Fig. 3. Modeling the function of liprin and LAR during active zone assembly. Active zone formation can be divided into five steps: (1) the synthesis of dense core vesicles (dark circles) in the Golgi complex; (2) the transport of dense core vesicles to the presynaptic terminus; (3) the targeting of dense core vesicles to appropriate sites on the membrane; (4) the fusion of dense core vesicles with the plasma membrane; and (5) the stabilization of active zone proteins. The LAR and liprin mutant phenotypes suggest that these proteins are essential for stabilizing numerous proteins in a condensed and functional active zone. In addition, proper neurotransmitter release at the active zone depends on the proper transport (6) of synaptic vesicles (white circles) to the presynaptic terminus. In Drosophila, liprin mutants have severe defects in synaptic vesicle transport, in which synaptic vesicles accumulate in axons.