Single cells of Neurospora crassa show circadian oscillations, light entrainment, temperature compensation, and phase synchronization

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Using a microfluidics device, fluorescence of a recorder (mCherry or mVenus) gene driven by a clock-controlled gene-2 promoter (ccg-2p) was measured simultaneously on over 1,000 single cells of Neurospora crassa every half hour for 10 days under each of varied light and temperature conditions.  Single cells were able to entrain to light over a wide range of day lengths including 6 hour (h), 12 h, or 36 h days.  In addition, the period of oscillations in fluorescence remained remarkably stable over a physiological range of temperatures from 20 oC to 30 oC (Q10 = 1.00-1.07).  These results provide evidence of an autonomous clock in most single cells of N. crassa.  While most cells had clocks, there was substantial variation between clocks as measured by their phase, raising the question of how such cellular clocks in single cells phase-synchronize to achieve circadian behavior in eukaryotic systems at the macroscopic level of 107 cells, where most measurements on the clock are performed.  Single cells were placed out of phase by allowing one population to receive 6 or 12 hours more light before lights out (D/D).  The average phase difference was reduced in the mixed population relative to two unmixed control populations.  

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