Opsins and mammalian photoentrainment

Bellingham, James; Foster, Russell G.

doi:10.1007/s00441-002-0573-4

Cited by 96 publications

(79 citation statements)

References 97 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…By itself, however, this finding did nothing to exclude an alternative model in which melanopsin served not as a photopigment but rather as a photoisomerase. According to this model, melanopsin might be essential for providing cis retinaldehyde chromophore to the actual ipRGC photopigment, which remained to be identified [3]. However, parallel studies provided evidence that melanopsin could form a functional photopigment, inasmuch as it mediated light-triggered G-protein activation in a biochemical assay [40].…”

Section: Identity and Properties Of The Iprgc Photopigmentmentioning

confidence: 99%

“…Both have been implicated to some degree in rhabdomeric phototransduction. In Drosophila ommatidial photoreceptors, IP 3 is not essential, and a membrane-delimited cascade involving DAG, polyunsaturated fatty acids, and/or PIP 2 itself appear to be playing an essential role [20]. The light-gated channels have been well characterized and represent the original members of the transient receptor potential (TRP) channel proteins, although their gating mechanism remains uncertain.…”

Section: Evidence For a Rhabdomeric Phosphoinositide Cascadementioning

confidence: 99%

See 1 more Smart Citation

Phototransduction in ganglion-cell photoreceptors

Berson

2007

Pflugers Arch - Eur J Physiol

145

View full text Add to dashboard Cite

A third class of photoreceptors has recently been identified in the mammalian retina. They are a rare cell type within the class of ganglion cells, which are the output cells of the retina. These intrinsically photosensitive retinal ganglion cells support a variety of physiological responses to daylight, including synchronization of circadian rhythms, modulation of melatonin release, and regulation of pupil size. The goal of this review is to summarize what is currently known concerning the cellular and biochemical basis of phototransduction in these cells. I summarize the overwhelming evidence that melanopsin serves as the photopigment in these cells and review the emerging evidence that the downstream signaling cascade, including the light-gated channel, might resemble those found in rhabdomeric invertebrate photoreceptors.Keywords Melanopsin . ipRGC . Photoreceptor . Rhabdomeric . Retina . Ganglion cell . Suprachiasmatic nucleus . TRPC Within the past decade, the existence of a previously unknown class of photoreceptor in the mammalian retina has come to light. These directly photosensitive neurons differ radically in form and function from the well-known rod and cone photoreceptors. They are a rare variety of retinal ganglion cells (RGCs), the class of retinal neurons sending axons through the optic nerve to synapse in the brain. For at least the prior century, it had gone without question that ganglion cells were entirely dependent on polysynaptic influences from rods and cones for their responsiveness to light (indeed, even today there is no reason to doubt this for most ganglion cells). However, as the new millennium dawned, this dogma was being challenged by behavioral studies showing the persistence of certain reflex responses to light in photoreceptor degenerate animals, e.g., [14,15,35,36], and the presence of a possible photopigment, melanopsin, in a rare population of ganglion cells [18,19,21,49,50]. In short order, it became clear that these cells possessed a capacity for autonomous phototransduction [5]. These intrinsically photosensitive RGCs (ipRGCs) are now recognized as playing key roles in synchronizing circadian rhythms to the day-night cycle, mediating the pupillary response to light, and modulation of melatonin release by the pineal gland. Many aspects of this rapidly developing story have been thoroughly summarized elsewhere [4,6,14,16,31,44,54,61]. The reader is referred to these reviews for background on the intellectual origins of the discovery of melanopsin and the ipRGCs, on their structure and physiology, and on their contribution to circadian photoentrainment and other nonimage-forming visual functions. The goal of the present review is to summarize the current state of knowledge concerning the nature of the transduction process in ipRGCs. Structural and functional properties of ipRGCs relevant to the phototransduction processThe ipRGCs represent a tiny minority of the RGCs of mammalian retinas (<1-2%) [9,21,51]. Like other ganglion cells, ipRGCs extend dendritic processes...

show abstract

Section: Identity and Properties Of The Iprgc Photopigmentmentioning

confidence: 99%

Section: Evidence For a Rhabdomeric Phosphoinositide Cascadementioning

confidence: 99%

Phototransduction in ganglion-cell photoreceptors

Berson

2007

Pflugers Arch - Eur J Physiol

145

View full text Add to dashboard Cite

show abstract

“…An investigation into the spectral and functional properties of melanopsin is also important in order to clarify its functional relationship to ancient VA opsins and the retinal G-proteincoupled receptor (RGR), two recently discovered class of opsin proteins (Bellingham and Foster, 2002;Shen et al, 1994). These novel opsins are expressed in retinal cells other than rod and cone photoreceptors, as well as nonocular tissue and appear to function as photopigments, and may mediate light signals involved in nonvisual photic responses, such as circadian photoentrainment (Bellingham and Foster, 2002).…”

Section: Melanopsin As a Photopigmentmentioning

confidence: 99%

“…In doing so, we found that the melanopsin was activated most efficiently by blue light between 420 and 440 nm, rather than the 480 nm green light predicted from the electrophysiological and behavioral experiments Lucas et al, 2001). This result suggests that the blue-shift in the melanopsin absorbance spectrum is also not a result of detergent solubilization.An investigation into the spectral and functional properties of melanopsin is also important in order to clarify its functional relationship to ancient VA opsins and the retinal G-proteincoupled receptor (RGR), two recently discovered class of opsin proteins (Bellingham and Foster, 2002;Shen et al, 1994). These novel opsins are expressed in retinal cells other than rod and cone photoreceptors, as well as nonocular tissue and appear to function as photopigments, and may mediate light signals involved in nonvisual photic responses, such as circadian photoentrainment (Bellingham and Foster, 2002).…”

mentioning

confidence: 99%

See 1 more Smart Citation

Melanopsin—Shedding Light on the Elusive Circadian Photopigment

Brown

Robinson

2004

Chronobiology International

View full text Add to dashboard Cite

Circadian photoentrainment is the process by which the brain's internal clock becomes synchronized with the daily external cycle of light and dark. In mammals, this process is mediated exclusively by a novel class of retinal ganglion cells that send axonal projections to the suprachiasmatic nuclei (SCN), the region of the brain that houses the circadian pacemaker. In contrast to their counterparts that mediate image-forming vision, SCN-projecting RGCs are intrinsically sensitive to light, independent of synaptic input from rod and cone photoreceptors. The recent discovery of these photosensitive RGCs has challenged the long-standing dogma of retinal physiology that rod and cone photoreceptors are the only retinal cells that respond directly to light and has explained the perplexing finding that mice lacking rod and cone photoreceptors can still reliably entrain their circadian rhythms to light. These SCN-projecting RGCs selectively express melanopsin, a novel opsin-like protein that has been proposed as a likely candidate for the photopigment in these cells. Research in the past three years has revealed that disruption of the melanopsin gene impairs circadian photoentrainment, as well as other nonvisual responses to light such as the pupillary light reflex. Until recently, however, there was no direct demonstration that melanopsin formed a functional photopigment capable of catalyzing G-protein activation in a light-dependent manner. Our laboratory has recently succeeded in expressing melanopsin in a heterologous tissue culture system and reconstituting a pigment with the 11-cis-retinal chromophore. In a reconstituted biochemical system, the reconstituted melanopsin was capable of activating transducin, the G-protein of rod photoreceptors, in a light-dependent manner. The absorbance spectrum of this heterologously expressed melanopsin, however, does not match that predicted by previous behavioral and electophysiological studies. Although melanopsin is clearly the leading candidate for the elusive photopigment of the circadian system, further research is needed to resolve the mystery posed by its absorbance spectrum and to fully elucidate its role in circadian photoentrainment. KeywordsMelanopsin; Circadian rhythm; Photoentrainment; Opsin SUNRISE, SUNSET, SUNRISE, SUNSET, SWIFTLY FLY THE YEARSEven as Tevyes laments the inexorable passage of time in these lyrics from Fiddler on the Roof, he concedes that the solar cycle of day and night has been a fact of life on Earth since the dawn of evolution. In fact, most living organisms-from cyanobacteria to man-have adapted their physiology and behavior to this daily cycle (Devlin and Kay, 2001;Dunlap, 1999;Harmer et al., 2001;Young and Kay, 2001 , 1972;Ralph et al., 1990). Like an old watch, however, this internal clock does not keep perfect time, and it must be reset each morning by dawn's early light, a process termed circadian photoentrainment. This process also allows the clock to be reset following travel across time zones and to adjust to seasonal differenc...

show abstract