The post-Golgi trafficking in Drosophila photoreceptors, in particular that of rhodopsin 1 (Rh1) to photoreceptive rhabdomeres at the plasma membrane, has been proven a useful model system to study the secretory pathway; this has been shown to require Rab11, a marker of recycling endosomes, but the exact mechanisms remain unknown. Akiko K. Satoh and colleagues recently found that Synaptobrevin (Syb), the orthologue of the human SNARE VAMP3 and another recycling endosome marker, localises to the trans-side of the Golgi stack, and in this work (Yamashita et al., 2022), they now address the role of the neuronal isoform nSyb in Rh1 transport. The authors show first that nSyb is essential for post-Golgi Rh1 transport, and, moreover, that nSyb also localises to post-Golgi vesicles at the base of rhabdomeres, identifying this factor for the first time as the SNARE involved in post-Golgi transport in photoreceptors, in addition to its well-described function in synaptic vesicle fusion. Furthermore, results obtained from nSyb-null photoreceptors of dark-reared flies suggest that nSyb also has a role in recycling of Rh1 via light-induced endocytosis, in addition to orchestrating the exocytosis of the newly synthesised protein. Taken together, the work presented here thus describes a new and unexpected role for nSyb in regulating rhodopsin distribution in Drosophila photoreceptors.
