Neurotransmitter-mediated collective rhythms in grouped Drosophila circadian clocks.

Over the past decades, fly Drosophila melanogaster has being used as a premier model organism to study molecular and genetic bases of circadian rhythms. Here the authors propose a multicellular heterogeneous model for which the network of Drosophila circadian oscillators consists of two groups, the self-sustained lateral neurons (LNs) communicating to each other and the damped dorsal neurons (DNs) receiving neurotransmitters only from the LNs without interaction within this group. By simulating different experimental conditions, the authors find that the proposed model, except for being capable of reproducing some known experimental results well, also can predict some interesting phenomena: 1) The DNs need neuronal projections from the LNs to be rhythmic and to synchronize; 2) the effect of communication on mean amplitude and mean period of two oscillatory groups is different; 3) communication delay can facilitate the network synchronization of the LNs; and 4) only the LNs lose rhythmicity under constant light conditions. These results reveal the mechanism of an integrated pacemaker that would govern behavioral and physiological rhythmicity of the model organism.

Noise-induced Synchronized Switching of a Multicellular System / 生物化学与生物物理进展

Genetic bistable systems are a large class of important biological systems. Bistability, the capacity to achieve two distinct stable steady states in response to a set of external stimuli, arises within biological systems ranging from the ? phage switch in bacteria to cellular signal transduction pathways in mammalian cells. On the other hand, the increasing experimental evidence in the form of bimodal population distribution has indicated that noise plays a very key role in the switching of bistable systems. However, the physiological mechanism underling noise-induced switching behaviors has not been well explored yet. In the previous work, it has been showed that noise can induce coherent switch for a single genetic Toggle switch system. Here the influence of several kinds of noises (including intracellular and extracellular noises) on synchronized switch was investigated for a multicell gene toggle switch network system. It has been found that multiplicative noises resulting from fluctuations of either synthesis or degradation rates and the additive noise within each cell (they altogether are called as intracellular noises) all can induce the synchronized switch, and that there exists an optimal noise intensity such that the synchronized switch is optimally achieved and the amplification factor has the maximal value. On the other hand, the extracellular noises arising from the stochastic fluctuation of the cellular environment, not only brings about the synchronized switch, but also enhances it by suppressing intracellular fluctuations when the intracellular noises are not enough to induce the synchronized switch. Finally, the influence of the diffusive rate of signal molecules affected by noise on the dynamics of the multicellular system was also investigated, showing that the larger the diffusive rate, the better the synchronized switch and the larger the amplification factor.