Required for the correct formation of synaptic vesicles at nerve terminals and has a role in the regulation of the synaptic vesicle exo-endocytic cycle. In larvae expressed in the synaptic neuropil of the central nervous system. Expressed throughout the larval brain, ventral nerve cord (VNC) and neuromuscular junction (NMJ) (at protein level). No obvious phenotype. Viable and fertile with normal basic motor functions. However in type 1b boutons at the larval neuromuscular junction of some mutants (30-40%), there is an increase in the number of synaptic vesicles with a large diameter and a decrease in vesicle density under resting conditions. Resolution of synaptic vesicles from endocytic cisternae following an intense stimulation is delayed, and consequently boutons display an increased number of cisternae. Mutant larvae also show an increase in the amplitude of spontaneous miniature excitatory junctional currents (mEJCs), but normal evoked excitatory junction currents (EJCs). No effect on synaptic growth, the number of synaptic vesicle release sites and vesicle budding. Belongs to the synaptogyrin family.