Genetic evidence for selective transport of opsin and arrestin by kinesin-II in mammalian photoreceptors

To test whether kinesin-II is important for transport in the mammalian phot oreceptor cilium, and to identify its potential cargoes, we used Cre-loxP m utagenesis to remove the kinesin-II subunit, KIF3A, specifically from photo receptors. Complete loss of KIF3A caused large accumulations of opsin, arre stin, and membranes within the photoreceptor inner segment, while the local ization of cu-transducin was unaffected. Other membrane, organelle, and tra nsport markers, as well as opsin processing appeared normal. Loss of KIF3A ultimately caused apoptotic photoreceptor cell death similar to a known ops in transport mutant. The data suggest that kinesin-II is required to transp ort opsin and arrestin from the inner to the outer segment and that blocks in this transport pathway lead to photoreceptor cell death as found in reti nitis pigmentosa.