RESUMEN

The day-active tree shrew may serve as an animal model of human-like diurnal rhythms. However, the molecular basis for circadian rhythms in this species has remained unclear. In the present study, we investigated the expression patterns of core circadian genes involved in transcriptional/translational feedback loops (TTFLs) in both central and peripheral tissues of the tree shrew. The expression of 12 core circadian genes exhibited similar rhythmic patterns in the olfactory bulb, prefrontal cortex, hippocampus, and cerebellum, while the hypothalamus exhibited the weakest oscillations. The rhythms in peripheral tissues, especially the liver, were much more robust than those in brain tissues. ARNTL and NPAS2 were weakly rhythmic in brain tissues but exhibited almost the strongest rhythmicity in peripheral tissues. CLOCK and CRY2 exhibited the weakest rhythms in both central and peripheral tissues, while NR1D1 and CIART exhibited robust rhythms in both tissues. Most of these circadian genes were highly expressed at light/dark transitions in both brain and peripheral tissues, such as ARNTL and NPAS2 peaking at dusk while PERs peaking at dawn. Additionally, the peripheral clock was phase-advanced relative to the brain clock, as there was a significant advance (2-4 h) for PER3, DBP, NR1D1 and NR1D2. Furthermore, these genes exhibited an anti-phasic relationship between the diurnal tree shrew and the nocturnal mouse (i.e., 12-h phasing differential). Collectively, our findings demonstrate a characteristic expression pattern of core circadian genes in the tree shrew, which may provide a means for elucidating molecular mechanisms of diurnal rhythms.

Asunto(s)

Relojes Circadianos , Tupaia , Animales , Encéfalo , Ritmo Circadiano/genética , Hipotálamo , Hígado , Ratones

RESUMEN

Most physiological systems show daily variations in functional output, entrained to the day-night cycle. Humans exhibit a daily rhythm in urinary voiding (micturition), and disruption of this rhythm (nocturia) has significant clinical impact. However, the underlying mechanisms are not well-understood. Recently, a circadian rhythm in micturition was demonstrated in rodents, correlated with functional changes in urodynamics, providing the opportunity to address this issue in an animal model. Smooth muscle cells from mouse bladder have been proposed to express a functional and autonomous circadian clock at the molecular level. In this study, we addressed whether a semi-intact preparation of mouse urinary bladder smooth muscle (UBSM) exhibited measurable differences in contractility between day and night. UBSM tissue strips were harvested at four time points over the diurnal cycle, and spontaneous (phasic) and nerve-evoked contractions were assessed using isometric tension recordings. During the active period (ZT12-24) when micturition frequency is higher in rodents, UBSM strips had no significant differences in maximal- (high K(+)) or nerve-evoked contractions compared to strips harvested from the resting period (ZT0-12). However, a diurnal rhythm in phasic contraction was observed, with higher amplitudes at ZT10. Consistent with the enhanced phasic amplitudes, expression of the BK K(+) channel, a key suppressor of UBSM excitability, was lower at ZT8. Higher expression of BK at ZT20 was correlated with an enhanced effect of the BK antagonist paxilline (PAX) on phasic amplitude, but PAX had no significant time-of-day dependent effect on phasic frequency or nerve-evoked contractions. Overall, these results identify a diurnal difference for one contractile parameter of bladder muscle. Taken together, the results suggest that autonomous clocks in UBSM make only a limited contribution to the integrated control of diurnal micturition patterns.