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Agarwal D, Dash N, Mazo KW, Chopra M, Avila MP, Patel A, Wong RM, Jia C, Do H, Cheng J, Chiang C, Jurlina SL, Roshan M, Perry MW, Rho JM, Broyer R, Lee CD, Weinreb RN, Gavrilovici C, Oesch NW, Welsbie DS, Wahlin KJ. Human retinal ganglion cell neurons generated by synchronous BMP inhibition and transcription factor mediated reprogramming. NPJ Regen Med 2023; 8:55. [PMID: 37773257 PMCID: PMC10541876 DOI: 10.1038/s41536-023-00327-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2022] [Accepted: 08/31/2023] [Indexed: 10/01/2023] Open
Abstract
In optic neuropathies, including glaucoma, retinal ganglion cells (RGCs) die. Cell transplantation and endogenous regeneration offer strategies for retinal repair, however, developmental programs required for this to succeed are incompletely understood. To address this, we explored cellular reprogramming with transcription factor (TF) regulators of RGC development which were integrated into human pluripotent stem cells (PSCs) as inducible gene cassettes. When the pioneer factor NEUROG2 was combined with RGC-expressed TFs (ATOH7, ISL1, and POU4F2) some conversion was observed and when pre-patterned by BMP inhibition, RGC-like induced neurons (RGC-iNs) were generated with high efficiency in just under a week. These exhibited transcriptional profiles that were reminiscent of RGCs and exhibited electrophysiological properties, including AMPA-mediated synaptic transmission. Additionally, we demonstrated that small molecule inhibitors of DLK/LZK and GCK-IV can block neuronal death in two pharmacological axon injury models. Combining developmental patterning with RGC-specific TFs thus provided valuable insight into strategies for cell replacement and neuroprotection.
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Affiliation(s)
- Devansh Agarwal
- Shu Chien-Gene Lay Department of Bioengineering, UC San Diego, La Jolla, CA, USA
- Viterbi Family Department of Ophthalmology & the Shiley Eye Institute, UC San Diego, La Jolla, CA, USA
| | - Nicholas Dash
- Viterbi Family Department of Ophthalmology & the Shiley Eye Institute, UC San Diego, La Jolla, CA, USA
| | - Kevin W Mazo
- Viterbi Family Department of Ophthalmology & the Shiley Eye Institute, UC San Diego, La Jolla, CA, USA
| | - Manan Chopra
- Viterbi Family Department of Ophthalmology & the Shiley Eye Institute, UC San Diego, La Jolla, CA, USA
| | - Maria P Avila
- Viterbi Family Department of Ophthalmology & the Shiley Eye Institute, UC San Diego, La Jolla, CA, USA
| | - Amit Patel
- Viterbi Family Department of Ophthalmology & the Shiley Eye Institute, UC San Diego, La Jolla, CA, USA
| | - Ryan M Wong
- Viterbi Family Department of Ophthalmology & the Shiley Eye Institute, UC San Diego, La Jolla, CA, USA
| | - Cairang Jia
- Viterbi Family Department of Ophthalmology & the Shiley Eye Institute, UC San Diego, La Jolla, CA, USA
| | - Hope Do
- Viterbi Family Department of Ophthalmology & the Shiley Eye Institute, UC San Diego, La Jolla, CA, USA
| | - Jie Cheng
- Department of Ophthalmology, Johns Hopkins School of Medicine, Baltimore, MD, USA
| | - Colette Chiang
- Viterbi Family Department of Ophthalmology & the Shiley Eye Institute, UC San Diego, La Jolla, CA, USA
| | - Shawna L Jurlina
- Viterbi Family Department of Ophthalmology & the Shiley Eye Institute, UC San Diego, La Jolla, CA, USA
| | - Mona Roshan
- Viterbi Family Department of Ophthalmology & the Shiley Eye Institute, UC San Diego, La Jolla, CA, USA
| | - Michael W Perry
- Department of Biological Sciences, UC San Diego, La Jolla, CA, USA
| | - Jong M Rho
- Department of Neurosciences, UC San Diego, La Jolla, CA, USA
| | - Risa Broyer
- Viterbi Family Department of Ophthalmology & the Shiley Eye Institute, UC San Diego, La Jolla, CA, USA
| | - Cassidy D Lee
- Viterbi Family Department of Ophthalmology & the Shiley Eye Institute, UC San Diego, La Jolla, CA, USA
| | - Robert N Weinreb
- Viterbi Family Department of Ophthalmology & the Shiley Eye Institute, UC San Diego, La Jolla, CA, USA
| | | | - Nicholas W Oesch
- Viterbi Family Department of Ophthalmology & the Shiley Eye Institute, UC San Diego, La Jolla, CA, USA
- Department of Psychology, UC San Diego, La Jolla, CA, USA
| | - Derek S Welsbie
- Viterbi Family Department of Ophthalmology & the Shiley Eye Institute, UC San Diego, La Jolla, CA, USA
| | - Karl J Wahlin
- Viterbi Family Department of Ophthalmology & the Shiley Eye Institute, UC San Diego, La Jolla, CA, USA.
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Carleton M, Oesch NW. Differences in the spatial fidelity of evoked and spontaneous signals in the degenerating retina. Front Cell Neurosci 2022; 16:1040090. [DOI: 10.3389/fncel.2022.1040090] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2022] [Accepted: 10/20/2022] [Indexed: 11/09/2022] Open
Abstract
Vision restoration strategies aim to reestablish vision by replacing the function of lost photoreceptors with optoelectronic hardware or through gene therapy. One complication to these approaches is that retinal circuitry undergoes remodeling after photoreceptor loss. Circuit remodeling following perturbation is ubiquitous in the nervous system and understanding these changes is crucial for treating neurodegeneration. Spontaneous oscillations that arise during retinal degeneration have been well-studied, however, other changes in the spatiotemporal processing of evoked and spontaneous activity have received less attention. Here we use subretinal electrical stimulation to measure the spatial and temporal spread of both spontaneous and evoked activity during retinal degeneration. We found that electrical stimulation synchronizes spontaneous oscillatory activity, over space and through time, thus leading to increased correlations in ganglion cell activity. Intriguingly, we found that spatial selectivity was maintained in rd10 retina for evoked responses, with spatial receptive fields comparable to wt retina. These findings indicate that different biophysical mechanisms are involved in mediating feed forward excitation, and the lateral spread of spontaneous activity in the rd10 retina, lending support toward the possibility of high-resolution vision restoration.
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McCormick LR, Levin LA, Oesch NW. Reduced Oxygen Impairs Photobehavior in Marine Invertebrate Larvae. Biol Bull 2022; 243:255-271. [PMID: 36548968 DOI: 10.1086/717565] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
AbstractOrganisms in coastal waters experience naturally high oxygen variability and steep oxygen gradients with depth, in addition to ocean deoxygenation. They often undergo diel vertical migration involving a change in irradiance that initiates a visual behavior. Retinal function has been shown to be highly sensitive to oxygen loss; here we assess whether visual behavior (photobehavior) in paralarvae of the squid Doryteuthis opalescens and the octopus Octopus bimaculatus is affected by low oxygen conditions, using a novel behavioral paradigm. Larvae showed an irradiance-dependent, descending photobehavior after extinction of the light stimulus, measured through the change in vertical position of larvae in the chamber. The magnitude of photobehavior was decreased as oxygen was reduced, and the response was entirely gone at <6.4 kPa partial pressure of oxygen (<74.7 μmol kg-1 at 15.3 °C) in D. opalescens paralarvae. Oxygen also affected photobehavior in O. bimaculatus paralarvae. The mean vertical velocity of paralarvae was unaffected by exposure to reduced oxygen, indicating that oxygen deficits selectively affect vision prior to locomotion. These findings suggest that variable and declining oxygen conditions in coastal upwelling areas and elsewhere will impair photobehavior and likely affect the distribution, migration behavior, and survival of highly visual marine species.
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Damle S, Carleton M, Kapogianis T, Arya S, Cavichini-Corderio M, Freeman WR, Lo YH, Oesch NW. Minimizing Iridium Oxide Electrodes for High Visual Acuity Subretinal Stimulation. eNeuro 2021; 8:ENEURO.0506-20.2021. [PMID: 34799411 PMCID: PMC8704424 DOI: 10.1523/eneuro.0506-20.2021] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2020] [Revised: 10/28/2021] [Accepted: 11/15/2021] [Indexed: 11/21/2022] Open
Abstract
Vision loss from diseases of the outer retina, such as age-related macular degeneration, is among the leading causes of irreversible blindness in the world today. The goal of retinal prosthetics is to replace the photo-sensing function of photoreceptors lost in these diseases with optoelectronic hardware to electrically stimulate patterns of retinal activity corresponding to vision. To enable high-resolution retinal prosthetics, the scale of stimulating electrodes must be significantly decreased from current designs; however, this reduces the amount of stimulating current that can be delivered. The efficacy of subretinal stimulation at electrode sizes suitable for high visual acuity retinal prosthesis are not well understood, particularly within the safe charge injection limits of electrode materials. Here, we measure retinal ganglion cell (RGC) responses in a mouse model of blindness to evaluate the stimulation efficacy of 10, 20, and 30 μm diameter iridium oxide electrodes within the electrode charge injection limits, focusing on measures of charge threshold and dynamic range. Stimulation thresholds were lower for smaller electrodes, but larger electrodes could elicit a greater dynamic range of spikes and recruited more ganglion cells within charge injection limits. These findings suggest a practical lower limit for planar electrode size and indicate strategies for maximizing stimulation thresholds and dynamic range.
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Affiliation(s)
- Samir Damle
- Department of Bioengineering, University of California San Diego, La Jolla, CA 92093
| | - Maya Carleton
- Department of Psychology, University of California San Diego, La Jolla, CA 92093
| | - Theodoros Kapogianis
- Department of Psychology, University of California San Diego, La Jolla, CA 92093
| | - Shaurya Arya
- Department of Electrical and Computer Engineering, University of California San Diego, La Jolla, CA 92161
| | - Melina Cavichini-Corderio
- Jacobs Retina Center at Shiley Eye Institute, Department of Ophthalmology, University of California San Diego, La Jolla, CA 92093
| | - William R Freeman
- Jacobs Retina Center at Shiley Eye Institute, Department of Ophthalmology, University of California San Diego, La Jolla, CA 92093
| | - Yu-Hwa Lo
- Department of Electrical and Computer Engineering, University of California San Diego, La Jolla, CA 92161
| | - Nicholas W Oesch
- Department of Psychology, University of California San Diego, La Jolla, CA 92093
- Jacobs Retina Center at Shiley Eye Institute, Department of Ophthalmology, University of California San Diego, La Jolla, CA 92093
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Damle S, Liu YH, Arya S, Oesch NW, Lo YH. Vertically integrated photo junction-field-effect transistor pixels for retinal prosthesis. Biomed Opt Express 2020; 11:55-67. [PMID: 32010499 PMCID: PMC6968743 DOI: 10.1364/boe.11.000055] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2019] [Revised: 11/20/2019] [Accepted: 11/24/2019] [Indexed: 06/10/2023]
Abstract
Optoelectronic retinal prostheses transduce light into electrical current for neural stimulation. We introduce a novel optoelectronic pixel architecture consisting of a vertically integrated photo junction-field-effect transistor (Photo-JFET) and neural stimulating electrode. Experimental measurements demonstrate that optically addressed Photo-JFET pixels utilize phototransistive gain to produce a broad range of neural stimulation current and can effectively stimulate retinal neurons in vitro. The compact nature of the Photo-JFET pixel can enable high resolution retinal prostheses with the smallest reported optoelectronic pixel size to help restore high visual acuity in patients with degenerative retinal diseases.
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Affiliation(s)
- Samir Damle
- Department of Bioengineering, University of California San Diego, 9500 Gilman Drive La Jolla, CA 92093, USA
| | - Yu-Hsin Liu
- Nanovision Biosciences, Inc., 3366 N. Torrey Pines Court, Suite 220, La Jolla, CA 92037, USA
| | - Shaurya Arya
- Department of Electrical and Computer Engineering, University of California San Diego, Engineer Ln, La Jolla, CA 92161, USA
| | - Nicholas W. Oesch
- Department of Psychology, University of California San Diego, 9500 Gilman Drive, CA 92093, USA
- Jacobs Retina Center at Shiley Eye Institute, Department of Ophthalmology, University of California San Diego, 9415 Campus Point Drive San Diego, CA 92093, USA
| | - Yu-Hwa Lo
- Jacobs Retina Center at Shiley Eye Institute, Department of Ophthalmology, University of California San Diego, 9415 Campus Point Drive San Diego, CA 92093, USA
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McCormick LR, Levin LA, Oesch NW. Vision is highly sensitive to oxygen availability in marine invertebrate larvae. J Exp Biol 2019; 222:jeb.200899. [DOI: 10.1242/jeb.200899] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2019] [Accepted: 04/12/2019] [Indexed: 01/28/2023]
Abstract
For many animals, evolution has selected for complex visual systems despite the high energetic demands associated with maintaining eyes and their processing structures. The metabolic demands of visual systems therefore make them highly sensitive to fluctuations in available oxygen. In the marine environment, oxygen changes over daily, seasonal, and inter-annual time scales and there are large gradients of oxygen with depth. Vision is linked to survival in many marine animals, particularly among the crustaceans, cephalopods, and fish, and early life stages of these groups rely on vision for prey capture, predator detection, and their distribution in the water column. Using in vivo electroretinogram recordings, we show that there is a decrease in retinal sensitivity to light in marine invertebrates when exposed to reduced oxygen availability. We found a 60-100% reduction in retinal responses in the larvae of cephalopods and crustaceans: the market squid (Doryteuthis opalescens), two-spot octopus (Octopus bimaculatus), tuna crab (Pleuroncodes planipes), and brachyuran crab (Metacarcinus gracilis). A decline in oxygen also decreases the temporal resolution of vision in D. opalescens. These results are the first demonstration that vision in marine invertebrates is highly sensitive to oxygen availability and that the thresholds for visual impairment from reduced oxygen are species-specific. Oxygen-impaired retinal function may change the visual behaviors crucial to survival in these marine larvae. These findings may impact our understanding of species’ vulnerability to ocean oxygen loss and suggest that researchers conducting electrophysiology experiments should monitor oxygen levels, as even small changes in oxygen may affect the results.
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Affiliation(s)
- Lillian R. McCormick
- Integrative Oceanography Division, Scripps Institution of Oceanography, La Jolla, CA 92093-0218, USA
| | - Lisa A. Levin
- Integrative Oceanography Division, Scripps Institution of Oceanography, La Jolla, CA 92093-0218, USA
- Center for Marine Biodiversity and Conservation, Scripps Institution of Oceanography, La Jolla, CA 92093-0218, USA
| | - Nicholas W. Oesch
- Department of Psychology, University of California San Diego, La Jolla, CA 92093, USA
- Department of Ophthalmology, University of California San Diego, La Jolla, CA 92093, USA
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Abstract
Inhibition shapes activity and signal processing in neural networks through numerous mechanisms mediated by many different cell types. Here, we examined how one type of GABAergic interneuron in the retina, the A17 amacrine cell, influences visual information processing. Our results suggest that A17s, which make reciprocal feedback inhibitory synapses onto rod bipolar cell (RBC) synaptic terminals, extend the luminance range over which RBC synapses compute temporal contrast and enhance the reliability of contrast signals over this range. Inhibition from other amacrine cells does not influence these computational features. Although A17-mediated feedback is mediated by both GABAA and GABAC receptors, the latter plays the primary role in extending the range of contrast computation. These results identify specific functions for an inhibitory interneuron subtype, as well as specific synaptic receptors, in a behaviorally relevant neural computation.
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Affiliation(s)
- Nicholas W. Oesch
- Synaptic Physiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, 35 Convent Drive, Bethesda, MD 20892-3701
- Present address: University of California, San Diego, Department of Psychology, Department of Ophthalmology, 9500 Gilman Drive MC#0109, La Jolla, CA 92093-0109
| | - Jeffrey S. Diamond
- Synaptic Physiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, 35 Convent Drive, Bethesda, MD 20892-3701
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Oesch NW, Diamond JS. Ribbon synapses compute temporal contrast and encode luminance in retinal rod bipolar cells. Nat Neurosci 2011; 14:1555-61. [PMID: 22019730 PMCID: PMC3225507 DOI: 10.1038/nn.2945] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2011] [Accepted: 09/07/2011] [Indexed: 11/09/2022]
Abstract
Contrast is computed throughout the nervous system to encode changing inputs efficiently. The retina encodes luminance and contrast over a wide range of visual conditions and must adapt its responses to maintain sensitivity and to avoid saturation. We examined the means by which one type of adaptation allows individual synapses to compute contrast and encode luminance in biphasic responses to step changes in light levels. Light-evoked depletion of the readily releasable vesicle pool (RRP) at rod bipolar cell ribbon synapses in rat retina limited the dynamic range available to encode transient, but not sustained, responses, thereby allowing the transient and sustained components of release to compute temporal contrast and encode mean light levels, respectively. A release/replenishment model revealed that a single, homogeneous pool of synaptic vesicles is sufficient to generate this behavior and that a partial depletion of the RRP is the dominant mechanism for shaping the biphasic contrast/luminance response.
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Affiliation(s)
- Nicholas W Oesch
- Synaptic Physiology Section, National Institute of Neurological Disorders and Stroke, US National Institutes of Health, Bethesda, Maryland, USA
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Oesch NW, Taylor WR. Tetrodotoxin-resistant sodium channels contribute to directional responses in starburst amacrine cells. PLoS One 2010; 5:e12447. [PMID: 20805982 PMCID: PMC2929195 DOI: 10.1371/journal.pone.0012447] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2010] [Accepted: 07/08/2010] [Indexed: 11/18/2022] Open
Abstract
The biophysical mechanisms that give rise to direction selectivity in the retina remain uncertain. Current evidence suggests that the directional signal first arises within the dendrites of starburst amacrine cells (SBACs). Two models have been proposed to explain this phenomenon, one based on mutual inhibitory interactions between SBACs, and the other positing an intrinsic dendritic mechanism requiring a voltage-gradient depolarizing towards the dendritic tips. We tested these models by recording current and voltage responses to visual stimuli in SBACs. In agreement with previous work, we found that the excitatory currents in the SBACs were directional, and remained directional when GABA receptors were blocked. Contrary to the mutual-inhibitory model, stimuli that produce strong directional signals in ganglion cells failed to reveal a significant inhibitory input to SBACs. Suppression of the tonic excitatory conductance, proposed to generate the dendritic voltage-gradient required for the dendrite autonomous model, failed to eliminate the directional signal in SBACs. However, selective block of tetrodotoxin-resistant sodium channels did reduce the strength of the directional excitatory signal in the SBACs. These results indicate that current models of direction-selectivity in the SBACs are inadequate, and suggest that voltage-gated excitatory channels, specifically tetrodotoxin-resistant sodium channels, are important elements in directional signaling. This is the first physiological evidence that tetrodotoxin-resistant sodium channels play a role in retinal information processing.
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Affiliation(s)
- Nicholas W Oesch
- Neuroscience Graduate Program, Oregon Health and Sciences University, Portland, Oregon, United States of America.
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Morgans CW, Bayley PR, Oesch NW, Ren G, Akileswaran L, Taylor WR. Photoreceptor calcium channels: Insight from night blindness. Vis Neurosci 2005; 22:561-8. [PMID: 16332266 DOI: 10.1017/s0952523805225038] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2005] [Accepted: 05/26/2005] [Indexed: 11/06/2022]
Abstract
The genetic locus for incomplete congenital stationary night blindness
(CSNB2) has been identified as the CACNA1f gene, encoding the
α1F calcium channel subunit, a member of the L-type family
of calcium channels. The electroretinogram associated with CSNB2
implicates α1F in synaptic transmission between retinal
photoreceptors and bipolar cells. Using a recently developed monoclonal
antibody to α1F, we localize the channel to ribbon active
zones in rod photoreceptor terminals of the mouse retina, supporting a
role for α1F in mediating glutamate release from rods.
Detergent extraction experiments indicate that α1F is part
of a detergent-resistant active zone complex, which also includes the
synaptic ribbons. Comparison of native mouse rod calcium currents with
recombinant α1F currents reveals that the
current–voltage relationship for the native current is shifted
approximately 30 mV to more hyperpolarized potentials than for the
recombinant α1F current, suggesting modulation of the
native channel by intracellular factors. Lastly, we present evidence for
L-type α1D calcium channel subunits in cone terminals of
the mouse retina. The presence of α1D channels in cones may
explain the residual visual abilities of individuals with CSNB2.
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Affiliation(s)
- Catherine W Morgans
- Neurological Sciences Institute, Oregon Health and Science University, Beaverton, OR 97006, USA.
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Martinez JP, Oesch NW, Ciuffetti LM. Characterization of the multiple-copy host-selective toxin gene, ToxB, in pathogenic and nonpathogenic isolates of Pyrenophora tritici-repentis. Mol Plant Microbe Interact 2004; 17:467-74. [PMID: 15141950 DOI: 10.1094/mpmi.2004.17.5.467] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
ToxB, a gene that encodes a 6.6-kDa host-selective toxin (HST), is present in several races of the wheat pathogen Pyrenophora tritici-repentis. To learn more about the multiple ToxB open reading frames (ORFs), six of the estimated nine copies from a race 5 isolate were cloned and analyzed. All six copies of ToxB have identical 261-bp ORFs and thus encode the same form of Ptr ToxB. Sequence analysis of regions flanking the cloned ToxB loci revealed that the majority of loci are associated with portions of retrotransposons and a transposon-like sequence. Data indicate that ToxB loci reside on two chromosomes, 3.5 and 2.7 Mb, with the majority of copies located on the 2.7 Mb chromosome. A related gene, referred to as toxb, from a nonpathogenic race 4 isolate was also cloned and characterized. This is interesting because, until now, HST genes have only been found in toxin-producing, pathogenic isolates of plant pathogenic fungi. The toxb gene from nonpathogenic isolates is 86% similar to ToxB, and data suggest that toxb is a single-copy gene. No toxb transcript was detected under culture conditions that favor the expression of ToxB; therefore, these genes differ in their transcriptional regulation.
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Affiliation(s)
- J Patrick Martinez
- Dept. of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, USA
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