|
|
|
 |
Circadian clocks. photic signal transduction. Drosophila behavior. seasonal adaptation. pre-mRNA splicing. protein phosphorylation and degradationThe main goal of our laboratory is to understand the molecular and biochemical bases of biological clocks. To achieve this goal. we are using the powerful genetics available in Drosophila in combination with biochemical. molecular and histochemical approaches. Daily fluctuations in biochemical. physiological and behavioral phenomena are governed by endogenous circadian (~24 hour) clocks that can be synchronized (entrained) by external time cues (zeitgebers). most notably the daily changes in light/dark and temperature. This adaptive feature of circadian clocks enables organisms to temporally align their physiology and behavior such that they occur at biologically advantageous times during the day. The isolation of "clock genes" has provided significant insights into the molecular underpinnings governing circadian rhythms. A common theme in clocks from bacteria to humans is that at the "heart" of these pacemakers lie transcriptional-translational feedback loops. The best characterized animal model system for a circadian clock is Drosophila melanogaster. where four clock proteins termed PERIOD (PER). TIMELESS (TIM). dCLOCK and CYCLE (CYC) function in a negative transcriptional autoregulatory loop. dCLOCK and CYC are members of the basic-helix-loop-helix (bHLH)/PAS (PER-ARNT-SIM) superfamily of transcription factors and are required for the daily stimulation of per and tim expression. PER and TIM form a complex in the cytoplasm that enters the nucleus in a temporally gated manner where they bind the dCLOCK-CYC heterodimer blocking its DNA binding activity. In the absence of denovo synthesis. the concentrations of PER and TIM in the nucleus decrease below threshold levels relieving autoinhibition. enabling the next round of per and tim transcript accumulation. Posttranscriptional mechanisms play an important role because they introduce "biochemical time constraints" that stretch the transcriptional feedback loop to ~24 hr and also allows it to respond to external stimuli. For example. light evokes the rapid degradation of TIM. the primary clock-specific photoresponse resetting the oscillatory mechanism. A blue-light photoreceptor called CRYPTOCHROME (CRY) has been implicated in transducing photic signals to TIM. Furthermore. the cytoplasmic phosphorylation of PER by the kinase DOUBLE-TIME (DBT) renders PER unstable. Cytoplasmic PER is stabilized by interacting with TIM which ensures that the accumulation and nuclear entry of the PER-TIM complex is a slow process creating a time-window for daily increases in the levels of per and tim transcripts. Our studies are geared towards isolating all the components that comprise a circadian timekeeping device and understanding how the daily changes in visible light and ambient temperature modulate the oscillatory mechanism. Selected PublicationsYang M, Lee JE, Padgett RW, Edery I. (2008) Circadian regulation of a limited set of conserved microRNAs in Drosophila. BMC Genomics. 9:83. Lee JE, Edery I. (2008) Circadian regulation in the ability of Drosophila to combat pathogenic infections. Curr Biol. 18(3):195-9. Ko HW, DiMassa S, Kim EY, Bae K, Edery I. (2007) Cis-combination of the classic per(S) and per(L) mutations results in arrhythmic Drosophila with ectopic accumulation of hyperphosphorylated PERIOD protein. J Biol Rhythms. 22(6):488-501. Kim EY, Ko HW, Yu W, Hardin PE, Edery I. (2007) A DOUBLETIME kinase binding domain on the Drosophila PERIOD protein is essential for its hyperphosphorylation, transcriptional repression and circadian clock function. Mol Cell Biol. 27(13):5014-28. Edery I. (2007) A blend of two circadian clocks, seasoned to perfection. Cell. 129(1):21-3. Chen WF, Majercak J, Edery I. (2006) Clock-gated photic stimulation of timeless expression at cold temperatures and seasonal adaptation in Drosophila. J Biol Rhythms. 21(4):256-71. Kim EY. Edery I. (2006) Balance between DBT/CKIepsilon kinase and protein phosphatase activities regulate phosphorylation and stability of Drosophila CLOCK protein. Proc Natl Acad Sci U S A. 103(16):6178-83. Ko HW. Edery I. (2005) Analyzing the degradation of PERIOD Protein by the ubiquitin-proteasome pathway in cultured Drosophila cells. Methods Enzymol. 393:394-408. Majercak. J.. Chen. W.-F. and Edery. I. (2004). Splicing of period 3' terminal intron is regulated by light. circadian clock factors and phospholipase C. Mol. Cell. Biol. 24: 3359-3372. Akten. B.. E. Jauch. G. K. Genova. E. Y. Kim. I. Edery. T. Raabe. F. R. Jackson. (2003). A role for CK2 in the Drosophila circadian oscillator. Nature Neurosci. 6. 251-257. Kim. E.Y.. Bae. K.. Ng. F.S.. Glossop. N.R.J.. Hardin. P.E. and Edery. I. (2002).Drosophila CLOCK protein is under posttranscriptional control and influences light-induced activity. Neuron 34:69-81. Ko. W.H.. Jiang. J. and Edery. I. (2002). A role for Slimb in the degradation of Drosophila PERIOD protein phosphorylated by DOUBLETIME. Nature 420:673-678. Edery. I. (2000). Circadian rhythms in a nutshell. Physiol. genomics 3:59-74. Bae. K.. Lee. C.. Hardin. P.H. and Edery. I. (2000). dCLOCK is present in limiting amounts and likely mediates daily interactions between the dCLOCK-CYC transcription factor and the PER-TIM complex. J. of Neurosci. 20:1746-1753. Majercak. J.. Sidote. D.. Hardin. P.H. and Edery. I. (1999). How a circadian clock adapts to seasonal decreases in temperature and day length. Neuron 24:219-230. Sidote. D. and Edery. I. (1999). Heat-induced degradation of PER and TIM in Drosophila bearing a conditional allele of the heat shock transcription factor gene. Chronobiology International 16: 519-525. Lee. C.. Bae. K. and Edery. I. (1998). The Drosophila CLOCK protein undergoes daily rhythms in abundance. phosphorylation. and interactions with the PER-TIM complex. Neuron. 21:857-867. |
|
