Meaningless minis? Mechanisms of neurotransmitter-receptor clustering

Initiation and maintenance of the postsynaptic neurotransmitter-receptor field are important steps during synapse formation and maturation, as they play a determinative role in regulating synaptic strength. However, the mechanisms directing neurotransmitter-receptor clustering and maintenance are poorly understood. Recently two models explaining glutamate-receptor clustering at the Drosophila neuromuscular junction have been proposed. One model postulates that release of an agent via single vesicle fusion events (minis) is required for the initiation of postsynaptic glutamate-receptor clustering, and that glutamate is not responsible for initiation or maintenance of the postsynaptic receptor field. The other model rules out a role for minis in initiation of clustering, and suggests a role for non-vesicular release of glutamate in receptor-field maintenance. Here, we compare and discuss the data underlying both models.