Posters 
Abstract
Circadian Regulation of Rhythms in mRNA Amount with Different Phases is Theoretically Possible Through an Identical Mechanism
 
Sigrid Jacobshagen1, Claire A. Rinehart1, Bruce Kessler2
Many nuclear genes in the green alga Chlamydomonas reinhardtii show a circadian rhythm in the amount of mRNA. The rhythms differ greatly in phase and amplitude. Circadian regulation for some of the genes could be traced to the level of transcription. We investigated, if the same circadian rhythm of transcription can give rise to rhythms in mRNA amount that differ in phase and amplitude simply based on different constant mRNA degradation rates. We modeled circadian transcription as a sine wave with a period of 24 h and mRNA degradation rates with various constant half-lives. Evaluation of the resulting patterns in mRNA amount revealed that indeed rhythms with various phases and amplitudes are possible. However, phase variations are clearly limited to a range of 0 to 6 h later than the phase of the transcriptional rhythm. We also developed a solvable differential equation based on the same parameters. The equation confirms that the phase of a rhythm in mRNA amount is limited to between 0 h and a quarter of the period later than the phase of the transcriptional rhythm. Based on the differential equation, we were able to relate the phase of a rhythm in mRNA amount solely to the phase of the transcriptional rhythm, its period, and the mRNA half-life. Likewise, the amplitude could be related solely to the amplitude of the transcriptional rhythm, its period, and the mRNA half-life. In conclusion, the circadian clock might regulate genes that show a circadian rhythm in mRNA amount through an identical mechanism as long as the phases do not differ by more than a quarter period.
1Department of Biology, Western Kentucky University, Bowling Green, KY, USA
2Department of Mathematics, Western Kentucky University, Bowling Green, KY, USA