Pigment dispersing factor
Encyclopedia
Pigment dispersing factor (pdf) is a gene that encodes for the protein PDF, which is part of a large family of neuropeptides
. The analogous hormone, pigment dispersing hormone (PDH) was named for the diurnal pigment movement effect it has in crustacean retinal cells, and was initially discovered in the central nervous system
of arthropod
s. The movement and aggregation of the pigments in retina
cells and extra-retinal cells is under a hypothesized split hormonal control. One hormonal set is responsible for concentrating chromatophoral
pigment and responds to changes in the length of darkness presented to the organism whereas another set is responsible for dispersion and responds to the light cycle. However, insect PDF genes do not function in such pigment migration since they lack the chromatophore.
The gene was first isolated and studied in Drosophila
by Jeffrey C. Hall's laboratory at Brandeis University in 1998, and has been found to function as a neuromodulator in controlling circadian rhythm
s.
s of this gene have been reported and are found in dorsal lateral neurons and the ventral lateral neurons in the Drosophila brain.
In a series of experiments done at Washington University School of Medicine
and Brandeis University
, pdf was shown to be critical for circadian output coordination. Flies mutant at the pdf gene locus displayed arrhythmic circadian oscillation. Further research demonstrated that selective ablation of the lateral ventral neurons that express the pdf gene did not affect flies' ability to entrain
to light, however, these flies were arrhythmic in constant conditions, indicating that PDF is not required for response to light, and is probably a part of the output pathway. In addition, utilizing time-series immunostainings
, Lin et. al. showed that PDF does not function in the maintenance of circadian rhythmicity in protein levels, but rather that it is required to coordinate rhythms among the various Drosophila pacemakers. These experiments thereby confirmed the importance of the coordination role pdf expression plays in regulating circadian locomotor activity in Drosophila.
As for localization of PDF, experiments at Brandeis University
have shown that PDF neuropeptide is expressed in small lateral ventral neurons (s-LNv) that specifically control morning anticipatory behavior. Since the Drosophila circadian clock is governed by a morning and an evening oscillator (M and E, respectively), Stoleru et al. used mosaic transgenic animals with different circadian periods to study the two oscillators. Their study showed that M-cells periodically send a "reset" signal which determines the oscillations of the E-cells. It is believed that the reset signal is PDF, because it is M-cell specific, plays a large role in maintaining normal rhythmicity, and functions similarly to the mammalian neuropeptide, VIP
.
Further evidence of distinct E and M peaks in Drosophila was provided by Grima et. al. This work confirmed that the small lateral ventral neurons, which express PDF, are necessary for the morning peak in Drosophila circadian rhythms. Flies lacking functional s-LNv did not possess a lights-on anticipatory activity for the morning peak. In another study on Pdf expression in lateral ventral neurons, it was discovered that Pdf from s-LNv is responsible for the maintenance of a free-running rhythm, while Pdf from large lateral ventral neurons is not required for normal behavior. Furthermore, it has been found that large LNv when working with other circadian neurons is sufficient to rescue the morning anticipation behavior and startle response in s-LNv-ablated flies. Thus, Pdfs role in setting the free-running rhythm and the timing of light dark cycles comes from both types of lateral ventral neurons.
In addition to the LNv, another study has found that a subset of the posterior dorsal neurons 1 (DN1(p)s) modulate the startle response to the onset of light and morning anticipatory behavior. The PDF-expressing neurons synapse onto DN1(p)s neurons and this combined (DN1(p)Pdfr) expression is sufficient to rescue part of the lack of morning anticipation and arrhythmicity.
There is new evidence that glial-neural signaling may physiologically modulate pdf in a calcium dependent manner. The glial cells, specifically astrocytes, in the adult Drosophila brain physiologically regulate circadian neurons, and affect the output PDF. Separate experiments using Gal4/UAS-regulated transgenes to alter glial release of internal calcium stores, glial vesicle trafficking, and membrane gradients all produced arrhythmic locomotor activity. Immunohistochemistry staining for the peptide in the LNv dorsal projections showed a significant reduction after disruption of glial functions, suggesting that PDF transport and release are affected by glial cells.
Other behavioral aspects of Drosophila such as eclosion activity have been monitored with ectopic expression of pdf, which in this case is concentrated in the dorsal central brain. These alterations in expression caused severely altered rhythmic behavior in eclosion of larvae, further substantiating the evidence that PDF modulates the rhythmic control of Drosophila behavior.
and homologs have been identified in organisms such as mosquitos and C.elegans
. A common misconception is that the PDF gene is found in vertebrates, such as rodents, chimpanzees, and humans.
Pdf has also been studied in the cricket Gryllus bimaculatus
; studies proved that Pdf is not necessary for generating the circadian rhythm, but involved in control of nocturnal behavior, entrainment, and the fine-tuning of the free-running period of the circadian clock.
Using liquid chromotography in conjunction with several biological assays, PDF, was also isolated in the insect Leucophaea maderae
, a cockroach.
A study on the larval Rhodnius prolixus brain showed that a clock exists even in the early stages of morphological and neurological development. The larval brain secretes neurohormones to control locomotor rhythmicity. While the lateral neurons in the optic lobe contain PDF, dorsal neurons lack the gene but are synapsed onto by their lateral counterparts, thus synchronizing the clock system. This study shows that insect PDF not only controls rhythmicity in behavior, but also hormone secretion and shows analogies to the mammalian SCN.
Neuropeptide
Neuropeptides are small protein-like molecules used by neurons to communicate with each other. They are neuronal signaling molecules, influence the activity of the brain in specific ways and are thus involved in particular brain functions, like analgesia, reward, food intake, learning and...
. The analogous hormone, pigment dispersing hormone (PDH) was named for the diurnal pigment movement effect it has in crustacean retinal cells, and was initially discovered in the central nervous system
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
of arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
s. The movement and aggregation of the pigments in retina
Retinal
Retinal, also called retinaldehyde or vitamin A aldehyde, is one of the many forms of vitamin A . Retinal is a polyene chromophore, and bound to proteins called opsins, is the chemical basis of animal vision...
cells and extra-retinal cells is under a hypothesized split hormonal control. One hormonal set is responsible for concentrating chromatophoral
Chromatophore
Chromatophores are pigment-containing and light-reflecting cells found in amphibians, fish, reptiles, crustaceans, and cephalopods. They are largely responsible for generating skin and eye colour in cold-blooded animals and are generated in the neural crest during embryonic development...
pigment and responds to changes in the length of darkness presented to the organism whereas another set is responsible for dispersion and responds to the light cycle. However, insect PDF genes do not function in such pigment migration since they lack the chromatophore.
The gene was first isolated and studied in Drosophila
Drosophila melanogaster
Drosophila melanogaster is a species of Diptera, or the order of flies, in the family Drosophilidae. The species is known generally as the common fruit fly or vinegar fly. Starting from Charles W...
by Jeffrey C. Hall's laboratory at Brandeis University in 1998, and has been found to function as a neuromodulator in controlling circadian rhythm
Circadian rhythm
A circadian rhythm, popularly referred to as body clock, is an endogenously driven , roughly 24-hour cycle in biochemical, physiological, or behavioural processes. Circadian rhythms have been widely observed in plants, animals, fungi and cyanobacteria...
s.
Gene characteristics
In Drosophila, the pdf gene is intronless and is located at 97B on the third chromosome. It exists in a single copy per haploid genome and the approximately 0.8 kb transcript is expressed in the Drosophila's head. The length of the cDNA clone in flies is 1080 base pairs and there is a single exon. Six alleleAllele
An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...
s of this gene have been reported and are found in dorsal lateral neurons and the ventral lateral neurons in the Drosophila brain.
Pdf role in the circadian pathways
In the Drosophila brain, a group of cells called the lateral ventral neurons are thought to be the principle pacemaker regulating the circadian rhythm of Drosophila locomotion. Variation in PDF levels, which is expressed by some of these specialized cells, is believed to be the primary output of oscillations within these cells, coordinating fly circadian behavior.In a series of experiments done at Washington University School of Medicine
Washington University School of Medicine
Washington University School of Medicine , located in St. Louis, Missouri, is one of the graduate schools of Washington University in St. Louis. One of the top medical schools in the United States, it is currently ranked 4th for research according to U.S. News and World Report and has been listed...
and Brandeis University
Brandeis University
Brandeis University is an American private research university with a liberal arts focus. It is located in the southwestern corner of Waltham, Massachusetts, nine miles west of Boston. The University has an enrollment of approximately 3,200 undergraduate and 2,100 graduate students. In 2011, it...
, pdf was shown to be critical for circadian output coordination. Flies mutant at the pdf gene locus displayed arrhythmic circadian oscillation. Further research demonstrated that selective ablation of the lateral ventral neurons that express the pdf gene did not affect flies' ability to entrain
Entrainment (chronobiology)
Entrainment, within the study of chronobiology, occurs when rhythmic physiological or behavioral events match their period and phase to that of an environmental oscillation. A common example is the entrainment of circadian rhythms to the daily light–dark cycle, which ultimately is determined by...
to light, however, these flies were arrhythmic in constant conditions, indicating that PDF is not required for response to light, and is probably a part of the output pathway. In addition, utilizing time-series immunostainings
Immunostaining
Immunostaining is a general term in biochemistry that applies to any use of an antibody-based method to detect a specific protein in a sample. The term immunostaining was originally used to refer to the immunohistochemical staining of tissue sections, as first described by Albert Coons in 1941...
, Lin et. al. showed that PDF does not function in the maintenance of circadian rhythmicity in protein levels, but rather that it is required to coordinate rhythms among the various Drosophila pacemakers. These experiments thereby confirmed the importance of the coordination role pdf expression plays in regulating circadian locomotor activity in Drosophila.
As for localization of PDF, experiments at Brandeis University
Brandeis University
Brandeis University is an American private research university with a liberal arts focus. It is located in the southwestern corner of Waltham, Massachusetts, nine miles west of Boston. The University has an enrollment of approximately 3,200 undergraduate and 2,100 graduate students. In 2011, it...
have shown that PDF neuropeptide is expressed in small lateral ventral neurons (s-LNv) that specifically control morning anticipatory behavior. Since the Drosophila circadian clock is governed by a morning and an evening oscillator (M and E, respectively), Stoleru et al. used mosaic transgenic animals with different circadian periods to study the two oscillators. Their study showed that M-cells periodically send a "reset" signal which determines the oscillations of the E-cells. It is believed that the reset signal is PDF, because it is M-cell specific, plays a large role in maintaining normal rhythmicity, and functions similarly to the mammalian neuropeptide, VIP
Vasoactive intestinal peptide
Vasoactive intestinal peptide also known as the vasoactive intestinal polypeptide or VIP is a peptide hormone containing 29 amino acid residues that is produced in many tissues of vertebrates including the gut, pancreas and suprachiasmatic nuclei of the hypothalamus in the brain...
.
Further evidence of distinct E and M peaks in Drosophila was provided by Grima et. al. This work confirmed that the small lateral ventral neurons, which express PDF, are necessary for the morning peak in Drosophila circadian rhythms. Flies lacking functional s-LNv did not possess a lights-on anticipatory activity for the morning peak. In another study on Pdf expression in lateral ventral neurons, it was discovered that Pdf from s-LNv is responsible for the maintenance of a free-running rhythm, while Pdf from large lateral ventral neurons is not required for normal behavior. Furthermore, it has been found that large LNv when working with other circadian neurons is sufficient to rescue the morning anticipation behavior and startle response in s-LNv-ablated flies. Thus, Pdfs role in setting the free-running rhythm and the timing of light dark cycles comes from both types of lateral ventral neurons.
In addition to the LNv, another study has found that a subset of the posterior dorsal neurons 1 (DN1(p)s) modulate the startle response to the onset of light and morning anticipatory behavior. The PDF-expressing neurons synapse onto DN1(p)s neurons and this combined (DN1(p)Pdfr) expression is sufficient to rescue part of the lack of morning anticipation and arrhythmicity.
There is new evidence that glial-neural signaling may physiologically modulate pdf in a calcium dependent manner. The glial cells, specifically astrocytes, in the adult Drosophila brain physiologically regulate circadian neurons, and affect the output PDF. Separate experiments using Gal4/UAS-regulated transgenes to alter glial release of internal calcium stores, glial vesicle trafficking, and membrane gradients all produced arrhythmic locomotor activity. Immunohistochemistry staining for the peptide in the LNv dorsal projections showed a significant reduction after disruption of glial functions, suggesting that PDF transport and release are affected by glial cells.
Other behavioral aspects of Drosophila such as eclosion activity have been monitored with ectopic expression of pdf, which in this case is concentrated in the dorsal central brain. These alterations in expression caused severely altered rhythmic behavior in eclosion of larvae, further substantiating the evidence that PDF modulates the rhythmic control of Drosophila behavior.
Homologs
Pdf is conserved across BilateriaBilateria
The bilateria are all animals having a bilateral symmetry, i.e. they have a front and a back end, as well as an upside and downside. Radially symmetrical animals like jellyfish have a topside and downside, but no front and back...
and homologs have been identified in organisms such as mosquitos and C.elegans
Caenorhabditis elegans
Caenorhabditis elegans is a free-living, transparent nematode , about 1 mm in length, which lives in temperate soil environments. Research into the molecular and developmental biology of C. elegans was begun in 1974 by Sydney Brenner and it has since been used extensively as a model...
. A common misconception is that the PDF gene is found in vertebrates, such as rodents, chimpanzees, and humans.
Pdf has also been studied in the cricket Gryllus bimaculatus
Gryllus bimaculatus
Gryllus bimaculatus is one of many cricket species known as the Field cricket. Also known as the African or Mediterranean field cricket or as the two-spotted cricket, it can be discriminated from other Gryllus species by the two dot-like marks on the base of its wings.This species of cricket is...
; studies proved that Pdf is not necessary for generating the circadian rhythm, but involved in control of nocturnal behavior, entrainment, and the fine-tuning of the free-running period of the circadian clock.
Using liquid chromotography in conjunction with several biological assays, PDF, was also isolated in the insect Leucophaea maderae
Cockroach
Cockroaches are insects of the order Blattaria or Blattodea, of which about 30 species out of 4,500 total are associated with human habitations...
, a cockroach.
A study on the larval Rhodnius prolixus brain showed that a clock exists even in the early stages of morphological and neurological development. The larval brain secretes neurohormones to control locomotor rhythmicity. While the lateral neurons in the optic lobe contain PDF, dorsal neurons lack the gene but are synapsed onto by their lateral counterparts, thus synchronizing the clock system. This study shows that insect PDF not only controls rhythmicity in behavior, but also hormone secretion and shows analogies to the mammalian SCN.
See also
- Circadian rhythmCircadian rhythmA circadian rhythm, popularly referred to as body clock, is an endogenously driven , roughly 24-hour cycle in biochemical, physiological, or behavioural processes. Circadian rhythms have been widely observed in plants, animals, fungi and cyanobacteria...
- Period (gene)Period (gene)Period is a gene located on the X chromosome of Drosophila melanogaster. Oscillations in levels of both per transcript and its corresponding protein PER have a period of approximately 24 hours and together play a central role in the molecular mechanism of the Drosophila biological clock driving...
- Suprachiasmatic nucleusSuprachiasmatic nucleusThe suprachiasmatic nucleus or nuclei, abbreviated SCN, is a tiny region on the brain's midline, situated directly above the optic chiasm. It is responsible for controlling circadian rhythms...
- 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,...
- NeuropeptideNeuropeptideNeuropeptides are small protein-like molecules used by neurons to communicate with each other. They are neuronal signaling molecules, influence the activity of the brain in specific ways and are thus involved in particular brain functions, like analgesia, reward, food intake, learning and...