Evidence for Kinesin-related Proteins Associated with the Axoneme of Retinal Photoreceptors

Situated at the junction between inner and outer segment, the connecting cilium of retinal photoreceptors supports regulated transport of molecules that function distally, while restricting diffusion of membrane proteins from one plasmalemmal domain to the other. Both functions are thought to be performed by a group of proteins stably or transiently associated with the axoneme. We have identified two types of unique polypeptides which associated with the axoneme in a nucleotide-dependent manner: they bind to the axonemes in the presence of adenosine monophosphate (AMP)-PNP, and are solubilized in the presence of adenosine triphosphate (ATP). The first group contained glyconjugates, previously shown to be part of the axoneme–plasmalemma cross-linkers at the connecting cilium. The second group cross-reacted with antibodies to two different conserved peptide sequences (called LAGSE and HIPYR) of kinesin-related proteins, and included polypeptides of∼85–97 kDa. Immunofluorescence microscopy of whole-mounted axonemes with the two anti-kinesin antibodies showed labeling throughout the axoneme, including the connecting cilium-basal body region. These results suggest that the identified proteins may serve as motor molecules for transport of material to the outer segment via the connecting cilium.