Abstract
Purpose::
Genetic studies have shown that the microtubule motor, kinesin-2, is required for the transport of opsin to the photoreceptor outer segment and photoreceptor cell viability. We have tested whether this motor is also required for the development of the photoreceptor outer segment, which involves growth of a cilium from the distal inner segment, followed by the amplification of the distal ciliary plasma membrane into photosensitive disk membranes.
Methods::
Mice carrying a floxed allele of Kif3a, which encodes the obligate motor subunit of kinesin-2, were mated with Crx-Cre transgenic mice, which express Cre in photoreceptor progenitor cells. Retinas from their progeny were prepared for electron microscopy in order to examine differentiating photoreceptor cells.
Results::
Without exception, photoreceptor cells in mutant (Kif3aflox/flox;Crx-Cre) mouse retinas failed to form cilia, and by P12, significant photoreceptor cell death had occurred.
Conclusions::
These results indicate that kinesin-2 is required for the formation of the photoreceptor cilium, in addition to transport along the ciliary axoneme in more mature photoreceptor cells, as indicated by earlier studies. Hence, the function of kinesin-2 in photoreceptor cells parallels that in other cells with cilia or flagella, with roles in both ciliogenesis and cilium maintenance.
Keywords: microscopy: electron microscopy • photoreceptors • retinal degenerations: cell biology