Relationship of atypical melatonin rhythm with two circadian clock outputs in B6D2F(1) mice

Circadian rhythms in body temperature, locomotor activity, and the circadian changes of plasma and pineal melatonin content were investigated in B6D2F(1) mice synchronized by 12 h of light and 12 h of darkness. During 8 wk continuous recording, activity and temperature displayed a marked stable and reproducible circadian rhythm, with both peaks occurring near the middle of darkness. Both 24- and 12-h rhythmic components were also significantly detected. Mean plasma melatonin concentration rose steadily during the light span and reached a maximum (30.6 +/- 10.0 pg/ml) at 11 h after light onset (HALO), then gradually decreased after the onset of darkness to a nadir (4.7 +/- 0.4 pg/ml) at 20 HALO. Mean pineal content followed a pattern parallel to that of plasma concentration (peak at 11 HALO: 17.7 +/- 1.0 pg/gland; trough at 17 HALO: 4.7 +/- 1.0 pg/gland). In addition, a second sharp peak was observed at 21 HALO (20.2 +/- 3.5 pg/gland). Plasma and pineal contents displayed large and statistically significant circadian changes, with a composite rhythm of period (24 + 12 h). This mouse model has predominant production and secretion of melatonin during the day. This possibly contributes to a similar coupling between chronopharmacology mechanisms and the rest-activity cycle in these mice and in human subjects.     

Characterization of fcp4 and fcp12, Two Additional Genes Encoding Light Harvesting Proteins of Cyclotella cryptica (Bacillariophyceae) and Phylogenetic Analysis of this Complex Gene Family

Abstract: Two additional cDNA clones containing genes which encode fucoxanthin chlorophyll a/c binding proteins (Fcps) of the centric diatom Cyclotella cryptica have been sequenced. The first cDNA clone containing fcp12 had an insert size of 871 base pairs (bp). The open reading frame (ORF) of 693 bp corresponds to a precursor protein of 231 amino acids with a molecular weight (Mr) of 25 200. For the mature Fcp12, a protein of 196 amino acids with a Mr of 21 700 is proposed. The second cDNA clone contained the fragmentary fcp4 with an insert of 805 bp. The ORF of 492 bp corresponds to a polypeptide of 164 amino acids with a Mr of 18 050. Phylogenetic analyses revealed that the proteins Fcp1, Fcp2, Fcp3 and Fcp5 are closely related to the Fcps of other diatoms, whereas Fcp6, Fcp7 and Fcp12 share the highest homology to the Fcp of the haptophyte Isochrysis galbana and to the light inducible proteins LI818r3 and LI818 of Chlamydomonas reinhardtii and Chlamydomonas eugametos. The subunit Fcp4 revealed some homology with the red algal LH subunits LhcaR1 and LhcaR2 of Porphyridium cruentum.     

Light regulation of assimilatory sulphate reduction in Arabidopsis thaliana

Adenosine 5'-phosphosulphate reductase (APR) is considered to be a key enzyme of sulphate assimilation in higher plants. We analysed the diurnal fluctuations of total APR activity and protein accumulation together with the mRNA levels of three APR isoforms of Arabidopsis thaliana. The APR activity reached maximum values 4 h after light onset in both shoots and roots; the minimum activity was detected at the beginning of the night. During prolonged light, the activity remained stable and low in shoots, but followed the normal rhythm in roots. On the other hand, the activity decreased rapidly to undetectable levels within 24 h of prolonged darkness both in shoots and roots. Subsequent re-illumination restored the activity to 50% in shoots and to 20% in roots within 8 h. The mRNA levels of all three APR isoforms showed a diurnal rhythm, with a maximum at 2 h after light onset. The variation of APR2 mRNA was more prominent compared to APR1 and APR3. 35SO42- feeding experiments showed that the incorporation of 35S into reduced sulphur compounds in vivo was significantly higher in light than in the dark. A strong increase of mRNA and protein accumulation as well as enzyme activity during the last 4 h of the dark period was observed, implying that light was not the only factor involved in APR regulation. Indeed, addition of 0.5% sucrose to the nutrient solution after 38 h of darkness led to a sevenfold increase of root APR activity over 6 h. We therefore conclude that changes in sugar concentrations are also involved in APR regulation.     

水稻叶片Rubisco 活化酶表达的昼夜变化

在 48h的自然光照、连续光照和连续黑暗处理下 ,水稻幼苗rcamRNA的含量均表现出昼夜节奏特性 ,其中以自然光周期中变化最为明显。在光暗交替的条件下 ,RCA含量虽也表现出明显的昼夜变化 ,但连续黑暗处理其含量持续下降 ,连续光照则其含量先上升然后下降 ,说明它不发生节昼现象。这些结果表明RCA表达在转录和翻译水平上的调控机制不同 ,转录既由光暗交替控制又受内生节奏调节 ,而翻译则更大程度上由光调节     

Photosynthetic Genes of Petunia (Mitchell) Are Differentially Expressed during the Diurnal Cycle

The petunia (Petunia [Mitchell]) chloroplast proteins, the chlorophyll a/b-binding (Cab) proteins, and the small subunit of ribulose bisphosphate carboxylase (RbcS) are encoded by nuclear genes that are expressed in a light-dependent manner. The steady-state concentrations of five cab mRNAs vary with a dramatic circadian rhythm in plants grown under a constant diurnal cycle (10 hours light, 14 hours dark). cab mRNA levels reach their maximum during the light period, but begin to drop prior to the dark period. These RNAs fall to their minimum concentration during the dark period and then begin to increase again in anticipation of the light. Within this general pattern, there are variations in expression among specific classes of cab genes. The light harvesting complex of photosystem II LHCII-type 1 cab mRNAs rise to a well-defined maximum at 2 hours prior to the dark period. All but one of these genes are expressed in anticipation of the light period. The LHCII type 2 cab mRNA and the LHC of photosystem I cab mRNA are expressed at more constant levels throughout the light period. The expression of these genes anticipates the light more than does the expression of the LHCII type 1 genes. The steady state mRNA levels for the petunia rbcS genes show no significant diurnal fluctuation.     

Acute Behavioral Responses to Light and Darkness in Nocturnal Mus musculus and Diurnal Arvicanthis niloticus

The term masking refers to immediate responses to stimuli that override the influence of the circadian timekeeping system on behavior and physiology. Masking by light and darkness plays an important role in shaping an organism's daily pattern of activity. Nocturnal animals generally become more active in response to darkness (positive masking) and less active in response to light (negative masking), and diurnal animals generally have opposite patterns of response. These responses can vary as a function of light intensity as well as time of day. Few studies have directly compared masking in diurnal and nocturnal species, and none have compared rhythms in masking behavior of diurnal and nocturnal species. Here, we assessed masking in nocturnal mice (Mus musculus) and diurnal grass rats (Arvicanthis niloticus). In the first experiment, animals were housed in a 12:12 light-dark (LD) cycle, with dark or light pulses presented at 6 Zeitgeber times (ZTs; with ZT0 = lights on). Light pulses during the dark phase produced negative masking in nocturnal mice but only at ZT14, whereas light pulses resulted in positive masking in diurnal grass rats across the dark phase. In both species, dark pulses had no effect on behavior. In the 2nd experiment, animals were kept in constant darkness or constant light and were presented with light or dark pulses, respectively, at 6 circadian times (CTs). CT0 corresponded to ZT0 of the preceding LD cycle. Rhythms in masking responses to light differed between species; responses were evident at all CTs in grass rats but only at CT14 in mice. Responses to darkness were observed only in mice, in which there was a significant increase in activity at CT 22. In the 3rd experiment, animals were kept on a 3.5:3.5-h LD cycle. Surprisingly, masking was evident only in grass rats. In mice, levels of activity during the light and dark phases of the 7-h cycle did not differ, even though the same animals had responded to discrete photic stimuli in the first 2 experiments. The results of the 3 experiments are discussed in terms of their methodological implications and for the insight they offer into the mechanisms and evolution of diurnality.     

Diurnal rhythm of drinking activity in the house musk shrew]

A diurnal rhythm of drinking activity in 7 male and 6 female house musk shrews (Jic: SUN) aged about one year was observed over a period of 10 days under a schedule of 12 hr light and 12 hr darkness (light on at 07:00). In general, the pattern of drinking activity was similar among both sexes, with around 24-hr diurnal rhythm. A few typical drinking patterns of these animals were represented as follows: 1) Drinking interval was very close in the dark phase, while it was a little too sparse in the light phase (n = 4). 2) Its interval remains stationary through a whole day (n = 5). 3) Drinking was performed between the latter half of light and the first half of dark phases (n = 4).     

Photoperiodic control of cytokinin transport and metabolism in Chenopodium rubrum

Cytokinin (CK) levels in the short-day plant Chenopodium rubrum L. are known to fluctuate diurnally. The aim of this work was to investigate if the diurnal changes are brought about by changes in transport and/or metabolism of CKs. The effect of photo-period on cytokinin transport was studied by analysing CK concentrations in root, leaf and apical exudates, respectively, under constant light (CL), a 12-h photoperiod (DL) inductive for flowering, DL in which darkness was interrupted at the end of hour 6 by 15 min red light (R), or by 15 min R followed by 30 min far-red irradiation (R/FR). The concentrations of cytokinins (zeatin, zeatin riboside, isopentenyladenine, isopen-tenyladenosine) in all three types of exudates were significantly higher in the first 12-h period after the end of 12 h darkness than in CL. The R break almost fully negated the effect of darkness and its effect was reversed by FR, showing the involvement of phytochrome in the regulation of CK transport. In the next 12-h interval, i.e. 12–24 h after the end of darkness, the CK level remained high in the leaf exudate only, but to a much lower extent than in the previous 12 h. The highest CK concentration (increase by 108%) was observed in apical exudates during inductive darkness. A comparison of the CKs present in the individual exudates indicates that those arriving at the apical part are derived mostly from leaves with varying contributions by the xylem. The metabolism of applied [³H]-zeatin riboside (ZR) was studied using HPLC separation of the metabolites. Metabolism was found to be very rapid and different glucosides, adenine and adenosine were the main metabolites after 12 h incubation with labelled ZR in all regimes tested. The only metabolite that seems to be under photoperiodic control is ZR-5′-monophosphate. It is as yet not clear if photoperiod controls the phosphorylation or dephosphorylation reaction. The activity of the main cytokinin degradative enzyme, cytokinin oxidase, did not change during the photoperiodic regimes tested.     

Running wheel size influences circadian rhythm period and its phase shift in mice

Running wheels are widely used in studies on biological rhythms. In mice wheel diameters have ranged from 11 cm to 23 cm. We provided mice with running wheels of two different sizes: 15 cm diameter and 11 cm diameter. The amount of running in the 12-h light:12-h dark condition and the endogenous period of wheel running in constant darkness was determined over 40 days. On the 1st day in constant darkness all animals were exposed to a 15-min light pulse at circadian time 13. The animals in the small wheel ran significantly less both in 12 h light: 12 h dark and constant darkness, and showed a longer endogenous period in constant darkness compared to animals in the large wheel. Moreover, after the light pulse at circadian time 13, mice in the small wheel showed a significantly smaller phase delay in running wheel activity than mice in the larger wheels. The data suggest that the magnitude of a photic phase shift depends on the amount and timing of activity the animals display in relation to this stimulus. It can be concluded that technical features of the running wheel can influence the circadian period of wheel running.     

Immuno-electron microscopic quantification of the fucoxanthin chlorophyll a/c binding polypeptides Fcp2, Fcp4, and Fcp6 of Cyclotella cryptica grown under low- and high-light intensities.

The diatom Cyclotella cryptica was grown under low- and high-intensity white light of 50 and 500 micromol photons m-2 s-1, respectively. Western immunoblotting showed that the diatom adapted its light-harvesting apparatus, giving rise to different amounts of distinct fucoxanthin chlorophyll a/c binding polypeptides (Fcp). The amount of Fcp2 was approximately two-fold higher under low-light than under high-light conditions, whereas the amount of Fcp6 increased four- to five-fold under high-light conditions. For Fcp4, no significant differences were detected in response to either light regime. Cells of Cyclotella grown under high- and low-light intensity were subjected to immunoelectron microscopy. Quantification of the gold label, expressed as gold particles per microm2, confirmed the results obtained by Western immunoblotting. Exposure to low light resulted in the detection of approximately six times more Fcp2-bound gold particles per microm2 in thylakoid membranes, whereas in cells grown under high light the number of Fcp6-bound gold particles increased ten-fold. For Fcp4, similar amounts of gold particles per microm2 were counted under the two light regimes. These immunocytochemical results confirmed molecular data derived from phylogenetic analyses of the sequences of genes encoding fucoxanthin chlorophyll a/c binding polypeptides (fcp genes) and from measurements of steady-state fcp mRNA concentrations. The results show that Fcp2 and Fcp6 accumulate under low- and high-light intensity, respectively, whereas Fcp4 seems to be constitutively synthesized.     

Photic phase response curve in Octodon degus: assessment as a function of activity phase preference

Light exposure during the early and late subjective night generally phase delays and advances circadian rhythms, respectively. However, this generality was recently questioned in a photic entrainment study in Octodon degus. Because degus can invert their activity phase preference from diurnal to nocturnal as a function of activity level, assessment of phase preference is critical for computations of phase reference [circadian time (CT) 0] toward the development of a photic phase response curve. After determining activity phase preference in a 24-h light-dark cycle (LD 12:12), degus were released in constant darkness. In this study, diurnal (n = 5) and nocturnal (n = 7) degus were randomly subjected to 1-h light pulses (30-35 lx) at many circadian phases (CT 1-6: n = 7; CT 7-12: n = 8; CT 13-18: n = 8; and CT 19-24: n = 7). The circadian phase of body temperature (Tb) onset was defined as CT 12 in nocturnal animals. In diurnal animals, CT 0 was determined as Tb onset + 1 h. Light phase delayed and advanced circadian rhythms when delivered during the early (CT 13-16) and late (CT 20-23) subjective night, respectively. No significant phase shifts were observed during the middle of the subjective day (CT 3-10). Thus, regardless of activity phase preference, photic entrainment of the circadian pacemaker in Octodon degus is similar to most other diurnal and nocturnal species, suggesting that entrainment mechanisms do not determine overt diurnal and nocturnal behavior.     

Sex differences in secretion pattern of neonatal rat Harderian gland under various environmental lighting conditions

1. Secretion pattern of Harderian gland of neonatal rats maintained under (a) diurnal lighting conditions; (b) continuous light or (c) continuous darkness was studied at light microscopy level. 2. All animals were placed in especially designed cages at 13:00 hr on day 1 and studied on day 7 at 13:00 and 23:00 hr, respectively. 3. Acini with intraluminal secretion were counted in glands from each animal and the results were separately grouped for male and female animals. 4. A diurnal rhythm in secretion pattern of rat Harderian gland in neonatal period was demonstrated. 5. A statistically significant difference was observed in the gland secretion pattern between males and females at both, 13:00 and 23:00 hr when the animals were kept under diurnal lighting conditions. 6. Under continuous light or continuous darkness, the diurnal rhythm in secretion pattern was lost and no significant differences were seen when data from males were compared to those from female neonates. 7. Results are discussed in terms of the possible function of Harderian gland as element of an extraretinal photoreceptor system involved in the regulation of pineal function in neonatal rats.     

Circadian rhythmicity in the expression of a novel light-regulated rice gene

We have identified and analyzed cDNAs corresponding to a single-copy gene from rice, designated lir1, whose expression exhibits dramatic diurnal fluctuations. The cDNAs encode a putative protein of 128 amino acids with no homology to known proteins. Lir1 mRNA accumulates in the light, reaching maximum and minimum steady-state levels at the end of the light and dark period, respectively. The oscillations of lir1 mRNA abundance persist after the plants have been transferred to continuous light or darkness. Plants germinated in the dark have very low levels of lir1 mRNA, whereas plants germinated in continuous light express lir1 at an intermediate but constant level. These results indicate that lir1 expression is controlled by light and a circadian clock.     

Circadian morphometric variation in gastric parietal cell populations of the rat

Summary Gastric parietal cells of rats maintained under standardized conditions and fed ad libitum were examined by electron microscopy at 6 time points of the 24-h day. Morphometric determinations were made on 4 cell characteristics. The volume density of secretory canaliculi was maximal at the mid-dark sampling point and decreased during the light phase; a secondary peak was seen 1 h before the onset of darkness. The surface density of microvesicles and RER fluctuated inversely with the pattern displayed by secretory canaliculi. The number of multivesicular bodies per cytoplasmic area exhibited a single peak, 1 h after the onset of darkness. It was further noted that parietal cells in the necks and bases of glands differed morphologically and that their organelle populations varied at individual circadian rates.     

Diurnal variations in plasma testosterone concentrations in the male lesser mouse lemur (Microcebus murinus)

In 6 isolated adult male lesser mouse lemurs, concentrations of testosterone in plasma were determinated at 6-h intervals over a 24-h period. Blood samples were collected at monthly intervals and for a period of 12 months under natural photoperiod. In this nocturnal prosimian, there were no apparent diurnal changes in testosterone concentrations during the non-breeding season (autumn). During seasonal sexual activity (January-August), diurnal changes in testosterone concentrations were characterized by a significant rise during the light phase. The daily testosterone peak occurred about 8.5 h after sunrise from February to July, but at the beginning (January) or at the end (August) of the breeding season, the daily testosterone peak was displaced to the morning. A circannual testosterone rhythm occurred with the highest testosterone values in May/June and the lowest values 6 months later. The dramatic fall in testosterone concentrations after the summer solstice may be associated with a change in the peripheral metabolism of testosterone.