Biochemical Events Related to Circadian Photoreceptor Shedding

The renewal of vertebrate photoreceptor outer segments is accomplished by the assembly of new disc membranes at the base and shedding of old membranes at the distal tip of the outer segment (Young and Bok, 1969). This intermittent shedding process occurs shortly after the onset of light in animals entrained to a schedule of 12 hours of light and 12 hours of darkness and follows a circadian rhythm in rats (LaVail, 1976, 1980; Goldman et al, 1980) but is light-driven in frogs (Basinger et al., 1976; Hollyfield et al, 1976). In Xenopus laevis, both circadian and light-driven mechanisms can be expressed depending on experimental conditions (Besharse et al, 1977a). The immediate regulation of light-driven shedding in the frog resides in the eye itself (Hollyfield and Basinger, 1978). The same is true of circadian shedding in the rat, with the added complication that re-entrainment of the retinal pacemaker requires input from the central nervous system (Teirstein, Goldman and O’Brien, 1980). These processes have been reviewed recently by Besharse (1982).KeywordsOuter SegmentPhospholipid SynthesisPhotoreceptor Outer SegmentFrog RetinaCell BioIThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.