Visual Pigment Renewal in the Mature Frog Retina

The developing chick retina from stages 39-45 has been examined by biochemical and electron microscope techniques. The levels of rhodopsin contained in the maturing chick retina were evaluated by detergent extraction and correlated with rod outer segment formation. It was found that the appearance of rhodopsin in significant levels preceded outer segment formation by at least 2 days, thus implying that rhodopsin is synthesized in the receptor cell inner segment and translocated to the outer limb when disk membrane biogenesis occurs. The level of rhodopsin continues to rise as the rod outer segment develops. Development of both rods and cones originates and proceeds most rapidly in the fundus or central region and proceeds toward the periphery. In general, rod outer segments were noted to develop far more rapidly than cone outer segments.

Section: Discussionsupporting

confidence: 70%

Correlation of rhodopsin biogenesis with ultrastructural morphogenesis in the chick retina.

Mason¹,

Bighouse²

1975

“…This confirms earlier findings of others (4, 60) and indicates that approximately 10°/0 of the outer segment protein is produced each day . Much of this continuously synthesized protein has been shown to be opsin, the protein constituent of rod visual pigment (2,20,21,41) .…”

Section: Light Microscope Radioautographymentioning

confidence: 99%

Photoreceptor-Pigment Epithelial Cell Relationships in Rats With Inherited Retinal Degeneration

LaVail

Sidman

O’Neil

1972

117

Protein synthesis and displacement in photoreceptor and pigment epithelial cells of inbred normal (Fisher) and mutant (RCS) rats with inherited retinal degeneration has been studied by light and electron microscope radioautography . Groups of animals 14, 15,17,19,27, 35, and 50 days of age were injected with amino acids-H 3 and killed at subsequent time intervals . In normal rats, radioactive protein synthesized in the rod inner segments was incorporated into outer segment saccules and displaced outward ; the total renewal time of outer segments at all ages was approximately 9 days . In RCS photoreceptors, outer segment displacement was slowed from the normal rate before day 17 and at all subsequent stages . Most of the newly synthesized protein appeared to migrate only into the basal third of the outer segments . Labeling of pigment epithelial cells in RCS rats was always heavier than in controls. Labeled protein was displaced as early as 1 hr postinjection from pigment epithelial cell somas into the apical processes, and by 2 hr postinjection was located in the adjacent lamellar whorls characteristic of the mutant rat retina . After 1 day, radioactivity was present in the 14, 15, 17, and 19 day series of RCS rats in the apical third of the outer segment layer (occupied mainly by extra lamellar material) while there were few silver grains in the middle third of the layer (occupied mainly by distal parts of outer segments) . The RCS pigment epithelial cells thus have an unusual synthetic role and appear to be a source of the extra lamellar material . Electron microscope examination revealed that many intact pigment epithelial cell processes were incorporated into the large whorls of extra lamellae . In addition, many disorganized outer segment saccules were observed in continuity with longer membranous lamellae and large lamellar whorls . The extra lamellar material therefore appears to be derived from both rod outer segments and pigment epithelial cells .This radioautographic study in rats with in-"These cells which maintain a close relationship herited retinal degeneration explores the relationthroughout life, arise from precursors in adjacent ship between photoreceptor cells and pigment sectors of neuroepithelium in the embryonic epithelial cells at late stages of retinal histogenesis . optic vesicle, and become permanently apposed

“…Much of this protein is orient the photosensitive molecules, which are opsin, the protein component of rod visual pigstructural components of the discs . ment (2,12,13,16) . In the rat, mouse, and frog, the outer segments Repeated assembly of new membranous discs at of rod visual cells undergo continual renewal (24) .…”

Section: Introductionmentioning

confidence: 99%

The Renewal of Rod and Cone Outer Segments in the Rhesus Monkey

Young

1971

327

149

The renewal of retinal rod and cone outer segments has been studied by radioautography in rhesus monkeys examined 2 and 4 days after injection of leucine-3 H . The cell outer segment consists of a stack of photosensitive, membranous discs . In both rods and cones some of the newly formed (radioactive) protein became distributed throughout the outer segment . Furthermore, in rods (but not in cones), there was a transverse band of concentrated radioactive protein slightly above the outer segment base 2 days after injection . This was due to the formation of new discs, into which labeled protein had been incorporated . At 4 days, these radioactive discs were located farther from the outer segment base . Repeated assembly of new discs had displaced them away from the basal assembly site and along the outer segment. Measurements of the displacement rate indicated that each retinal rod produces 80-90 discs per day, and that the entire complement of outer segment discs is replaced every 9-13 days . To compensate for the continual formation of new discs, groups of old discs are intermittently shed from the apical end of the cell and phagocytized by the pigment epithelium . Each pigment epithelial cell engulfs and destroys about 2000-4000 rod outer segment discs daily. The similarity between visual cells in the rhesus monkey and those in man suggests that the same renewal processes occur in the human retina .