RPGR and retinal degeneration: To achieve this aim, knock-out cell lines for RPGR and several interactor genes (PDE6D, INPP5E and RPGRIP1L, all three are also involved in retinal degeneration) were generated with the CRISPR/Cas9 system allowing to demonstrate that PDE6D is necessary for a correct ciliary localization of prenylated proteins such as RPGR and INPP5E, but that RPGR is not essential for the localization of INPP5E in the cilia [39].