ENTRAINMENT ELICITS PERIOD AFTEREFFECTS IN NEUROSPORA CRASSA

Abstract

Circadian clocks continue to oscillate in constant conditions with their own period (τ) and entrain to a cyclic environment by adjusting their intrinsic period to that of the zeitgeber. When circadian clocks are released from entrained to constant conditions, the τ of their initial free-run often depends on the nature of the prior zeitgeber. These postentrainment effects on period (τ-aftereffects) have predominantly been reported for animals but, so far, not fungi. The authors therefore investigated τ aftereffects in the classic circadian model system Neurospora crassa. The standard laboratory strain frq⁺, the short-period mutant frq¹, and the long-period mutant frq⁷ were entrained to 11 different photoperiods in a 24-h day (2–22 h) and to zeitgebers with six different T (16–26 h), and then released to constant darkness. τ-Aftereffects in response to different photoperiods correlated weakly with prior photoperiod in frq⁺ and were unsystematic in both period mutant strains. Strength and direction of the τ-aftereffect in zeitgeber cycles with different T depended on their length and on the strain, showing a negative correlation with zeitgeber length in frq⁺ and positive correlations in frq¹ and frq⁷. It has been proposed that τ-aftereffects are based on interactions of oscillators within a cellular network. The present findings in Neurospora, which grows as a syncytium, suggest that τ-aftereffects also exist in circadian systems based on multioscillatory networks organized at the molecular level. (Author correspondence: [email protected])

Keywords:

• Aftereffect
• Circadian clock
• Entrainment
• Free-running rhythm
• Neurospora crassa

ACKNOWLEDGMENTS

Our work was supported by the German Science Foundation (DFG, RO 656-14 and RO 656-12) and the European Commission (EUCLCOCK, FP6, integrated project). We thank Astrid Bauer, Manfred Gödel, and Tanja Radic for valuable help in the lab, and Hans Distel and Ryan K. Oyama for carefully revising the manuscript.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.