Browsing by Subject "Rhodopsin"

Now showing 1 - 4 of 4

Open Access
PEDF Deletion Induces Senescence and Defects in Phagocytosis in the RPE.
(International journal of molecular sciences, 2022-07) Rebustini, Ivan T; Crawford, Susan E; Becerra, S Patricia
The retinal pigment epithelium (RPE) expresses the Serpinf1 gene to produce pigment epithelium-derived factor (PEDF), a retinoprotective protein that is downregulated with cell senescence, aging and retinal degenerations. We determined the expression of senescence-associated genes in the RPE of 3-month-old mice that lack the Serpinf1 gene and found that Serpinf1 deletion induced H2ax for histone H2AX protein, Cdkn1a for p21 protein, and Glb1 gene for β-galactosidase. Senescence-associated β-galactosidase activity increased in the Serpinf1 null RPE when compared with wild-type RPE. We evaluated the subcellular morphology of the RPE and found that ablation of Serpinf1 increased the volume of the nuclei and the nucleoli number of RPE cells, implying chromatin reorganization. Given that the RPE phagocytic function declines with aging, we assessed the expression of the Pnpla2 gene, which is required for the degradation of photoreceptor outer segments by the RPE. We found that both the Pnpla2 gene and its protein PEDF-R declined with the Serpinf1 gene ablation. Moreover, we determined the levels of phagocytosed rhodopsin and lipids in the RPE of the Serpinf1 null mice. The RPE of the Serpinf1 null mice accumulated rhodopsin and lipids compared to littermate controls, implying an association of PEDF deficiency with RPE phagocytosis dysfunction. Our findings establish PEDF loss as a cause of senescence-like changes in the RPE, highlighting PEDF as both a retinoprotective and a regulatory protein of aging-like changes associated with defective degradation of the photoreceptor outer segment in the RPE.
Open Access
Selective loss of RPGRIP1-dependent ciliary targeting of NPHP4, RPGR and SDCCAG8 underlies the degeneration of photoreceptor neurons.
(Cell Death Dis, 2012-07-19) Patil, H; Tserentsoodol, N; Saha, A; Hao, Y; Webb, M; Ferreira, PA
The retinitis pigmentosa GTPase regulator (RPGR) and nephrocystin-4 (NPHP4) comprise two key partners of the assembly complex of the RPGR-interacting protein 1 (RPGRIP1). Mutations in RPGR and NPHP4 are linked to severe multisystemic diseases with strong retinal involvement of photoreceptor neurons, whereas those in RPGRIP1 cause the fulminant photoreceptor dystrophy, Leber congenital amaurosis (LCA). Further, mutations in Rpgrip1 and Nphp4 suppress the elaboration of the outer segment compartment of photoreceptor neurons by elusive mechanisms, the understanding of which has critical implications in uncovering the pathogenesis of syndromic retinal dystrophies. Here we show RPGRIP1 localizes to the photoreceptor connecting cilium (CC) distally to the centriole/basal body marker, centrin-2 and the ciliary marker, acetylated-α-tubulin. NPHP4 abuts proximally RPGRIP1, RPGR and the serologically defined colon cancer antigen-8 (SDCCAG8), a protein thought to partake in the RPGRIP1 interactome and implicated also in retinal-renal ciliopathies. Ultrastructurally, RPGRIP1 localizes exclusively throughout the photoreceptor CC and Rpgrip1(nmf247) photoreceptors present shorter cilia with a ruffled membrane. Strikingly, Rpgrip1(nmf247) mice without RPGRIP1 expression lack NPHP4 and RPGR in photoreceptor cilia, whereas the SDCCAG8 and acetylated-α-tubulin ciliary localizations are strongly decreased, even though the NPHP4 and SDCCAG8 expression levels are unaffected and those of acetylated-α-tubulin and γ-tubulin are upregulated. Further, RPGRIP1 loss in photoreceptors shifts the subcellular partitioning of SDCCAG8 and NPHP4 to the membrane fraction associated to the endoplasmic reticulum. Conversely, the ciliary localization of these proteins is unaffected in glomeruli or tubular kidney cells of Rpgrip1(nmf247), but NPHP4 is downregulated developmentally and selectively in kidney cortex. Hence, RPGRIP1 presents cell type-dependent pathological effects crucial to the ciliary targeting and subcellular partitioning of NPHP4, RPGR and SDCCAG8, and acetylation of ciliary α-tubulin or its ciliary targeting, selectively in photoreceptors, but not kidney cells, and these pathological effects underlie photoreceptor degeneration and LCA.
Open Access
The evolving capabilities of rhodopsin-based genetically encoded voltage indicators.
(Curr Opin Chem Biol, 2015-08) Gong, Yiyang
Protein engineering over the past four years has made rhodopsin-based genetically encoded voltage indicators a leading candidate to achieve the task of reporting action potentials from a population of genetically targeted neurons in vivo. Rational design and large-scale screening efforts have steadily improved the dynamic range and kinetics of the rhodopsin voltage-sensing domain, and coupling these rhodopsins to bright fluorescent proteins has supported bright fluorescence readout of the large and rapid rhodopsin voltage response. The rhodopsin-fluorescent protein fusions have the highest achieved signal-to-noise ratios for detecting action potentials in neuronal cultures to date, and have successfully reported single spike events in vivo. Given the rapid pace of current development, the genetically encoded voltage indicator class is nearing the goal of robust spike imaging during live-animal behavioral experiments.
Open Access
The receptor kinase family: primary structure of rhodopsin kinase reveals similarities to the beta-adrenergic receptor kinase.
(Proc Natl Acad Sci U S A, 1991-10-01) Lorenz, W; Inglese, J; Palczewski, K; Onorato, JJ; Caron, MG; Lefkowitz, RJ
Light-dependent deactivation of rhodopsin as well as homologous desensitization of beta-adrenergic receptors involves receptor phosphorylation that is mediated by the highly specific protein kinases rhodopsin kinase (RK) and beta-adrenergic receptor kinase (beta ARK), respectively. We report here the cloning of a complementary DNA for RK. The deduced amino acid sequence shows a high degree of homology to beta ARK. In a phylogenetic tree constructed by comparing the catalytic domains of several protein kinases, RK and beta ARK are located on a branch close to, but separate from the cyclic nucleotide-dependent protein kinase and protein kinase C subfamilies. From the common structural features we conclude that both RK and beta ARK are members of a newly delineated gene family of guanine nucleotide-binding protein (G protein)-coupled receptor kinases that may function in diverse pathways to regulate the function of such receptors.