The Scientist 13[5]:0, Mar. 01, 1999

Notebook

Notebook

By Multiple

	David Holtzman and Friend

SNAKE LOGIC David Holtzman, an assistant professor of brain and cognitive science at the University of Rochester, has loved snakes since childhood. But in college, when he wanted to investigate how snake brains develop, he found that serpents weren't exactly model organisms. "I wanted to devise a task that could show that snakes can learn as well as rodents--if you ask them to do the right thing," he recalls. Now Holtzman and his colleagues are doing just that (D.A. Holtzman et al., "Spatial learning of an escape task by young corn snakes, Elpahe guttata guttata," Animal Behaviour, 57:51-60, November 1998.) Rather than stuffing a four-foot corn snake into a not-much-longer maze, they use an "arena," which is a black, bathtub-like contraption with eight holes and strategically placed markings from which the animals can navigate. And the snakes do so quite well. At first it takes a snake more than 700 seconds to locate a hole. By day four, it's 400 seconds, and some do it in under 30 seconds. "In the 1950s, people tried to run snakes through mazes. This didn't work out, because it isn't natural for a snake to be in a maze--but they are darn good at escaping from and diving into holes," Holtzman says. The snakes have bits of aluminum foil on their heads so that a video camera can record their movements. The work has implications beyond vindicating snakes from their reputation as poor maze-runners. Says Holtzman, "We are looking at how experience influences certain brain changes. Understanding the mechanisms that regulate neurogenesis in any animal might help devise ways to stimulate that to happen in people."

SHINGLES VACCINE Childhood chicken pox comes back to haunt 1.2 million people in the United States each year, in the painful rash shingles. Current vaccines protect only against chicken pox, but a new recombinant vaccine invented by Abbas Vafai, who recently became chief of the biologics branch at the Centers for Disease Control and Prevention in Atlanta, promises to squelch both conditions. Varicella-zoster virus (VZV), a DNA virus that encodes only five glycoproteins, causes chicken pox. "Following primary infection, VZV becomes latent in sensory ganglia and may reactivate years later to produce shingles," says Vafai. People with suppressed immunity, such as the elderly and those with AIDS, cancer, or transplants, are at risk for VZV reappearance. Rarely, shingles can progress to painful neuralgia or encephalitis. The current vaccine is effective against chicken pox but not shingles because it is too much like real VZV--it's live but attenuated, and can hide in ganglia and emerge years later to cause shingles, says Vafai. The new recombinant vaccine, in contrast, consists of the gene encoding the portion of the most abundant and immunogenic viral glycoprotein that binds antibody. Plus, the vector enables mammalian cells to secrete the peptide product, a talent that previous recombinant VZV vaccines couldn't muster. "This vaccine does not contain the viral genetic material to become latent, and so it cannot subsequently reactivate to produce shingles," Vafai adds.

REST AND MOTION Timing is everything in bone marrow transplantation. Cells taking a "time out" from the cell cycle--a stage called Go--are more likely to find and repopulate depleted bone marrow than cells in G1, a more active stage. Using human hematopoietic cells and an immune-deficient mouse model, Edward Srour, associate professor of medicine and pediatrics at the Indiana University School of Medicine, and coworkers show that pushing cells into G1 squelches engraftment ability (A. Gothot et al., Blood, 92:2641-9, Oct. 15, 1998). "This is the most detailed examination of what happens to engraftment potential of cells as they progress into the active phase of the cell cycle," Srour says. The researchers used cytokines to push cells from their quiescent Go state, then detected those reaching G1 by telltale RNA synthesis as they awoke. "When Go cells are pushed into G1, they are unable to engraft, or do so poorly compared to those in Go," he adds. Loss of engraftment ability with cell cycle reentry may explain low efficiency of retroviral gene transfer. "The virus requires at least one cell division to integrate its DNA into the genome. Our work shows that even before cells integrate the transferred genetic material, they are already compromised," Srour says. Cells segueing from Go to G1 may be less successful for an indirect reason. Adds Srour, "Maybe cells in Go and G1 have equal engraftment potential, but only Go knows how to get to the bone marrow."

A PATHWAY LESS TRAVELED In Japan, researchers trying to pinpoint the metabolic defect in the most common form of diabetes have taken a pathway less traveled, and that may make all the difference. Among sufferers from Type II diabetes, insulin from ß cells in the pancreas is either secreted or used insufficiently. Metabolism of glucose, the body's main source of energy, triggers the release of insulin. In mammals, the Krebs cycle is an important pathway in this process, but the work of 15 Japanese scientists led by Takashi Kadowaki, an internist at the Graduate School of Medicine, University of Tokyo, indicates that another less- investigated pathway may be even more important in ß cells. It involves the molecule NADH, a reduced form of nicotinamide adenine dinucleotide that is transferred to the cell's energy-producing mitochondria by a chemical shuttle system (K. Eto et al., "Role of NADH shuttle system in glucose-induced activation of mitochondrial metabolism and insulin secretion," Science, 283:981-5, Feb. 12, 1999). When Kadowaki's group developed mice that lacked this shuttle system, they found that glucose-induced insulin secretion was abolished. "The shuttle system plays a central role in glucose-induced insulin secretion by regulating the Krebs cycle," Kadowaki concludes. The team's next step is to investigate whether the shuttle system itself is regulated by a pathway that has a defect in Type II diabetes sufferers. Ultimately, such work could produce a new diagnostic marker for use long before patients actually develop diabetes.

AIDS VACCINE, YES, BUT WHEN? "The only answer to the HIV epidemic will be a vaccine," David Baltimore, head of the AIDS Vaccine Research Committee (AVRC), told a standing-room-only crowd at the recent annual meeting of the American Association for the Advancement of Science. However, despite President Bill Clinton's challenge to the scientific community last year to produce an AIDS vaccine by 2007, Baltimore would not predict whether that deadline would be met. "I have no idea whether it will take nine years or 19 years," he said bluntly. "We cannot rush into trials just because the president would like us to come up with a vaccine." HIV's tenacity in fighting back has been frustrating scientists' efforts to develop a vaccine, but Baltimore insisted he is optimistic. In a comment that caused a wave of chuckles, he reminded the audience, "No scientist will ever say something can't happen." The AIDS vaccine remains the Holy Grail of scientific research. "Although the situation is not good now--we're not going to have a vaccine in the next few years--it's not wholly bleak," Baltimore opined. "There are many new avenues at the present and we should, in fact, be able to make a vaccine given enough time, energy and resources." In the meantime, the goal is to develop a "deep knowledge" of HIV, Baltimore said, and stay ahead of it by maintaining very strict regimens of compliance with treatment and putting out new drugs that the virus can't mutate around so easily.

BRUSHING AWAY HPV The genital warts of human papillomavirus (HPV) are associated with almost all the cervical malignancies that annually kill about 250,000 women worldwide. Now a compound commonly used in toothpaste and other personal care products has been shown to inactivate papillomavirus in human cell cultures and in animals (M.K. Howett et al., "A broad-spectrum microbicide with virucidal activity against sexually transmitted viruses," Antimicrobial Agents and Chemotherapy, 43:314-21, Feb. 1999). "For more than 20 years, people have been using this agent in the lab to take proteins apart," remarks lead author Mary K. Howett, a microbiology and immunology professor at Pennsylvania State University College of Medicine. Her multidisciplinary group tried about 15 surfactants and detergents to unfold HPV protein before they succeeded with sodium dodecyl sulfate (SDS). In preliminary work, the team had demonstrated that SDS is a potent inactivator of herpes simplex virus Type II and HIV Type I, apparently removing their envelopes. That led them to think SDS might unfold non-enveloped viral proteins, as in HPV. Not only were they right, but SDS can be applied in concentrations much lower than those found in personal care products, boding well for toxicity studies in animals and humans that are being conducted by the National Institute of Allergy and Infectious Diseases, which primarily funded this study. Although approval for human use will take years to accomplish, Howett says topical vaginal application of SDS eventually may protect women from being infected or from infecting partners with HPV and other sexually transmitted viruses.

ON PANDEMIC EVOLUTION New findings suggest that the virus causing the 1918 influenza pandemic may have been harbored by mammals rather than birds before the disease broke out, killing 20-40 million people worldwide (A.H. Reid et al., "Origin and evolution of the 1918 'Spanish' influenza virus hemagglutinin gene," Proceedings of the National Academy of Sciences, 96:1651-6, Feb. 1999). This would differentiate its evolution from that of the century's other two such pandemics, in 1957 and 1968, which are more avian than mammalian in the sequence of the hemagglutinin (HA) gene. HA binds to receptors on host cells to initiate infection, and only one amino acid change may be needed to allow an avian HA subtype to bind to a receptor subtype shared by both swine and humans, but not by birds. The 1918 virus might have mutated as it moved from birds to pigs to humans, although research biologist and lead author Ann H. Reid cautions, "We don't know if that single amino acid change is sufficient for the virus to adapt from the bird to the swine." She and colleagues at the Armed Forces Institute of Pathology in Washington, D.C., are using formalin-fixed influenza RNA from two soldiers who died in the 1918 pandemic and from one Inuit victim frozen in Alaskan permafrost for their analyses. They have not uncovered a reason why the 1918 strain was so virulent, but the work continues. "We hope to sequence the entire genome and are planning to be about halfway done at the end of this year."

ENGINEERING A MALARIA VACCINE Packing the antigen coding sequences from nine natural malaria epitopes into one synthetic gene may provide better protection from the parasite. The parasite causes 1.5- 3 million deaths and 300-500 million new cases annually--many of them resistant to existing vaccines, according to the Atlanta-based Centers for Disease Control and Prevention (CDC). In a rabbit model study, the vaccine produced antibodies that prevented malaria parasites from invading liver cells and from replicating in the blood. Moreover, in vitro assays of protection "revealed that the vaccine-elicited antibodies strongly inhibited sporozoite invasion of hepatoma cells and growth of blood stage parasites in the presence of monocytes," researchers write (Y.P. Shi et al., "Immunogenicity and in vitro protective efficacy of a recombinant multistage Plasmodium falciparum candidate vaccine," (Proceedings of the National Academy of Sciences, 96:1615-20, Feb. 16, 1999.) These findings demonstrate that natural immunity can be a guide for vaccine development and that a multicomponent, multistage malaria vaccine can induce multiple layers of immunity, according to Altaf A. Lal, chief of the molecular vaccine section of the Division of Parasitic Diseases at the CDC and one of the authors. Single immunizations in mice and rabbits elicited antibody responses against all stages of the human malaria parasite, Lal notes: "If at one stage the parasite breaks through, there will be a second layer of immunity to protect against infection at the next stage." In an accompanying commentary, Anthony Holder, head of the division of parasitology at the National Institute for Medical Research in London, agrees about the importance of a multiple component vaccine (A.A. Holder, "Malaria vaccines," PNAS, 96:1167-9, Feb. 16, 1996). "But whether the multiple components used in this particular vaccine are the right multiple components or if they are the sum total of what you would really need is still questionable," he tells The Scientist. The vaccine will next be tested in vivo in monkey models at the CDC.

The Scientist 13[5]:0, Mar. 01, 1999