David S. Papermaster - US grants

Polarized distribution of membrane proteins is a characteristic of most differentiated cells and is especially expressed in retinal photoreceptors. We seek to determine to cellular mechanisms of sorting and vectorial distribution of membrane proteins from sites of synthesis to sites of function. Prior studies have concentrated on opsin biosynthesis and demonstrated the role of the Golgi and post-Golgi vesicles in opsin transport to the apex of the rod inner segment. These studies have employed high resolution techniques of immunocytochemistry at the EM level. Antigens are localized in the interior of cells as well as on cell surfaces using polyclonal or mouse monoclonal antibodies on thin sections of retinas embedded in Lowicryl K4M, albumin or frozen sucrose. The distribution of cell surface antigens is being explored by new techniques of ultrahigh resolution scanning electron microscopy using thin (2nm) niobium or tantalum coatings. Bound antibodies are detected by the streptavidin-biotin-bridge technique using biotinyl antibodies and streptavidin-gold or using streptavidin followed by biotinyl-albumin-gold or biotinyl-ferritin conjugates. Labeling densities are quantitated by semiautomated mophometry. Antiopsin antibodies will be used to study rod outer segment disk morphogenesis and terminal stages of opsin transport from the periciliary ridge complex to the outer segment along the connecting cilium plasma membrane. Antibodies to toad retina and brain (Na+, K+) ATPase will be generated and compared for specificity and cross reactivity with presently available polyclonal and monoclonal antibodies against toad kidney ATPase. New monoclonal antibodies will be generated to other photoreceptor and retinal neuron plasma membranes as probes of the sorting of membrane proteins in the Golgi apparatus. Specificity of the antibodies will be further evaluated by binding to electrophoretic transblots of retinal proteins and purified ATPase and its proteolytic fragments. The use of several types of antibodies to several different antigens in photoreceptors and other retinal neurons should allow us to determine the degree to which our findings regarding specific sorting of opsin can be generalized to other retinal membrane proteins. Double label techniques should directly evaluate the role of the Golgi in sorting of these proteins.

[unreadable] DESCRIPTION (provided by applicant): Why photoreceptors die when expressing mutant proteins such as rhodopsin, and why cones should die in such instances when they do not express the mutated gene is still unclear. X. laevis frogs have abundant rods and cones in their retinas and develop a functioning retina within 14 days post-fertilization. We developed models of retinal degeneration in transgenic X. laevis. Adult transgenic frogs transmit the transgenes to offspring. We have generated more than 100 transgenic lines and published studies of 56 transgenic animals in 6 years. We aim 1) to evaluate the localization, function and impact of mutations of prominin-1 on rods. Prominin-1 is a pentaspan membrane protein localized exclusively to basal disks in rods and mutations of it cause retinal degeneration in humans. We have isolated the cDNA of Xenopus prominin-1 and made GFP fusion constructs that localize appropriately. We have also prepared antibodies to GST-fusion peptides of prominin and will use the antibodies and the fusion peptides in pull-down assays to isolate prominin's binding partners. The protein will be evaluated to determine which domains account for its unusual localization and it will be mutated to evaluate the impact by comparison with human mutations. 2) A new model of retinal degeneration has been created by expression of mutant rab8T22N which induces apoptosis early in the development of central rods, blocks docking of post-Golgi membranes to the base of the cilium and leads to formation of a nearly all-cone retina after 14 d. We will pursue the binding partners of rab8 in order to determine its role in vesicle docking. 3) We are initiating new studies of moesin in photoreceptors because perturbation of its localization has been shown in propranolol treated retinas similar to the effects of rab8T22N. We will use moesin PERM and actin binding domain fragments to block its function by expression of the fragments in transgenic frogs to determine the impact, in vivo, of the competition with endogenous moesin. 4) We will investigate the potential amelioration of cone death by antiapoptotic agents in our models of retinal degeneration in which the rods die early. Since the cones survive even beyond metamorphosis in the absence of rods, but eventually die, we will seek cone-preserving agents that may provide potential therapies in human retinal degenerations. [unreadable] [unreadable]

Polarized distribution of membrane proteins is a characteristic of most differentiated cells and is especially expressed in retinal photoreceptors. We seek to determine to cellular mechanisms of sorting and vectorial distribution of membrane proteins from sites of synthesis to sites of function. Prior studies have concentrated on opsin biosynthesis and demonstrated the role of the Golgi and post-Golgi vesicles in opsin transport to the apex of the rod inner segment. These studies have employed high resolution techniques of immunocytochemistry at the EM level. Antigens are localized in the interior of cells as well as on cell surfaces using polyclonal or mouse monoclonal antibodies on thin sections of retinas embedded in Lowicryl K4M, albumin or frozen sucrose. The distribution of cell surface antigens is being explored by new techniques of ultrahigh resolution scanning electron microscopy using thin (2nm) niobium or tantalum coatings. Bound antibodies are detected by the streptavidin-biotin-bridge technique using biotinyl antibodies and streptavidin-gold or using streptavidin followed by biotinyl-albumin-gold or biotinyl-ferritin conjugates. Labeling densities are quantitated by semiautomated mophometry. Antiopsin antibodies will be used to study rod outer segment disk morphogenesis and terminal stages of opsin transport from the periciliary ridge complex to the outer segment along the connecting cilium plasma membrane. Antibodies to toad retina and brain (Na+, K+) ATPase will be generated and compared for specificity and cross reactivity with presently available polyclonal and monoclonal antibodies against toad kidney ATPase. New monoclonal antibodies will be generated to other photoreceptor and retinal neuron plasma membranes as probes of the sorting of membrane proteins in the Golgi apparatus. Specificity of the antibodies will be further evaluated by binding to electrophoretic transblots of retinal proteins and purified ATPase and its proteolytic fragments. The use of several types of antibodies to several different antigens in photoreceptors and other retinal neurons should allow us to determine the degree to which our findings regarding specific sorting of opsin can be generalized to other retinal membrane proteins. Double label techniques should directly evaluate the role of the Golgi in sorting of these proteins.

Polarized distribution of membrane proteins is a characteristic of most differentiated cells and is especially expressed in retinal photoreceptors. We seek to determine to cellular mechanisms of sorting and vectorial distribution of membrane proteins from sites of synthesis to sites of function. Prior studies have concentrated on opsin biosynthesis and demonstrated the role of the Golgi and post-Golgi vesicles in opsin transport to the apex of the rod inner segment. These studies have employed high resolution techniques of immunocytochemistry at the EM level. Antigens are localized in the interior of cells as well as on cell surfaces using polyclonal or mouse monoclonal antibodies on thin sections of retinas embedded in Lowicryl K4M, albumin or frozen sucrose. The distribution of cell surface antigens is being explored by new techniques of ultrahigh resolution scanning electron microscopy using thin (2nm) niobium or tantalum coatings. Bound antibodies are detected by the streptavidin-biotin-bridge technique using biotinyl antibodies and streptavidin-gold or using streptavidin followed by biotinyl-albumin-gold or biotinyl-ferritin conjugates. Labeling densities are quantitated by semiautomated mophometry. Antiopsin antibodies will be used to study rod outer segment disk morphogenesis and terminal stages of opsin transport from the periciliary ridge complex to the outer segment along the connecting cilium plasma membrane. Antibodies to toad retina and brain (Na+, K+) ATPase will be generated and compared for specificity and cross reactivity with presently available polyclonal and monoclonal antibodies against toad kidney ATPase. New monoclonal antibodies will be generated to other photoreceptor and retinal neuron plasma membranes as probes of the sorting of membrane proteins in the Golgi apparatus. Specificity of the antibodies will be further evaluated by binding to electrophoretic transblots of retinal proteins and purified ATPase and its proteolytic fragments. The use of several types of antibodies to several different antigens in photoreceptors and other retinal neurons should allow us to determine the degree to which our findings regarding specific sorting of opsin can be generalized to other retinal membrane proteins. Double label techniques should directly evaluate the role of the Golgi in sorting of these proteins.

DESCRIPTION (adapted from the applicant's abstract): The principal investigator seeks to link mutations that can induce retinal degeneration in humans with disordered rhodopsin biosynthesis/transport and photoreceptor cell death. Many human retinal degenerations involve mutant genes expressed only in rods, yet cones die. How the injury of rods leads to cone death is unclear. The specific aims of this application are to: (1) develop transgenic Xenopus laevis as a model system to determine factors that perturb rhodopsin synthesis and transport and (2) develop models of retinal degeneration in transgenic Xenopus laevis to permit assessment of the impact of the death of rods on cone survival. To accomplish this, the investigator will determine: (1) where the transgene products are localized within photoreceptor cells; (2) the effect of the transgene products on the biosynthesis and transport of outer segment membrane proteins; and (3) their impact on photoreceptor cell viability. Preliminary results have been obtained using the opsin promoter to drive expression of green fluorescent protein (GFP) and GFP fusion proteins. The transgene products are expressed only in the major rods and are detectable 5 days after fertilization in the eye of the living tadpole. Since the frog retina is cone-rich, these transgenic frogs are suitable for examining the interaction of dying rods and the neighboring cones as models of human retinitis pigmentosa.