A novel system for receptor transport in the arthropod photoreceptor cells

为了研究携带视紫红质囊泡的运输途径，我们使用抗视紫红蛋白抗体对果蝇视网膜进行了荧光显微镜检查。结果表明，紫红质在横纹肌膜出现之前，已浓缩到细胞质大囊泡（rlv，直径约200 nm）中。TRP是微绒毛膜上的钙通道蛋白，在RLV中共定位，而Na^+-K^+ atp酶不被转运到囊泡中。电镜观察发现rlv为多泡核内体。通过降低Rab11活性，视紫红质不能到达横纹肌，而是以分散在细胞质中的囊泡积累。横纹肌组织也被阻断。这些数据表明Rab11的减少抑制了MVE的生物发生和横纹肌膜的运输。为了进一步研究视紫红质的转运，我们用涂有抗视蛋白抗体的磁珠分离了携带视紫红质的囊泡。免疫印迹分析表明，分离的囊泡含有未成熟的视紫红质。对这些囊泡的进一步生化分析正在进行中。由于甲壳类动物的眼睛具有更大的组织尺寸，因此在视紫红质转运的生化研究中优于果蝇的眼睛。我们最近发现，在特定的光照条件下，MVEs在对虾的感光细胞中积累。这表明这些细胞适合用于囊泡运输的生化研究。

To investigate the traffic pathway of rhodopsin-carrying vesicles, we carried out fluorescence microscopic examination of the Drosophila retina using anti-opsin antibody. The results K demonstrated that rhodopsin is concentrated into cytoplasmic large vesicles (RLVs, >200 nm in diameter) prior to its appearance in rhabdomeric membrane. TRP, a calcium channel protein on microvillar membrane, is co-localized in RLV, while Na^+-K^+ ATPase is not transported into the vesicles. Electronmicroscopic observation identified RLVs as multivesicular endosomes (MVEs). By reducing Rab11 activity, rhodopsin failed to reach the rhabdomere and instead accumulated in vesicles dispersed throughout the cytoplasm. Organization of rhabdomere was also blocked. These data indicate Rab11 reduction inhibits MVE biogenesis and rhabdomere membrane traffic. For further investigation of rhodopsin transport, we isolated rhodopsin-carrying vesicles using magnetic beads coated with anti-opsin antibody. Immunoblot analysis demonstrated that the isolated vesicles Contained immature rhodopsin. Further biochemical analysis of these vesicles is in process. Considering the much larger tissue size, eyes of crustacean is superior to those of Drosophila for biochemical studies of rhodopsin transport. We recently found that MVEs accumulate in prawn photoreceptor cells under a particular light condition. This suggests that the cells would be suitable for biochemical studies of vesicle transport.