A Circadian Clock of Drosophila: Effects of Deuterium Oxide and Mutations at the period Locus

Mutations at the period (per) locus (1:1.3; 3B1-2) in Drosophila melanogaster lengthen (per^L), shorten (per⁵), or abolish (per°) overt circadian rhythmi-city. Deuterium oxide lengthens the free-running circadian period. We tested the effects of deuterium on three mutants of the per gene (per⁵ per^L, and per°) and wild-type Drosophila melanogaster (per⁺) to assess interactions. With increasing concentrations of deuterium, the free-running circadian period of locomotor activity rhythms increased. The dose-response was linear in all genotypes tested. With increasing dosages ofdeuterium, circadian rhythms became weaker as evidenced by the signal-to-noise ratio (SNR). Genotype and deuterium changed circadian period length independently and additively, showing no interaction. SNRs for all genotypes converged on a low level as deuterium concentration increased. Deuterium increased life span, except at high concentrations (40 and 50%).     

Rhythmic expression of circadian clock genes in human leukocytes and beard hair follicle cells

Evaluating individual circadian rhythm traits is crucial for understanding the human biological clock system. The present study reports characterization of physiological and molecular parameters in 13 healthy male subjects under a constant routine condition, where interfering factors were kept to minimum. We measured hormonal secretion levels and examined temporal expression profiles of circadian clock genes in peripheral leukocytes and beard hair follicle cells. All 13 subjects had prominent daily rhythms in melatonin and cortisol secretion. Significant circadian rhythmicity was found for PER1 in 9 subjects, PER2 in 3 subjects, PER3 in all 13 subjects, and BMAL1 in 8 subjects in leukocytes. Additionally, significant circadian rhythmicity was found for PER1 in 5 of 8 subjects tested, PER2 in 2 subjects, PER3 in 6 subjects, and BMAL1 in 3 subjects in beard hair follicle cells. The phase of PER1 and PER3 rhythms in leukocytes correlated significantly with that of physiological rhythms. Our results demonstrate that leukocytes and beard hair follicle cells possess an endogenous circadian clock and suggest that PER1 and PER3 expression would be appropriate biomarkers and hair follicle cells could be a useful tissue source for the evaluation of biological clock traits in individuals.     

Effects of the circadian mutation 'tau' on the Harderian glands of Syrian hamsters

The Syrian hamster Harderian gland (HG) is an organ continually exposed to oxidative stress caused by high concentrations of porphyric metabolites. According to previous studies, melatonin, which is rhythmically secreted by the pineal gland and tonically produced by the HG, antagonizes the oxidative damage. HGs exhibit a strong gender-dependent correlation between porphyrins, melatonin, and histological appearance. In HGs of both sexes, we have investigated effects of a single gene defect in the circadian clock system (tau mutation) causing a shortened free-running period and an advanced maximum of circulating melatonin. Comparisons were made with wild-type animals, one group of which received daily pharmacological injections of melatonin in late photophase. Changes were observed in histological characteristics, porphyrin content, antioxidant enzyme activities, and damage of proteins and lipids. HGs of tau hamsters showed morphological changes which can be partially interpreted in terms of increased damage. Additionally, tau females exhibited a many-fold augmentation in the percentage of so-called type II cells, which are otherwise typical for the male glands. In tau hamsters of both sexes, major antioxidative enzyme activities (superoxide dismutase, glutathione reductase, and catalase) were markedly enhanced, a presumably compensatory response to increased oxidative stress. Higher oxidative damage in tau HGs was directly demonstrable by a many-fold increase in protein carbonyl. Rises in antioxidative enzymes were also observed upon injections of melatonin; this was, however, not accompanied by changes in protein carbonyl, so that enzyme inductions by the hormone should be understood as protective actions. Our data are not only in accordance with findings on protective effects by melatonin, but also with our earlier observation made in Drosophila that perturbations in the circadian system lead to increased oxidative stress.     

Casein kinase I: another cog in the circadian clockworks

Multiple components of the circadian central clock are phosphoproteins, and it has become increasingly clear that posttranslational modification is an important regulator of circadian rhythm in diverse organisms, from dinoflagellates to humans. Genetic studies in Drosophila have identified double-time (dbt), a serine/threonine protein kinase that is highly homologous to human casein kinase I epsilon (CKIε), as the first kinase linked to behavioral rhythms. Identification of a missense mutation in CKIε as the tau mutation in the Syrian hamster places CKIε within the core clock machinery in mammals. Most recently, identification of a phosphorylation site mutant of hPER2 in a family with an inherited circadian rhythm abnormality strongly suggests that PER2 is a physiologically relevant substrate of CKI. Phosphorylation may regulate multiple properties of clock proteins, including stability and intracellular localization. (Chronobiology International, 18(3), 389-398, 2001)     

Variations in the antioxidant system and circadian rhythms of goldfish,Carassius auratus,exposed to ammonia: profile of the effects of green LED spectra

The present study evaluated effects of green light emitting diode (LED) spectra on oxidative stress and circadian rhythms in goldfish exposed to various concentrations (0.25 and 0.5 mg/L) of NH₃, under a white fluorescent bulb (control; simulated natural period) and green LED light. We measured mRNA expression and activity of antioxidant enzymes (superoxide dismutase and catalase) and mRNA expression of circadian rhythms (period 2), in addition to levels of plasma hydrogen peroxide, cortisol and melatonin. Damage to nuclear DNA was assessed using the comet assay. All stress indicators and melatonin were significantly lower in the green LED group than in the control group. With an increase in the concentration of ammonia, the observed effects became even more significant and generally increased with time. Comparatively, damage to the nuclear DNA was greater in the 0.5 mg/L NH₃ group, and lower in the green LED group. The Period 2 mRNA expression reduced as increasing ammonia treatment but increased as green LED exposed. We have suggested that Green LED reduced levels of oxidative stress, which suggests an antioxidant effect against NH₃ toxicity. Additionally, ammonia is affected the circadian rhythms and the green LED wavelength is able to regulate effectively the circadian rhythm.     

Locomotor Activity Rhythms in Cave Catfishes, Genus Taunayia, from Eastern Brazil (Teleostei: Siluriformes: Heptapterinae)

We studied the locomotor rhythmicity in heptapterine catfishes, genus Taunayia, under free-running conditions (DD) and LD cycles (12:12). Taunayia sp., anophthalmic and depigmented undescribed species from a cave in northeastern Brazil, is the fourth Brazilian troglobitic catfish studied with focus on circadian rhythms. Weak free-running rhythmicity, with absence of significant circadian components, was observed for this species when compared to the epigean, eyed relatives. On the other hand, the studied troglobitic catfishes in general presented significant circadian rhythms under LD cycles, with activity peaks in the night phase probably corresponding to nocturnal activity pattern inherited from their epigean ancestors. However, no residual oscillations were observed after transition from LD to DD. This indicates masking of activity by light-dark cycles. Regression of circadian rhythmicity in the stable, permanently dark subterranean habitat was also observed for other cave fishes. Such regression corroborates the notion that circadian rhythmicity is mainly selected in the epigean environment by ecological factors, namely daily cycles of light and/or temperature.