Joseph Takahashi
Encyclopedia
Joseph S. Takahashi is a Japanese American
neurobiologist and geneticist
. Takahashi is a professor at University of Texas Southwestern Medical Center
as well as an investigator at the Howard Hughes Medical Institute
. Takahashi's research group discovered the genetic basis for the mammal
ian circadian clock in 1994 and identified the Clock
gene in 1997. Takahashi was elected to the National Academy of Sciences
in 2003.
in Rockville, Maryland
in 1970. Takahashi attended Swarthmore College
and graduated with a degree in biology in 1974. He worked with Patricia DeCoursey at the University of South Carolina
for a year after graduation and then applied to work with Michael Menaker at the University of Texas, Austin. Menaker ultimately moved to the University of Oregon
where Takahashi received his neuroscience Ph.D. in 1981. Takahashi was a postdoctoral fellow at the National Institute of Mental Health
for two years under Martin Zatz before assuming a faculty position in Northwestern University
's Department of Neurobiology and Physiology in 1983, where he held a 26 year tenure. Takahashi joined the faculty at the University of Texas Southwestern Medical Center at Dallas
in 2008 as their Loyd B. Sands Distinguished Chair in Neuroscience. Takahashi also serves as a member of the Scientific Advisory Board of Hypnion, Inc., a company focused on the development of novel therapeutics for central nervous system disorders affecting sleep and wake-alertness as well as circadian rhythm abnormalities. He also serves as a member of the editorial boards of Neuron
, Physiological Genomics and Journal of Biological Rhythms
culture system in vitro to understand circadian oscillations, and they demonstrated that the suprachiasmatic nucleus
(SCN) of the hypothalamus
, which had been identified as the control center for circadian rhythms in mammals, played the same role in birds. The authors also collaborated with DeCoursey and used hamsters to demonstrate that the photoreceptor system responsible for entrainment of circadian rhythms is different from that of the visual system.
In 2010 Takahashi, Buhr, and Yoo examined how the SCN entrains to environmental temperature and how that entrainment regulates body temperature thereby effecting the synchronization of all autonomous circadian cells in the mammalian body. This discovery has implications for evolutionary history, because it suggests that homeothermic animals can use this system for internal circadian synchronization.
studied the mechanisms of mammalian suprachiasmatic nuclei entrainment to environmental light cycles. They explored the relationship between phosphorylated cyclic adenosine monophosphate response element binding protein (CREB
) and c-fos
transcription, a protein previously indicated as a component of the photic entrainment pathway. Using immunoprecipitation
, Takahashi and Greenberg were able to show that light induced CREB phosphorylation occurs only during the subjective night. Given that CREB has been been shown to regulate c-fos transcription in PC12
pheochromocytoma cells, Takahashi and Greenberg were able to conclude that phosphorylation of CREB in the SCN may play an important role in mammalian photic entrainment.
After the in vitro research on the pineal gland culture system used to understand circadian oscillations, the limitations of the cell culture system were evident and Takahashi switched methods to begin using forward genetics
and positional cloning--tools which required no advanced knowledge of the underlying mechanism—to understand the genetic and molecular bases of circadian rhythms. Using mutated mouse strains, Takahashi and his colleagues isolated strains with abnormal period length and discovered the clock gene in 1994. They cloned the mammalian circadian clock gene in 1997.
In 2000, Takahashi made what he calls one of his most significant contributions to the field, which was the cloning of the mutant tau gene identified in 1988 by Menaker and Martin Ralph. Since its discovery in 1988, the tau gene had been studied thoroughly, however, due to limited genomic resources in hamsters, the organism in which it was discovered, a problem existed preventing further study. Through the use of a genetically directed representational difference analysis (GDRDA), the fragments of DNA that differed between the mutant and wild type hamsters. With this information, Takahashi then used positional syntenic cloning to identify synteny
with the human genome. This revealed that the gene is closely related to the gene doubletime (dbt) in Drosophila
, and casein kinase 1 epsilon (CKIe) in humans, both of which interact with and regulate PER
levels
and obesity.
In 2000, he and his colleagues at Northwestern recognized that clock mutant mice slept 1 to 2 hours less per night than wild type mice. Additionally, because these mice lack the circadian system that regulates consolidated sleep at a certain time of day, sleep in clock mutants is spread out throughout the day in both light-dark cycles and in complete darkness. This mutation results in less REM sleep and more time spent in earlier sleep phases.
In 2005, he collaborated with Joseph Bass and reported the effects of mutations in the clock gene on the metabolism and physiology of mice. Their experiments compared weight gain in Clock mutant mice to that of control mice and showed that mutant mice were more likely to gain weight. Such a discovery influenced them to pursue exploration of the clock gene's role in appetite and energy. In Clock mutant mice, they reported depressed levels of orexin
, a neuropeptide involved in regulation of eating. This result provides further evidence that the clock gene has a profound impact on metabolic processes in mice.
It has since been discovered that metabolism itself plays a role in regulating the clock. In 2009, Takahashi and his colleagues discovered that nicotinamide phosphoribosyltransferase
(NAMPT) mediated synthesis of metabolic coenzyme nicotinamide adenine dinucleotide
(NAD+), which both oscillate on a daily cycle, may play an important role in regulating circadian activity. By measuring the oscillations of NAMPT and NAD+ levels in the livers of both wild-type and mutant mice they determined that oscillations in NAMPT regulated NAD+ which in turn regulated the deacetylase SIRT1.
In 2007, Takahashi and his colleagues at Northwestern ran a forward mutagenesis screen
in mice looking for variations in circadian oscillations and subsequently identified a mutant which they named overtime (Ovtm). Using positional cloning, genetic complementation, and in-situ hybridization Takahashi and colleagues discovered that Ovtm was a point mutation
that caused a loss of function in FBXL3
– an F-box protein
– and was expressed throughout the brain and in the SCN
. Assaying expression of known circadian clock genes in the Ovtm mutants, they observed a marked decrease in PER1
and PER2
protein and mRNA levels in the brain and a significant decrease in cry2 mRNA levels only. Takahashi and his colleagues proposed that FBXL3 is a target site for protein degradation on the CRY2 protein, which would explain relatively normal CRY2 protein levels. Negative feedback
by other elements of the circadian clock could then lead to the roughly 26 hour free-running period observed in Ovtm mice.
Japanese American
are American people of Japanese heritage. Japanese Americans have historically been among the three largest Asian American communities, but in recent decades have become the sixth largest group at roughly 1,204,205, including those of mixed-race or mixed-ethnicity...
neurobiologist and geneticist
Geneticist
A geneticist is a biologist who studies genetics, the science of genes, heredity, and variation of organisms. A geneticist can be employed as a researcher or lecturer. Some geneticists perform experiments and analyze data to interpret the inheritance of skills. A geneticist is also a Consultant or...
. Takahashi is a professor at University of Texas Southwestern Medical Center
University of Texas Southwestern Medical Center
The University of Texas Southwestern Medical Center is one of the biomedical research institutions of the University of Texas System, incorporating three degree-granting institutions, four affiliated hospitals, including Parkland Memorial, the teaching hospital, and biomedical research...
as well as an investigator at the Howard Hughes Medical Institute
Howard Hughes Medical Institute
Howard Hughes Medical Institute is a United States non-profit medical research organization based in Chevy Chase, Maryland. It was founded by the American businessman Howard Hughes in 1953. It is one of the largest private funding organizations for biological and medical research in the United...
. Takahashi's research group discovered the genetic basis for the mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
ian circadian clock in 1994 and identified the Clock
CLOCK
Clock is a gene encoding a basic-helix-loop-helix-PAS transcription factor that affects both the persistence and period of circadian rhythms...
gene in 1997. Takahashi was elected to the National Academy of Sciences
United States National Academy of Sciences
The National Academy of Sciences is a corporation in the United States whose members serve pro bono as "advisers to the nation on science, engineering, and medicine." As a national academy, new members of the organization are elected annually by current members, based on their distinguished and...
in 2003.
Background
Takahashi graduated from Richard Montgomery High SchoolRichard Montgomery High School
Richard Montgomery High School is a secondary public school located in Rockville, Maryland.Richard Montgomery High School is named for Richard Montgomery, an American General who died while attempting to capture the British-held city of Quebec...
in Rockville, Maryland
Rockville, Maryland
Rockville is the county seat of Montgomery County, Maryland, United States. It is a major incorporated city in the central part of Montgomery County and forms part of the Baltimore-Washington Metropolitan Area. The 2010 U.S...
in 1970. Takahashi attended 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....
and graduated with a degree in biology in 1974. He worked with Patricia DeCoursey at the University of South Carolina
University of South Carolina
The University of South Carolina is a public, co-educational research university located in Columbia, South Carolina, United States, with 7 surrounding satellite campuses. Its historic campus covers over in downtown Columbia not far from the South Carolina State House...
for a year after graduation and then applied to work with Michael Menaker at the University of Texas, Austin. Menaker ultimately moved to the University of Oregon
University of Oregon
-Colleges and schools:The University of Oregon is organized into eight schools and colleges—six professional schools and colleges, an Arts and Sciences College and an Honors College.- School of Architecture and Allied Arts :...
where Takahashi received his neuroscience Ph.D. in 1981. Takahashi was a postdoctoral fellow at the National Institute of Mental Health
National Institute of Mental Health
The National Institute of Mental Health is one of 27 institutes and centers that make up the National Institutes of Health...
for two years under Martin Zatz before assuming a faculty position in Northwestern University
Northwestern University
Northwestern University is a private research university in Evanston and Chicago, Illinois, USA. Northwestern has eleven undergraduate, graduate, and professional schools offering 124 undergraduate degrees and 145 graduate and professional degrees....
's Department of Neurobiology and Physiology in 1983, where he held a 26 year tenure. Takahashi joined the faculty at the University of Texas Southwestern Medical Center at Dallas
University of Texas Southwestern Medical Center at Dallas
The University of Texas Southwestern Medical Center is one of the biomedical research institutions of the University of Texas System, incorporating three degree-granting institutions, four affiliated hospitals, including Parkland Memorial, the teaching hospital, and biomedical research...
in 2008 as their Loyd B. Sands Distinguished Chair in Neuroscience. Takahashi also serves as a member of the Scientific Advisory Board of Hypnion, Inc., a company focused on the development of novel therapeutics for central nervous system disorders affecting sleep and wake-alertness as well as circadian rhythm abnormalities. He also serves as a member of the editorial boards of Neuron
Neuron (journal)
Neuron is a neuroscience scientific journal published by Cell Press. It has been in continuous publication since 1988....
, Physiological Genomics and Journal of Biological Rhythms
Studies of the SCN--the circadian pacemaker
In the early 1980s, Takahashi and Menaker studied the bird pineal glandPineal gland
The pineal gland is a small endocrine gland in the vertebrate brain. It produces the serotonin derivative melatonin, a hormone that affects the modulation of wake/sleep patterns and seasonal functions...
culture system in vitro to understand circadian oscillations, and they demonstrated that the suprachiasmatic nucleus
Suprachiasmatic nucleus
The 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...
(SCN) of the hypothalamus
Hypothalamus
The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
, which had been identified as the control center for circadian rhythms in mammals, played the same role in birds. The authors also collaborated with DeCoursey and used hamsters to demonstrate that the photoreceptor system responsible for entrainment of circadian rhythms is different from that of the visual system.
In 2010 Takahashi, Buhr, and Yoo examined how the SCN entrains to environmental temperature and how that entrainment regulates body temperature thereby effecting the synchronization of all autonomous circadian cells in the mammalian body. This discovery has implications for evolutionary history, because it suggests that homeothermic animals can use this system for internal circadian synchronization.
Studies of circadian properties of mammalian clock genes
The research of Takahashi has led to many developments in understanding how the circadian clock of mammals affects physiology and relationships with the environment. In 1993, Takahashi and Michael GreenbergMichael E. Greenberg
Michael Greenberg is an American neuroscientist who specializes in neurobiology at the molecular level.- Biography :...
studied the mechanisms of mammalian suprachiasmatic nuclei entrainment to environmental light cycles. They explored the relationship between phosphorylated cyclic adenosine monophosphate response element binding protein (CREB
CREB
CREB is a cellular transcription factor. It binds to certain DNA sequences called cAMP response elements , thereby increasing or decreasing the transcription of the downstream genes....
) and c-fos
C-Fos
In the field of molecular biology and Genetics, c-Fos is a protein encoded by the FOS gene.-Structure and function:c-Fos is a cellular proto-oncogene belonging to the immediate early gene family of transcription factors. c-Fos has a leucine-zipper DNA binding domain, and a transactivation domain at...
transcription, a protein previously indicated as a component of the photic entrainment pathway. Using immunoprecipitation
Immunoprecipitation
Immunoprecipitation is the technique of precipitating a protein antigen out of solution using an antibody that specifically binds to that particular protein. This process can be used to isolate and concentrate a particular protein from a sample containing many thousands of different proteins...
, Takahashi and Greenberg were able to show that light induced CREB phosphorylation occurs only during the subjective night. Given that CREB has been been shown to regulate c-fos transcription in PC12
PC12 cells
PC12 is a cell line derived from a pheochromocytoma of the rat adrenal medulla. PC12 cells stop dividing and terminally differentiate when treated with nerve growth factor...
pheochromocytoma cells, Takahashi and Greenberg were able to conclude that phosphorylation of CREB in the SCN may play an important role in mammalian photic entrainment.
After the in vitro research on the pineal gland culture system used to understand circadian oscillations, the limitations of the cell culture system were evident and Takahashi switched methods to begin using forward genetics
Forward genetics
Forward genetics is an approach that encompasses several means of identifying the gene or set of genes that are responsible for a particular phenotype within an organism. Initially, this entailed the generation of random mutations in an organism, often through radiation or insertional mutagenesis...
and positional cloning--tools which required no advanced knowledge of the underlying mechanism—to understand the genetic and molecular bases of circadian rhythms. Using mutated mouse strains, Takahashi and his colleagues isolated strains with abnormal period length and discovered the clock gene in 1994. They cloned the mammalian circadian clock gene in 1997.
In 2000, Takahashi made what he calls one of his most significant contributions to the field, which was the cloning of the mutant tau gene identified in 1988 by Menaker and Martin Ralph. Since its discovery in 1988, the tau gene had been studied thoroughly, however, due to limited genomic resources in hamsters, the organism in which it was discovered, a problem existed preventing further study. Through the use of a genetically directed representational difference analysis (GDRDA), the fragments of DNA that differed between the mutant and wild type hamsters. With this information, Takahashi then used positional syntenic cloning to identify synteny
Synteny
In classical genetics, synteny describes the physical co-localization of genetic loci on the same chromosome within an individual or species. The concept is related to genetic linkage: Linkage between two loci is established by the observation of lower-than-expected recombination frequencies...
with the human genome. This revealed that the gene is closely related to the gene doubletime (dbt) in Drosophila
Drosophila
Drosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...
, and casein kinase 1 epsilon (CKIe) in humans, both of which interact with and regulate PER
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...
levels
Non-circadian phenotypes of the clock mutant mouse
Since indentifying the clock mutant in 1994, Takahashi has continued his research on this mutation and has applied it to studying clinical disorders, such a irregular sleep homeostasisHomeostasis
Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...
and obesity.
In 2000, he and his colleagues at Northwestern recognized that clock mutant mice slept 1 to 2 hours less per night than wild type mice. Additionally, because these mice lack the circadian system that regulates consolidated sleep at a certain time of day, sleep in clock mutants is spread out throughout the day in both light-dark cycles and in complete darkness. This mutation results in less REM sleep and more time spent in earlier sleep phases.
In 2005, he collaborated with Joseph Bass and reported the effects of mutations in the clock gene on the metabolism and physiology of mice. Their experiments compared weight gain in Clock mutant mice to that of control mice and showed that mutant mice were more likely to gain weight. Such a discovery influenced them to pursue exploration of the clock gene's role in appetite and energy. In Clock mutant mice, they reported depressed levels of orexin
Orexin
Orexins, also called hypocretins, are the common names given to a pair of excitatory neuropeptide hormones that were simultaneously discovered by two groups of researchers in rat brains....
, a neuropeptide involved in regulation of eating. This result provides further evidence that the clock gene has a profound impact on metabolic processes in mice.
It has since been discovered that metabolism itself plays a role in regulating the clock. In 2009, Takahashi and his colleagues discovered that nicotinamide phosphoribosyltransferase
Nicotinamide phosphoribosyltransferase
Nicotinamide phosphoribosyltransferase also known as pre-B-cell colony-enhancing factor 1 or visfatin is an enzyme that in humans is encoded by the PBEF1 gene...
(NAMPT) mediated synthesis of metabolic coenzyme nicotinamide adenine dinucleotide
Nicotinamide adenine dinucleotide
Nicotinamide adenine dinucleotide, abbreviated NAD, is a coenzyme found in all living cells. The compound is a dinucleotide, since it consists of two nucleotides joined through their phosphate groups. One nucleotide contains an adenine base and the other nicotinamide.In metabolism, NAD is involved...
(NAD+), which both oscillate on a daily cycle, may play an important role in regulating circadian activity. By measuring the oscillations of NAMPT and NAD+ levels in the livers of both wild-type and mutant mice they determined that oscillations in NAMPT regulated NAD+ which in turn regulated the deacetylase SIRT1.
Continued mutagenesis studies
Using mutagenesis screens (forward genetics) found both the clock mutant mouse and the tau mutant hamster. Takahashi's lab has continued use of this method in order to lead to discoveries of the role of the circadian clock in vision, learning, memory, stress, and addiction, among other behavioral properites.In 2007, Takahashi and his colleagues at Northwestern ran a forward mutagenesis screen
ENU
ENU, also known as N-ethyl-N-nitrosourea , is a highly potent mutagen. For a given gene in mice, ENU can induce 1 new mutation in every 700 loci. It is also toxic at high doses....
in mice looking for variations in circadian oscillations and subsequently identified a mutant which they named overtime (Ovtm). Using positional cloning, genetic complementation, and in-situ hybridization Takahashi and colleagues discovered that Ovtm was a point mutation
Point mutation
A point mutation, or single base substitution, is a type of mutation that causes the replacement of a single base nucleotide with another nucleotide of the genetic material, DNA or RNA. Often the term point mutation also includes insertions or deletions of a single base pair...
that caused a loss of function in FBXL3
FBXL3
F-box/LRR-repeat protein 3 is a protein that in humans is encoded by the FBXL3 gene.-Further reading:...
– an F-box protein
F-box protein
F-box proteins are proteins containing at least one F-box domain. The first identified F-box protein is one of three components of the SCF complex, which mediates ubiquitination of proteins targeted for degradation by the proteasome....
– and was expressed throughout the brain and in the SCN
Suprachiasmatic nucleus
The 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...
. Assaying expression of known circadian clock genes in the Ovtm mutants, they observed a marked decrease in PER1
PER1
Period circadian protein homolog 1 is a protein that in humans is encoded by the PER1 gene....
and PER2
PER2
Period circadian protein homolog 2 is a protein that in humans is encoded by the PER2 gene.PER2 contains glucocorticoid response elements and a GRE within the core clock gene Per2 is continuously occupied during rhythmic expression and essential for glucocorticoid regulation of PER2 in vivo...
protein and mRNA levels in the brain and a significant decrease in cry2 mRNA levels only. Takahashi and his colleagues proposed that FBXL3 is a target site for protein degradation on the CRY2 protein, which would explain relatively normal CRY2 protein levels. Negative feedback
Negative feedback
Negative feedback occurs when the output of a system acts to oppose changes to the input of the system, with the result that the changes are attenuated. If the overall feedback of the system is negative, then the system will tend to be stable.- Overview :...
by other elements of the circadian clock could then lead to the roughly 26 hour free-running period observed in Ovtm mice.
Notable papers
- Ramsey KM, Yoshino J, Brace CS, Abrassart D, Kobayashi Y, Marcheva B, Hong HK, Chong JL, Buhr ED, Lee C, Takahashi JS, Imai S, Bass J (2009) Circadian clock feedback cycle through NAMPT-mediated NAD+ biosynthesis. Science 324:651-4. This paper discusses the circadian cycle of Clock-Bmal activating the transcription of Cry1, 2, and Per proteins which represses Clock-Bmal transcription creating daily cycling of transcription and channel activation. Specifically, Takahashi looks at NAD+ and NAMPT levels in the liver.