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Cellular and Molecular Biology

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Visualization of Synaptic Vesicle Fusion Under EM

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You are a graduate student in the lab of Sir Bernard Katz. Eager to earn your Ph. D, you accept a project trying to observe the fusion of synaptic vesicles with the plasma membrane, a key event in the release of neurotransmitter.

The only way you can visualize the fusion of membranes is by using transmission electron microscopy (TEM) since this is the only method with the resolving power needed to see synaptic vesicles and plasma membrane.

After years of failed attempts to visualize this event, you find that the harsh fixatives and sample preparation necessary for TEM studies actually distort the plasma membrane, preventing any observation of membrane fusion.

How do you solve this problem?

A

You invent a method of sample preparation where the sample is frozen in vitreous ice nearly instantaneously. This method does not distort membranes.

B

You set up a program for automated image acquisition and tiling (tiling meaning the serial acquisition of images by automatic panning across the entire sample). This method allows you to review many thousands of images over a larger sample area. In this way you can capture the event which may not occur frequently enough for you to capture by manually acquiring images.

C

You decide to switch from electron microscopy to a light microscopy approach, Förster Resonance Energy Transfer (FRET). With this approach you label a vesicle protein and a SNARE fusion protein to quantitatively measure binding of those proteins as a proxy for vesicle fusion.

D

As vesicles fuse the presynaptic membrane changes shape/composition very briefly. You realize that this can be measured as a transient change in membrane capacitance. You then used electrophysiological methods to measure changes in capacitance attributed to vesicle fusion.