title: Circadian Activators Are Expressed Days before They Initiate Clock Function in Late Pacemaker Neurons from Drosophila.
abstract: Circadian pacemaker neurons in the Drosophila brain control daily rhythms in locomotor activity. These pacemaker neurons can be subdivided into early or late groups depending on whether rhythms in period (per) and timeless (tim) expression are initiated at the first instar (L1) larval stage or during metamorphosis, respectively. Because CLOCK-CYCLE (CLK-CYC) heterodimers initiate circadian oscillator function by activating per and tim transcription, a Clk-GFP transgene was used to mark when late pacemaker neurons begin to develop. We were surprised to see that CLK-GFP was already expressed in four of five clusters of late pacemaker neurons during the third instar (L3) larval stage. CLK-GFP is only detected in postmitotic neurons from L3 larvae, suggesting that these four late pacemaker neuron clusters are formed before the L3 larval stage. A GFP-cyc transgene was used to show that CYC, like CLK, is also expressed exclusively in pacemaker neurons from L3 larval brains, demonstrating that CLK-CYC is not sufficient to activate per and tim in late pacemaker neurons at the L3 larval stage. These results suggest that most late pacemaker neurons develop days before novel factors activate circadian oscillator function during metamorphosis.
authors.affiliation: Department of Biology and Center for Biological Clocks Research, Texas A&M University, College Station, Texas 77845-3258.
authors.forename: Tianxin
authors.initials: T
authors.lastname: Liu
authors.affiliation: Department of Biology and Center for Biological Clocks Research, Texas A&M University, College Station, Texas 77845-3258.
authors.forename: Guruswamy
authors.initials: G
authors.lastname: Mahesh
authors.affiliation: Department of Biology and Center for Biological Clocks Research, Texas A&M University, College Station, Texas 77845-3258.
authors.forename: Jerry H
authors.initials: JH
authors.lastname: Houl
authors.affiliation: Department of Biology and Center for Biological Clocks Research, Texas A&M University, College Station, Texas 77845-3258 phardin@bio.tamu.edu.
authors.forename: Paul E
authors.initials: PE
authors.lastname: Hardin
mesh_terms: D056930:ARNTL Transcription Factors / Q000235:genetics; D000367:Age Factors; D000818:Animals; D030801:Animals, Genetically Modified; D001683:Biological Clocks / Q000235:genetics / Q000502:physiology*; D001921:Brain / Q000166:cytology* / Q000254:growth & development; D056926:CLOCK Proteins / Q000235:genetics; D002940:Circadian Rhythm / Q000235:genetics*; D004330:Drosophila; D029721:Drosophila Proteins / Q000235:genetics; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D007814:Larva; D018613:Microscopy, Confocal; D009043:Motor Activity / Q000235:genetics; D009474:Neurons / Q000502:physiology*; D011679:Pupa
chemical_list: D056930:ARNTL Transcription Factors; C120526:Clk protein, Drosophila; D029721:Drosophila Proteins; C112805:cyc protein, Drosophila; D049452:Green Fluorescent Proteins; D056926:CLOCK Proteins
keywords: cell determination; circadian clock; clock proteins; gene expression; pacemaker neurons