Abstract
Purpose :
The intraflagellar transport (IFT) complexes have a well-established role in the assembly and maintenance of primary cilia, including photoreceptor outer segments. The focus of our study was IFT20, a non-conventional subunit of the IFT-B particle that associates with the rest of IFT-B reversibly and is thought to play a role in recruiting IFT cargo from the Golgi to the cilium. We sought to explore the role of IFT20 in photoreceptor cells by analyzing the phenotype of the conditional IFT20 knockout.
Methods :
A rod-specific knockout of IFT20 in mice was generated by crossing a floxed IFT20 line with the iCre75 line that expresses Cre under control of the rhodopsin promoter. While Cre expression in this line begins as early as postnatal day 7, the depletion of IFT20 protein does not complete until after photoreceptor outer segments are fully developed. This allowed us to study the function of IFT20 in outer segment maintenance independent of its role in the outer segment development.
Results :
We found that the depletion of IFT20 protein from rods was followed by a complete degeneration of these cells within a period of several weeks. During this period of time, outer segment structure rapidly disintegrates followed by cell death. Yet, our analysis of outer segment resident proteins during the short window when outer segments are still present revealed only a minor mislocalization of rhodopsin and no mislocalization of peripherin-2. Interestingly, mislocalized rhodopsin was not found in the inner segment biosynthetic membranes but rather in extracellular vesicles accumulating around photoreceptor cell bodies.
Conclusions :
Taken together, this data suggest that the primary function of IFT20 in photoreceptors is in ciliary maintenance rather than in post-Golgi protein transport.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.