Figure 8.

Model for exocyst-mediated trafficking of ciliary and outer segment proteins. A, mRNA is generated by transcription in the nucleus, and proteins are translated from mRNA in the endoplasmic reticulum and then sent to the trans-Golgi network for packaging into vesicles for transport to their final cellular destination. Ciliary and outer segment proteins are found in vesicles that have a small GTPase, Rab8, on the surface, which binds to exocyst complex member Exoc6. Exoc6, bound to the vesicle containing the ciliary and outer segment proteins, then interacts with the central exocyst complex protein Exoc5, which, in turn, brings the vesicle to the rest of the exocyst, itself localized to the primary cilium by another small GTPase, Cdc42. B, when this ciliogenic pathway is perturbed, the result in a global zebrafish knockout of exoc5 is defects in multiple ciliated organs, including the eye. In mice with a photoreceptor-specific knockout of Exoc5, the result is retinal degeneration and blindness. Scale bar, 0.268 mm.