マウス視交叉上核における光周性を司る２振動体の局在

A master circadian clock of mammals is located in the suprachiasmatic nucleus (SCN) which is entrained by the light-dark (LD) cycle. Transcription-translation feedback loops involving several clock genes are the molecular machinery for rhythm generation, where Per gene plays a key role. Adaptation to the photoperiod is an essential strategy for organisms living in the high latitudes, and the mechanism is currently explained by two mutually coupled circadian oscillators. However, the localization of these oscillators remains elusidated. Adult mice carrying luciferase reporter genes at downstream of the mPer1 promoter were used. They were housed in three LD conditions, LD12:12, LD6:18 or LD18:6 for three weeks. The anterior and posterior SCN slices were cultured separately to monitor Per1 expression for 5days. In addition, spontaneous locomotor activity was monitored by thermal sensors. When transferred from LD12:12 to LD18:6, the activity time was compressed from 12.4h to 7h. On the other hand, in LD6:18 the activity time was lengthened by 1.6h with the activity-onset phase-advanced. In the SCN from LD12:12, the circadian peak in the posterior SCN phase-leaded the peak in the anterior SCN by 2.5h. In LD6:18, the peaks of both rhythms were located at nearly the same time of day, whereas in LD18:6, two peaks were observed in the anterior SCN which were evident in the first several days of culture, but eventually merged into one single peak. The results suggest that the two distinct oscillators reside in the SCN which respond differently to different photoperiods. [J Physiol Sci. 2006;56 Suppl:S209]