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18 | NewScientist | 12 February 2011 The brain’s constant gardener JUST as gardeners prune unwanted growths from flowers, the brain has its own molecular secateurs for trimming back unwanted connections. Now we know what’s doing the pruning. Peter Scheiffele at the University of Basel, Switzerland, and colleagues used microscopes to view the developing brains of mice engineered so that individual neurons and their connections showed up in different colours. During development, purkinje cells in the cerebellum, vital for movement, initially formed a multitude of connections, many of which were later pruned away by bone morphogenic protein 4 (BMP4), a protein normally associated with bone growth and healing. In mice engineered to lack the protein, the abnormal connections remained, suggesting BMP4 is key to the trimming (PLoS Biology, DOI: 10.1371/journal.pbio.1001013). The team says it is not clear whether the unwanted connections are indispensable stepping stones or routine “overshoots” but the discovery may throw new light on diseases thought to result from misconnections during brain development, such as autism. HIV-like infection banished from mice FOR the first time, an HIV-like infection has been cleared from an animal without the use of antiviral drugs. Marc Pellegrini from the Walter and Eliza Hall Institute of Medical Research in Melbourne, Australia, and colleagues infected mice with a virus that mimics HIV. Eight days later, the mice were injected with human interleukin-7 (IL-7) – an immune cell protein – or a placebo, once a day for three weeks. “Usually mice never clear this virus,” says Pellegrini. But 30 days later, those given treatment had cleared most of the infection and removed all of it by 60 days (Cell, DOI: 10.1016/j.cell.2011.01.011). The explanation seems to lie in a protein called SOCS3, which stops immune cells working. When infection strikes, SOCS3 becomes more active to protect body tissue from an overzealous immune system. But in an overwhelming infection like HIV the brakes are put on too early and infection persists. Blood tests showed that IL-7 curbed the production of SOCS3 in a type of immune cell called a FEARS that bird extinction could have devastating effects on plant populations are being realised. Two bird species, the bellbird and the stitchbird, recently became extinct on New Zealand’s North Island. The flowering shrub Rhabdothamnus solandri (pictured) relies on these birds, as well as two other species, for pollination. Dave Kelly from the University of Canterbury in Christchurch, New Zealand, and colleagues compared how the plant fared on the North Island with its survival on three smaller islands where these birds live still. To provide a reference point, they also hand-pollinated flowers on 79 plants across the four islands, and compared their fruit production with untouched flowers. Around 70 per cent of the hand-pollinated flowers produced fruit in all locations. Without human help, just 22 per cent of the flowers on the North Island produced fruit, compared with 58 per cent on the small islands (Science, DOI: 10.1126/ science.1199092). Since birds pollinate a large proportion of flowering plants, the problem is likely to occur worldwide. If birds go extinct, plants could follow ROB SUISTED/NATUREPICS.COM T-cell, thereby boosting T-cell response. Since IL-7 doesn’t appear to affect other immune cells, drugs could be developed to turn off SOCS3 for short periods to reinvigorate T-cells without causing damage to body tissue. Sharon Lewin at the Burnet Institute in Melbourne says the finding that IL-7 can clear the virus without the help of antiviral drugs is very interesting. HIV uses the host’s cells to replicate, which makes it difficult to design antivirals that stop the virus without harming healthy cells. Humans only win by knowing rules YOU probably aren’t much smarter than a chimp when it comes to cooperative games – you just know the rules. Games are often used to test primates’ ability to reason about cooperation. In one game two players independently choose one of two tokens: one that always yields a small reward, or one that gives a big reward only if both players choose it. Humans quickly settle into the second strategy to maximise the reward, but other primates prove less able. Is this down to better reasoning, or merely because humans have had the rules explained to them? Sarah Brosnan, at Georgia State University in Atlanta, and colleagues replayed the game with humans, chimps and capuchin monkeys, but made all participants learn the rules by trial and error. Humans still performed the best, but not nearly as well as in previous tests. They also fared only slightly better than the other species, with just five of the 26 human pairs adopting the maximum-reward strategy (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1016269108). This suggests that language, not reasoning ability, accounts for most of the apparent human superiority at this game. MARY ANN MCDONALD/CORBIS IN BRIEF For new stories every day, visit www.NewScientist.com/news
