The active zone is the presynaptic region in the nerve terminals that mediates neurotransmitter release and is composed a dense collection of proteins called the cytomatrix at the active zone (CAZ). The CAZ proteins are thought to mediate synapse formation and regulate neurotransmitter release [, ].Bassoon is a CAZ protein that is involved in the formation of the retinal photoreceptor ribbon synapses, which is specialised for tonic release of neurotransmitter in the dark []. It plays a partin the early formation and delivery of precursor spheres to nascent ribbon synaptic sites and in ribbon anchoring during later stages of photoreceptor ribbon synaptogenesis [].