title: The Lingulodinium circadian system lacks rhythmic changes in transcript abundance.
abstract: BACKGROUND
  Almost all cells display circadian rhythms, approximately 24-hour period changes in their biochemistry, physiology or behavior. These rhythms are orchestrated by an endogenous circadian clock whose mechanism is based on transcription-translation feedback loops (TTFL) where the translated products of clock genes act to inhibit their own transcription.
  
  
  RESULTS
  We have used RNA-Seq to measure the abundance of all transcripts in an RNA-Seq-derived de novo gene catalog in two different experiments. One compared midday and midnight in a light-dark cycle (ZT6 and ZT18) and under constant light (CT6 and CT18). The second compared four different times (ZT2, ZT6, ZT14 and ZT18) under a light dark cycle. We show here that despite an elaborate repertoire of biological rhythms, the unicellular dinoflagellate Lingulodinium had no detectable daily variation in the abundance of any transcript in an RNA-Seq-derived de novo gene catalog. We also examined the timing of the bioluminescence and photosynthesis rhythms in the presence of the transcription inhibitors actinomycin D and cordycepin. We found that the timing of the two rhythms was unchanged even when transcription rates had decreased to roughly 5% the levels of untreated cells.
  
  
  CONCLUSIONS
  The lack of detectable daily variation in transcript levels indicates that the endogenous circadian timer of Lingulodinium does not require rhythmic RNA. If the circadian timer is considered as a limit cycle oscillator, then cellular time in this organism must be defined by variations in state variables that do not include the amount of a clock gene transcript.
authors.affiliation: Département de Sciences Biologiques, Université de Montréal, Institut de Recherche en Biologie Végétale, 4101 Sherbrooke est, Montréal, Québec, H1X 2B2, Canada. sougatairbv20@gmail.com.
authors.forename: Sougata
authors.initials: S
authors.lastname: Roy
authors.affiliation: Département de Sciences Biologiques, Université de Montréal, Institut de Recherche en Biologie Végétale, 4101 Sherbrooke est, Montréal, Québec, H1X 2B2, Canada. mathieu.beauchemin@umontreal.ca.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Beauchemin
authors.affiliation: Département de Sciences Biologiques, Université de Montréal, Institut de Recherche en Biologie Végétale, 4101 Sherbrooke est, Montréal, Québec, H1X 2B2, Canada. steve.dagenais-bellefeuille@umontreal.ca.
authors.forename: Steve
authors.initials: S
authors.lastname: Dagenais-Bellefeuille
authors.affiliation: Centre d'Innovation Génome Québec, McGill University, 740 Docteur Penfield, Montréal, Québec, H3A 1A4, Canada. louis.letourneau@mail.mcgill.ca.
authors.forename: Louis
authors.initials: L
authors.lastname: Letourneau
authors.affiliation: Département de Sciences Biologiques, Université de Montréal, Institut de Recherche en Biologie Végétale, 4101 Sherbrooke est, Montréal, Québec, H1X 2B2, Canada. mario.cappadocia@umontreal.ca.
authors.forename: Mario
authors.initials: M
authors.lastname: Cappadocia
authors.affiliation: Département de Sciences Biologiques, Université de Montréal, Institut de Recherche en Biologie Végétale, 4101 Sherbrooke est, Montréal, Québec, H1X 2B2, Canada. david.morse@umontreal.ca.
authors.forename: David
authors.initials: D
authors.lastname: Morse
mesh_terms: D057906:Circadian Clocks; D002940:Circadian Rhythm; D003609:Dactinomycin / Q000737:chemistry; D003839:Deoxyadenosines / Q000737:chemistry; D004141:Dinoflagellida / Q000235:genetics*; D008027:Light; D017440:Photoperiod; D011500:Protein Synthesis Inhibitors / Q000737:chemistry; D012313:RNA / Q000235:genetics / Q000302:isolation & purification; D017423:Sequence Analysis, RNA
chemical_list: D003839:Deoxyadenosines; D011500:Protein Synthesis Inhibitors; D003609:Dactinomycin; D012313:RNA; C058120:cordycepin