for individuals who've had acute spinal chord injury, 40% of them show some spontaneous recovery. I'm not sure that that kind of thing is generally known, so just because you have anecdotal stories, the improvement doesn't necessarily mean it was down to a treatment.
Anna Lacey talking to Nature's Jo Marchant. As always the stories we're discussing this week are available online at http://www.nature.com/nature and you can access them with a personal subscription to Nature or through an institutional site license. The details of both of these options are available from http://www.nature.com. If you have any comments or feedback for us, incidentally, the address to write to is mailto:podast@nature.com. And now to microscopy and how Stefan Hell from the Max Planck Institute in Gottingen, Germany, is able to see with a confocal light microscope what would previously have taken an electron microscope. He and his colleagues have used stimulated emission depletion, or STED for short, to watch what happens as individual vesicles or packets of neurotransmitter, which each measure just 14 nanometres across, are discharged from nerve endings. They've done this by using a fluorescent dye coupled to an antibody which recognizes a protein in the vesicles. The microscope emits two beams of light, one central beam stimulates the dye to fluoresce whilst the second beam, which is arranged in a doughnut shape around the first, de-excites the dye molecules, keeping the excited zone extremely tight. In fact it's 10 times smaller than with a standard confocal microscope which normally sees an area about 200 nanometers across. (Nature 440, 935-939; 2006); (Nature 440, 879-880; 2006)
Stefan Hell: We have developed a fluorescent light microscope that is able to resolve far beyond the defraction resolution limit. As a result of that, we've been able to visualize, for the first time, the synoptic vesicles that transmit neurotransmitters in order to help neurons to communicate.
Chris Smith: How does this new technique work?
Stefan Hell: Because of the phenomenon of defraction, it is not possible, in the regular microscope, to make fluorescent spots that are smaller than about 200 nanometers. If you have structure that are much below that size you cannot see these structures individually and so, in this work, we reduced the spot area by an order of magnitude and, as a result of that, we've been able to identify proteins that belonged individual synoptic vesicles.
Chris Smith: How are you achieving that reduction in area though?
Stefan Hell: We use a physical phenomenon which is referred to as stimulated emission. Now everyone knows that a fluorescent molecule can be excited but it's also possible to de-excite a fluorescent marker by light. This has been used in order to de-excite the molecules that are the outer part of the florescent spot.
Chris Smith: How does it de-excite them though?
Stefan Hell: Basically a photon which has a longer wavelength, so a lower energy photon, hits an excited molecule and pushes to the ground state. The excess energy is taken away by a second photon which is identical to the simulating photon. How the decisive point is that one needs only a finite brightness or intensity of the quenching beam in order to get the molecule down to the ground state. So the trick is that we use a higher intensity than what is actually needed and that we can arrange the de-excitation light in a doughnut around the de-excitation spot. Then if you crank up the power so that the de-excitation takes place everywhere in the focal region, except at the very centre of that donut, by doing that we can squeeze the spot size theoretically even down to a molecular scale.
Chris Smith: So you're bringing, literally, within the range of a light microscope what was previously only the domain of the electron microscope?
Stefan Hell: Yes, that is perfectly correct and we think that by perfecting this physical concept, by making it work almost ideally, in the end it will be possible to get a spatial resolution which is at a scale of, sort of, electron microscope resolving about five nanometers or so. We are not there yet but I think the odds are not bad that the technical issues that remain to be solved will be solved in the end.
Stefan Hell from the Max Planck Institute in Gottingen Germany. Now finally this week, researchers have unearthed another intriguing piece of the puzzle linking some of the earliest humanoid remains in Africa a woodland inhabiting species called Ardipithecus, which lived about five million years ago with the more recent Australopithecus species that inhabited more open terrain and was around about three and a half million year ago. Tim White and his colleagues have been working in the Afar region of Ethiopia where they have unearthed skull and teeth remains dating back about 4.1 million years, making them the earliest Australopithecus specimens yet found. (Nature 440, 883-889 (2006) ).
Tim White: Well, we've discovered some fossils from a time period that has previously been unrepresented in the Ethiopian sequences we're working in, in the Afar region of Ethiopia. The fossils there are dated to 4.1 million years ago and this is the earliest species of Australopithecus that's yet been found.
Chris Smith: What's the significance of that, though, how does it fit in with the evolution of mankind?
Tim White: We understand human evolution much better now than ever before. Largely due to these new fossil discoveries coming out of Africa. Up until the 1990s we only sort of knew this Lucy fossil of Australopithecus afarensis, we didn't know where that came from. And we found a whole new genus and species in the 90s, Ardipithecus ramidus, but we didn't understand, well, the relationships, how that Ardipithecus ramidus, that very primitive hominid dated to four and a half million years ago, how it became Australopithecus that Raymond Dart named in Nature 80 years ago We have now found the earliest species of this and what we see is a succession in this particular part of the Afar of sedimentary rocks and from those rocks we've extracted fossils now from four and a half million, from 4.1 million, the one's we're announcing here in this paper and also the Lucy species, which follows these at about three and a half million. And we see, progressively, more and more humanlike characteristics, in these fossils. So what this is, is a documentation of human evolution in a previously, very poorly known time period.
Chris Smith: Ardipithecus presumably gave rise to these guys, either by replacement or by something being added, in other words they all sort of cross fertilised each other I suppose, a way of putting it. Do you think that's a reasonable thought?
Tim White: Yes, when we looked to the record older than 4.2 million years ago, we see no evidence of this, what we call megadontia, this enlarged cheek teeth that we see in Australopithecus. Ardipithecus had thinner enamel, smaller back teeth and what this tells us is that the diet shifted between Ardipithecus, the more primitive form, and Australopithecus,the more evolved form. And so what this seems to indicate is that these Australopithecus primates were expanding their dietary niche to include things that were tougher, harder, more course resources, out in more open habitats so it was an expansion of the dietary niche that was one of the very first steps in human evolution.
Chris Smith: And if you could draw up a wish list of what you'd really like to find, in order to fill in the missing gaps that remain, what would it be?
Tim White: Well, the funny thing about this game is every time you find a new hominid fossil it creates two gaps, one younger and one older. So the fossil record we get is very fragmentary, we try to piece that together and we've done pretty well at that, extending that record back to the six million year point. Now the next step is tying these back together to the last common ancestor that we shared with the great apes and that common ancestor probably lived about seven, eight million years ago in Africa and so that's really the focus now, we'd really like to know what that creature was like.
Tim White from the University of California at Berkley. We wish him luck in his search for the eight million n year old ancestor, lining us to the great apes. Well, that's about it for this week and thanks for your company. Next week we'll be exploring the world of tailor-made drugs and ice-bound lakes, but in the meantime remember that nature and all of the other journals and resources produced by the Nature Publishing Group are available on line, including through institutional site licensed access. There is more information about this at our website at http://www.nature.com, but now, if you still have an appetite for more science, have a listen to this week's Naked Scientistspodcast where we'll be looking at meteorology and the science of weather prediction and climate modelling. That's the Naked Scientists podcast which is freely available from the http://www.thenakedscientists.com.
Production on this week's Nature podcast was by Anna Lacey in the Department of Pathology at Cambridge University and I'm Chris Smith.
