Neuronal circuits are formed through synaptic connections between defined populations of neurons. The regulated assembly and disassembly of synaptic connections ensures precise connectivity during development and during plasticity of the mature circuit. In contrast, the inappropriate loss of synaptic connections leads to a disruption of neuronal circuits and to progressive neurodegenerative disorders. Therefore, identification of the molecular mechanisms controlling synaptic connectivity is essential for our understanding of neuronal circuit function and plasticity in development and disease. more