October 9, 2009
In Southeast Asia, an all-too-common parasite is known to increase the incidence of bile duct cancer in infected individuals. A paper just released in PLoS Pathogens shows how this happens. Knowing the molecular pathway that leads from parasite infection to cancer will almost certainly speed up the search for a cure for this cancer, and will probably add to our understanding of cancer in general.
Cancer is, of course, a category of diseases rather than a single disease. What holds cancer together as a coherent set of conditions is the inappropriate increase of cell proliferation in some tissue or another. Cell proliferation is, of course, normal and expected at some times and places. When an organism is growing there is quite a bit of proliferation. When a wound is healing, cell division must be sped up. Therefore, mechanisms have evolved to increase the rate of cell division, and many cancers are simply this mechanism operating in an inappropriate and sometimes out of control way.
The cause of inappropriate cell proliferation can be a genetic mutation, caused in turn by the chance mutation of an already susceptible gene, or by some kind of chemical or physical irritant.
Or it can be a fluke.
A fluke is a kind of worm in the class Trematoda. There are about 20,000 species of Trematoda, and many of them are parasites that live in mollusks and vertebrates. Commonly, Trematoda spend part of their life cycle in a mollusk, then move to a vertebrate host, and then move back to the mollusk host, as they reproduce alternatively using asexual and sexual mechanisms.
Opisthorchis viverrini, also known as the Southeast Asian or Oriental liver fluke, lives in a certain genus of freshwater snails and in humans, and when it lives in humans, it seems to predispose the humans to cholangiocarcinoma, which is cancer of the bile ducts.
The research reported yesterday identified a certain protein that is very similar to a human growth hormone, but that is found in and produced by the fluke.
Scientists knew that a particular protein of a type known as granulin was produced by the fluke, and it was known that other versions of granulin cause unchecked proliferation of cells. So they isolated the gene for the fluke version of the granulin, and placed the gene in bacteria which allows the production of sufficient quantities of the protein to use in experiments. This, in turn, allowed them to test the hypothesis that this fluke-produced protein acts like other granulin molecules in causing cancer-like growth of cells.
It turns out that fluke produced granulin is an effective cancer-causing agent.
The fluke appears to use the granulin to induce cell growth for its own nutrient supply. In addition, the fluke-produced granulin induces specific antibodies in the host that neutralize the granulin. So, there seems to be something of an arms race between parasite (fluke) and host (human).
Now that the protein is both characterized and linked to the cancer, it may be possible to produce a drug that will fight it, or to refocus efforts on the fluke infection itself to reduce the prevalence of this cancer. Also, the Opisthorchis viverrini system may now serve as a useful model for the study of growth hormone induced cancers.
Another reason that this research is very important is that there were two very strong hypotheses for the prevalence of this cancer in southeast Asia. The fluke could have caused the cancer by simply irritating the cells where the fluke lives. Alternatively, the people in regions where this fluke are common also have a diet high in a particular chemical compound called nitrosamines, abundant in the fermented fish eaten in the region, and thought to be possibly cancer-causing. While this research does not rule those ideas out, it does strongly suggest that fluke-excreted granulin is the culprit that should be addressed first.
This research is published in an OpenAccess journal, so you can read the original by clicking here.
October 8, 2009
NASA’s Spitzer Space Telescope has discovered a new ring around Saturn. This ring is very different from those previously known. In some ways, this ring resembles the “accretionary disk” found around some stars more than it resembles the thin, orderly rings that Saturn is famous for.
The new ring is much larger than any of the planet’s other rings and is tilted about 27 degrees off the main plane of rings. It starts about six million kilometers out from the planet, and is about 12 million kilometers wide. The moon Phoebe orbits just within this ring and is tentatively thought to be responsible for the ring’s existence. It would appear that as Phoebe circles around Saturn, it occasionally collides with comets, which are obliterated, with the debris from the collision contributing to the ring.
This ring is different from the other rings not only in its angle, but also in its thickness. The better known Saturnian rings are very thin (about 10 meters thick), but this mega-ring measures about 2.5 million kilometers thick. That is roughly 20 times the diameter of Saturn. As Anne Verbiscer, one of the authors of the study reporting this feature, puts it, “This is one supersized ring. If you could see the ring [from Earth], it would span the width of two full moons’ worth of sky, one on either side of Saturn.”
The ring appears to be made out of very dispersed particles of ice and dust, which were visible to the Spitzer telescope using its infrared detectors. The particles are spread out so thinly that if you were in the thickest part in a spacecraft, you would not easily detect the ring’s existence. The Spitzer instruments were able to “see” the ring only because they were very sensitive to even tiny amounts of infrared radiation emanating from the particles making up the ring.
The discovery helps solve a mystery regarding the Saturnian moon Iapetus. Iapetus has an odd appearance whereby one side is bright and the other is really dark, in a pattern resembling a yin-yang symbol. The dark area is called the Cassini Regio, after Giovanni Cassini who discovered Iapetus in 1671 and later described its dark side.
Iapetus, the previously known rings of Saturn and most of Saturn’s moons circle in one direction, while the newly discovered mega ring circles the other way. It appears that the material from this ring splatters Iapetus—think of bugs hitting a windshield—as the moon and the ring move in opposite directions.
For more information, see NASA’s Spitzer Space Telescope web site.
October 7, 2009
Scientists from Britain and Japan used sophisticated techniques to study the feeding behavior of the black-browed albatross (Thalassarche melanophrys) at sea. A lot of useful information came out of this study, but the single item you will likely hear most about is a really cool photograph, taken by the albatross itself, of a killer whale.
It is difficult to study albatross because they fly hundreds of kilometers across open ocean, flying faster than a boat can sail, to find food. Since you can’t just follow them, and since their open ocean feeding area is very large, observing albatross feeding behavior can’t be done reliably.
The new study addressed this problem by using miniature digital cameras attached to the backs of four birds breeding at colonies on Bird Island, South Georgia in the Southern Ocean. The resulting pictures showed albatrosses foraging in groups while at sea to collect food for their chicks. The cameras included a depth meter and a thermometer. The depth information was intended to indicate when the albatross would dive underwater for food, and the temperature meter indicates when the bird is settled on the sea surface or dives into water.
The following diagram shows what these information resulting from an instrument-fitted albatross flight looks like:
The X-axis is time, showing that this particular flight that took over two hours. The squiggly line along the top indicates temperature and the vertical lines along the lower part of the chart indicate depth. The bird appears to make four dives and later on sits on the water for a while (indicated by the cooling down without a dive event). The camera took photographs on a regular basis, and the Xes in the diagram indicate a photograph with another organism in it, generally another albatross. This shows that the albatross tracked in this diagram dived and presumably fed in the vicinity of other birds. The X with the red circle indicates a photograph of special interest, this one:
Here you can see two birds, one higher and one lower than the bird with the camera, and the three birds together seem to be closing in on a whale. This is an orca, a.k.a. killer whale.
This image showed that the killer whale broke the surface and that three other albatrosses were also apparently following the whale. This image was, unfortunately, followed by subsequent images that were obscured by feathers. However, the rapidly decreasing external temperature suggests that the bird landed on the sea surface after the encounter with the killer whale…
The camera is small, weighing about 82 grams. Although the camera slightly changes the aerodynamic shape of the albatross, it did not affect the breeding success of the study birds. In all, over 28,000 pictures were taken with the albatross mounted cameras. According to Dr Richard Phillips from British Antarctic Survey (BAS), “These images are really interesting. They show us that albatrosses associate with marine mammals in the same way as tropical seabirds often do with tuna. In both cases the prey (usually fish) are directed to the surface and then it’s easy hunting for the birds.”
October 6, 2009
On Friday, October 9, two space ships will crash into the moon, and you will be able to see it happen.
All you need to do is find the crater Cabeus, which is near the Moon’s south pole. Be watching at 11:30 UT (That’s 4:30 a.m. Pacific Time, 6:30 a.m. Central.) Bring your telescope. It should be a pretty good telescope. According to NASA:
“We expect the debris plumes to be visible through mid-sized backyard telescopes 10 inches and larger,” says Brian Day of NASA/Ames. Day is an amateur astronomer and the Education and Public Outreach Lead for LCROSS. “The initial explosions will probably be hidden behind crater walls, but the plumes will rise high enough above the crater’s rim to be seen from Earth.”
If you live in the eastern part of the United States or anywhere towards daylight (east) from there, it may be too bright. Hawaii is ideal within the US, but anywhere west of the Mississippi is a potential viewing spot. I live four blocks east of the Mississippi, so I guess I’ll have to drag my telescope down to the shore and canoe across for better viewing!
There is another way to see the impacts: Tune in NASA TV. Coverage starts at 3:15 a.m. PDT. In some areas, you may get that station on your local cable system.
But why are the spaceships crashing into the Moon? Has something gone terribly wrong? Are we being invaded by aliens?
Well, this is an experiment cooked up by NASA to see if there is water on the Moon. First, a rocket called The Centaur will hit the moon. This rocket weighs about 2,200 kg and it is going fast, so there will be a great deal of energy released. A huge plume of debris will be blown up as much as 10 kilometers. This plume will be observed from earth, the Hubble space telescope, and the Lunar Reconnaissance Orbiter (LRO), and analyzed for presence of water.
However, close behind The Centaur will be the LCROSS space ship. This craft has instrumentation on it that will allow a much more detailed analysis of the plume. LCROSS will fly into the plume sent up by The Centaur, analyze the material really fast, and send its data back to earth. And then … it will also crash into the moon.
“If there’s water there, or anything else interesting, we’ll find it,” says Tony Colaprete of NASA Ames, the mission’s principal investigator.
LCROSS will hit the moon about four minutes after The Centaur. The most interesting statement in NASA’s press release regarding this experiment is probably this one:
“Remember, we’ve never done this before. We’re not 100% sure what will happen, and big surprises are possible.”
If you are interested in viewing this spectacular lunar experiment at a public event (and the public events are quite diverse as to what they offer, see if there is one in your area and refer to the LCROSS Viewer’s Guide.
October 5, 2009
An important finding was reported last week in the same issue of Science as the new studies of Ardipithecus, and unfortunately, overshadowed by the news of the 4-million-year-old hominid. This finding may turn out to be even more important because it relates not to the evolution of a single species, but to the recovery of life in general on Earth following one of the greatest catastrophes ever.
I’m referring to a paper by Julio Sepúlveda and others called “Rapid Resurgence of Marine Productivity After the Cretaceous-Paleogene Mass Extinction.”
Sepúlveda and colleagues examined marine sediments in Denmark that date to the period following the K-T mass extinction event. That event consisted of an impact on the Earth of a large asteroid 65 million years ago and the subsequent extinction of many species including all the dinosaurs. It is thought that there was a huge drop in the biological activity in the oceans after the event because the sun was largely blocked out, reducing photosynthesis in ocean-living algae. Without sun, the algae would have died off, and without algae, which are at the base of the oceanic food chain, other life forms in the ocean would die off or become very rare. The more widely accepted reconstructions of what happened indicate that this oceanic die-off did indeed happen, and that it took up to three million years for the ecosystems of the open ocean to recover from this impact. (Near-shore ecosystems have been thought to recover much more quickly.) The relatively lifeless post-impact open ocean is sometimes referred to as the “Stangelove ocean” in reference to the character in the apocalyptic movie “Dr. Strangelove.”
That previous research, however, was based on the examination of fossils of marine organisms including algae that leave an easily fossilized “skeleton” of silica, which indeed are sparse for a very long time after the impact. However, it is possible that certain types of organisms that do not leave behind fossils, such as cynobacteria, were abundant and would remain undetected in the fossil record.
The paper by Sepúlveda and colleagues used a different kind of evidence to look for open ocean biological activity and found it, in abundance, possibly within a century after the impact. If this proves to be true, then the darkening of the sky following the impact must have been fairly short term, and the observed long-term disruption of the ocean’s ecosystems must have a different explanation.
“Primary productivity came back quickly, at least in the environment we were studying,” according to Roger Summons, one of the paper’s authors. “The atmosphere must have cleared up rapidly. People will have to rethink the recovery of the ecosystems. It can’t be just [because of] the lack of food supply.”
The method this research team used was to look for isotopically distinct materials in the ocean sediments they examined, as well as molecules that could only have been formed by living things.
The sediments they looked in consist of a 37-centimeter-thick layer of clay in Denmark. Within this clay, which was deposited in relatively shallow near-shore environments, are hydrocarbon molecules produced by living organisms that are reasonably well preserved from 65 million years ago. These molecules indicate the existence of extensive open oceanic photosynthesis that would not have been possible under the “Strangelove ocean” model.
The way the analysis works can be understood this way: The ocean has a lot of dissolved carbon in it. This carbon exists in the form of more than one isotope. An isotope is a version of an element that is only a tiny bit different in its nuclear composition, and most elements lighter than Uranium have multiple non-radioactive isotopes. If there was no life in the ocean, the carbon would reach a certain equilibrium with respect to the proportion of each isotope, so sediments that included carbon would have a predictable ratio of these isotopes. (Note: This has nothing to do with radiocarbon dating. See this blog post for more on the potential confusion about that issue.)
Living forms use carbon, but when carbon is taken from the surrounding environment certain isotopes are incorporated into biological tissue more readily than others. Which isotopes are used and in what way by biological systems, and the exact reason for this, is complex and far beyond the scope of a mere blog post! Suffice it to say that when a geochemist looks at a sample of carbon, using very sensitive instruments, she can tell if this carbon has come from a non-biological system vs. a biological system. Beyond this, it is even possible to tell what kind of biological system is represented.
Sepúlveda’s team was able to tell that the carbon in these post-impact sediments could only have been assembled into these hydrocarbons (and other compounds) in a functioning open ocean ecosystem with plenty of algae photosynthesizing away at a pretty good clip. Since these sediments were deposited right after the impact, the “Strangelove” ocean theory, with a vast lifeless sea, is highly unlikely.