Rods and cones là gì

Figure 1.

The Periciliary Ridge Complex [PRC] is formed by 9 ridges and grooves surrounding the base of the connecting cilium. Arrow points to an opsin laden vesicle fusing with the groove of the PRC. Reprinted, with permission, from Papermaster DS, Schneider BG, Besharse JC. Vesicular transport of newly synthesized opsin from the Golgi apparatus toward the rod outer segment: ultrastructural immunocytochemical and autoradiographic evidence in Xenopus retinas. Invest Ophthalmol Vis Sci. 1985;26:1386–1404. © Association for Research in Vision and Ophthalmology.

Figure 1.

The Periciliary Ridge Complex [PRC] is formed by 9 ridges and grooves surrounding the base of the connecting cilium. Arrow points to an opsin laden vesicle fusing with the groove of the PRC. Reprinted, with permission, from Papermaster DS, Schneider BG, Besharse JC. Vesicular transport of newly synthesized opsin from the Golgi apparatus toward the rod outer segment: ultrastructural immunocytochemical and autoradiographic evidence in Xenopus retinas. Invest Ophthalmol Vis Sci. 1985;26:1386–1404. © Association for Research in Vision and Ophthalmology.

Figure 2.

Comparison of the distribution of GFP and GFP fusion proteins in the rods of transgenic frogs. [A] GFP fills the cytoplasm and nucleoplasm of the inner segment and synaptic-terminal. Only a small amount is found in the rod outer segment [ROS] because the impenetrable disks occupy most of the volume there. [B] GFP-CT44 is a fusion protein of GFP with the last 44 amino acids of Xenopus rhodopsin. It is membrane bound because its cysteines are palmitoylated and it localizes nearly exclusively to the ROS. [C] GFP-AAR is a fusion protein of GFP with the last 39 amino acids of the C-terminal of the α-adrenergic receptor [AAR], a heptahelical receptor resembling rhodopsin in overall structure. In contrast to GFP-CT44, GFP-AAR localizes predominantly to the synaptic terminal. [D] GFP-AAR-CC-CT8 is a fusion protein of GFP, the C-terminal of AAR which has had its last 8 amino acids replaced by the last 8 amino acids of Xenopus rhodopsin. The switch of this small domain changes the distribution of the fusion protein from the synaptic terminal [C] to the ROS to resemble GFP-CT-44 [B]. Thus the localization signal of rhodopsin in rods resides within the last 8 amino acids of its sequence. Reprinted, with permission, from Tam BM, Moritz OL, Hurd LB, Papermaster DS. Identification of an outer segment targeting signal in the COOH terminus of rhodopsin using transgenic Xenopus laevis. J Cell Biol. 2000;151:1369–1380. © Rockefeller University Press.

Figure 2.

Comparison of the distribution of GFP and GFP fusion proteins in the rods of transgenic frogs. [A] GFP fills the cytoplasm and nucleoplasm of the inner segment and synaptic-terminal. Only a small amount is found in the rod outer segment [ROS] because the impenetrable disks occupy most of the volume there. [B] GFP-CT44 is a fusion protein of GFP with the last 44 amino acids of Xenopus rhodopsin. It is membrane bound because its cysteines are palmitoylated and it localizes nearly exclusively to the ROS. [C] GFP-AAR is a fusion protein of GFP with the last 39 amino acids of the C-terminal of the α-adrenergic receptor [AAR], a heptahelical receptor resembling rhodopsin in overall structure. In contrast to GFP-CT44, GFP-AAR localizes predominantly to the synaptic terminal. [D] GFP-AAR-CC-CT8 is a fusion protein of GFP, the C-terminal of AAR which has had its last 8 amino acids replaced by the last 8 amino acids of Xenopus rhodopsin. The switch of this small domain changes the distribution of the fusion protein from the synaptic terminal [C] to the ROS to resemble GFP-CT-44 [B]. Thus the localization signal of rhodopsin in rods resides within the last 8 amino acids of its sequence. Reprinted, with permission, from Tam BM, Moritz OL, Hurd LB, Papermaster DS. Identification of an outer segment targeting signal in the COOH terminus of rhodopsin using transgenic Xenopus laevis. J Cell Biol. 2000;151:1369–1380. © Rockefeller University Press.

Figure 3.

GFP-wt-rab8 is a fusion protein of GFP and the normal sequence of canine rab8. The green fluorescence of the protein is contrasted with that of membrane glycoproteins labeled with rhodamine-wheat germ agglutinin [red]. The nucleus [N] is stained blue with Hoechst dye. The yellow color of the Golgi [G] and the post-Golgi pathway is a result of the overlap of the GFP-rab8 and the glycosylated membranes of the Golgi, and post-Golgi compartments. Note the bright spot near the junction of the inner and outer segments between the mitochondria [M]. This likely represents the vesicles that are docking at the PRC. Some GFP-rab8 is seen at the synapse [S]. Reprinted, with permission, from Moritz OL, Tam BM, Hurd LL, Peranen J, Deretic D, Papermaster DS. Mutant rab8 impairs docking and fusion of rhodopsin-bearing post-Golgi membranes and causes cell death of transgenic Xenopus rods. Mol Biol Cell. 2001;12:2341–2351. © The American Society for Cell Biology.

Figure 3.

GFP-wt-rab8 is a fusion protein of GFP and the normal sequence of canine rab8. The green fluorescence of the protein is contrasted with that of membrane glycoproteins labeled with rhodamine-wheat germ agglutinin [red]. The nucleus [N] is stained blue with Hoechst dye. The yellow color of the Golgi [G] and the post-Golgi pathway is a result of the overlap of the GFP-rab8 and the glycosylated membranes of the Golgi, and post-Golgi compartments. Note the bright spot near the junction of the inner and outer segments between the mitochondria [M]. This likely represents the vesicles that are docking at the PRC. Some GFP-rab8 is seen at the synapse [S]. Reprinted, with permission, from Moritz OL, Tam BM, Hurd LL, Peranen J, Deretic D, Papermaster DS. Mutant rab8 impairs docking and fusion of rhodopsin-bearing post-Golgi membranes and causes cell death of transgenic Xenopus rods. Mol Biol Cell. 2001;12:2341–2351. © The American Society for Cell Biology.

Figure 4.

Retinas of transgenic X. laevis expressing GFP-rab-T822N or GFP-rab8-wt. GFP-rab-T822N is an “off” mutant form of rab8 fused to the C-terminal of GFP. This protein is toxic to newly forming rods. Its expression is turned on just as the cells differentiate. [A] GFP-rab8-T22N Most of the rods have died by 14 days leaving behind a nearly all cone retina. Frog cones have refractile oil droplets in the inner segment. Only a few newly added rods survive at the periphery. [B] GFP-wt-rab 8. The rods survive and the retinal organization is normal. H&E stained sections of 14 dpf tadpole retinas. From Moritz et al. submitted for publication.

Figure 4.

Retinas of transgenic X. laevis expressing GFP-rab-T822N or GFP-rab8-wt. GFP-rab-T822N is an “off” mutant form of rab8 fused to the C-terminal of GFP. This protein is toxic to newly forming rods. Its expression is turned on just as the cells differentiate. [A] GFP-rab8-T22N Most of the rods have died by 14 days leaving behind a nearly all cone retina. Frog cones have refractile oil droplets in the inner segment. Only a few newly added rods survive at the periphery. [B] GFP-wt-rab 8. The rods survive and the retinal organization is normal. H&E stained sections of 14 dpf tadpole retinas. From Moritz et al. submitted for publication.

Figure 5.

Electron micrograph of the junction of the inner and outer segments of a peripheral rod expressing GFP-rab8-T22N. The mutant induces the accumulation of tubulo-vesicular membranes adjacent to the PRC. Controls expressing GFP-wt-rab8 have only a few vesicles at that site [not shown]. Reprinted, with permission, from Moritz OL, Tam BM, Hurd LB, Peranen J, Deretic D, Papermaster DS. A rab8 mutant causes accumulation of rhodopsin-bearing membranes and cell death in transgenic Xenopus rods. Mol Biol Cell. 2001;12:2341–2351. © American Society for Cell Biology.

Figure 5.

Electron micrograph of the junction of the inner and outer segments of a peripheral rod expressing GFP-rab8-T22N. The mutant induces the accumulation of tubulo-vesicular membranes adjacent to the PRC. Controls expressing GFP-wt-rab8 have only a few vesicles at that site [not shown]. Reprinted, with permission, from Moritz OL, Tam BM, Hurd LB, Peranen J, Deretic D, Papermaster DS. A rab8 mutant causes accumulation of rhodopsin-bearing membranes and cell death in transgenic Xenopus rods. Mol Biol Cell. 2001;12:2341–2351. © American Society for Cell Biology.