Crag/Rab10/Ehbp1 regulate the basolateral transport of Na+K+ATPase in Drosophila photoreceptors

Cells in situ are often polarized and have multiple plasma membrane domains. To establish and maintain these domains, polarized transport is essential, and its impairment results in genetic disorders. Nevertheless, the underlying mechanisms of polarized transport have not been elucidated. Drosophila photoreceptor offers an excellent model to study this. We found that Rab10 impairment significantly reduced basolateral Na+K+ATPase levels, mislocalizing it to the stalk membrane, a domain of the apical plasma membrane. Furthermore, the shrunken basolateral and the expanded stalk membrane were accompanied with abnormalities in the Golgi cisternae of Rab10-impaired retinas. The deficiencies of Rab10-GEF Crag or the Rab10 effector Ehbp1 phenocopied Rab10 deficiency, indicating that Crag, Rab10, and Ehbp1 work together for polarized trafficking of membrane proteins to the basolateral membrane. These phenotypes were similar to the deficiency of AP1/clathrin, which is known to be involved in the basolateral transport in other systems. Additionally, Crag/Rab10/Ehbp1 colocalized with AP1/clathrin on the trans-side of Golgi stacks. Taken together, these results indicated that AP1/clathrin and Crag/Rab10/Ehbp1 collaborated in polarized basolateral transport, presumably in the budding process in the trans-Golgi network.