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Archive - Mar 2013

March 21st

Testing Visual Acuity of Archerfish Which Target Prey above the Water

A modified version of an eye test used to assess visual acuity in the military has been given to archerfish by scientists to help explain how these remarkable fish are able to accurately spit down tiny insects high above the water’s surface. Dr. Shelby Temple, now at the University of Bristol in the UK, and his team at the University of Queensland and the University of Western Australia used a modified version of the Landolt C test to discover just how fine a detail the archerfish could resolve. The researchers first trained the fish to spit at one of two letters – an ‘O’ or a ‘C’ – by rewarding them with food. Then they showed them small versions of both letters together and recorded which letter they spat at. Dr. Temple said: "This modified Landolt C test works because the only difference between the two letters is the gap in the ‘C’ so in order to tell the difference and spit at the right target to get their reward the fish must be able to resolve the gap." To test the archerfish's resolving power, the size of the letters were decreased in steps to see just how small they could go. The scientists then compared these behavioural results to the fishes' predicted acuity based on measurements of the photoreceptor density in their retinas. The results, published online ahead of print in the journal Vision Research, show that archerfish are one of the most visually acute freshwater fish, able to resolve approximately 3.5 cycles per degree with the part of their retina that looks up and forwards, which is not surprising given their interesting foraging strategy. Archerfish have a special way of hunting for food that involves spitting jets of water at aerial insects above the water’s surface.

Smelling Different Genome Odors and Mate Choice--Results Point to More Than MHC

It’s a theory much discussed in the media – that animals and humans are able to smell certain genes linked to the immune system – which in turn influences their choice of mate. The genes in question are known as MHC (major histocompatibility complex) genes. Selecting a mate with very different MHC genes from one’s own makes sense, because your offspring will then have a greater variety of immunity genes – and a correspondingly greater resistance to disease. But until now, no scent offering information about MHC genes had been discovered among those scents emitted by humans and animals. Now researchers from the University of Tübingen’s Immunology department and the Proteome Center in Germany, working with their colleagues from the University of Saarland, also in Germany, have managed to do just that. Their results, published online on March 19, 2013 in Nature Communications, will lead scientists to review the “sniff out a mate” theory. It is well known that the MHC genes determine which MHC peptides a cell presents at its surface to the immune system’s killer cells. These peptides are usually composed of the body’s own proteins and therefore do not set off any reaction. But if the MHC peptides come from a virus, the immune system’s killer cells can recognize that and attack it. According to one current theory, the MHC peptides also communicate the smell which offers information about MHC genes – a theory tested in mice. Special sensor cells were found which are able to recognize and distinguish the various MHC peptides from one another. Experiments have shown that synthetic MHC peptides in high concentrations were able to influence the behavior of mice, and that mouse urine carries what is believed to be the smell of MHC genes. Until now, it was not known whether MHC peptides even occurred naturally in urine.

March 20th

New Imaging Agent Enables Better Cancer Detection, More Accurate Staging

Researchers at the University of California (UC), San Diego School of Medicine have shown that a new imaging dye, designed and developed at the UC San Diego Moores Cancer Center, is an effective agent in detecting and mapping cancers that have reached the lymph nodes. The radioactive dye called Technetium Tc-99m tilmanocept, successfully identified cancerous lymph nodes and did a better job of marking cancers than the current standard dye. Results of the Phase III clinical trial were published online on March 20, 2013 in the Annals of Surgical Oncology. "Tilmanocept is a novel engineered radiopharmaceutical specifically designed for sentinel lymph node detection," said David R. Vera, Ph.D., the drug's inventor, who is a professor in the UCSD Department of Radiology. "The molecule, developed at UC San Diego School of Medicine, offers surgeons a new tool to accurately detect and stage melanoma and breast cancers while in the operating room." On March 13, 2013, tilmanocept received U.S. Food and Drug Administration (FDA) approval. After a cancer diagnosis, surgeons want to be sure that the disease has not spread to a patient's lymph nodes, especially the sentinel nodes that may be the first place that a cancer reaches. The lymphatic system is a network of vessels and ducts that carry disease-fighting cells throughout the body, but can also act as a way for cancer cells to access the bloodstream. By surgically removing and examining the sentinel nodes that drain a tumor, doctors can better determine if a cancer has spread. "Tilmanocept advances the molecular targeting in breast cancer.

Baffling Rare Blood Type (Vel-Negative) Finally Explained

In the early 1950’s, a 66-year-old woman, sick with colon cancer, received a blood transfusion. Then, unexpectedly, she suffered a severe rejection of the transfused blood. Reporting on her case, the French medical journal Revue D’Hématologie identified her as, simply, “Patient Vel.” After a previous transfusion, it turns out, Mrs. Vel had developed a potent antibody against some unknown molecule found on the red blood cells of most people in the world—but not found on her own red blood cells. But what was this molecule? Nobody could find it. A blood mystery began, and, from her case, a new blood type, “Vel-negative,” was described in 1952. Soon it was discovered that Mrs. Vel was not alone. Though rare, it is estimated now that over 200,000 people in Europe and a similar number in North America are Vel-negative, about 1 in 2,500. For these people, successive blood transfusions could easily turn to kidney failure and death. So, for sixty years, doctors and researchers have hunted—unsuccessfully—for the underlying cause of this blood type. But now a team of scientists from the University of Vermont (UVM) and France has found the missing molecule—a tiny protein called SMIM1—and the mystery is solved. Reporting in the journal EMBO Molecular Medicine, UVM’s Dr. Bryan Ballif, Dr. Lionel Arnaud of the French National Institute of Blood Transfusion, and their colleagues explain how they uncovered the biochemical and genetic basis of Vel-negative blood. “Our findings promise to provide immediate assistance to health-care professionals should they encounter this rare but vexing blood type,” says Dr. Ballif. The pre-publication results were presented online on March 18, 2013, and the finalized report will be published, as an open-access article, in the next edition of the journal. Last year, Drs.

Plants Recognize and Respond Specifically to Predators

Insect or microbe: plants recognize their attackers and respond by producing specific internal signals that induce the appropriate chemical defenses. That is the main conclusion of a study at the Center for Medical, Agricultural and Veterinary Entomology operated in Gainesville, Florida (USA) by the USDA’s Agricultural Research Service, to which the team around Professor Ted Turlings of the University of Neuchâtel, Switzerland, has contributed. The study was published online on March 18, 2013 in PNAS. When attacked, plants produce cascades of molecular reactions aimed at neutralizing their specific opponents. In response to insect attack plants produce toxins that directly affect the herbivore, but they also emit an odorous cry for help that attracts natural enemies of the pest, thus ensuring indirect protection of the plants. However, the biochemical mechanisms which trigger these defenses have been poorly understood until now. The research to which the biologists of the University of Neuchâtel contributed is directed precisely at this missing link. It has led to the identification of a peptide called ZmPep3, which maize plants produce when their leaves are eaten by herbivorous caterpillars. This peptide triggers the production of insecticidal substances, as well as the emission of a particular odor that specifically attracts natural enemies of the pest, in this case a parasitic wasp that lays its eggs in the caterpillars. To determine the attractiveness of odorous signals, the Gainesville team turned to the Neuchâtel group of experts, known for their discovery of the cry for help in plants.

March 17th

Nuclear DNA Sequencing Clarifies Relationship Between Polar Bears and Brown Bears

At the end of the last ice age, a population of polar bears was stranded by the receding ice on a few islands in southeastern Alaska. Male brown bears swam across to the islands from the Alaskan mainland and mated with female polar bears, eventually transforming the polar bear population into brown bears. Evidence for this surprising scenario emerged from a new genetic study of polar bears and brown bears led by researchers at the University of California (UC), Santa Cruz. The findings,published on March 14, 2013 in the open-access journal PLOS Genetics, upend prevailing ideas about the evolutionary history of the two species, which are closely related and known to produce fertile hybrids. Previous studies suggested that past hybridization had resulted in all polar bears having genes that came from brown bears. But the new study indicates that episodes of gene flow between the two species occurred only in isolated populations and did not affect the larger polar bear population, which remains free of brown bear genes. At the center of the confusion is a population of brown bears that lives on Alaska's Admiralty, Baranof, and Chicagof Islands, known as the ABC Islands. These bears--clearly brown bears in appearance and behavior--have striking genetic similarities to polar bears. "This population of brown bears stood out as being really weird genetically, and there's been a long controversy about their relationship to polar bears. We can now explain it, and instead of the convoluted history some have proposed, it's a very simple story," said coauthor Dr. Beth Shapiro, associate professor of ecology and evolutionary biology at the UC Santa Cruz (UCSC). Dr. Shapiro and her colleagues analyzed genome-wide DNA sequence data from seven polar bears, an ABC Islands brown bear, a mainland Alaskan brown bear, and a black bear.

March 15th

Tapeworm Genome Sequencing Reveals Potential Weaknesses to Existing Human Drugs

For the first time, researchers have mapped the genomes of tapeworms to reveal potential drug targets on which existing drugs could act. The genome sequences provide a new resource that offers faster ways to develop urgently needed and effective treatments for these debilitating diseases. The results were published online in an open-access article in Nature on March 13, 2013 by Wellcome Trust Sanger Institute scientists and collaborators. Tapeworms cause two of the World Health Organization's 17 neglected tropical diseases; echinococcosis and cysticercosis. The research team sequenced the genomes of four species of tapeworm to explore the genetics and underlying biology of this unusual parasite. As an adult it can live relatively harmlessly in the gut, but its larvae can spread through the body with devastating effects. The larvae form cysts in the internal organs or tissues of humans and other animals. These cysts proliferate or grow in the body, much like cancer. In some species this can cause complications such as blindness and epilepsy; with others it may lead to death. "Tapeworm infections are prevalent across the world and their devastating burden is comparable to that of multiple sclerosis or malignant melanoma," says Dr. Matthew Berriman, senior author from the Wellcome Trust Sanger Institute. "These genome sequences are helping us to immediately identify new targets for much-needed drug treatment. In addition, exploring the parasites' full DNA sequences is driving our understanding of its complex biology, helping the research community to focus on the most effective drug candidates." Normally, researchers identify new targets for drugs to combat diseases by comparing a pathogen's genome sequence with the human host's DNA to find differences between them.

March 11th

Gene Expression Studies Show Antarctic and Arctic Insects Use Different Genetic Mechanisms to Cope With Lack of Water

Although they live in similarly extreme ecosystems at opposite ends of the world, Antarctic insects appear to employ entirely different methods at the genetic level to cope with extremely dry conditions than their counterparts that live north of the Arctic Circle, according to National Science Foundation (NSF)-funded researchers. Writing in the December 11, 2012 issue of PNAS, the researchers concluded, "Polar arthropods have developed distinct... mechanisms to cope with similar desiccating conditions." The researchers noted that aside from the significance of the specific discovery about the genetics of how creatures cope in polar environments, the new finding is important because it shows how relatively new and developing scientific techniques, including genomics, are opening new scientific vistas in the Polar Regions, which were once thought to be relatively uniform and, relatively speaking, scientifically sterile environments. "It's great to have an Antarctic animal that has entered the genomic era," said David Denlinger, a distinguished professor of entomology at Ohio State University and a co-author of the paper. "This paper, which analyzed the expression of thousands of genes in response to the desiccating environment of Antarctica, is just one example of the power that the genomic revolution offers for advancing polar science." The collaborative research--which included contributions from scientists at Ohio State University, the Centre National de la Recherche Scientifique (National Center for Scientific Research) in France, Catholic University of Louvain in Belgium, Stanford University, and Miami University in Ohio--was supported in part by the Division of Polar Programs in NSF's Geosciences Directorate. Polar Programs manages the U.S. Antarctic Program, through which it coordinates all U.S.

March 11th

Study Shows How Fruit Fly Gained Its Wings

Scientists have delved more deeply into the evolutionary history of the fruit fly than ever before to reveal the genetic activity that led to the development of wings – a key to the insect’s ability to survive. The wings themselves are common research models for this and other species’ appendages. But until now, scientists did not know how the fruit fly,Drosophila melanogaster, first sprouted tiny buds that became flat wings. A cluster of only 20 or so cells present in the fruit fly’s first day of larval life was analyzed to connect a gene known to be active in the embryo and the gene that triggers the growth of wings. Researchers determined that the known embryonic gene, called Dpp, sends the first signal to launch the activation of a gene called vn. That signal alone is dramatic, because it crosses cell layers. The activation of the vn gene lasts just long enough to turn on a target gene that combines with additional signals to activate genes responsible for cell growth and completion of wing development. “Our work shows how when you add a gene into the equation, you get a wing. The clue is that one growth factor, Dpp, turns on another growth factor, vn, but just for a short period of time. You absolutely need a pulse of this activity to turn on yet another gene cascade that gives you a wing, but if vn is active for too long, a wing wouldn’t form,” said Dr. Amanda Simcox, professor of molecular genetics at The Ohio State University and lead author of the study. “We learned all this from investigating 20 tiny cells. The events could be responsible for this big event in evolutionary history, when the insect got its wing.

Single MicroRNA Keeps Segmentation “Clock” Running in Embryos

New research shows that a tiny piece of RNA has an essential role in ensuring that embryonic tissue segments form properly. The study, conducted in chicken embryos, determined that this piece of RNA regulates cyclical gene activity that defines the timing of the formation of tissue segments that later become muscle and vertebrae. Genes involved in this activity are turned on and off in an oscillating pattern that matches the formation of each tissue segment. If the timing of these genes’ activity doesn’t remain tightly regulated, the tissue either won’t form at all or will form with defects. One gene long associated with this segmentation “clock” is called Lfng. Researchers established in this study that a single microRNA – a tiny segment of RNA that has no role in producing any protein – is key to turning off Lfng at precisely the right time as tissues form in this oscillating pattern. When the microRNA was deleted or manipulated so that it wouldn’t bind when it was supposed to, the oscillatory pattern of the genetic clock was broken and tissue development was abnormal. “It’s a big deal to find that a single interaction between a microRNA and its target has this very profound effect when you interfere with its function,” said Dr. Susan Cole, associate professor of molecular genetics at The Ohio State University and lead author of the study. “There are very few cases where interfering with just one microRNA during development can make this much of a difference. But here, this regulation is so tight that this turns out to be incredibly important.