Experimental and Mathematical Analyses Relating Circadian Period and Phase of Entrainment in Neurospora crassa

Abstract

Circadian rhythms are observed in most organisms on earth and known to play a major role in successful adaptation to the 24 h cycling environment. Circadian phenotypes are characterized by a free running period that is observed in constant conditions and an entrained phase that is observed in cyclic conditions. Thus, the relationship between the free running period and phase of entrainment is of interest. A popular simple rule has been that the entrained phase is the expression of the period in a cycling environment, i.e., that a short period causes an advanced phase, and a long period causes a delayed phase. However, there are experimental data that are not explained by this simple relationship, and no systematic study has been done to explore all possible period-phase relationships. Here we show the existence of stable period-phase relationships that are exceptions to this rule. First, we analyzed period-phase relationships using populations with different degrees of genome complexity. Second, we generated isogenic F1 populations by crossing 14 classical period mutants to the same female, and analyzed two populations with a short period/delayed phase and a long period/advanced phase. Third, we generated a mathematical model to account for such variable relationships between period and phase. Our analyses support the view that the circadian period of an organism is not the only predictor of the entrained phase.

Inhibitor of DNA binding 2 (Id2) Regulates Photic Entrainment Responses in Mice: Differential Responses of the Id2-/- Mouse Circadian System Are Dependent on Circadian Phase and on Duration and Intensity of Light

“…In other animal and human studies, an increased deviation of endogenous period length away from the environmental T cycle (e.g., 24-h LD cycle) or a decreased strength of the zeitgeber (e.g., light intensity) often result in marked increases in the phase angle (Pittendrigh and Daan, 1976;Jones et al, 1999;Dunlap et al, 2004;Gronfier et al, 2007). However, more recent genetic studies of the Neurospora clock question the assumed predictive/correlative relationship between period length and phase angle (Lee et al, 2017), and so the observation that Id2-/-mice express a normal period length but an altered phase angle is not a complete aberration. The phase angle difference in Id2-/-mice (smaller and delayed relative to WT mice under LD 12:12 conditions) is observed not only with wheel-running activity and by monitoring general activity within the cage but also in their profiles of feeding activity (Mathew et al, 2013), suggesting that this behavioral phase reflects the phase of the central pacemaker.…”

Entrainment Dynamics of Forced Hierarchical Circadian Systems Revealed by 2-Dimensional Maps

“…In turn, they show that this leads to faster reentrainment of the oscillators in a jet lag scenario. Lee et al [25] directly introduced a linear phase model to study the entrainment processes. They found that the period of the central and peripheral Whereas a shift of light phasing accompanied by a desynchronization is equivalent to changing both…”

Targeted Disruption of the Inhibitor of DNA Binding 4 (Id4) Gene Alters Photic Entrainment of the Circadian Clock

“…In other animal and human studies, an increased deviation of endogenous period length away from the environmental T-cycle (24-h LD cycle) or a decreased strength of the zeitgeber (light intensity) often results in marked increases in the phase angle [5,22,31,32]. A popular simple rule is that a short period length produces an advanced phase relationship with the cycling environment, although there are exceptions to this predictive/correlative relationship [33]. In this study, we revealed that Id4−/− mice expressed a shorter freerunning period length.…”