MICROSCOPY Vol.47▶No.2 2012
â– Feature Article: Morphology of Biological Clocks

Visualize Time in the Brain Clock

Kazuyuki Seo and Hitoshi Okamura

Abstract: The suprachiasmatic nucleus (SCN) of the hypothalamus is known as the circadian center, which signals synchronizes the numerous cell clocks in the peripheral organs. We made a transgenic mice bearing Per1-promoter fused to firefly luciferase gene, and made a long-term monitoring system of the clock gene expression across hundreds of neurons within the mammalian SCN in organotypic slice culture. Differentially phased neuronal clocks are topographically arranged across the SCN. Synchronous oscillations of thousands of cellular clocks in the SCN are coordinated by precisely timed cell-cell communication, the principle of which is largely unknown. By the real time monitoring system, we demonstrated that the amount of RGS16 (regulator of G protein signalling), a protein known to inactivate Gαi, increases in the morning, allowing time-dependent activation of intracellular cyclic AMP signalling in the SCN. Gene ablation of Rgs16 lengthens circadian period of behavioural rhythm. RGS16-dependent temporal regulation of intracellular G protein signalling coordinates the intercellular synchrony of SCN pacemaker neurons and defines the 24 h rhythm in behaviour. The real time imaging system will clarify a variety of mechanisms in the brain at molecular level.

Key words: Suprachiasmatic nucleus, Clock gene, RGS16, circadian rhythm, real time imaging