Fig. 5. (A) Photoreceptor and retinal pigment epithelial (RPE) cells. At the tip of the photoreceptor inner segment (IS), myosin VIIa may be involved in opsin transfer (green arrow) to the connecting cilium and its transport to the outer segments (OS). (B) In RPE cells, melanosomes (M) display fast, bidirectional microtubule-dependent long-range movements in the cell body driven by kinesin/dynein motor proteins (1). Upon reaching the plus end of the microtubule at the periphery, myosin VIIa may be involved in the transfer (green arrow) of these organelles towards the actin filaments (2). Rab27a, which is targeted to the melanosome membrane, interacts with its effector, MyRIP/Slac2c, which in turn binds to myosin VIIa. Myosin VIIa then enables the retention and/or local movement of the melanosomes along the actin filaments of the microvilli (3). Myosin VIIa also plays a role in the transfer of phagosomes from the microvilli to the cell body (4; orange arrow). (C) At outer-disk–RPE-cell interface, protocadherin 15 present at the membrane of photoreceptor outer segments may serve to sense its immediate environment. For instance, through its extracellular domain, it may engage in heterophilic interactions with unidentified cadherin(s) in RPE cells to ensure proper alignment of the outer disks and apical microvilli. Harmonin b expressed in the photoreceptor outer disks is expected also to play a role in disk structure. N, nucleus.