Most land animals walk forward by default, but can switch to backward walking when they sense an obstacle or danger in the path ahead. The impulse to change walking direction is likely to be transmitted by descending neurons of the brain that control local motor circuits within the central nervous system. This neuronal input can change walking direction by adjusting the order or timing of individual leg movements.
Screening for flies with altered walking patterns
In the current study, Dickson and his team aimed to understand the fly’s change in walking direction at the cellular level. Using a novel technology known as thermogenetics, they were able to identify the neurons in the brain that cause a change in locomotion. Their studies involved screening large numbers of flies with it which specific neurons were activated by heat, producing certain behaviors only when warmed to 30°C, but not at 24°C . Analysing several thousand flies, the researchers looked for strains that exhibited altered walking patterns compared to control animals.
Moonwalker-neurons control backward walking
Using the thermogenetic screen, the IMP-researchers isolated four lines of flies that walked backward on heat activation. They were able to track down these changes to specific nerve cells in the fly brain which they dubbed „moonwalker neurons“. They could also show that silencing the activity of these neurons using tetanus toxin rendered the flies unable to walk backward.
Among the moonwalker neurons, the activity of descending MDN-neurons is required for flies to walk backward when they encounter an obstacle. Input from MDN brain cells is sufficient to induce backward walking in flies that would otherwise walk forward. Ascending moonwalker neurons (MAN) promote persistent backward walking, possibly by inhibiting forward walking.
“This is the first identification of specific neurons that carry the command for the switch in walking direction of an insect”, says Salil Bidaye, lead author of the study. “Our findings provide a great entry point into the entire walking circuit of the fly. “
Although there are obvious differences in how insects and humans walk, it is likely that there are functional analogies at a neural circuit level. Insights into the neural basis of insect walking could also generate applications in the field of robotics. To date, none of the engineered robots that are used for rescue or exploration missions can walk as robustly as animals. Understanding how insects change their walking direction at a neuronal level would reveal the mechanistic basis of achieving such robust walking behavior.
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The paper “Neuronal Control of Drosophila Walking Direction” by Salil S. Bidaye, Christian Machacek, Yang Wu and Barry Dickson is published in SCIENCE on 3 April, 2014.
Illustration & Videos
An illustration and videos to be used free of charge in connection with this press release can be downloaded from the IMP website: www.imp.ac.at/pressefoto-moonwalk
About Barry Dickson
Barry Dickson studied mathematics, computer science and genetics at the Universities of Melbourne and Queensland, Australia. After two years as a research assistant at the Salk Institute, San Diego, he moved to Zurich to work towards his PhD with Ernst Hafen at the University of Zurich, Switzerland. For his postdoctoral research, he joined Corey Goodman at the University of California in Berkeley. In 1998, Dickson joined the IMP in Vienna as Group Leader, and in 2006 was appointed Scientific Director of the institute. Since 2013, Barry Dickson is a Group Leader at the Janelia Farm Research Campus of the Howard Hughes Medical Institute.
About Salil Bidaye
Salil Bidaye received his Integrated Masters in Biotechnology from the University of Pune, India. From 2008 until 2013, he was a doctoral student at the Research Institute of Molecular Pathology in Vienna and received his PhD from the University of Vienna. At present, Salil Bidaye is a Postdoctoral Scholar at the Department of Molecular and Cell Biology of the University of California, Berkeley.
About the IMP
The Research Institute of Molecular Pathology (IMP) in Vienna is a basic biomedical research institute largely sponsored by Boehringer Ingelheim. With over 200 scientists from 37 nations, the IMP is committed to scientific discovery of fundamental molecular and cellular mechanisms underlying complex biological phenomena. Research areas include cell and molecular biology, neurobiology, disease mechanisms and computational biology.