Fig. 2. Intrinsic membrane protein compartmentalization within the OS.

Schematic of a mammalian rod in the region of the CC. Intrinsic membrane proteins are thought to be delivered to the apical/periciliary membrane on rhodopsin transport carrier (RTC) vesicles, where they fuse (see text for details). Membrane proteins then enter the CC/transition zone, possibly mediated by the BBSome. Proteins destined for disc and plasma membrane transport to the lamellar membranes most likely by diffusion. Eventually the nascent disc membranes are enclosed by the plasma membrane through a mechanism that separates plasma membrane proteins, the CNG gated channel-Na⁺/Ca²⁺,K⁺ exchanger complex, from the disc proteins, rhodopsin and peripherin 2, which likely occurs during peripherin 2-Rom1-mediated disc rim expansion (see text). Note that this schematic is not meant to be an exhaustive representation of all OS membrane protein transport, or of disc morphogenesis.