Wild females of Pyrrhocoris apterus exhibit seasonal changes in neuroendocrine activity and, consequently, reproduction. Long days (18 h light/6 h dark) (LD) stimulate reproduction, whereas short days (12 h light/12 h dark) (SD) induce reproductive arrest (diapause). This study reveals how photoperiod influences the expression of the circadian clock gene, period (per) in the insect's head. There is only a weak diurnal rhythm in per mRNA expression under LD and SD. However, levels of per mRNA are consistently higher (up to 10-fold) under SD than under LD. The influence of photoperiod on per gene expression is linked to a developmental output (diapause vs. reproduction); mutant females, reproducing under both LD and SD, show low per mRNA levels under both photoperiodic conditions. Thus, the magnitude of per gene expression may be important to the translation of photoperiodic signals into a hormonal message. Levels of per mRNA are related to properties of locomotor activity rhythms. Low per mRNA levels (displayed by wild females in LD and mutant females in both LD and SD) are associated with long free-running periods (τ~26-27 h) and late peaks of activity (ψR,L~10-12 h), whereas high per mRNA levels coincide with short free-running periods (τ~24 h) and early peaks of activity (ψR,L~4-6 h). Overall, the data provide a background for a molecular approach to the long-standing question about the role of the circadian system in insect photoperiodism.
Circadian clock plays an essential role in orchestrating daily physiology, and its disruption can evoke metabolic diseases such as obesity. L-Carnitine can reduce blood lipid levels, and ameliorate fatty liver through regulating lipid metabolism. However, whether L-Carnitine administration may affect the disturbance of lipid metabolism and circadian rhythm of mice induced by prolonged circadian disruption is still unknown. Herein, we investigated the effects of L-Carnitine on conditions of circadian clock and lipid metabolism through a chronic jet-lag mice model which was developed by reversing 12 h light/12 h dark cycle every 4 days for a continuous 12 weeks. Results showed that L-Carnitine administration significantly decreased levels of serum glutamic-oxaloacetic transaminase (GOT) and triglycerides (TG), which were remarkably elevated by chronic jet-lag. More importantly, quantitative real-time polymerase chain reaction (qRT-PCR) analysis indicated that L-Carnitine supplementation would effectively counteract the negative
alterations in gene expression which related to lipid metabolism (Srebp1, Acaca, Fasn, and Scd1), metabolic regulator (mTOR)
and circadian rhythm (Bmal1 , Per1, Cry1 and Dec1 ) in the liver of
mice subjected to the chronic jet-lag. As a conclusion, L-Carnitine was partly effective in preventing the disruption of circadian clock and lipid metabolic disorders induced by the chronic jet-lag.