Architectural principles in central mammalian synapses

Synapses transduce action potentials into neurotransmitter release with extraordinary efficiency and temporal precision. To execute this function, it is imperative that the Ca2+ trigger signal is rapid and fast to efficiently activate the synaptic vesicle fusion machinery. Mechanistic analysis revealed that both efficient fusion and efficient Ca2+ secretion coupling depends on closing the distances as much as possible between membranes and between Ca2+ channels and release machinery. Also, postsynaptic neurotransmitter receptors need to be close to sites of vesicle fusion to maximize postsynaptic responses. While most molecular players of synaptic function are known, whether and how they are spatially arranged are still poorly understood. I will present electron microscopy compatible live labelling approaches for pre- and postsynaptic players and analyzed their intrinsic position in the synapse in relationship to synaptic vesicle docking and fusion function. We demonstrate physical alignment of synaptic vesicles, Ca2+ channels and postsynaptic AMPA receptors and fusion sites. Moreover, we show that forced transsynaptic coupling of Ca2+ channel subunits with postsynaptic AMPA receptors are sufficient in rescuing loss of synaptic organization and function upon loss of RIM/RBP, arguing that the core executors of synaptic transmission can also act as organizer of the synaptic apparatus.