A new paper out in Nature, brakes through the diffraction barrier to see things that have never been seen before. Using this novel fluorescence-microscopy technique called STED (stimulated emission depletion), Willig et al., see Kiss and Run. And yes they see it!
OK ... I know, you have 2 questions. How does STED work? and What is Kiss and Run?
Rayleigh's law of resolution maxima, which says that you can never resolve two dots that are closer together than the ~size of the wave-length of light used to probe the sample, defines how small we microscopists can see in the two dimensional plain of the sample. What people have been able to take advantage of is to use a third dimension (usually time) to resolve slightly smaller structures in certain brightfield applications (hard to do, and you must track the sample in a living cell under certain conditions). Now Willig et.al, use a dot of excitation light to stimulate a point in the sample and a emission donut to quench the excitation surrounding the excitation dot to reduce the effective probing size of the light. This excitation dot can then be moved across the field like a conventional confocal microscope (in much the same way that a TV monitor is scanned). Previously, under the best conditions one would get a resolution of ~ 300nm for fluorescence microscopy, now this has been pushed down to about 70nm. Theoretically the resolution could go down indefinitely.
Now to Kiss and Run. When a vesicle fuses with a membrane, what happens to the vesicle? One would think that it flattens out and becomes part of the target membrane. However some researchers have suspected that the vesicle partially fuses and spews out some of its contents without losing its curvature then quickly buds right back off the target membrane. Click here to see a movie of Kiss and Run vs regular fusion. So the problem is that synaptic vesicles that are thought to undergo Kiss and Run are just too small to image (~40nm). But now with STED we can finally take a peek.
Nature even has a brief review of the new technique. Click here for the article.
Ref: Katrin I. Willig, Silvio O. Rizzoli, Volker Westphal, Reinhard Jahn, and Stefan W. Hell. STED microscopy reveals that synaptotagmin remains clustered after synaptic vesicle exocytosis.
Nature 440:935-939
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