Retinal rod photoreceptor-specific gene mutation perturbs cone pathway development.

Rod-specific photoreceptor dystrophies are complicated by the delayed death of genetically normal neighboring cones. In transgenic (Tg) swine with a rod-specific (rhodopsin) gene mutation, cone photoreceptor physiology was normal for months but later declined, consistent with delayed cone cell death. Surprisingly, cone postreceptoral function was markedly abnormal when cone photoreceptor physiology was still normal. The defect was localized to hyperpolarizing cells postsynaptic to the middle wavelength-sensitive cones. Recordings throughout postnatal development indicated a failure of cone circuitry maturation, a novel mechanism of secondary cone abnormality in rod dystrophy. The results have implications for therapy for human retinal dystrophies and raise the possibility that rod afferent activity plays a role in the postnatal maturation of cone retinal circuitry.     

The circadian clock in the retina controls rod-cone coupling

Although rod and cone photoreceptor cells in the vertebrate retina are anatomically connected or coupled by gap junctions, a type of electrical synapse, rod-cone electrical coupling is thought to be weak. Using tracer labeling and electrical recording in the goldfish retina and tracer labeling in the mouse retina, we show that the retinal circadian clock, and not the retinal response to the visual environment, controls the extent and strength of rod-cone coupling by activating dopamine D(2)-like receptors in the day, so that rod-cone coupling is weak during the day but remarkably robust at night. The results demonstrate that circadian control of rod-cone electrical coupling serves as a synaptic switch that allows cones to receive very dim light signals from rods at night, but not in the day. The increase in the strength and extent of rod-cone coupling at night may facilitate the detection of large dim objects.     

Good epidemiologic practice in retinitis pigmentosa: from phenotyping to biobanking

Inherited retinal dystrophies, such as retinitis pigmentosa (RP), include a group of relatively rare hereditary diseases caused by mutations in genes that code for proteins involved in the maintenance and function of the photoreceptor cells (cones and rods). The different forms of RP consist of progressive neurodegenerative disorders which are generally related to various and severe limitations of visual performances. In the course of typical RP (rod-cone dystrophy), the affected individuals first experience night-blindness and/or visual field constriction (secondary to rod dysfunctions), followed by variable alterations of the central vision (due to cone damages). On the other hand, during the atypical form of RP (cone-rod dystrophy), the cone's functionalities are prevalently disrupted in comparison with the rod's ones. The basic diagnosis of RP relies upon the documentation of unremitting loss in photoreceptor activity by electroretinogram and/or visual field testing. The prevalence of all RP typologies is variably reported in about one case for each 3000-5000 individuals, with a total of about two millions of affected persons worldwide. The inherited retinal dystrophies are sometimes the epiphenomenon of a complex framework (syndromic RP), but more often they represent an isolated disorder (about 85-90 % of cases). Although 200 causative RP mutations have been hitherto detected in more than 100 different genes, the molecular defect is identifiable in just about the 50% of the analyzed patients with RP. Not only the RP genotypes are very heterogeneous, but also the patients with the same mutation can be affected by different phenotypic manifestations. RP can be inherited as autosomal dominant, autosomal recessive or X-linked trait, and many sporadic forms are diagnosed in patients with no affected relatives. Dissecting the clinico-genetic complexity of RP has become an attainable objective by means of large-scale research projects, in which the collaboration between ophthalmologists, geneticists, and epidemiologists becomes a crucial aspect. In the present review, the main issues regarding clinical phenotyping and epidemiologic criticisms of RP are focused, especially highlighting the importance of both standardization of the diagnostic protocols and appropriateness of the disease's registration systems.     

Genetic dissection reveals two separate pathways for rod and cone regeneration in the teleost retina

Development of therapies to treat visual system dystrophies resulting from the degeneration of rod and cone photoreceptors may directly benefit from studies of animal models, such as the zebrafish, that display continuous retinal neurogenesis and the capacity for injury-induced regeneration. Previous studies of retinal regeneration in fish have been conducted on adult animals and have relied on methods that cause acute damage to both rods and cones, as well as other retinal cell types. We report here the use of a genetic approach to study progenitor cell responses to photoreceptor degeneration in the larval and adult zebrafish retina. We have compared the responses to selective rod or cone degeneration using, respectively, the XOPS-mCFP transgenic line and zebrafish with a null mutation in the pde6c gene. Notably, rod degeneration induces increased proliferation of progenitors in the outer nuclear layer (ONL) and is not associated with proliferation or reactive gliosis in the inner nuclear layer (INL). Molecular characterization of the rod progenitor cells demonstrated that they are committed to the rod photoreceptor fate while they are still mitotic. In contrast, cone degeneration induces both Müller cell proliferation and reactive gliosis, with little change in proliferation in the ONL. We found that in both lines, proliferative responses to photoreceptor degeneration can be observed as 7 days post fertilization (dpf). These two genetic models therefore offer new opportunities for investigating the molecular mechanisms of selective degeneration and regeneration of rods and cones.     

HDAC inhibition ameliorates cone survival in retinitis pigmentosa mice

Cone photoreceptor cell death in inherited retinal diseases, such as Retinitis Pigmentosa (RP), leads to the loss of high acuity and color vision and, ultimately to blindness. In RP, a vast number of mutations perturb the structure and function of rod photoreceptors, while cones remain initially unaffected. Extensive rod loss in advanced stages of the disease triggers cone death by a mechanism that is still largely unknown. Here, we show that secondary cone cell death in animal models for RP is associated with increased activity of histone deacetylates (HDACs). A single intravitreal injection of an HDAC inhibitor at late stages of the disease, when the majority of rods have already degenerated, was sufficient to delay cone death and support long-term cone survival in two mouse models for RP, affected by mutations in the phosphodiesterase 6b gene. Moreover, the surviving cones remained light-sensitive, leading to an improvement in visual function. RNA-seq analysis of protected cones demonstrated that HDAC inhibition initiated multi-level protection via regulation of different pro-survival pathways, including MAPK, PI3K-Akt, and autophagy. This study suggests a unique opportunity for targeted pharmacological protection of secondary dying cones by HDAC inhibition and creates hope to maintain vision in RP patients even in advanced disease stages.Subject terms: Neuroscience, Neurological disorders     

Rip3 knockdown rescues photoreceptor cell death in blind pde6c zebrafish

Achromatopsia is a progressive autosomal recessive retinal disease characterized by early loss of cone photoreceptors and later rod photoreceptor loss. In most cases, mutations have been identified in CNGA3, CNGB3, GNAT2, PDE6C or PDE6H genes. Owing to this genetic heterogeneity, mutation-independent therapeutic schemes aimed at preventing cone cell death are very attractive treatment strategies. In pde6c^w59 mutant zebrafish, cone photoreceptors expressed high levels of receptor-interacting protein kinase 1 (RIP1) and receptor-interacting protein kinase 3 (RIP3) kinases, key regulators of necroptotic cell death. In contrast, rod photoreceptor cells were alternatively immunopositive for caspase-3 indicating activation of caspase-dependent apoptosis in these cells. Morpholino gene knockdown of rip3 in pde6c^w59 embryos rescued the dying cone photoreceptors by inhibiting the formation of reactive oxygen species and by inhibiting second-order neuron remodelling in the inner retina. In rip3 morphant larvae, visual function was restored in the cones by upregulation of the rod phosphodiesterase genes (pde6a and pde6b), compensating for the lack of cone pde6c suggesting that cones are able to adapt to their local environment. Furthermore, we demonstrated through pharmacological inhibition of RIP1 and RIP3 activity that cone cell death was also delayed. Collectively, these results demonstrate that the underlying mechanism of cone cell death in the pde6c^w59 mutant retina is through necroptosis, whereas rod photoreceptor bystander death occurs through a caspase-dependent mechanism. This suggests that targeting the RIP kinase signalling pathway could be an effective therapeutic intervention in retinal degeneration patients. As bystander cell death is an important feature of many retinal diseases, combinatorial approaches targeting different cell death pathways may evolve as an important general principle in treatment.     

Synaptic plasticity and functionality at the cone terminal of the developing zebrafish retina

Previous studies have analyzed photoreceptor development, some inner retina cell types, and specific neurotransmitters in the zebrafish retina. However, only minor attention has been paid to the morphology of the synaptic connection between photoreceptors and second order neurons even though it represents the transition from the light sensitive receptor to the neuronal network of the visual system. Here, we describe the appearance and differentiation of pre- and postsynaptic elements at cone synapses in the developing zebrafish retina together with the maturation of the directly connecting second order neurons and a dopaminergic third order feedback-neuron from the inner retina. Zebrafish larvae were examined at developmental stages from 2 to 7dpf (days postfertilization) and in the adult. Synaptic maturation at the photoreceptor terminals was examined with antibodies against synapse associated proteins. The appearance of synaptic plasticity at the so-called spinule-type synapses between cones and horizontal cells was assessed by electron microscopy, and the maturation of photoreceptor downstream connection was identified by immunocytochemistry for GluR4 (AMPA-type glutamate receptor subunit), protein kinase beta(1) (mixed rod-cone bipolar cells), and tyrosine hydroxylase (dopaminergic interplexiform cells). We found that developing zebrafish retinas possess first synaptic structures at the cone terminal as early as 3.5dpf. Morphological maturation of these synapses at 3.5-4dpf, together with the presence of synapse associated proteins at 2.5dpf and the maturation of second order neurons by 5dpf, indicate functional synaptic connectivity and plasticity between the cones and their second order neurons already at 5dpf. However, the mere number of spinules and ribbons at 7dpf still remains below the adult values, indicating that synaptic functionality of the zebrafish retina is not entirely completed at this stage of development.     

A mathematical model for photoreceptor interactions

The interactions between rods and cones in the retina have been the focus of innumerable experimental and theoretical biological studies in previous decades yet the understanding of these interactions is still incomplete primarily due to the lack of a unified concept of cone photoreceptor organization and its role in retinal diseases. The low abundance of cones in many of the non-primate mammalian models that have been studied make conclusions about the human retina difficult. A more complete knowledge of the human retina is crucial for counteracting the events that lead to certain degenerative diseases, in particular those associated with photoreceptor cell death (e.g., retinitis pigmentosa). In an attempt to gain important insight into the role and interactions of the rods and the cones we develop and analyze a set of mathematical equations that model a system of photoreceptors and incorporate a direct rod-cone interaction. Our results show that the system can exhibit stable oscillations, which correspond to the rhythmic renewal and shedding of the photoreceptors. In addition, our results show the mathematical necessity of this rod-cone direct interaction for survival of both and gives insight into this mechanism.     

Photoreceptor cell death, proliferation and formation of hybrid rod/S-cone photoreceptors in the degenerating STK38L mutant retina

A homozygous mutation in STK38L in dogs impairs the late phase of photoreceptor development, and is followed by photoreceptor cell death (TUNEL) and proliferation (PCNA, PHH3) events that occur independently in different cells between 7-14 weeks of age. During this period, the outer nuclear layer (ONL) cell number is unchanged. The dividing cells are of photoreceptor origin, have rod opsin labeling, and do not label with markers specific for macrophages/microglia (CD18) or Müller cells (glutamine synthetase, PAX6). Nestin labeling is absent from the ONL although it labels the peripheral retina and ciliary marginal zone equally in normals and mutants. Cell proliferation is associated with increased cyclin A1 and LATS1 mRNA expression, but CRX protein expression is unchanged. Coincident with photoreceptor proliferation is a change in the photoreceptor population. Prior to cell death the photoreceptor mosaic is composed of L/M- and S-cones, and rods. After proliferation, both cone types remain, but the majority of rods are now hybrid photoreceptors that express rod opsin and, to a lesser extent, cone S-opsin, and lack NR2E3 expression. The hybrid photoreceptors renew their outer segments diffusely, a characteristic of cones. The results indicate the capacity for terminally differentiated, albeit mutant, photoreceptors to divide with mutations in this novel retinal degeneration gene.     

Oxidative damage is a potential cause of cone cell death in retinitis pigmentosa

Retinitis pigmentosa (RP) is a prevalent cause of blindness caused by a large number of different mutations in many different genes. The mutations result in rod photoreceptor cell death, but it is unknown why cones die. In this study, we tested the hypothesis that cones die from oxidative damage by performing immunohistochemical staining for biomarkers of oxidative damage in a transgenic pig model of RP. The presence of acrolein- and 4-hydroxynonenal-adducts on proteins is a specific indicator that lipid peroxidation has occurred, and there was strong immunofluorescent staining for both in cone inner segments (IS) of two 10-month-old transgenic pigs in which almost all rods had died, compared to faint staining in two 10-month-old control pig retinas. In 22- and 24-month-old transgenic pigs in which all rods and many cones had died, staining was strong in cone axons and some cell bodies as well as IS indicating progression in oxidative damage between 10 and 22 months. Biomarkers for oxidative damage to proteins and DNA also showed progressive oxidative damage to those macromolecules in cones during the course of RP. These data support the hypothesis that the death of rods results in decreased oxygen consumption and hyperoxia in the outer retina resulting in gradual cone cell death from oxidative damage. This hypothesis has important therapeutic implications and deserves rapid evaluation.     

Mechanisms of cell death in rhodopsin retinitis pigmentosa: implications for therapy

Retinitis pigmentosa (RP) is a group of retinal degenerative diseases that are characterised primarily by the loss of rod photoreceptor cells. Mutations in rhodopsin are the most common cause of autosomal-dominant RP (ADRP). Here, we propose a new classification for rhodopsin mutations based on their biochemical and cellular properties. Several different potential gain-of-function mechanisms for rhodopsin ADRP are described and discussed. Possible dominant-negative mechanisms, which affect the processing, translocation or degradation of wild-type rhodopsin, are also considered. Understanding the molecular and cellular consequences of rod-opsin mutations and the underlying disease mechanisms in ADRP are essential to develop future therapies for this class of retinal dystrophies.     

Testing for a Gap Junction-Mediated Bystander Effect in Retinitis Pigmentosa: Secondary Cone Death Is Not Altered by Deletion of Connexin36 from Cones

Retinitis pigmentosa (RP) relates to a group of hereditary neurodegenerative diseases of the retina. On the cellular level, RP results in the primary death of rod photoreceptors, caused by rod-specific mutations, followed by a secondary degeneration of genetically normal cones. Different mechanisms may influence the spread of cell death from one photoreceptor type to the other. As one of these mechanisms a gap junction-mediated bystander effect was proposed, i.e., toxic molecules generated in dying rods and propagating through gap junctions induce the death of healthy cone photoreceptors. We investigated whether disruption of rod-cone coupling can prevent secondary cone death and reduce the spread of degeneration. We tested this hypothesis in two different mouse models for retinal degeneration (rhodopsin knockout and rd1) by crossbreeding them with connexin36-deficient mice as connexin36 represents the gap junction protein on the cone side and lack thereof most likely disrupts rod-cone coupling. Using immunohistochemistry, we compared the progress of cone degeneration between connexin36-deficient mouse mutants and their connexin36-expressing littermates at different ages and assessed the accompanied morphological changes during the onset (rhodopsin knockout) and later stages of secondary cone death (rd1 mutants). Connexin36-deficient mouse mutants showed the same time course of cone degeneration and the same morphological changes in second order neurons as their connexin36-expressing littermates. Thus, our results indicate that disruption of connexin36-mediated rod-cone coupling does not stop, delay or spatially restrict secondary cone degeneration and suggest that the gap junction-mediated bystander effect does not contribute to the progression of RP.     

Pharmacology of the skate electroretinogram indicates independent ON and OFF bipolar cell pathways

Organization of afferent information into parallel ON and OFF pathways is a critical feature of the vertebrate visual system. All afferent visual information in the vertebrate retina reaches the inner plexiform layer (IPL) via bipolar cells. It is at the bipolar cell level that separation of ON and OFF information first appears for afferent information from cones. This may also hold true for the rod pathway of cold-blooded vertebrates, but not for mammals. The all-rod retina of the skate presents an opportunity to examine such pathways in a retina having but a single class of photoreceptor. Immunocytochemical evidence suggests that both ON and OFF bipolar cells are present in the skate retina. We examined the pharmacology of the skate electroretinogram (ERG) to test the hypothesis that independent ON and OFF bipolar cell pathways are functional as rod afferent pathways from outer to inner plexiform layer in the skate. 100 microM 2-amino-4-phosphonobutyric acid (APB) reversibly blocked the skate ERG b-wave. A small d-wave-like OFF component of the ERG revealed by DC recording of response to a prolonged (10 s) flash of light was reduced or blocked by 5 mM kynurenic acid (KYN). We found that addition of 200 microM picrotoxin to the Ringer''s solution revealed prominent ON and OFF components of the skate ERG while reducing the c-wave. These ON and OFF components were reversibly blocked by 100 microM APB and 5 mM KYN, respectively. Reversible block of the OFF component by KYN was also accomplished in the presence of 500 microM N-methyl-DL-aspartate. From these findings, we conclude that ON and OFF bipolar cells are likely to be functional as parallel afferent interplexiform pathways in the all-rod retina of the skate.     

Molecular Evolutionary Analysis of Vertebrate Transducins: A Role for Amino Acid Variation in Photoreceptor Deactivation

Transducin is a heterotrimeric G protein that plays a critical role in phototransduction in the rod and cone photoreceptor cells of the vertebrate retina. Rods, highly sensitive cells that recover from photoactivation slowly, underlie dim-light vision, whereas cones are less sensitive, recover more quickly, and underlie bright-light vision. Transducin deactivation is a critical step in photoreceptor recovery and may underlie the functional distinction between rods and cones. Rods and cones possess distinct transducin α subunits, yet they share a common deactivation mechanism, the GTPase activating protein (GAP) complex. Here, we used codon models to examine patterns of sequence evolution in rod (GNAT1) and cone (GNAT2) α subunits. Our results indicate that purifying selection is the dominant force shaping GNAT1 and GNAT2 evolution, but that GNAT2 has additionally been subject to positive selection operating at multiple phylogenetic scales; phylogeny-wide analysis identified several sites in the GNAT2 helical domain as having substantially elevated dN/dS estimates, and branch-site analysis identified several nearby sites as targets of strong positive selection during early vertebrate history. Examination of aligned GNAT and GAP complex crystal structures revealed steric clashes between several positively selected sites and the deactivating GAP complex. This suggests that GNAT2 sequence variation could play an important role in adaptive evolution of the vertebrate visual system via effects on photoreceptor deactivation kinetics and provides an alternative perspective to previous work that focused instead on the effect of GAP complex concentration. Our findings thus further the understanding of the molecular biology, physiology, and evolution of vertebrate visual systems.     

The fine structure of the pigment epithelium and photoreceptor cells of the newt,Triturus viridescens dorsalis (Rafinesque)

The morphology of the retinal pigment epithelium and photoreceptor cells has been studied in the common newt Triturus viridescens dorsalis by light, conventional transmission and scanning electron microscopy. The pigment epithelium is formed by a single layer of low rectangular cells, separated by a multilayered membrane (Bruch's membrane) from the vessels of the choriocapillaris. The scleral border of the pigment epithelium is highly infolded and each epithelial cell contains smooth endoplasmic reticulum, myeloid bodies, mitochondria, lysosomes, phagosomes and an oval nucleus. Inner, pigment laden, epithelial processes surround the photoreceptor outer and inner segments. The three retinal photoreceptor types, rods, single cones and double cones, differ in both external and internal appearance. The newt, rod, outer segments appear denser than the cones in both light and electron micrographs, due to a greater number of rod lamellae per unit distance of outer segment and to the presence of electron dense intralamellar bands. The rod outer segments possess deep incisures in the lamellae while the cone lamellae lack incisures. Both rod and cone outer segments are supported by a peripheral array of dendritic processes containing longitudinal filaments which originate in the inner segment. The inner segment mitochondria, forming the rod ellipsoid, arelong and narrow while those in the cone are spherical to oval in shape. The inner segments of all three receptor cell types also contain a glycogen-filled paraboloid and a myoid region, just outside the nucleus, rich in both rough and smooth endoplasmic reticulum. The elongate, cylindrical nuclei differ in density. The rod nuclei are denser than those of the cones, contain clumped chromatin and usually extend further vitreally. Similarly, the cytoplasm of the rod synaptic terminal is denser than its cone counterpart and contains synaptic vesicles almost twice as large as those of the cones. Photoreceptor synapses in rods and cones are established by both superficial and invaginated contacts with bipolar or horizontal cells.     

Antioxidants slow photoreceptor cell death in mouse models of retinitis pigmentosa

Retinitis pigmentosa (RP) is a heterogeneous group of diseases in which one of a wide variety of mutations selectively causes rod photoreceptor cell death. After rods die, cone photoreceptors gradually die resulting in blindness. Antioxidants reduce cone cell death in rd1/rd1 mice indicating that cones die from oxidative damage in that model of rapidly progressive RP. In this study, we sought to determine if this observation could be generalized to models of other types of RP, rd10/rd10 mice, a model of more slowly progressive recessive RP, and Q344ter mice, a model of rapidly progressive dominant RP. Compared to appropriate vehicle-treated controls, rd10/rd10 and Q344ter mice treated between P18 and P35 with a mixture of antioxidants previously found to be effective in rd1/rd1 mice showed significantly greater cone survival. Antioxidant-treated rd10/rd10 mice showed preservation of cone function as shown by a significant increase in photopic ERG b-wave amplitudes, and surprisingly showed temporary preservation of scotopic a-wave amplitudes, prolonged rod survival, and slowed depletion of rhodopsin mRNA. These data suggest that oxidative damage contributes to cone cell death regardless of the disease causing mutation that leads to the demise of rods, and that in more slowly progressive rod degenerations, oxidative damage may also contribute to rod cell death. Protection from oxidative damage may be a broadly applicable treatment strategy in RP.     

The crystal structure of GCAP3 suggests molecular mechanism of GCAP-linked cone dystrophies

Absorption of light by visual pigments initiates the phototransduction pathway that results in degradation of the intracellular pool of cyclic-GMP (cGMP). This hydrolysis promotes the closing of cGMP-gated cation channels and consequent hyperpolarization of rod and cone photoreceptor cell membranes. Guanylate cyclase-activating proteins (GCAPs) are a family of proteins that regulate retinal guanylate cyclase (GC) activity in a Ca2+-dependent manner. At high [Ca2+], typical of the dark-adapted state (approximately 500 nM), GCAPs inhibit retinal GCs. At the low [Ca2+] (approximately 50 nM) that occurs after the closing of cGMP-gated channels, GCAPs activate retinal GCs to replenish dark-state cGMP levels. Here, we report the crystal structure of unmyristoylated human GCAP3 with Ca2+ bound. GCAP3 is an EF-hand Ca2+-binding protein with Ca2+ bound to EF2, 3 and 4, while Ca2+ binding to EF-hand 1 is disabled. GCAP3 contains two domains with the EF-hand motifs arranged in a tandem array similar to GCAP2 and members of the recoverin subfamily of Ca2+-binding proteins. Residues not involved in Ca2+ binding, but conserved in all GCAPs, cluster around EF1 in the N-terminal domain and may represent the interface with GCs. Five point mutations in the closely related GCAP1 have been linked to the etiology of cone dystrophies. These residues are conserved in GCAP3 and the structure suggests important roles for these amino acids. We present a homology model of GCAP1 based on GCAP3 that offers insight into the molecular mechanism underlying the autosomal dominant cone dystrophies produced by GCAP1 mutations.     

Identification of a Circadian Clock-Controlled Neural Pathway in the Rabbit Retina

Background

Although the circadian clock in the mammalian retina regulates many physiological processes in the retina, it is not known whether and how the clock controls the neuronal pathways involved in visual processing.

Methodology/Principal Findings

By recording the light responses of rabbit axonless (A-type) horizontal cells under dark-adapted conditions in both the day and night, we found that rod input to these cells was substantially increased at night under control conditions and following selective blockade of dopamine D₂, but not D₁, receptors during the day, so that the horizontal cells responded to very dim light at night but not in the day. Using neurobiotin tracer labeling, we also found that the extent of tracer coupling between rabbit rods and cones was more extensive during the night, compared to the day, and more extensive in the day following D₂ receptor blockade. Because A-type horizontal cells make synaptic contact exclusively with cones, these observations indicate that the circadian clock in the mammalian retina substantially increases rod input to A-type horizontal cells at night by enhancing rod-cone coupling. Moreover, the clock-induced increase in D₂ receptor activation during the day decreases rod-cone coupling so that rod input to A-type horizontal cells is minimal.

Conclusions/Significance

Considered together, these results identify the rod-cone gap junction as a key site in mammals through which the retinal clock, using dopamine activation of D₂ receptors, controls signal flow in the day and night from rods into the cone system.     

Modeling retinal degeneration using patient-specific induced pluripotent stem cells

Retinitis pigmentosa (RP) is the most common inherited human eye disease resulting in night blindness and visual defects. It is well known that the disease is caused by rod photoreceptor degeneration; however, it remains incurable, due to the unavailability of disease-specific human photoreceptor cells for use in mechanistic studies and drug screening. We obtained fibroblast cells from five RP patients with distinct mutations in the RP1, RP9, PRPH2 or RHO gene, and generated patient-specific induced pluripotent stem (iPS) cells by ectopic expression of four key reprogramming factors. We differentiated the iPS cells into rod photoreceptor cells, which had been lost in the patients, and found that they exhibited suitable immunocytochemical features and electrophysiological properties. Interestingly, the number of the patient-derived rod cells with distinct mutations decreased in vitro; cells derived from patients with a specific mutation expressed markers for oxidation or endoplasmic reticulum stress, and exhibited different responses to vitamin E than had been observed in clinical trials. Overall, patient-derived rod cells recapitulated the disease phenotype and expressed markers of cellular stresses. Our results demonstrate that the use of patient-derived iPS cells will help to elucidate the pathogenic mechanisms caused by genetic mutations in RP.