Ignacio Provencio
Encyclopedia
Ignacio Provencio is an American
neuroscientist
and the discoverer of melanopsin
, a photopigment found in specialized photosensitive ganglion cell
s of the mammalian retina
. Provencio served as the program committee chair of the Society for Research on Biological Rhythms from 2008 to 2010.
, Germany and attended Lebanon Catholic High School
in Lebanon, PA. During his undergraduate career at Swarthmore College
, Provencio became interested in neuroscience while studying crayfish, cockroaches, and fireflies under Jon Copeland. From 1987 to 1989 he worked as a lab technician in Steve Reppert
's research laboratory at Massachusetts General Hospital
, where he was introduced to the field of circadian biology
. He graduated in 1987 from Swarthmore College with a B.A. in Biology and went on to earn his Ph.D.
from the University of Virginia
, a university with a strong network of circadian biologists, in 1996. During his postdoctoral training at Uniformed Services University, Provencio held assistant and associate professorships at Uniformed Services University, Department of Anatomy, Physiology, and Genetics where he still maintains an adjunct associate professorship. He is now an Associate Professor at the University of Virginia.
as a novel human opsin
that is expressed only in the eyes. The unique inner retinal localization of melanopsin indicated that melanopsin was not involved in image formation. Later, he demonstrated that the melanopsin pigment might be involved in entrainment
of a circadian oscillator
to light cycles in mammals.
He found that blind mice lacking classic outer-retinal photoreceptors (rods
and cones
) still had eye-mediated responses to light. Mice with the melanopsin gene knocked out
but with functional rods and cones were also able to entrain. However, when melanopsin was knocked out in blind mice without rods and cones, they exhibited “complete loss of photoentrainment of the circadian oscillator, pupillary light responses, photic suppression of arylalkylamine-N-acetyltransferase transcript, and acute suppression of locomotor activity by light.” Provencio concluded that either melanopsin-containing retinal ganglion cells or outer-retinal photoreceptors (rods and cones) are sufficient to induce a response to light. However, in the absence of either rods and cones or melanopsin, melanopsin becomes necessary for photoentrainment of the circadian oscillator and for other photic responses.
To further investigate the role of melanopsin in light-induced phase shifting in mammals, the Provencio lab studied the locomotor activities of melanopsin-null mice (Opn4 -/-) in response to light. The Opn4 -/- mice showed similar circadian behaviors as the normal mice: they entrained to light/dark cycles and free-ran under constant darkness in a way expected from the normal mice. Researchers in Provencio's lab thus concluded that melanopsin
was not involved in the functioning of the master clock oscillation. On the other hand, Opn4-/- mice had difficulties adjusting to new phases in response to pulses of monochromatic light. The implication was that melanopsin was necessary for phase resetting but other mechanisms of light inputs might be involved in circadian entrainment as well.
In 2008, the Provencio lab was able to specifically destroy melanopsin cells in the fully developed mouse retina using an immunotoxin
made of an anti-melanopsin antibody
conjugated to the protein saporin
. This resulted in lowered responsiveness to light/dark cycles; a similar characteristic was observed in gene-knockout mutants lacking rods, cones or melanopsin. Furthermore, light-induced negative masking, mediated by rods, cones and/or melanopsin cells, was missing in the mice lacking melanopsin cells. Therefore, Provencio suggested that cells containing melanopsin might be required to transmit rod and/or cone information for certain non-image forming visual responses.
and its function in photoentrainment supports earlier studies showing that some blind patients can entrain to a daily light cycle. Since retinal ganglion cells that express melanopsin have also been found in humans, these studies suggest that blind humans who still retain functional melanopsin cells are those who are able to entrain to daily light cycles. These studies also show that blind patients who cannot entrain and lack melanopsin cells have a significantly greater risk of suffering from circadian rhythm sleep disorder
s. While enucleation
of blind patients and babies was a common practice for cosmetic or analgesic reasons, doctors now must make a more cautious decision on whether to enucleate blind patients, especially infants, because they may still have functioning photosensitive retinal ganglion cells that express melanopsin. In addition, there are now studies attempting to optimize light therapy
for those with circadian rhythm sleep disorders that specifically try to stimulate melanopsin cells in blind patients.
In a 2006 study, Provencio explored the role of the protein RPE65
for photoentrainment. RPE65 is an important protein found in intrinsically photosensitive retinal ganglion cells (ipRGCs) that is necessary for regeneration of visual chromophore
in rods and cones. RPE65 knockout mice (Rpe65(-/-)) showed much weaker phase shifts when compared to rodless, coneless mice, which suggested that RPE65 might have other roles.
To further define the functions of RPE65, Provencio took Rpe65(-/-) mice and also eliminated rods. The technique used for this was insertion of the rdta transgene
, which selectively kills rods. They found that circadian photosensitivity
returned in these mice without RPE65 protein and without rods, versus mice without RPE65 protein that still had rods.
Provencio also took Rpe65(-/-) mice and crossed them with melanopsin
knockout mice (Opn4(-/-)). This created double RPE and melanopsin knockout mice, which resulted in abnormal photoentrainment and diurnal behavior.
From these results, Provencio concluded that RPE65 is not necessary for the function of ipRGCs. However, because of the interesting restoration of circadian photosensitivity in rodless, RPE-less mice, there seems to be a mechanism by which rods can influences ipRGCs and rods may interact.
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
neuroscientist
Neuroscientist
A neuroscientist is an individual who studies the scientific field of neuroscience or any of its related sub-fields...
and the discoverer of melanopsin
Melanopsin
Melanopsin is a photopigment found in specialized photosensitive ganglion cells of the retina that are involved in the regulation of circadian rhythms, pupillary light reflex, and other non-visual responses to light. In structure, melanopsin is an opsin, a retinylidene protein variety of...
, a photopigment found in specialized photosensitive ganglion cell
Photosensitive ganglion cell
Photosensitive ganglion cells, also called photosensitive Retinal Ganglion Cells , intrinsically photosensitive Retinal Ganglion Cells or melanopsin-containing ganglion cells, are a type of neuron in the retina of the mammalian eye.They were discovered in the early 1990sand are, unlike other...
s of the mammalian retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
. Provencio served as the program committee chair of the Society for Research on Biological Rhythms from 2008 to 2010.
Biography
Provencio was born in BitburgBitburg
Bitburg It is situated approx. 25 km north-west of Trier, and 50 km north-east of Luxembourg . One American airbase, Spangdahlem Air Base, is located nearby.-History:...
, Germany and attended Lebanon Catholic High School
Lebanon Catholic High School
Lebanon Catholic High School is a private, Roman Catholic high school in Lebanon, Pennsylvania, USA. It is located in the Roman Catholic Diocese of Harrisburg.-Background:...
in Lebanon, PA. During his undergraduate career at Swarthmore College
Swarthmore College
Swarthmore College is a private, independent, liberal arts college in the United States with an enrollment of about 1,500 students. The college is located in the borough of Swarthmore, Pennsylvania, 11 miles southwest of Philadelphia....
, Provencio became interested in neuroscience while studying crayfish, cockroaches, and fireflies under Jon Copeland. From 1987 to 1989 he worked as a lab technician in Steve Reppert
Steven M. Reppert
Steven M. Reppert is an American neuroscientist who has made seminal contributions to the field of circadian biology over the last three decades. His research has focused largely on the physiological, cellular, and molecular basis of circadian rhythms in mammals and more recently on circadian clock...
's research laboratory at Massachusetts General Hospital
Massachusetts General Hospital
Massachusetts General Hospital is a teaching hospital and biomedical research facility in the West End neighborhood of Boston, Massachusetts...
, where he was introduced to the field of circadian biology
Chronobiology
Chronobiology is a field of biology that examines periodic phenomena in living organisms and their adaptation to solar- and lunar-related rhythms. These cycles are known as biological rhythms. Chronobiology comes from the ancient Greek χρόνος , and biology, which pertains to the study, or science,...
. He graduated in 1987 from Swarthmore College with a B.A. in Biology and went on to earn his Ph.D.
Ph.D.
A Ph.D. is a Doctor of Philosophy, an academic degree.Ph.D. may also refer to:* Ph.D. , a 1980s British group*Piled Higher and Deeper, a web comic strip*PhD: Phantasy Degree, a Korean comic series* PhD Docbook renderer, an XML renderer...
from the University of Virginia
University of Virginia
The University of Virginia is a public research university located in Charlottesville, Virginia, United States, founded by Thomas Jefferson...
, a university with a strong network of circadian biologists, in 1996. During his postdoctoral training at Uniformed Services University, Provencio held assistant and associate professorships at Uniformed Services University, Department of Anatomy, Physiology, and Genetics where he still maintains an adjunct associate professorship. He is now an Associate Professor at the University of Virginia.
Role of melanopsin in photic responses
In 2000, Provencio identified melanopsinMelanopsin
Melanopsin is a photopigment found in specialized photosensitive ganglion cells of the retina that are involved in the regulation of circadian rhythms, pupillary light reflex, and other non-visual responses to light. In structure, melanopsin is an opsin, a retinylidene protein variety of...
as a novel human opsin
Opsin
Opsins are a group of light-sensitive 35–55 kDa membrane-bound G protein-coupled receptors of the retinylidene protein family found in photoreceptor cells of the retina. Five classical groups of opsins are involved in vision, mediating the conversion of a photon of light into an electrochemical...
that is expressed only in the eyes. The unique inner retinal localization of melanopsin indicated that melanopsin was not involved in image formation. Later, he demonstrated that the melanopsin pigment might be involved in entrainment
Entrainment
Entrainment may refer to:* Air entrainment, the intentional creation of tiny air bubbles in concrete* Brainwave entrainment, the practice of entraining one's brainwaves to a desired frequency...
of a circadian oscillator
Circadian oscillator
Circadian oscillators are components of the biological clocks that regulate the activities of organisms in relation to environmental cycles and provide an internal temporal framework...
to light cycles in mammals.
He found that blind mice lacking classic outer-retinal photoreceptors (rods
Rod cell
Rod cells, or rods, are photoreceptor cells in the retina of the eye that can function in less intense light than can the other type of visual photoreceptor, cone cells. Named for their cylindrical shape, rods are concentrated at the outer edges of the retina and are used in peripheral vision. On...
and cones
Cone cell
Cone cells, or cones, are photoreceptor cells in the retina of the eye that are responsible for color vision; they function best in relatively bright light, as opposed to rod cells that work better in dim light. If the retina is exposed to an intense visual stimulus, a negative afterimage will be...
) still had eye-mediated responses to light. Mice with the melanopsin gene knocked out
Gene knockout
A gene knockout is a genetic technique in which one of an organism's genes is made inoperative . Also known as knockout organisms or simply knockouts, they are used in learning about a gene that has been sequenced, but which has an unknown or incompletely known function...
but with functional rods and cones were also able to entrain. However, when melanopsin was knocked out in blind mice without rods and cones, they exhibited “complete loss of photoentrainment of the circadian oscillator, pupillary light responses, photic suppression of arylalkylamine-N-acetyltransferase transcript, and acute suppression of locomotor activity by light.” Provencio concluded that either melanopsin-containing retinal ganglion cells or outer-retinal photoreceptors (rods and cones) are sufficient to induce a response to light. However, in the absence of either rods and cones or melanopsin, melanopsin becomes necessary for photoentrainment of the circadian oscillator and for other photic responses.
To further investigate the role of melanopsin in light-induced phase shifting in mammals, the Provencio lab studied the locomotor activities of melanopsin-null mice (Opn4 -/-) in response to light. The Opn4 -/- mice showed similar circadian behaviors as the normal mice: they entrained to light/dark cycles and free-ran under constant darkness in a way expected from the normal mice. Researchers in Provencio's lab thus concluded that melanopsin
was not involved in the functioning of the master clock oscillation. On the other hand, Opn4-/- mice had difficulties adjusting to new phases in response to pulses of monochromatic light. The implication was that melanopsin was necessary for phase resetting but other mechanisms of light inputs might be involved in circadian entrainment as well.
In 2008, the Provencio lab was able to specifically destroy melanopsin cells in the fully developed mouse retina using an immunotoxin
Immunotoxin
An immunotoxin is a human-made protein that consists of a targeting portion linked to a toxin. When the protein binds to that cell, it is taken in through endocytosis, and the toxin kills the cell...
made of an anti-melanopsin antibody
Antibody
An antibody, also known as an immunoglobulin, is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects such as bacteria and viruses. The antibody recognizes a unique part of the foreign target, termed an antigen...
conjugated to the protein saporin
Saporin
Saporin is a protein that is useful in biological research applications, especially studies of behavior. Saporin is a so-called ribosome inactivating protein , due to its N-glycosidase activity, from the seeds of Saponaria officinalis . It was first described by Fiorenzo Stirpe and his colleagues...
. This resulted in lowered responsiveness to light/dark cycles; a similar characteristic was observed in gene-knockout mutants lacking rods, cones or melanopsin. Furthermore, light-induced negative masking, mediated by rods, cones and/or melanopsin cells, was missing in the mice lacking melanopsin cells. Therefore, Provencio suggested that cells containing melanopsin might be required to transmit rod and/or cone information for certain non-image forming visual responses.
Entrainment in blind patients
Provencio's discovery of melanopsinMelanopsin
Melanopsin is a photopigment found in specialized photosensitive ganglion cells of the retina that are involved in the regulation of circadian rhythms, pupillary light reflex, and other non-visual responses to light. In structure, melanopsin is an opsin, a retinylidene protein variety of...
and its function in photoentrainment supports earlier studies showing that some blind patients can entrain to a daily light cycle. Since retinal ganglion cells that express melanopsin have also been found in humans, these studies suggest that blind humans who still retain functional melanopsin cells are those who are able to entrain to daily light cycles. These studies also show that blind patients who cannot entrain and lack melanopsin cells have a significantly greater risk of suffering from circadian rhythm sleep disorder
Circadian rhythm sleep disorder
Circadian rhythm sleep disorders are a family of sleep disorders affecting, among other things, the timing of sleep. People with circadian rhythm sleep disorders are unable to sleep and wake at the times required for normal work, school, and social needs. They are generally able to get enough sleep...
s. While enucleation
Enucleation
Enucleation is removal of the eye, leaving the eye muscles and remaining orbital contents intact. This type of ocular surgery is indicated for a number of different ocular tumors, in eyes that have suffered severe trauma, and in eyes that are blind and painful owing to other...
of blind patients and babies was a common practice for cosmetic or analgesic reasons, doctors now must make a more cautious decision on whether to enucleate blind patients, especially infants, because they may still have functioning photosensitive retinal ganglion cells that express melanopsin. In addition, there are now studies attempting to optimize light therapy
Light therapy
Light therapy or phototherapy consists of exposure to daylight or to specific wavelengths of light using lasers, light-emitting diodes, fluorescent lamps, dichroic lamps or very bright, full-spectrum light, usually controlled with various devices...
for those with circadian rhythm sleep disorders that specifically try to stimulate melanopsin cells in blind patients.
Recent studies
Provencio's research team has found that in albino mice, the amount of melanopsin protein in various retinal cells varies based on the environmental light conditions. In constant light conditions, melanopsin cell number did not increase. However, when these constant-light mice were exposed to light-dark schedules, there was regain of melanopsin cell number. This study shows that bouts of darkness or the order of light and dark periods may control the normal development of the melanopsin system.In a 2006 study, Provencio explored the role of the protein RPE65
RPE65
Retinal pigment epithelium-specific 65 kDa protein is a protein that in humans is encoded by the RPE65 gene.-Function:The retinal pigment epithelium-specific 65 kDa protein is located in the retinal pigment epithelium and is involved in the conversion of all-trans retinol to 11-cis retinal during...
for photoentrainment. RPE65 is an important protein found in intrinsically photosensitive retinal ganglion cells (ipRGCs) that is necessary for regeneration of visual chromophore
Chromophore
A chromophore is the part of a molecule responsible for its color. The color arises when a molecule absorbs certain wavelengths of visible light and transmits or reflects others. The chromophore is a region in the molecule where the energy difference between two different molecular orbitals falls...
in rods and cones. RPE65 knockout mice (Rpe65(-/-)) showed much weaker phase shifts when compared to rodless, coneless mice, which suggested that RPE65 might have other roles.
To further define the functions of RPE65, Provencio took Rpe65(-/-) mice and also eliminated rods. The technique used for this was insertion of the rdta transgene
Transgene
A transgene is a gene or genetic material that has been transferred naturally or by any of a number of genetic engineering techniques from one organism to another....
, which selectively kills rods. They found that circadian photosensitivity
Photosensitivity
Photosensitivity is the amount to which an object reacts upon receiving photons, especially visible light.- Human medicine :Sensitivity of the skin to a light source can take various forms. People with particular skin types are more sensitive to sunburn...
returned in these mice without RPE65 protein and without rods, versus mice without RPE65 protein that still had rods.
Provencio also took Rpe65(-/-) mice and crossed them with melanopsin
Melanopsin
Melanopsin is a photopigment found in specialized photosensitive ganglion cells of the retina that are involved in the regulation of circadian rhythms, pupillary light reflex, and other non-visual responses to light. In structure, melanopsin is an opsin, a retinylidene protein variety of...
knockout mice (Opn4(-/-)). This created double RPE and melanopsin knockout mice, which resulted in abnormal photoentrainment and diurnal behavior.
From these results, Provencio concluded that RPE65 is not necessary for the function of ipRGCs. However, because of the interesting restoration of circadian photosensitivity in rodless, RPE-less mice, there seems to be a mechanism by which rods can influences ipRGCs and rods may interact.
See also
- MelanopsinMelanopsinMelanopsin is a photopigment found in specialized photosensitive ganglion cells of the retina that are involved in the regulation of circadian rhythms, pupillary light reflex, and other non-visual responses to light. In structure, melanopsin is an opsin, a retinylidene protein variety of...
- ChronobiologyChronobiologyChronobiology is a field of biology that examines periodic phenomena in living organisms and their adaptation to solar- and lunar-related rhythms. These cycles are known as biological rhythms. Chronobiology comes from the ancient Greek χρόνος , and biology, which pertains to the study, or science,...
- University of VirginiaUniversity of VirginiaThe University of Virginia is a public research university located in Charlottesville, Virginia, United States, founded by Thomas Jefferson...
- Steven M. ReppertSteven M. ReppertSteven M. Reppert is an American neuroscientist who has made seminal contributions to the field of circadian biology over the last three decades. His research has focused largely on the physiological, cellular, and molecular basis of circadian rhythms in mammals and more recently on circadian clock...
External links
- Ignacio Provencio, Department of Biology, University of Virginia
- The Society for Research on Biological Rhythms
- List of Publications (Pubmed)