The molecular organization of presynaptic active zones during calcium influx-triggered neurotransmitter release is the focus of intense investigation. The Drosophila coiled-coil domain protein Bruchpilot (BRP) was observed in donut-shaped structures centered at active zones of neuromuscular synapses by using subdiffraction resolution STED (stimulated emission depletion) fluorescence microscopy. At brp mutant active zones, electron-dense projections (T-bars) were entirely lost, Ca2+ channels were reduced in density, evoked vesicle release was depressed, and short-term plasticity was altered. BRP-like proteins seem to establish proximity between Ca2+ channels and vesicles to allow efficient transmitter release and patterned synaptic plasticity.

We report attainment of subdiffraction resolution using stimulated emission depletion (STED) microscopy with GFPlabeled samples. The B70 nm lateral resolution attained in this study is demonstrated by imaging GFP-labeled viruses and the endoplasmic reticulum (ER) of a mammalian cell. Our results mark the advent of nanoscale biological microscopy with genetically encoded markers.

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