Systematic modeling-driven experiments identify distinct molecular clockworks underlying hierarchically organized pacemaker neurons

Abstract

In metazoan organisms, circadian (∼24 h) rhythms are regulated by pacemaker neurons organized in a master–slave hierarchy. Although it is widely accepted that master pacemakers and slave oscillators generate rhythms via an identical negative feedback loop of transcription factor CLOCK (CLK) and repressor PERIOD (PER), their different roles imply heterogeneity in their molecular clockworks. Indeed, in Drosophila, defective binding between CLK and PER disrupts molecular rhythms in the master pacemakers, small ventral lateral neurons (sLNvs), but not in the slave oscillator, posterior dorsal neuron 1s (DN1ps). Here, we develop a systematic and expandable approach that unbiasedly searches the source of the heterogeneity in molecular clockworks from time-series data. In combination with in vivo experiments, we find that sLNvs exhibit higher synthesis and turnover of PER and lower CLK levels than DN1ps. Importantly, light shift analysis reveals that due to such a distinct molecular clockwork, sLNvs can obtain paradoxical characteristics as the master pacemaker, generating strong rhythms that are also flexibly adjustable to environmental changes. Our results identify the different characteristics of molecular clockworks of pacemaker neurons that underlie hierarchical multi-oscillator structure to ensure the rhythmic fitness of the organism.

Spatially coordinated collective phosphorylation filters spatiotemporal noises for precise circadian timekeeping

“…We calculated several features (e.g., period, amplitude, correlation time) from the oscillatory time series. First, in Figure 2G, we calculated the correlation time 55,56 and the relative amplitude 31 , as done in previous studies. Specifically, to calculate the correlation time, we estimated parameters τ C and P by fitting to the autocorrelation function where x ( t ) is the R n time series obtained from the simulation.…”

“…This filtering mechanism has barely been investigated. Even the widely used mathematical models of the circadian clock assume that PER is homogenously distributed in the cytoplasm, and thus they are not able to capture the cytoplasmic trafficking of PER [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] . Notably, it has been shown that when the cytoplasmic trafficking of Hes1 molecules is incorporated into a mathematical model, the period of Hes1 oscillation greatly changes (~three-fold) 32 .…”

Combined multiple transcriptional repression mechanisms generate ultrasensitivity and oscillations

“…cooperative oligomerization). Thus, sequestration has recently been adopted for mathematical models of circadian clocks [21,[24][25][26][27][28][29][30][31]. However, Heidebrecht et al pointed out that the tightness of the binding between the activator and repressor required for the sequestration to generate sustained rhythms is beyond the physiologically plausible binding affinity [32].…”

“…cooperative oligomerization). Thus, sequestration has recently been adopted for mathematical models of circadian clocks [ 21 , 24 – 31 ]. However, Heidebrecht et al .…”

Time-keeping and decision-making in living cells: Part I

“…Hafner et al [37] suggested that heterogeneity of circadian clocks in the SCN decreases the sensitivity of the network to brief perturbations while simultaneously improving its adaptation to long-term entrainment signals. Recent studies found that the heterogeneous responses of master and slave clock neurons to entrainment signals are critical for strong, adjustable circadian rhythms [48]. Studies by Vasalou et al [49,50] and by Ananthasubramaniam et al [51] have focused on the roles of neurotransmitters in synchronizing circadian oscillators in the SCN.…”