Synapse is a highly specialized structure for communication between two neurons or between a neuron and a muscle cell. Many neuronal defects can be reflected at synapses. So far, UBE3A’s role at synapses has not been elucidated. Our preliminary analyses show that synapse development is abnormal in dube3a mutants with overgrown synapses. This aim seeks to further characterize synaptic defects using Drosophila neuromuscular junction (NMJ) synapses as a model system. A combination of three different techniques will be used to discover synaptic defects in dube3a mutants at morphological, ultrastructural and physiological levels.