Shigeki Watanabe is the 2015 grand prize winner in the annual international competition for The Eppendorf & Science Prize for Neurobiology. Watanabe is being recognized for development of a technique that will allow researchers to visualize nerve cell activity on a scale not previously possible.
Photo courtesy of Shigeki Watanabe
"Nerve cells, or neurons, operate on a millisecond time scale, but the traditional electron microscopy methods are too slow to track changes that occur in these cells," said Watanabe, who pursued his Ph.D. research at the University of Utah with Dr. Erik Jorgensen and his postdoctoral work in the Rosenmund laboratory at the Charité Universitätsmedizin in Berlin, Germany. "We developed a novel technique, called 'flash-and-freeze.' to visualize these changes.
The technique will contribute to a better understanding of neurological diseases such as Alzheimer's disease and Parkinson's.
Human nerves fire constantly — working in support of the many physical and mental demands we put on our bodies. To better understand how our nervous system sustains such a high level of activity, Watanabe and colleagues at the University of Utah have been studying how neurons recycle synaptic vesicles, small cellular structures that release neurotransmitters, the primary means of neuron-to-neuron communication.
After neurons are stimulated, synaptic vesicles fuse with the cell membrane, releasing their chemical signals. This process happens over and over, reducing the vesicle supply. To counteract this, vesicles are recycled.
Scientists have previously proposed two models by which vesicle recycling happens — a faster model called kiss-and-run and a slower model based on the protein clathrin. Despite extensive research over four decades, scientists still don't know which model dominates when, and they are hampered in part by a lack of techniques for visualizing vesicle recycling on a fine scale.
Seeking to more closely observe the synaptic vesicle recycling process, Watanabe and his colleagues took advantage of a light-sensitive ion channel called channelrhodopsin, which serves as a switch to stimulate neurons; when light flashes, neurons engineered to express channelrhodopsin are activated, causing the synaptic vesicles they harbor to fuse at nerve terminals. Watanabe and colleagues engineered mouse hippocampal neurons to express channelrhodopsin, stimulated these neurons, and then froze them at different time points following stimulation.
A series of electron micrographs showing the order of the membrane movements at the synaptic terminal. Synaptic vesicles fuse and collapse into the membrane (panels 1-4). Subsequently, they are recovered by ultrafast endocytosis (panels 5-12). The whole process completes in 100 milliseconds. | Shigeki Watanabe
"We were able to capture snapshots of the events at different time points, in effect, generating a 'flip-book' of membrane movement during synaptic transmission with millisecond temporal resolution," Watanabe said.
"Shigeki Watanabe's work gives new insights into the process of neurotransmitter release, one of the most fundamental functions of every nervous system," said Dr. Peter Stern, Science's senior editor, who chaired the Prize jury.
While the synaptic vesicle recycling process has been thought to be slow, on the order of 10 seconds to 20 seconds, Watanabe's research showed it happens on the order of 50 milliseconds.
"His technique has pushed the boundaries of the time resolution under which these processes can now be studied by neuroscientists," Stern added.
The Eppendorf and Science Prize in Neurobiology recognizes outstanding international neurobiological research based on current methods and advances in the field of molecular and cell biology by a young early-career scientist, as described in a 1,000-word essay based on research performed within the last three years. The grand prize winner receives $25,000 from Eppendorf.
In his award-winning essay, "Slow or fast? — A tale of synaptic vesicle recycling," which will be published in the 2 October issue of Science, Watanabe describes how he was surprised to observe that vesicles are molded anew from structures inside the neurons called endosomes; scientists had previously thought that synaptic vesicles were regenerated at the cell surface.
His use of flash-and-freeze also revealed that the vesicle recycling mechanism seems to have two components-an ultrafast mechanism followed by a slower one. "The ultrafast mechanism rapidly clears the fusion sites of excess membrane," he wrote. "The slower mechanism, a clathrin-dependent process, reconstitutes vesicles at a more leisurely pace from endosomes — nevertheless it only requires 2-3 seconds, which is considered rapid for any mechanism."
He concludes that the ultrafast mechanism is not a kiss-and-run model, as some might suspect, and the slow mechanism does not operate at the plasma membrane, as the clathrin model is thought to. He suggests disagreement between his results and those that led to these two models may result from differences in experimental conditions, among other issues.
"In the future, I plan to apply these techniques to study the changes that occur on the other side of the synapse," said Watanabe, the 14th winner of the prize. "I hope to explore how memory is stored in our nervous system."
Watanabe and the following finalists will be recognized at the annual meeting of the Society for Neuroscience on Sunday, 18 October 2015, in Chicago, Illinois.
Julija Krupic, for her essay "Brain crystals." Krupic received her Ph.D. from the University College London as well as an undergraduate degree from Vilnius University and a Ph.D. from University College London (UCL). She is currently a Sir Henry Wellcome Fellow at UCL, where she conducts research on how place cell activity guides animal behavior. In 2016, Julija will move to the Salk Institute where she will study how connectivity affects the functional properties of place cells.
Jeremiah Cohen, for his essay "Dopamine and serotonin signals for reward across timescales." Cohen received his undergraduate degree from Brandeis University, a Ph.D. in neuroscience from Vanderbilt University, and completed his postdoctoral work at Harvard University. His laboratory in the Solomon H. Snyder Department of Neuroscience at Johns Hopkins University investigates the neural circuits underlying reward, mood, and decision making.
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