mPer1 Expression Research Articles

L-Ornithine affects peripheral clock gene expression in mice.

The peripheral circadian clock is entrained by factors in the external environment such as scheduled feeding, exercise, and mental and physical stresses. In addition, recent studies in mice demonstrated that some food components have the potential to control the peripheral circadian clock during scheduled feeding, although information about these components remains limited. l-Ornithine is a type of non-protein amino acid that is present in foods and has been reported to have various physiological functions. In human trials, for example, l-ornithine intake improved a subjective index of sleep quality. Here we demonstrate, using an in vivo monitoring system, that repeated oral administration of l-ornithine at an early inactive period in mice induced a phase advance in the rhythm of PER2 expression. By contrast, l-ornithine administration to mouse embryonic fibroblasts did not affect the expression of PER2, indicating that l-ornithine indirectly alters the phase of PER2. l-Ornithine also increased plasma levels of insulin, glucose and glucagon-like peptide-1 alongside mPer2 expression, suggesting that it exerts its effects probably via insulin secretion. Collectively, these findings demonstrate that l-ornithine affects peripheral clock gene expression and may expand the possibilities of L-ornithine as a health food.

Development of circadian oscillators in neurosphere cultures during adult neurogenesis.

Circadian rhythms are common in many cell types but are reported to be lacking in embryonic stem cells. Recent studies have described possible interactions between the molecular mechanism of circadian clocks and the signaling pathways that regulate stem cell differentiation. Circadian rhythms have not been examined well in neural stem cells and progenitor cells that produce new neurons and glial cells during adult neurogenesis. To evaluate circadian timing abilities of cells undergoing neural differentiation, neurospheres were prepared from the mouse subventricular zone (SVZ), a rich source of adult neural stem cells. Circadian rhythms in mPer1 gene expression were recorded in individual spheres, and cell types were characterized by confocal immunofluorescence microscopy at early and late developmental stages in vitro. Circadian rhythms were observed in neurospheres induced to differentiate into neurons or glia, and rhythms emerged within 3–4 days as differentiation proceeded, suggesting that the neural stem cell state suppresses the functioning of the circadian clock. Evidence was also provided that neural stem progenitor cells derived from the SVZ of adult mice are self-sufficient clock cells capable of producing a circadian rhythm without input from known circadian pacemakers of the organism. Expression of mPer1 occurred in high frequency oscillations before circadian rhythms were detected, which may represent a role for this circadian clock gene in the fast cycling of gene expression responsible for early cell differentiation.

Circadian genes Period 1 and Period 2 in the nucleus accumbens regulate anxiety‐related behavior

It has been suggested for some time that circadian rhythm abnormalities underlie the development of multiple psychiatric disorders. However, it is unclear how disruptions in individual circadian genes might regulate mood and anxiety. Here we found that mice lacking functional mPeriod 1 (mPer1) or mPeriod 2 (mPer2) individually did not have consistent behavioral abnormalities in measures of anxiety-related behavior. However, mice deficient in both mPer1 and mPer2 had an increase in levels of anxiety-like behavior in multiple measures. Moreover, we found that mPer1 and mPer2 expression was reduced in the nucleus accumbens (NAc) after exposure to chronic social defeat stress, a paradigm that led to increased anxiety-related behavior. Following social defeat, chronic treatment with fluoxetine normalized Per gene expression towards wild-type levels. Knockdown of both mPer1 and mPer2 expression via RNA interference specifically in the NAc led to a similar increase in anxiety-like behavior as seen in the mutant animals. Taken together, these results implicate the Per genes in the NAc in response to stress and the development of anxiety.

Time-dependent repression of mPer2 expression in the suprachiasmatic nucleus by inhalation anesthesia with sevoflurane

Some anesthetics can affect gene expression. Previously, we reported that sevoflurane anesthesia drastically and reversibly repressed the expression of mouse Per2 (mPer2), a core clock gene in the suprachiasmatic nucleus (SCN). In the current study, we examined the time-dependent effect of sevoflurane on mPer2 expression and its interactions with the circadian rest/activity rhythm of mice. During certain hours of the day, mice were anesthetized with 2.5% sevoflurane in 40% oxygen for 4h. The expression level of mPer2 in the SCN was measured by in situ hybridization using a radiolabeled cRNA probe. Anesthesia during the morning hours showed the greatest repressive effect on mPer2 expression. Sevoflurane anesthesia repressed mPer2 expression during the conditions of light/dark and constant dark, and the light conditions modified the repression rate under anesthesia. Moreover, anesthesia in the morning also repressed mPer2 expression the following day. This dominant effect of anesthesia in the morning indicates that sevoflurane anesthesia affects the onset of mPer2 transcription. Behavior analysis revealed that the anesthetic treatment also induced a phase-delay in the rest/activity rhythm. However, no time-dependent effects of anesthesia on the circadian rest/activity rhythm were observed. Further investigation into the molecular events caused by anesthesia are required to explain atypical clinical signs observed in patients after surgical procedures, such as fatigue, sleep disorder, mood alteration and delirium.

Rhythmic Interaction between Period1 mRNA and hnRNP Q Leads to Circadian Time-Dependent Translation

The mouse PERIOD1 (mPER1) protein, along with other clock proteins, plays a crucial role in the maintenance of circadian rhythms. mPER1 also provides an important link between the circadian system and the cell cycle system. Here we show that the circadian expression of mPER1 is regulated by rhythmic translational control of mPer1 mRNA together with transcriptional modulation. This time-dependent translation was controlled by an internal ribosomal entry site (IRES) element in the 5' untranslated region (5'-UTR) of mPer1 mRNA along with the trans-acting factor mouse heterogeneous nuclear ribonucleoprotein Q (mhnRNP Q). Knockdown of mhnRNP Q caused a decrease in mPER1 levels and a slight delay in mPER1 expression without changing mRNA levels. The rate of IRES-mediated translation exhibits phase-dependent characteristics through rhythmic interactions between mPer1 mRNA and mhnRNP Q. Here, we demonstrate 5'-UTR-mediated rhythmic mPer1 translation and provide evidence for posttranscriptional regulation of the circadian rhythmicity of core clock genes.

Synchronization of Circadian Per2 Rhythms and HSF1-BMAL1:CLOCK Interaction in Mouse Fibroblasts after Short-Term Heat Shock Pulse

Circadian rhythms are the general physiological processes of adaptation to daily environmental changes, such as the temperature cycle. A change in temperature is a resetting cue for mammalian circadian oscillators, which are possibly regulated by the heat shock (HS) pathway. The HS response (HSR) is a universal process that provides protection against stressful conditions, which promote protein-denaturation. Heat shock factor 1 (HSF1) is essential for HSR. In the study presented here, we investigated whether a short-term HS pulse can reset circadian rhythms. Circadian Per2 rhythm and HSF1-mediated gene expression were monitored by a real-time bioluminescence assay for mPer2 promoter-driven luciferase and HS element (HSE; HSF1-binding site)-driven luciferase activity, respectively. By an optimal duration HS pulse (43°C for approximately 30 minutes), circadian Per2 rhythm was observed in the whole mouse fibroblast culture, probably indicating the synchronization of the phases of each cell. This rhythm was preceded by an acute elevation in mPer2 and HSF1-mediated gene expression. Mutations in the two predicted HSE sites adjacent (one of them proximally) to the E-box in the mPer2 promoter dramatically abolished circadian mPer2 rhythm. Circadian Per2 gene/protein expression was not observed in HSF1-deficient cells. These findings demonstrate that HSF1 is essential to the synchronization of circadian rhythms by the HS pulse. Importantly, the interaction between HSF1 and BMAL1:CLOCK heterodimer, a central circadian transcription factor, was observed after the HS pulse. These findings reveal that even a short-term HS pulse can reset circadian rhythms and cause the HSF1-BMAL1:CLOCK interaction, suggesting the pivotal role of crosstalk between the mammalian circadian and HSR systems.

The Influence of Circadian Gene Per2 on Cell Damaged by Ultraviolet C

It has been shown that circadian genes not only play an important role on circadian rhythms, but also participate in other physiological and pathological activities, such as drug dependence, cancer development and radiation injury. The Per2, an indispensable component of the circadian clock, not only modulates circadian oscillations, but also regulates organic function. In the present study, we applied mPER2-upregulated NIH3T3 cells to reveal the relationship of mPer2 and the cells damaged by ultraviolet C (UVC). NIH3T3 cells at the peak of the expression of mPer2 induced by phorbol 12-myristate 13-acetate (PMA) demonstrated little damage by UVC evaluated by MTT assay, cell growth curves and cell colony-forming assay, compared with that at the nadir of the expression of mPer2. Overexpression of mPER2, accompanied p53 upregulated, also demonstrated protective effect on NIH3T3 cells damaged by UVC. These results suggest that mPer2 plays a protective effect on cells damaged by UVC, whose mechanism may be involved in upregulated p53.

Androgens Modulate Structure and Function of the Suprachiasmatic Nucleus Brain Clock

Gonadal hormones can modulate circadian rhythms in rodents and humans, and androgen receptors are highly localized within the core region of the mouse suprachiasmatic nucleus (SCN) brain clock. Although androgens are known to modulate neural plasticity in other CNS compartments, the role of androgens and their receptors on plasticity in the SCN is unexplored. In the present study, we ask whether androgens influence the structure and function of the mouse SCN by examining the effects of gonadectomy (GDX) on the structure of the SCN circuit and its responses to light, including induction of clock genes and behavioral phase shifting. We found that after GDX, glial fibrillary acidic protein increased with concomitant decreases in the expression of the synaptic proteins synaptophysin and postsynaptic density 95. We also found that GDX exerts effects on the molecular and behavioral responses to light that are phase dependent. In late night [circadian time (CT)21], GDX increased light-induced mPer1 but not mPer2 expression compared with intact (INT) controls. In contrast, in early night (CT13.5), GDX decreased light induced mPer2 but had no effect on mPer1. At CT13.5, GDX animals also showed larger phase delays than did INT. Treatment of GDX animals with the nonaromatizable androgen dihydrotestosterone restored glial fibrillary acidic protein, postsynaptic density 95, and synaptophysin in the SCN and reinstated the INT pattern of molecular and behavioral responses to light. Together, the results reveal a role for androgens in regulating circuitry in the mouse SCN, with functional consequences for clock gene expression and behavioral responses to photic phase resetting stimuli.

The general anesthetic sevoflurane affects the expression of clock gene mPer2 accompanying the change of NAD+ level in the suprachiasmatic nucleus of mice

Sevoflurane is an anesthetic for the general anesthesia. In this study, we showed that sevoflurane anesthesia affects the expression of mouse Per2 (mPer2), which is a clock gene in the brain which is considered the organ where the anesthetics act in. 64.5% of mPer2 circadian expression was repressed under anesthesia in the suprachiasmatic nucleus (SCN) of the brain. After recovering from the anesthesia, the repressed mPer2 expression was restored to the same level as in non anesthesia-treated mice. This repression pattern was also observed in the subsequent phases of diurnal mPer2 expression. However, obvious phase-shift in the mPer2 expression was not showed in this study. On the other hand, the behavior analysis in this experiment exhibited that the phases in the circadian behavioral rhythm were shifted backwards. We also measured the NAD+ level in the SCN, which was a mediator regulating the mPer2 expression. Then, significant increase of NAD+ was detected under the anesthesia. These results indicate that the anesthesia induces the increase of NAD+, and consequently leads to the repression of mPer2 expression and modifies the circadian expression pattern and diurnal behavioral rhythm of mice. Furthermore, the modification of mPer2 expression by the anesthesia is considered to affect various gene expressions.

The Transcriptional Repressor ID2 Can Interact with the Canonical Clock Components CLOCK and BMAL1 and Mediate Inhibitory Effects on mPer1 Expression

ID2 is a rhythmically expressed HLH transcriptional repressor. Deletion of Id2 in mice results in circadian phenotypes, highlighted by disrupted locomotor activity rhythms and an enhanced photoentrainment response. ID2 can suppress the transactivation potential of the positive elements of the clock, CLOCK-BMAL1, on mPer1 and clock-controlled gene (CCG) activity. Misregulation of CCGs is observed in Id2(-/-) liver, and mutant mice exhibit associated alterations in lipid homeostasis. These data suggest that ID2 contributes to both input and output components of the clock and that this may be via interaction with the bHLH clock proteins CLOCK and BMAL1. The aim of the present study was to explore this potential interaction. Coimmunoprecipitation analysis revealed the capability of ID2 to complex with both CLOCK and BMAL1, and mammalian two-hybrid analysis revealed direct interactions of ID2, ID1 and ID3 with CLOCK and BMAL1. Deletion of the ID2 HLH domain rendered ID2 ineffective at inhibiting CLOCK-BMAL1 transactivation, suggesting that interaction between the proteins is via the HLH region. Immunofluorescence analysis revealed overlapping localization of ID2 with CLOCK and BMAL1 in the cytoplasm. Overexpression of CLOCK and BMAL1 in the presence of ID2 resulted in a significant reduction in their nuclear localization, revealing that ID2 can sequester CLOCK and BMAL1 to the cytoplasm. Serum stimulation of Id2(-/-) mouse embryonic fibroblasts resulted in an enhanced induction of mPer1 expression. These data provide the basis for a molecular mechanism through which ID2 could regulate aspects of both clock input and output through a time-of-day specific interaction with CLOCK and BMAL1.

Nighttime dim light exposure alters the responses of the circadian system

The daily light dark cycle is the most salient entraining factor for the circadian system. However, in modern society, darkness at night is vanishing as light pollution steadily increases. The impact of brighter nights on wild life ecology and human physiology is just now being recognized. In the present study, we tested the possible detrimental effects of dim light exposure on the regulation of circadian rhythms, using CD1 mice housed in light/dim light (LdimL, 300 lux:20 lux) or light/dark (LD, 300 lux:1 lux) conditions. We first examined the expression of clock genes in the suprachiasmatic nucleus (SCN), the locus of the principal brain clock, in the animals of the LD and LdimL groups. Under the entrained condition, there was no difference in PER1 peak expression between the two groups, but at the trough of the PER 1 rhythm, there was an increase in PER1 in the LdimL group, indicating a decrease in the amplitude of the PER1 rhythm. After a brief light exposure (30 min, 300 lux) at night, the light-induced expression of mPer1 and mPer2 genes was attenuated in the SCN of LdimL group. Next, we examined the behavioral rhythms by monitoring wheel-running activity to determine whether the altered responses in the SCN of LdimL group have behavioral consequence. Compared to the LD controls, the LdimL group showed increased daytime activity. After being released into constant darkness, the LdimL group displayed shorter free-running periods. Furthermore, following the light exposure, the phase shifting responses were smaller in the LdimL group. The results indicate that nighttime dim light exposure can cause functional changes of the circadian system, and suggest that altered circadian function could be one of the mechanisms underlying the adverse effects of light pollution on wild life ecology and human physiology.

Methylation analyses on promoters of mPer1, mPer2, and mCry1 during perinatal development

Recent studies revealed dramatic changes in circadian clock genes’ expression during the perinatal period. In this study, we characterized DNA methylation for three clock genes mPer1, mPer2, and mCry1 at their selected promoter regions during development. Results for the suprachiasmatic nucleus (SCN) and liver (at embryonic day 19, postnatal day 1 and postnatal day 7) were compared to those of sperm. Few methylations were detected for the mPer2 and mCry1 promoters. The 3rd E-box region of the mPer1 promoter exhibited methylation only in sperm. Significant demethylation was observed in the 4th E-box region of the mPer1 promoter between E19 and P1 in the SCN but not in liver tissue. This demethylation state was maintained at P7 for the SCN. Luciferase reporter assays using in vitro methylated promoters revealed an inhibitory effect of promoter methylation on mPer1 expression. The results suggested that epigenetic mechanisms such as DNA methylation might contribute to the developmental expression of clock genes.

Elevated mPer1 gene expression in tumor stroma imaged through bioluminescence

The tumor stroma has significant effects on cancer cell growth and metastasis. Interactions between cancer and stromal cells shape tumor progression through poorly understood mechanisms. One factor regulating tumor growth is the circadian timing system that generates daily physiological rhythms throughout the body. Clock genes such as mPer1 serve in molecular timing events of circadian oscillators and when mutated can disrupt circadian rhythms and accelerate tumor growth. Stimulation of mPer1 by cytokines suggests that the timing of circadian oscillators may be altered by these tumor-derived signals. To explore tumor and stromal interactions, the pattern of mPer1 expression was imaged in tumors generated through subcutaneous injection of Lewis lung carcinoma (LLC) cells. Several imaging studies have used bioluminescent cancer cell lines expressing firefly luciferase to image tumor growth in live mice. In contrast, this study used non-bioluminescent cancer cells to produce tumors within transgenic mice expressing luciferase controlled by the mPer1 gene promoter. Bioluminescence originated only in host cells and was significantly elevated throughout the tumor stroma. It was detected through the skin of live mice or by imaging the tumor directly. No effects on the circadian timing system were detected during three weeks of tumor growth according to wheel-running rhythms. Similarly, no effects on mPer1 expression outside the tumor were found. These results suggest that mPer1 activity may play a localized role in the interactions between cancer and stromal cells. The effects might be exploited clinically by targeting the circadian clock genes of stromal cells.

Epigenetic analysis of mPer1 promoter in peripheral tissues

E-boxes targeted by BMAL1-CLOCK dimers are crucial for the rhythmic expression of mPer1. We investigated whether DNA methylation, especially E-box CpG methylation, plays a role in the regulation of mPer1 oscillations in mice. E-box-containing amplicons were examined in liver, thymus and testis around-the-clock using bisulfite sequencing, combined bisulfite restriction analysis (COBRA) and bisulfite pyrosequencing. Results indicated that mPer1 E-boxes were only hypomethylated in all tissues at all circadian stages, suggesting that E-boxes are open to BMAL1-CLOCK dimers at all times, and thus E-box methylation is most likely not involved in global regulation of the mPer1 rhythm. In addition, low but noticeable methylation of E-box 3 and/or 4 and a sub-group of CpGs nearby were identified in all three tissues, indicating this region as area of preferred methylation, and may have a role in silencing mPer1 transcription.

High expression of the circadian gene mPer2 diminishes the radiosensitivity of NIH 3T3 cells

Period2 is a core circadian gene, which not only maintains the circadian rhythm of cells but also regulates some organic functions. We investigated the effects of mPeriod2 (mPer2) expression on radiosensitivity in normal mouse cells exposed to 60Co-gamma-rays. NIH 3T3 cells were treated with 12-O-tetradecanoylphorbol-13-acetate (TPA) to induce endogenous mPer2 expression or transfected with pcDNA3.1(+)-mPer2 and irradiated with 60Co-gamma-rays, and then analyzed by several methods such as flow cytometry, colony formation assay, RT-PCR, and immunohistochemistry. Flow cytometry and colony formation assay revealed that irradiated NIH 3T3 cells expressing high levels of mPer2 showed a lower death rate (TPA: 24 h 4.3% vs 12 h 6.8% and control 9.4%; transfection: pcDNA3.1-mPer2 3.7% vs pcDNA3.1 11.3% and control 8.2%), more proliferation and clonogenic survival (TPA: 121.7 +/- 6.51 vs 66.0 +/- 3.51 and 67.7 +/- 7.37; transfection: 121.7 +/- 6.50 vs 65.3 +/- 3.51 and 69.0 +/- 4.58) both when treated with TPA and transfected with mPer2. RT-PCR analysis showed an increased expression of bax, bcl-2, p53, c-myc, mre11, and nbs1, and an increased proportionality of bcl-2/bax in the irradiated cells at peak mPer2 expression compared with cells at trough mPer2 expression and control cells. However, no significant difference in rad50 expression was observed among the three groups of cells. Immunohistochemistry also showed increased protein levels of P53, BAX and proliferating cell nuclear antigen in irradiated cells with peak mPer2 levels. Thus, high expression of the circadian gene mPer2 may reduce the radiosensitivity of NIH 3T3 cells. For this effect, mPer2 may directly or indirectly regulate the expressions of cell proliferation- and apoptosis-related genes and DNA repair-related genes.

Induction of mPer1 expression by GnRH in pituitary gonadotrope cells involves EGR-1

We reported earlier that gonadotropin-releasing hormone (GnRH) activates period1 ( mPer1) gene expression in immortalized gonadotropes through protein kinase C and p42/44 mitogen-activated protein kinase pathways. GnRH stimulation also leads to the upregulation of early growth response protein 1 (EGR-1), a critical transcription factor for GnRH-induced luteinizing hormone beta (LHβ) synthesis. The parallels between the GnRH–LHβ and the GnRH–mPer1 pathways led us to explore whether EGR-1 is involved in the regulation of mPer1 expression in gonadotropes. Of particular interest was the presence of an EGR-1 binding site in the proximal promoter of the mPer1 gene. Stimulation of LβT2 gonadotrope cells with a GnRH agonist caused the rapid induction of Egr-1 mRNA, which was rapidly followed by mPer1 expression. Chromatin immunoprecipitation revealed that the mPer1 promoter can bind EGR-1, while site-directed mutagenesis experiments confirmed the involvement of Egr-1 sequences in maintaining basal and allowing GnRH-stimulated mPer1 transcription. By means of RNA interference experiments, it could also be demonstrated that silencing of Egr-1 expression resulted in markedly lower mPer1 transcript levels. This silencing effect of the Egr-1 siRNA could be rescued by transfecting the cells with an EGR-1 overexpression vector. In summary, these results all point to a role for the EGR-1 protein in transactivating both the LHβ as well as the mPer1 gene in pituitary gonadotrope cells.

The mammalian molecular clockwork controls rhythmic expression of its own input pathway components.

The core molecular clockwork in the suprachiasmatic nucleus (SCN) is based on autoregulatory feedback loops of transcriptional activators (CLOCK/NPAS2 and BMAL1) and inhibitors (mPER1-2 and mCRY1-2). To synchronize the phase of the molecular clockwork to the environmental day and night condition, light at dusk and dawn increases mPer expression. However, the signal transduction pathways differ remarkably between the day/night and the night/day transition. Light during early night leads to intracellular Ca(2+) release by neuronal ryanodine receptors (RyRs), resulting in phase delays. Light during late night triggers an increase in guanylyl cyclase activity, resulting in phase advances. To date, it is still unknown how the core molecular clockwork regulates the availability of the respective input pathway components. Therefore, we examined light resetting mechanisms in mice with an impaired molecular clockwork (BMAL1(-/-)) and the corresponding wild type (BMAL1(+/+)) using in situ hybridization, real-time PCR, immunohistochemistry, and a luciferase reporter system. In addition, intracellular calcium concentrations (Ca(2+)(i)) were measured in SCN slices using two-photon microscopy. In the SCN of BMAL1(-/-) mice Ryr mRNA and RyR protein levels were reduced, and light-induced mPer expression was selectively impaired during early night. Transcription assays with NIH3T3 fibroblasts showed that Ryr expression was activated by CLOCK::BMAL1 and inhibited by mCRY1. The Ca(2+)(i) response of SCN cells to the RyR agonist caffeine was reduced in BMAL1(-/-) compared with BMAL1(+/+) mice. Our findings provide the first evidence that the mammalian molecular clockwork influences Ryr expression and thus controls its own photic input pathway components.

The dorsomedial hypothalamic nucleus is not necessary for food‐anticipatory circadian rhythms of behavior, temperature or clock gene expression in mice

Circadian rhythms in mammals are regulated by a light-entrainable circadian pacemaker in the hypothalamic suprachiasmatic nucleus and food-entrainable oscillators located elsewhere in the brain and body. The dorsomedial hypothalamic nucleus (DMH) has been proposed to be the site of oscillators driving food-anticipatory circadian rhythms, but this is controversial. To further evaluate this hypothesis, we measured clock gene, temperature and activity rhythms in intact and DMH-ablated mice. A single 4-h midday feeding after an overnight fast induced mPer1 and mPer2 mRNA expression in the DMH, arcuate nucleus, nucleus of the solitary tract and area postrema, and reset daily rhythms of mPer1, mPer2 and mBMAL1 in the DMH, arcuate and neocortex. These rhythms persisted during 2 days of food deprivation after 12 days of scheduled daytime feeding. Acute induction of DMH mPer1 and mPer2 was N-methyl-D-aspartate (NMDA) receptor-dependent, whereas rhythmic expression after 6 days of restricted feeding was not. Thermal DMH lesions did not affect acute induction or rhythmic expression of clock genes in other brain regions in response to scheduled daytime feeding. DMH lesions attenuated mean daily activity levels and nocturnality but did not affect food-anticipatory rhythms of activity and body temperature in either light-dark or constant darkness. These results confirm that the DMH and other brain regions express circadian clock gene rhythms sensitive to daytime feeding schedules, but do not support the hypothesis that DMH oscillations drive food-anticipatory behavioral or temperature rhythms.

Period 2 regulates neural stem/progenitor cell proliferation in the adult hippocampus

BackgroundNewborn granule neurons are generated from proliferating neural stem/progenitor cells and integrated into mature synaptic networks in the adult dentate gyrus of the hippocampus. Since light/dark variations of the mitotic index and DNA synthesis occur in many tissues, we wanted to unravel the role of the clock-controlled Period2 gene (mPer2) in timing cell cycle kinetics and neurogenesis in the adult DG.ResultsIn contrast to the suprachiasmatic nucleus, we observed a non-rhythmic constitutive expression of mPER2 in the dentate gyrus. We provide evidence that mPER2 is expressed in proliferating neural stem/progenitor cells (NPCs) and persists in early post-mitotic and mature newborn neurons from the adult DG. In vitro and in vivo analysis of a mouse line mutant in the mPer2 gene (Per2Brdm1), revealed a higher density of dividing NPCs together with an increased number of immature newborn neurons populating the DG. However, we showed that the lack of mPer2 does not change the total amount of mature adult-generated hippocampal neurons, because of a compensatory increase in neuronal cell death.ConclusionTaken together, these data demonstrated a functional link between the constitutive expression of mPER2 and the intrinsic control of neural stem/progenitor cells proliferation, cell death and neurogenesis in the dentate gyrus of adult mice.

Effect of intermittent fasting on circadian rhythms in mice depends on feeding time

Calorie restriction (CR) resets circadian rhythms and extends life span. Intermittent fasting (IF) also extends life span, but its affect on circadian rhythms has not been studied. To study the effect of IF alongside CR, we imposed IF in FVB/N mice or IF combined with CR using the transgenic FVB/N alphaMUPA mice that, when fed ad libitum, exhibit spontaneously reduced eating and extended life span. Our results show that when food was introduced during the light period, body temperature peak was not disrupted. In contrast, IF caused almost arrhythmicity in clock gene expression in the liver and advanced mPer2 and mClock expression. However, IF restored the amplitudes of clock gene expression under disruptive light condition regardless whether the animals were calorically restricted or not. Unlike daytime feeding, nighttime feeding yielded rhythms similar to those generated during ad libitum feeding. Taken together, our results show that IF can affect circadian rhythms differently depending on the timing of food availability, and suggest that this regimen induces a metabolic state that affects the suprachiasmatic nuclei (SCN) clock.