Functions of neuronal Synaptobrevin in the post-Golgi transport of Rhodopsin in Drosophila photoreceptors

Polarized transport is essential for constructing multiple plasma membrane domains in the cell. Drosophila photoreceptors are an excellent model system to study the mechanisms of polarized transport. Rab11 is the key factor regulating the post-Golgi transport of rhodopsin 1 (Rh1; also known as NinaE), a photoreceptive protein, to the rhabdomere, a photoreceptive plasma membrane. Here, we found that neuronal Synaptobrevin (nSyb) colocalizes with Rab11 on the trans-side of Golgi stacks and post-Golgi vesicles at the rhabdomere base, and nSyb deficiency impairs rhabdomeric transport and induces accumulation of Rh1 and vesicles in the cytoplasm; this is similar to the effects of Rab11 loss. These results indicate that nSyb acts as a post-Golgi SNARE toward rhabdomeres. Surprisingly, in Rab11-, Rip11- and nSyb-deficient photoreceptors, illumination enhances cytoplasmic accumulation of Rh1, which colocalizes with Rab11, Rabenosyn5, nSyb and Arrestin 1 (Arr1). Arr1 loss, but not Rab5 dominant negative (Rab5DN) protein expression, inhibits the light-enhanced cytoplasmic Rh1 accumulation. Rab5DN inhibits the generation of Rh1-containing multivesicular bodies rather than Rh1 internalization. Overall, these results indicate that exocytic Rh1 mingles with endocytosed Rh1 and is then transported together to rhabdomeres.