**9. Retinal Cilia and Phosphoinositides**

Phosphoinositides, and especially PI(4,5)P2 and PI(4)P, have been proposed to play important roles in assembly, disassembly, and regulation of primary cilia [52,58–62]. The lipid content of cilia is different from that of the plasma membrane, and a membrane diffusion barrier surrounding the cilium has been demonstrated (see [63] for a review). Two PI-5-phosphatases, INPP5E and OCRL, essential for cilium function have been reported to be localized to the cilium [41,64–66]
