Effect of Network Architecture on Synchronization and Entrainment Properties of the Circadian Oscillations in the Suprachiasmatic Nucleus
Figure 2
Scheme of the single-cell circadian oscillator.
The intracellular oscillator consists of interlocked positive and negative transcriptional/translational feedback loops. In the negative feedback loop, Per and Cry genes (treated as a single variable) inhibit their own transcription by preventing BMAL1 activity. In the positive feedback loop, the PER/CRY complex activates the transcription of their common transcriptional activator, Bmal1 [24]. The release of the neurotransmitter is activated by PER/CRY. In turn, the neurotransmitter activates, in the downstream cell, a signaling cascade (involving PKA and CREB) that increases Per/Cry mRNA expression [23]. In this model, light enhances Per/Cry mRNA expression. In this schematic representation, solid arrows denote transport, translation steps, or phosphorylation/dephosphorylation reactions, while dashed arrows denote transcriptional or post-translational regulations. The stars indicate the active (phosphorylated or complexed) forms of the proteins.