Identification of cone classes in <i>Xenopus</i> retina by immunocytochemistry and staining with lectins and vital dyes

Zhang, Jie; Kleinschmidt, Jochen; Sun, Paranee; Witkovsky, Paul

doi:10.1017/s0952523800006982

Cited by 31 publications

(30 citation statements)

References 20 publications

(1 reference statement)

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“…The collecting area of cones (0.8 m 2 ) was estimated by scaling the rod-collecting area by the ratio of the cone-torod volumes. Using the dimensions of red cones from Zhang et al (1994), we determined that, at threshold, each cone absorbs one photon every 10 s. This rate is comparable to that estimated for rod thresholds, and implies that in Xenopus tadpoles, cones may have the capacity to signal the absorption of single photons. This is a controversial notion because a cone responds to a single photon with a decrease of Ͻ0.1-0.5% of its dark current (Donner et al 1998;Perry and McNaughton 1991;Schnapf et al 1990), which is not large enough to reliably signal single photoisomerizations.…”

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confidence: 61%

“…We fitted the data primarily by decreasing the scaling factor of the middle wavelength component. Because there is no evidence that the Xenopus retina possess green-sensitive cones (Witkovsky et al 1981;Zhang et al 1994), the change in the spectral sensitivity most likely reflects a change in the response properties of principal rods. The weighted sum in Fig.…”

Section: Circadian Modulation Of Spectral Sensitivitymentioning

confidence: 99%

“…4) indicates that cones mediate the optomotor responses to highfrequency stimuli. Cones constitute about 50% of photoreceptors in the Xenopus retina, of which 90% are red-sensitive (Zhang et al 1994). We estimated the number of photoisomerizations per cone using the same procedure as described above for rods.…”

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confidence: 99%

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Circadian Modulation of Temporal Properties of the Rod Pathway in LarvalXenopus

Solessio

Scheraga²,

Engbretson³

et al. 2004

Journal of Neurophysiology

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. Circadian clocks are integral components of visual systems. They help adjust an animal's vision to diurnal changes in ambient illumination. To understand how circadian clocks may adapt visual sensitivity, we investigated the spatial and temporal properties of optomotor responses of young Xenopus laevis tadpoles (Nieuwkoop and Faber, developmental stage 48) using a modified 2-alternative preferential-viewing method. We maintained animals in constant darkness and measured temporal sensitivity during their subjective day and night. We found that their behavioral responses can be explained in terms of 2 mechanisms with different temporal properties. The more sensitive mechanism operates at low temporal frequencies and intermediate wavelengths ( max ϭ 520 nm), properties consistent with rod signals. Threshold for this mechanism is approximately 0.04 photoisomerizations rod Ϫ1 s Ϫ1 , consistent with single-photon detection. A less-sensitive mechanism responds to higher temporal frequencies (cutoff ϭ 12 Hz) and has broad spectral sensitivity (370 -720 nm), consistent with multiple classes of cone signals. This cone mechanism does not change, but the cutoff frequency of the more sensitive rod mechanism shifts from 0.35 Hz at night to 1.1 Hz during the subjective day, thereby enhancing the animal's sensitivity to dim rapidly changing stimuli. This day-night shift in rod temporal cutoff frequency cycles in complete darkness, characteristic of an endogenous circadian rhythm. The temporal properties of the behaviorally measured rod mechanism correspond closely with those of the electrophysiologically measured retinal response, indicating that the rod signals are modulated at the level of the outer retina.

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confidence: 61%

Section: Circadian Modulation Of Spectral Sensitivitymentioning

confidence: 99%

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Circadian Modulation of Temporal Properties of the Rod Pathway in LarvalXenopus

Solessio

Scheraga²,

Engbretson³

et al. 2004

Journal of Neurophysiology

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“…2). Furthermore, the GFP-positive cells were identified as rod photoreceptors; they exhibited long outer segments characteristic of rods and lacked the oil droplets found only in cones (22)(23)(24)(25). None of the animals demonstrated a mosaic expression pattern.…”

Section: Human ␤-Pde Promoter Is Active In Xenopus Embryos and A Seqmentioning

confidence: 99%

Nrl and Sp Nuclear Proteins Mediate Transcription of Rod-specific cGMP-phosphodiesterase β-Subunit Gene

Lerner

Gribanova

et al. 2001

Journal of Biological Chemistry

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cGMP-phosphodiesterase (PDE) is the key effector in rod photoreceptor signal transduction. Mutations in the gene encoding its catalytic ␤-subunit (␤-PDE) cause retinal degenerations leading to blindness. We report that the short ؊93 to ؉53 sequence in the upstream region of this gene is sufficient for ␤-PDE transcription in both Y79 human retinoblastoma cells and Xenopus embryo heads maintained ex vivo. This sequence also functions as a minimal rod-specific promoter in transgenic Xenopus tadpoles. The Nrl transcription factor binds in vitro to the ␤Ap1/NRE regulatory element located within this region and transactivates it when overexpressed in nonretinal 293 embryonic kidney cells. We also found a G/Crich activator element, ␤/GC, important for promoter activity in Y79 retinoblastoma cells and Xenopus embryos. Both the ubiquitous Sp1 and the central nervous system-specific Sp4 transcription factors are expressed in retina and interact with this element in vitro. Electrophoretic mobilities of ␤/GC-Y79 nuclear protein complexes are altered by antibodies against Sp1 and Sp4. Thus, our results implicate Nrl, Sp1, and Sp4 in transcriptional regulation of the rod-specific minimal ␤-PDE promoter. We also conclude that Xenopus laevis is an efficient system for analyzing the human ␤-PDE promoter and may be used to study other human retinal genes ex vivo and in vivo.The vertebrate retina is a highly specialized sensory extension of the central nervous system responsible for light perception and conversion into a neural stimulus, phototransduction as well as the initial visual signal integration and processing. Phototransduction occurs both in rod and cone photoreceptors. During rod phototransduction, rhodopsin-activated transducin activates cGMP-phosphodiesterase (PDE), 1 which leads to the hydrolysis of cGMP and closure of the cGMP-gated transmembrane cationic channels causing hyperpolarization of the plasma membrane and photoreceptor signaling (1).The rod photoreceptor-specific cGMP-PDE is a membraneassociated heterotetrameric enzyme composed of two catalytic ␣-and ␤-subunits and two inhibitory ␥-subunits (2). Each of these subunits is essential for normal cGMP-PDE activity required for phototransduction and the maintenance of retinal health. Mutations in the ␤-subunit of cGMP-PDE (␤-PDE) are currently the most common known cause of autosomal recessive retinitis pigmentosa (3). In addition, mutations in the ␤-PDE gene result in congenital stationary night blindness (4) and retinal degeneration in animal models (5-8). Recently, genetic defects in transcription mechanisms that control the expression of several retina-specific genes have been linked to different types of retinal disorders (9 -12). Thus, it became important to elucidate the molecular events that regulate transcription of the ␤-PDE gene, because abnormalities in these control mechanisms may be detrimental for photoreceptor function and structural integrity.The objective of this investigation was to determine the cis-acting elements and the trans-acting nucle...

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“…Xenopus is particularly well suited for studying retinal development and gene regulation; rapid histogenesis (38,39), relative abundance of rods (55%) and cones (45%) (40,41), efficient methods for gene delivery (42,43) and transgenesis (44,45) provide unique experimental strategies to address questions of cell-specific gene expression in vertebrates. We have cloned genomic fragments that contain 5Ј regulatory regions of the Xenopus rod arrestin gene and used transient transfections and transgenic approaches to study promoter function.…”

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confidence: 99%