title: Genetics and neurobiology of circadian clocks in mammals.
abstract: In animals, circadian behavior can be analyzed as an integrated system, beginning with genes and leading ultimately to behavioral outputs. In the last decade, the molecular mechanism of circadian clocks has been unraveled primarily by the use of phenotype-driven (forward) genetic analysis in a number of model systems. Circadian oscillations are generated by a set of genes forming a transcriptional autoregulatory feedback loop. In mammals, there is a "core" set of circadian genes that form the primary negative feedback loop of the clock mechanism (Clock/Npas2, Bmal1, Per1, Per2, Cry1, Cry2, and CK1epsilon). A further dozen candidate genes have been identified and have additional roles in the circadian gene network such as the feedback loop involving Rev-erbalpha. Despite this remarkable progress, it is clear that a significant number of genes that strongly influence and regulate circadian rhythms in mammals remain to be discovered and identified. As part of a large-scale N-ethyl-N-nitrosourea mutagenesis screen using a wide range of nervous system and behavioral phenotypes, we have identified a number of new circadian mutants in mice. Here, we describe a new short-period circadian mutant, part-time (prtm), which is caused by a loss-of-function mutation in the Cryptochrome1 (Cry1) gene. We also describe a long-period circadian mutant named Overtime (Ovtm). Positional cloning and genetic complementation reveal that Ovtm is encoded by the F-box protein FBXL3, a component of the SKP1-CUL1-F-box protein (SCF) E3 ubiquitin ligase complex. The Ovtm mutation causes an isoleucine to threonine (I364T) substitution leading to a loss of function in FBXL3 that interacts specifically with the CRYPTOCHROME (CRY) proteins. In Ovtm mice, expression of the PERIOD proteins PER1 and PER2 is reduced; however, the CRY proteins CRY1 and CRY2 are unchanged. The loss of FBXL3 function leads to a stabilization of the CRY proteins, which in turn leads to a global transcriptional repression of the Per and Cry genes. Thus, Fbxl3(Ovtm) defines a molecular link between CRY turnover and CLOCK/BMAL1-dependent circadian transcription to modulate circadian period.
authors.affiliation: Howard Hughes Medical Institute, Northwestern University 2205 Tech Drive Evanston, IL 60208, USA.|Center for Functional Genomics, Northwestern University 2205 Tech Drive Evanston, IL 60208, USA.
authors.forename: Sandra M
authors.initials: SM
authors.lastname: Siepka
authors.affiliation: Howard Hughes Medical Institute, Northwestern University 2205 Tech Drive Evanston, IL 60208, USA.|Center for Functional Genomics, Northwestern University 2205 Tech Drive Evanston, IL 60208, USA.
authors.forename: Seung-Hee
authors.initials: SH
authors.lastname: Yoo
authors.affiliation: Howard Hughes Medical Institute, Northwestern University 2205 Tech Drive Evanston, IL 60208, USA.|Center for Functional Genomics, Northwestern University 2205 Tech Drive Evanston, IL 60208, USA.
authors.forename: Junghea
authors.initials: J
authors.lastname: Park
authors.affiliation: Department of Biological Sciences College of Medicine Florida State University Tallahassee, FL 32306, USA.
authors.forename: Choogon
authors.initials: C
authors.lastname: Lee
authors.affiliation: Howard Hughes Medical Institute, Northwestern University 2205 Tech Drive Evanston, IL 60208, USA.|Center for Functional Genomics, Northwestern University 2205 Tech Drive Evanston, IL 60208, USA.|Department of Neurobiology and Physiology Northwestern University 2205 Tech Drive Evanston, IL 60208, USA.
authors.forename: Joseph S
authors.initials: JS
authors.lastname: Takahashi
mesh_terms: D056930:ARNTL Transcription Factors; D000595:Amino Acid Sequence; D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000502:physiology; D056926:CLOCK Proteins; D002940:Circadian Rhythm / Q000235:genetics* / Q000502:physiology; D003001:Cloning, Molecular; D056931:Cryptochromes; D044783:F-Box Proteins / Q000235:genetics / Q000502:physiology; D025461:Feedback, Physiological; D005260:Female; D005420:Flavoproteins / Q000235:genetics / Q000502:physiology; D006706:Homeostasis; D008297:Male; D008322:Mammals / Q000235:genetics / Q000502:physiology; D051379:Mice; D008954:Models, Biological; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009446:Neurobiology; D010641:Phenotype; D017386:Sequence Homology, Amino Acid; D015534:Trans-Activators / Q000235:genetics / Q000502:physiology
chemical_list: D056930:ARNTL Transcription Factors; D051792:Basic Helix-Loop-Helix Proteins; D056926:CLOCK Proteins; D056931:Cryptochromes; D044783:F-Box Proteins; D005420:Flavoproteins; D015534:Trans-Activators; C538961:Bmal1 protein, mouse; C538964:Cry1 protein, mouse; C538967:Cry2 protein, mouse; C538944:Clock protein, mouse