The role of circadian rhythmicity in reproduction

Circadian Disruption Impacts Fetal Development in Mice Using High-Frequency Ultrasound

The developmental origins of health and disease theory suggests that environmental exposures during early life, particularly during prenatal life, can greatly influence health status later in life. Irregular light-dark cycles, such as those experienced during shift work, result in the repeated disruption of circadian rhythms, which negatively impacts physiological and behavioral cycles. The purpose of our study was to assess parameters in the developing mouse embryo and fetus using high frequency ultrasound when exposed to circadian disruption. Pregnant female mice were subjected to a seven-hour advanced circadian disrupted protocol or remained on a normal 12/12 light-dark cycle throughout pregnancy. Significant differences were observed in placental length (p = 0.00016), placental thickness (p = 0.0332), and stomach diameter (p = 0.0186) at E14.5-18.5. These findings suggest that circadian disruption in pregnant dams, mimicking shift work, alters embryonic and fetal development in specific organs in utero.

Chronobiotics: classifications of existing circadian clock modulators, future perspectives

The review summarizes recent achievements and future prospects in the use of chronobiotics for regulating circadian rhythms regulation. Special attention is paid to the mechanisms' action, their classification, and the impact of chemical interventions on the biological clock. Chronobiotics defined as a diverse group of compounds capable of restoring disrupted circadian functions, addressing challenges such as irregular work schedules, artificial light exposure or ageing. The review categorizes these compounds by their pharmacological effects, molecular targets, and chemical structures, underlining their ability to enhance or inhibit key circadian components like CLOCK, BMAL1, PER, and CRY. A particular focus is placed on the therapeutic applications of chronobiotics, including their potential for treating sleep disorders, metabolic issues, and age-related rhythm disturbances, underscoring their wide-ranging applicability in health care. Chronobiotic compounds have promising roles in maintaining physiological rhythms, supporting healthy aging, and enhancing personalised health care. Given their diverse therapeutic potential, chronobiotics are positioned as a significant avenue for further clinical application, marking them as a crucial area of ongoing research and innovation.

Hypertension disrupts the vascular clock in both sexes

Blood pressure (BP) displays a circadian rhythm and disruptions in this pattern elevate cardiovascular risk. Although both central and peripheral clock genes are implicated in these processes, the importance of vascular clock genes is not fully understood. BP, vascular reactivity, and the renin-angiotensin-aldosterone system display overt sex differences, but whether changes in circadian patterns underlie these differences is unknown. Therefore, we hypothesized that circadian rhythms and vascular clock genes would differ across sex and would be blunted by angiotensin II (ANG II)-induced hypertension. ANG II infusion elevated BP and disrupted circadian patterns similarly in both males and females. In females, an impact on heart rate (HR) and locomotor activity was revealed, whereas in males hypertension suppressed baroreflex sensitivity (BRS). A marked disruption in the vascular expression patterns of period circadian regulator 1 (Per1) and brain and muscle aryl hydrocarbon receptor nuclear translocator like protein 1 (Bmal1) was noted in both sexes. Vascular expression of the G protein-coupled estrogen receptor (Gper1) also showed diurnal synchronization in both sexes that was similar to that of Per1 and Per2 and disrupted by hypertension. In contrast, vascular expression of estrogen receptor 1 (Esr1) showed a diurnal rhythm and hypertension-induced disruption only in females. This study shows a strikingly similar impact of hypertension on BP rhythmicity, vascular clock genes, and vascular estrogen receptor expression in both sexes. We identified a greater impact of hypertension on locomotor activity and heart rate in females and on baroreflex sensitivity in males and also revealed a diurnal regulation of vascular estrogen receptors. These insights highlight the intricate ties between circadian biology, sex differences, and cardiovascular regulation.NEW & NOTEWORTHY This study reveals that ANG II-induced hypertension disrupts the circadian rhythm of blood pressure in both male and female mice, with parallel effects on vascular clock gene and estrogen receptor diurnal patterns. Notably, sex-specific responses to hypertension in terms of locomotor activity, heart rate, and baroreflex sensitivity are revealed. These findings pave the way for chronotherapeutic strategies tailored to mitigate cardiovascular risks associated with disrupted circadian rhythms in hypertension.

Circadian temperature rhythm in breeding sows: differences between days in oestrus and anoestrus after weaning

BACKGROUND

Mammals are subject to circadian rhythms for the control of various physiological events. One of the parameters known to be subject to variations throughout the day is body temperature, which is also subject to influences such as environmental temperature. However, there are not many studies on these rhythms in breeding sows. The aim of this study was to determine the circadian parameters for body temperature in post-weaning sows during oestrus period, throughout the seasons in a warm climate.

RESULTS

Differences were observed in inter-daily stability, intra-daily fragmentation and cycle length comparing the summer sows with the other seasons. Differences were also observed in the period that the sows were in oestrus compared to the non-oestrus period for intra-daily fragmentation, with these differences being more important in the warm seasons compared to the cold seasons. The parameters normalised by COSINOR also showed significant differences when comparing seasons, especially in the acrophase of the temperature maximum. Another significant finding was an increase in vaginal temperature during oestrus in sows monitored in summer compared to the other seasons. Correlations between body, vaginal and environmental temperature were observed.

CONCLUSION

There is a seasonal influence on the circadian rhythm of temperature and summer is clearly the season with the greatest differences in circadian parameters when compared to the other seasons. The extreme summer conditions seem to definitely influence this rhythm and make the body and vaginal temperature of the sows different from the rest of the year. The increase in period robustness in both body and vaginal temperature during the days when sows are in oestrus could be related to the hormonal events of oestrus and ovulation and seems to be independent of weather since it occurs in all controlled seasons. However, this robustness is significantly higher in summer than in the other seasons both in the oestrus period and on days when sows are not in oestrus.

Importance of preovulatory estradiol on uterine receptivity and luteal function

Animals that exhibited estrus had greater pregnancy success compared to animals that did not exhibit estrus before fixed-time AI (FTAI). Estradiol is synthesized in bovine ovarian follicles under gonadotropin regulation and can directly and indirectly regulate the uterine receptivity and luteal function. Estradiol concentrations at FTAI impacted oviductal gene expression and has been reported to play an important role in establishing the timing of uterine receptivity. These changes have been reported to impact uterine pH and sperm transport to the site of fertilization. After fertilization, preovulatory estradiol has been reported to improve embryo survival likely by mediating changes in uterine blood flow, endometrial thickness and changes in histotroph. Cows with greater estradiol concentrations at the time of GnRH-induced ovulation also had a larger dominant follicle size and greater circulating progesterone concentrations on day 7. Therefore, it is impossible to accurately determine the individual benefit of greater estradiol concentrations prior to ovulation and greater progesterone concentrations following ovulation to pregnancy establishment, as these two measurements are confounded. Research has indicated an importance in the occurrence and timing of increasing preovulatory concentrations of estradiol, but increasing estradiol concentrations by supplementation may not be sufficient to increase fertility. Increased production of estradiol by the preovulatory follicle may be required to enhance fertility through the regulation of sperm transport, fertilization, oviductal secretions, the uterine environment, and embryo survival.

Circadian desynchrony disturbs the function of rat spermatozoa

Decreased male fertility is a growing health problem that requires a better understanding of molecular events regulating reproductive competence. Here the effects of circadian desynchrony on the rat spermatozoa functionality were studied. Circadian desynchrony was induced in rats that lived for 2 months under disturbed light conditions designed to mimic shiftwork in humans (two days of constant light, two days of continual dark, and three days of 14:10 h light:dark schedule). Such a condition abolished circadian oscillations in the rats' voluntary activity, followed by a flattened transcriptional pattern of the pituitary gene encoding follicle stimulating hormone subunit (Fshb), and genes important for germ cell maturation (Tnp1 and Prm2) as well as the clock in seminiferous tubules. However, the number of spermatozoa isolated from the epididymis of the rats suffering from circadian desynchrony did not deviate from the controls. Nevertheless, spermatozoa functionality, estimated by motility and progesterone-induced acrosome reaction, was reduced compared to the control. These changes were associated with the altered level of main markers of mitochondrial biogenesis (Pprgc1a/PGC1A, Nrf1/NRF1, Tfam, Cytc), decreased mitochondrial DNA copy number, ATP content, and clock genes (Bmal1/BMAL1, Clock, Cry1/2, and Reverba). The principal-component-analysis (PCA) points to a positive association of the clock and mitochondrial biogenesis-related genes in spermatozoa from rats suffering circadian desynchrony. Altogether, the results show the harmful effect of circadian desynchrony on spermatozoa functionality, targeting energetic homeostasis.

Circadian regulation of mTORC1 signaling via Per2 dependent mechanism disrupts folliculogenesis and oocyte maturation in female mice

mTOR (mammalian target of Rapamycin) is an important signaling pathway involved in several crucial ovarian functions including folliculogenesis and oocyte maturation. The circadian rhythm regulates multiple physiological processes and PER2 is one of the core circadian rhythm components. mTOR is regulated by the circadian clock and in turn, the rhythmic mTOR activities strengthen the clock function. Our current study aims to investigate a possible interconnection between the circadian clock and the mTORC1 signaling pathway in folliculogenesis and oocyte maturation. Here we demonstrate that the circadian system regulates mTORC1 signaling via Per2 dependent mechanism in the mouse ovary. To investigate the effect of constant light on ovarian and oocyte morphology, animals were housed 12:12 h L:D group in standard lightening conditions and the 12:12 h L:L group in constant light for one week. Food intake and body weight changes were measured. Ovarian morphology, follicle counting, and oocyte aging were evaluated. Afterward, western blot for mTOR, p-mTOR, p70S6K, p-p70S6K, PER2, and Caspase-3 protein levels was performed. The study demonstrated that circadian rhythm disruption caused an alteration in their food intake and decrease in primordial follicle numbers and an increase in the number of atretic follicles. It caused an increase in oxidative stress and a decrease in ZP3 expression in oocytes. Decreased protein levels of mTOR, p-mTOR, p70S6K, and PER2 were shown. The results showed that the circadian clock regulates mTORC1 through PER2 dependent mechanism and that decreased mTORC1 activity can contribute to premature aging of mouse ovary. In conclusion, these results suggest that the circadian clock may control ovarian aging by regulating mTOR signaling pathway through Per2 expression.

Circle(s) of Life: The Circadian Clock from Birth to Death

Most lifeforms on earth use endogenous, so-called circadian clocks to adapt to 24-h cycles in environmental demands driven by the planet’s rotation around its axis. Interactions with the environment change over the course of a lifetime, and so does regulation of the circadian clock system. In this review, we summarize how circadian clocks develop in humans and experimental rodents during embryonic development, how they mature after birth and what changes occur during puberty, adolescence and with increasing age. Special emphasis is laid on the circadian regulation of reproductive systems as major organizers of life segments and life span. We discuss differences in sexes and outline potential areas for future research. Finally, potential options for medical applications of lifespan chronobiology are discussed.

Effects of time-restricted feeding on letrozole-induced mouse model of polycystic ovary syndrome

The present study aimed to investigate whether time-restricted feeding (TRF) ameliorates metabolic and reproductive phenotypes in a letrozole-induced mouse model of polycystic ovary syndrome (PCOS). Sixty female C57BL/6 N mice were randomly divided into two groups according to the type of food received: either a chow or a 60% high-fat diet. Those mice were subcutaneously implanted with letrozole or placebo pellets at four weeks of age. Then, letrozole-treated mice were randomly assigned to different feeding regimens: (1) TRF for 4 h (ZT12-ZT16) or (2) ad libitum diet. After 4 weeks of dietary intervention, estrous cycles were determined with daily vaginal smear examination, and serial tail-tip blood sampling was performed at 5-min intervals for 2 h to measure the luteinizing hormone (LH) pulse frequency, amplitude, and mean LH levels in the diestrus cycle stage. Letrozole-treated mice in the ad libitum group demonstrated multiple PCOS-like phenotypes including ovulatory dysfunction, polycystic ovaries, and increased body weight, parametrial fat weight, adipocyte size and inflammation, and higher expression of Cyp17, Cyp19, and Fshr in the ovary, and Kiss1r and Gnrh in the hypothalamus, elevated serum testosterone levels, and more rapid and elevated LH pulsatility, with increased pulse frequency, amplitude, and mean levels in the diestrus stage, compared with the controls. After TRF for 4 weeks, those phenotypes reverted to normal levels in letrozole-treated mice, except the percentage of diestrus cycles indicating the arrest of estrous cycling which did not differ between the TRF and ad libitum groups. Our results demonstrate that TRF has therapeutic effects on the reproductive and metabolic phenotypes of a letrozole-induced mouse model of PCOS.

Suprachiasmatic nucleus and vagus nerve trigger preovulatory LH and ovulation

In brief

In the proestrus day, the neural and endocrine signals modulate ovarian function. This study shows vagus nerve plays a role in the multisynaptic pathways of communication between the suprachiasmatic nucleus and the ovaries where such neural information determines ovulation.

Abstract

The suprachiasmatic nucleus (SCN) regulates the activity of several peripheral organs through a parasympathetic-sympathetic pathway. Previously, we demonstrated that atropine (ATR) microinjection in the right SCN of rats during proestrus blocks ovulation. In the present study, we analysed whether the vagus nerve is one of the neural pathways by which the SCN regulates ovulation. For this, CIIZ-V strain cyclic rats on the day of proestrus were microinjected with a saline solution (vehicle) or ATR in the right or left SCN, which was followed by ventral laparotomy or ipsilateral vagotomy to the microinjection side. Some animal groups were sacrificed (i) on the same day of the surgery to measure oestradiol, progesterone and luteinizing hormone (LH) levels or (ii) at 24 h after surgery to evaluate ovulation. The left vagotomy in rats microinjected with ATR in the left SCN did not modify ovulation. In rats with ATR microinjection in the right SCN, the right vagotomy increased the levels of steroids and LH on the proestrus and ovulatory response. The present results suggest that the right vagus nerve plays a role in the multisynaptic pathways of communication between the SCN and the ovaries and indicate that such neural information participates in the regulation of the oestradiol and progesterone surge, which triggers the preovulatory peak of LH and determines ovulation.

The role of upper and lower genital tract microbiota alterations in term chorionamnionitis: A prospective study

Objective

This study aimed to compare the dynamics of lower and upper genital tract microbiota in normal term pregnancy, histological chorioamnionitis (HCA), and clinical chorioamnionitis (CCA) patients to provide a reference for the diagnosis and treatment of chorioamnionitis (CAM) patients.

Methods

We prospectively collected vaginal and cervical secretions, as well as placenta tissues, fetal membranes, and amniotic fluid from normal-term pregnant women, HCA and CCA patients. Then, we performed genomic DNA extraction and PCR amplification for all samples. The eligible samples were analyzed by 16S ribosomal RNA (16S rRNA) sequencing. Additionally, all placenta tissues were histopathologically examined, and neonatal pharyngeal swabs and placenta tissues from the HCA and CCA groups were subjected to microbial culture.

Results

A total of 85 term pregnant women were enrolled in this study, including 34 in the normal group (N), 37 in the HCA group, and 14 in the CCA group. A total of 171 qualified samples were analyzed by 16S rRNA sequencing. The results suggested that the cervical microbiota was highly similar to the vaginal microbiota in normal term parturients, with Lactobacillus as the dominant bacterium. Moreover, there was no difference in the alpha and beta diversity of vaginal microbiota between the N, HCA, and CCA groups at the genus level. Besides, no significant differences were detected in cervical microbiome among the three groups. Regarding intrauterine microorganisms, the N and HCA groups had similar microbial composition but were different from the CCA group. No microbe was detected in the placental tissue of normal term parturients, while some microorganisms were found in the intrauterine amniotic fluid and fetal membrane samples. Regardless of cultivation or 16S rRNA sequencing, an extremely low microbial positive rate was detected in HCA and CCA intrauterine samples. Compared to the normal group, Lactobacillus was significantly reduced in the CCA group intrauterine, and Ureaplasma and Enterococcus increased with no statistically significant.

Conclusion

The N, HCA and CCA groups had similar composition of vaginal and cervical microflora. Some normal-term pregnant women can harbor non-pathogenic microbiota in the uterine cavity. Sterile inflammation is more frequent than microbial-associated inflammation in term HCA and CCA parturients.

Timed restricted feeding cycles drive daily rhythms in female rats maintained in constant light but only partially restore the estrous cycle

Light at night is an emergent problem for modern society. Rodents exposed to light at night develop a loss of circadian rhythms, which leads to increased adiposity, altered immune response, and increased growth of tumors. In female rats, constant light (LL) eliminates the estrous cycle leading to a state of persistent estrus. The suprachiasmatic nucleus (SCN) drives circadian rhythms, and it interacts with the neuroendocrine network necessary for reproductive function. Timed restricted feeding (RF) exerts a powerful entraining influence on the circadian system, and it can influence the SCN activity and can restore rhythmicity or accelerate re-entrainment in experimental conditions of shift work or jet lag. The present study explored RF in female rats exposed to LL, with the hypothesis that this cyclic condition can rescue or prevent the loss of daily rhythms and benefit the expression of the estrous cycle. Two different feeding schedules were explored: 1. A 12-h food/12-h fasting schedule applied to arrhythmic rats after 3 weeks in LL, visualized as a rescue strategy (LL + RFR, 3 weeks), or applied simultaneously with the first day of LL as a preventive strategy (LL + RFP, 6 weeks). 2. A 12-h window of food intake with food given in four distributed pulses (every 3 h), applied after 3 weeks in LL, as a rescue strategy (LL + PR, 3 weeks) or applied simultaneously with the first day of LL as a preventive strategy (LL + PP, 6 weeks). Here, we present evidence that scheduled feeding can drive daily rhythms of activity and temperature in rats exposed to LL. However, the protocol of distributed feeding pulses was more efficient to restore the day–night activity and core temperature as well as the c-Fos day–night change in the SCN. Likewise, the distributed feeding partially restored the estrous cycle and the ovary morphology under LL condition. Data here provided indicate that the 12-h feeding/12-h fasting window determines the rest-activity cycle and can benefit directly the circadian and reproductive function. Moreover, this effect is stronger when food is distributed along the 12 h of subjective night.

Neuronal Bmal1 regulates retinal angiogenesis and neovascularization in mice

Circadian clocks in the mammalian retina regulate a diverse range of retinal functions that allow the retina to adapt to the light-dark cycle. Emerging evidence suggests a link between the circadian clock and retinopathies though the causality has not been established. Here we report that clock genes are expressed in the mouse embryonic retina, and the embryonic retina requires light cues to maintain robust circadian expression of the core clock gene, Bmal1. Deletion of Bmal1 and Per2 from the retinal neurons results in retinal angiogenic defects similar to when animals are maintained under constant light conditions. Using two different models to assess pathological neovascularization, we show that neuronal Bmal1 deletion reduces neovascularization with reduced vascular leakage, suggesting that a dysregulated circadian clock primarily drives neovascularization. Chromatin immunoprecipitation sequencing analysis suggests that semaphorin signaling is the dominant pathway regulated by Bmal1. Our data indicate that therapeutic silencing of the retinal clock could be a common approach for the treatment of certain retinopathies like diabetic retinopathy and retinopathy of prematurity.

Constitutional delay of growth and puberty in female mice is induced by circadian rhythm disruption in utero

Constitutional delay of growth and puberty (CDGP) refers to the late onset of puberty. CDGP is associated with poor psychosocial outcomes and elevated risk of cardiovascular and osteoporotic diseases, especially in women. The environmental factors that contribute to CDGP are poorly understood. Here, we investigated the effects of chronic circadian disturbance (CCD) during the fetal stage on the pubertal development of female mice. Compared to non-stressed female (NS-F) mice that were not exposed to CCD in utero, adolescent CCD female (CCD-F) mice exhibited phenotypes that were consistent with CDGP, including lower body weight, reduced levels of circulating gonadal hormones, decreased expression of gonadal hormones and steroid synthesis-related enzymes in the ovary and hypothalamus, irregular estrus cycles, and tardive vaginal introitus initial opening (VO) days (equivalent to the menarche). Phenotypic differences in the above-noted parameters were not observed in CCD-F mice once they had reached adulthood. The expression of genes involved in fatty acid metabolism was perturbed in the ovary and hypothalamus of CCD-F mice. In addition, the ovaries of these animals exhibited altered diurnal expression profiles of circadian clock genes. Together, our findings not only suggest that CCD during fetal development may result in delayed puberty in female mice, they also offer insights on potential mechanisms that underlie CDGP.

Stress alters the transcriptional activity of Leydig cells dependently on the diurnal time

The increasing amount of data points to the circadian timing system as an essential part of processes regulating androgen homeostasis. However, the relationship between stress response, timekeeping-, and steroidogenesis-related systems is unexplored. Here, the stress-response of the testosterone-producing rat Leydig cells depending on the time of stressful events was studied. The study analyzes the effects of 3-hour immobilization (IMO) applied at different periods during the day. The IMO performed once (1xIMO) or repeated in 10 consecutive days (10xIMO). Both types of IMO increased corticosterone and decreased testosterone blood level. However, the effect of 10xIMO occurring in the active phase on blood testosterone was less pronounced. This is related to different sensitivity to IMO-events depending on the diurnal time. Most steroidogenesis-related genes (Lhcgr, Cyp11a1, Hsd3b1/2, Cyp17a1) were down-regulated in the inactive but unchanged or even up-regulated in the active phase of the day. Both types of IMO stimulated the expression of clock elements Bmal1/BMAL1, Per1/PER1 regardless of the day's stage and reduced Rev-erba in the inactive phase. The principal-component-analysis (PCA) confirmed a major shift, for both IMO-types, in the transcription of the genes across the passive/active stage. Further, 10xIMO changed a diurnal pattern of the glucocorticoid receptor (Nr3c1/GR) expression while the observed time-dependent IMO-response of the Leydig cells correlated with different corticosterone engagements. Altogether, the Leydig cell's stress-response depends on the daytime of the stressful event, emphasizing the importance of the circadian-system in supporting androgen homeostasis and male fertility.

Impact of sleep patterns upon female neuroendocrinology and reproductive outcomes: a comprehensive review

Sleep is vital to human bodily function. Growing evidence indicates that sleep deprivation, disruption, dysrhythmia, and disorders are associated with impaired reproductive function and poor clinical outcomes in women. These associations are largely mediated by molecular-genetic and hormonal pathways, which are crucial for the complex and time sensitive processes of hormone synthesis/secretion, folliculogenesis, ovulation, fertilization, implantation, and menstruation. Pathologic sleep patterns are closely linked to menstrual irregularity, polycystic ovarian syndrome, premature ovarian insufficiency, sub/infertility, and early pregnancy loss. Measures of success with assisted reproductive technology are also lower among women who engage in shift work, or experience sleep disruption or short sleep duration. Extremes of sleep duration, poor sleep quality, sleep disordered breathing, and shift work are also associated with several harmful conditions in pregnancy, including gestational diabetes and hypertensive disorders. While accumulating evidence implicates pathologic sleep patterns in impaired reproductive function and poor reproductive outcomes, additional research is needed to determine causality and propose therapeutic interventions.

Critical Roles of the Circadian Transcription Factor BMAL1 in Reproductive Endocrinology and Fertility

Brain and muscle aryl-hydrocarbon receptor nuclear translocator like protein1 (BMAL1), a core component of circadian oscillation, is involved in many physiological activities. Increasing evidence has demonstrated the essential role of BMAL1 in reproductive physiology. For instance, BMAL1-knockout (KO) mice were infertile, with impaired reproductive organs and gametes. Additionally, in BMAL1-KO mice, hormone secretion and signaling of hypothalamus-pituitary-gonadal (H-P-G) hormones were also disrupted, indicating that H-P-G axis was impaired in BMAL1-KO mice. Moreover, both BMAL1-KO mice and BMAL1-knockdown by small interfering RNA (siRNA) in vitro cultured steroidogenic cells showed that BMAL1 was associated with gonadal steroidogenesis and expression of related genes. Importantly, BMAL1 also participates in pathogenesis of human reproductive diseases. In this review, we elaborate on the impaired reproduction of BMAL1-KO mice including the reproductive organs, reproductive endocrine hormones, and reproductive processes, highlighting the vital role of BMAL1 in fertility and reproductive endocrinology.

Novel InDel variations of the Cry2 gene are associated with litter size in Australian White sheep

Cryptochrome 2 (Cry2) gene regulates circadian rhythm and affects reproduction and pregnancy. Therefore, this study aimed to explore polymorphisms of the Cry2 gene and their associations with litter size at different parity in Australian White (AuW) ewes. Five putative insertion or deletion mutations within the Cry2 gene were selected to study their association with litter size. Two novel deletion mutations were identified in intronic region of Cry2 gene and were genotyped by agarose gel electrophoresis and DNA sequencing. The polymorphism information content (PIC) indicated that both mutations were low polymorphism in tested groups. Statistical analysis revealed that the P1-Del-6-bp was significantly correlated with litter size at third parity (P = 0.010), in which individuals with insertion/deletion (ID) genotype had larger litter size than insertion/insertion (II) genotype (P < 0.05). Whereas, the P2-Del-6-bp was significantly correlated with litter size at first parity (P = 0.036), in which individuals with insertion/insertion (II) genotype had larger litter size than insertion/deletion (ID) genotype (P < 0.05). Collectively, these findings may provide new insights to expedite molecular breeding in sheep through marker-assisted selection strategies (MAS).

Melatonin regulates proliferation and apoptosis of endometrial stromal cells via MT1

Endometrial dysfunction is an important factor for implantation failure. The function of the endometrium is regulated by multiple factors like sex hormones and circadian rhythms. Endometrial stromal cells (ESCs) are a major cellular component in the endometrium, which is essential for proper physiological activities of the endometrium and the establishment of pregnancy. Melatonin, as a circadian-controlled hormone, plays beneficial roles in the regulation of reproductive processes. MT1, a melatonin receptor, can regulate cell proliferation and apoptosis. Whether melatonin-MT1 signal affects biological function of ESCs remains unknown. Here, we showed that MT1 was expressed in human ESCs (hESCs), which could be regulated by estrogen and progesterone. MT1 knockdown inhibited proliferative activity and promoted apoptosis of hESCs by activating caspase-3 and upregulating the Bax/Bcl2 ratio. Melatonin could reverse the effect of MT1 knockdown on proliferative activity and apoptosis of hESCs. Melatonin could promote proliferative activity of hESCs via the JNK/P38 signal pathway and repress the apoptosis of hESCs via the JNK signal pathway. Moreover, in vivo experiments showed that MT1 expression was decreased in endometrial cells from mice with disrupted circadian rhythm, accompanied by increased apoptosis and suppressed proliferative activity, which could be alleviated by administration of melatonin. These results showed the regulatory effect of melatonin-MT1 signal on biological behaviors of ESCs, which might provide a novel therapeutic strategy for endometrial dysfunction induced by disrupted circadian rhythm.

Circadian misalignment measured by social jetlag from early to late pregnancy and its association with nutritional status: a longitudinal study

A mismatch between circadian and social clocks leads to a circadian misalignment, which has been widely measured by social jetlag (SJL). There are several studies measuring SJL, but it has not been studied in pregnant women. Therefore, this study aimed to identify the occurrence of SJL throughout pregnancy and to verify whether there is an effect of pre-pregnancy body mass index (BMI) on SJL throughout pregnancy. The baseline of the present study was conducted with 205 1st trimester pregnant women of whom 100 were followed in their 2nd and 3rd trimester. SJL was calculated based on the absolute difference between mid-sleep time on workdays versus work-free days. The pre-pregnancy BMI and current BMI (kg/m²) were calculated. Linear regression and Generalised Estimating Equation (GEE) adjusted for confounders were used to determine the association between SJL and the gestational trimesters (time), and anthropometric variables. Most of the pregnant women (54.5%) presented SJL > 1 h in the first gestational trimester. We also found an isolated effect of the gestation trimester on the SJL mean. In this sense, pregnant women had a decrease in SJL from the second to the third trimester (1.33 ± 0.08 versus 1.12 ± 0.07, respectively; p = 0.012). GEE analyzes showed that pregnant women of a normal weight showed a decrease in SJL from the second to the third trimester (1.29 ± 0.11 and 0.93 ± 0.08, respectively, p = 0.032), but this was not found in the other groups of nutritional status (underweight, overweight and obesity). In addition, a positive association between SJL and pre-gestational BMI in the third trimester (β = 0.200, p = 0.046) was found. SJL is quite prevalent during the gestational period and excessive BMI both before and during pregnancy is associated with an increased risk of having SJL > 1 h in the third and second trimesters, respectively. In addition, pregnant women of normal weight—but not underweight or overweight—had decreased SJL from the second to the third trimester.

Clock-controlled arylalkylamine N-acetyltransferase (aaNAT) regulates circadian rhythms of locomotor activity in the American cockroach, Periplaneta americana, via melatonin/MT2-like receptor

Melatonin (MEL) orchestrates daily and seasonal rhythms (eg, locomotion, sleep/wake cycles, and migration among other rhythms) in diverse organisms. We investigated the effects of pharmacological doses (0.03-1 mM) of exogenous MEL intake in the cockroach, Periplaneta americana, on locomotor activity. As per os MEL concentration increased, cockroach locomotor rhythm in light-dark (LD) cycles became more synchronized. The ratio of night activity to 24-h activity increased and the acrophase (peak) slightly advanced. MEL application also influenced total activity bouts in the free-running rhythm. Since MEL slightly influenced τ in the free-running rhythms, it is not a central element of the circadian pacemaker but must influence mutual coupling of multi-oscillatory system components. Arylalkylamine N-acetyltransferase (aaNAT) regulates enzymatic production of MEL. aaNAT activities vary in circadian rhythms, and the immunoreactive aaNAT (aaNAT-ir) is colocalized with the key clock proteins cycle (CYC)-ir and pigment-dispersing factor (PDF)-ir These are elements of the central pacemaker and its output pathway as well as other circadian landmarks such as the anterior and posterior optic commissures (AOC and POC, respectively). It also partially shares immunohistochemical reactivity with PER-ir and DBT-ir neurons. We analyzed the role of Pamericana aaNAT1 (PaaaNAT1) (AB106562.1) by injecting dsRNA^aaNAT1 . qPCR showed a decrease in accumulations of mRNAs encoding PaaaNAT1. The injections led to arrhythmicity in LD cycles and the arrhythmicity persisted in constant dark (DD). Continuous administration of MEL resynchronized the rhythm after arrhythmicity was induced by dsRNA^aaNAT1 injection, suggesting that PaaaNAT is the key regulator of the circadian system in the cockroach via MEL production. PaaaNAT1 contains putative E-box regions which may explain its tight circadian control. The receptor that mediates MEL function is most likely similar to the mammalian MT2, because injecting the competitive MT2 antagonist luzindole blocked MEL function, and MEL injection after luzindole treatment restored MT function. Human MT2-ir was localized in the circadian neurons in the cockroach brain and subesophageal ganglion. We infer that MEL and its synthesizing enzyme, aaNAT, constitute at least one circadian output pathway of locomotor activity either as a distinct route or in association with PDF system.

Effects of artificial light at night (ALAN) on gene expression of Aquatica ficta firefly larvae

Artificial light at night (ALAN) is a major driver of firefly population declines, but its physiological effects are not well understood. To investigate the impact of ALAN on firefly development, we exposed larval Aquatica ficta fireflies to ALAN for two weeks. High larval mortality was observed in the periods of 1-68 days and 106-134 days post-treatment, which may represent the short- and long-term impacts of ALAN. We then profiled the transcriptome of larval Aquatica ficta fireflies following two weeks of ALAN exposure. A total of 1262 (1.67% out of 75777 unigenes) were differentially expressed in the treatment group: 1157 were down-regulated, and 105 were up-regulated. Up-regulated unigenes were related to regulation of hormone levels, ecdysteroid metabolic process, and response to stimulus; down-regulated unigenes were related to negative regulation of insulin receptor signaling, germ cell development, oogenesis, spermatid development, and regulation of neuron differentiation. Transcriptome results suggest that the endocrine, reproductive, and neural development of firefly larvae could be impaired by even relatively brief period of ALAN exposure. This report contributes a much-needed molecular perspective to the growing body of research documenting the fitness impacts of ALAN on bioluminescent fireflies.

A Crosstalk between the Biorhythms and Gatekeepers of Longevity: Dual Role of Glycogen Synthase Kinase-3

This review discusses genetic and molecular pathways that link circadian timing with metabolism, resulting in the emergence of positive and negative regulatory feedback loops. The Nrf2 pathway is believed to be a component of the anti-aging program responsible for the healthspan and longevity. Nrf2 enables stress adaptation by activating cell antioxidant defense and other metabolic processes via control of expression of over 200 target genes in response to various types of stress. The GSK3 system represents a “regulating valve” that controls fine oscillations in the Nrf2 level, unlike Keap1, which prevents significant changes in the Nrf2 content in the absence of oxidative stress and which is inactivated by the oxidative stress. Furthermore, GSK3 modifies core circadian clock proteins (Bmal1, Clock, Per, Cry, and Rev-erbα). Phosphorylation by GSK3 leads to the inactivation and degradation of circadian rhythm-activating proteins (Bmal1 and Clock) and vice versa to the activation and nuclear translocation of proteins suppressing circadian rhythms (Per and Rev-erbα) with the exception of Cry protein, which is likely to be implicated in the fine tuning of biological clock. Functionally, GSK3 appears to be one of the hubs in the cross-regulation of circadian rhythms and antioxidant defense. Here, we present the data on the crosstalk between the most powerful cell antioxidant mechanism, the Nrf2 system, and the biorhythm-regulating system in mammals, including the impact of GSK3 overexpression and knockout on the Nrf2 signaling. Understanding the interactions between the regulatory cascades linking homeostasis maintenance and cell response to oxidative stress will help in elucidating molecular mechanisms that underlie aging and longevity.

The Circadian Physiology: Implications in Livestock Health

Circadian rhythms exist in almost all types of cells in mammals. Thousands of genes exhibit approximately 24 h oscillations in their expression levels, making the circadian clock a crucial regulator of their normal functioning. In this regard, environmental factors to which internal physiological processes are synchronized (e.g., nutrition, feeding/eating patterns, timing and light exposure), become critical to optimize animal physiology, both by managing energy use and by realigning the incompatible processes. Once the circadian clock is disrupted, animals will face the increased risks of diseases, especially metabolic phenotypes. However, little is known about the molecular components of these clocks in domestic species and by which they respond to external stimuli. Here we review evidence for rhythmic control of livestock production and summarize the associated physiological functions, and the molecular mechanisms of the circadian regulation in pig, sheep and cattle. Identification of environmental and physiological inputs that affect circadian gene expressions will help development of novel targets and the corresponding approaches to optimize production efficiency in farm animals.

The Role of GnIH in Biological Rhythms and Social Behaviors

Gonadotropin-inhibitory hormone (GnIH) was first discovered in the Japanese quail, and peptides with a C-terminal LPXRFamide sequence, the signature protein structure defining GnIH orthologs, are well conserved across vertebrate species, including fish, reptiles, amphibians, avians, and mammals. In the mammalian brain, three RFamide-related proteins (RFRP-1, RFRP-2, RFRP-3 = GnIH) have been identified as orthologs to the avian GnIH. GnIH is found primarily in the hypothalamus of all vertebrate species, while its receptors are distributed throughout the brain including the hypothalamus and the pituitary. The primary role of GnIH as an inhibitor of gonadotropin-releasing hormone (GnRH) and pituitary gonadotropin release is well conserved in mammalian and non-mammalian species. Circadian rhythmicity of GnIH, regulated by light and seasons, can influence reproductive activity, mating behavior, aggressive behavior, and feeding behavior. There is a potential link between circadian rhythms of GnIH, anxiety-like behavior, sleep, stress, and infertility. Therefore, in this review, we highlight the functions of GnIH in biological rhythms, social behaviors, and reproductive and non-reproductive activities across a variety of mammalian and non-mammalian vertebrate species.

Seasonal differences in the transcriptome profile of the Zhedong white goose (Anser cygnoides) pituitary gland

In animals, the adaptation to breed at the time of greatest survival of the young is known as seasonal reproduction. This is mainly controlled by the photoperiod, which stimulates the hypothalamic-pituitary-gonadal axis and starts the breeding season. Herein, we have determined the seasonal changes in gene expression patterns of Zhedong white geese pituitary glands under a natural photoperiodism, conducted at autumn equinox (AE), winter solstice (WS), spring equinox (SE), and summer solstice (SS). Pairwise comparisons of WS vs. AE, SE vs. WS, SS vs. SE, and AE vs. SS resulted in 1,139, 33, 704, and 3,503 differently expressed genes, respectively. When compared with SS, AE showed downregulation of genes, such as vasoactive intestinal peptide receptor, prolactin receptor, and thyroid hormone receptor beta, whereas gonadotropin-releasing hormone II receptor was upregulated, indicating that these genes may be responsible for the transition from cessation to egg laying. In addition, the expression levels of 5 transcription factors (POU1F1, Pitx2, NR5A1, NR4A2, and SREBF2) and 6 circadian clock-associated genes (Clock, Per2, ARNTL2, Eya3, Dio2, and NPAS2) also changed seasonally. Gene Ontology term and Kyoto Encyclopedia of Genes and Genomes enrichment analysis revealed that “response to oxidative stress” and steroid biosynthesis pathway also participate in regulating the reproduction seasonality of geese. Overall, these results contribute to the identification of genes involved in seasonal reproduction, enabling a better understanding of the molecular mechanism underlying seasonal reproduction of geese.

It's about time: clocks in the developing lung

The discovery of peripheral intracellular clocks revealed circadian oscillations of clock genes and their targets in all cell types, including those in the lung, sparking exploration of clocks in lung disease pathophysiology. While the focus has been on the role of these clocks in adult airway diseases, clock biology is also likely to be important in perinatal lung development, where it has received far less attention. Historically, fetal circadian rhythms have been considered irrelevant owing to lack of external light exposure, but more recent insights into peripheral clock biology raise questions of clock emergence, its concordance with tissue-specific structure/function, the interdependence of clock synchrony and functionality in perinatal lung development, and the possibility of lung clocks in priming the fetus for postnatal life. Understanding the perinatal molecular clock may unravel mechanistic targets for chronic airway disease across the lifespan. With current research providing more questions than answers, it is about time to investigate clocks in the developing lung.

Effect of Light-Dark Cycle Misalignment on the Hypothalamic-Pituitary-Gonadal Axis, Testicular Oxidative Stress, and Expression of Clock Genes in Adult Male Rats

This study investigated the influence of circadian misalignment on the male reproductive system. Adult Sprague-Dawley male rats were exposed to prolonged light (20 h light : 4 h dark) or prolonged darkness (4 h light : 20 h dark) for 12 consecutive weeks. The somatic index of seminal vesicles and prostates increased due to prolonged light exposure. Sperm count and motility were enhanced solely by prolonged light exposure, whereas the percentage of sperm abnormalities was reduced by both prolonged light and darkness. The serum levels of reproductive hormones (follicle-stimulating hormone, luteinizing hormone, testosterone, and prolactin) were elevated, and the estradiol level was reduced by long-term light and dark exposure. Testicular total antioxidant capacity and antioxidant enzyme activities were improved, and lipid peroxidation was inhibited following chronic exposure to light or dark. Chronic light exposure increased, but chronic darkness decreased, testicular nitric oxide production. The mRNA expression of the hypothalamic and testicular clock genes including PER1-2, CRY1-2, BMAL1, CLOCK, and Rev-Erbα was altered by circadian disruption. Prolonged light exposure decreased the levels of thyroid hormones and suppressed the mRNA expression of adiponectin receptors 1 and 2. The immunohistochemical expression of proliferating cell nuclear antigen was decreased only by chronic darkness. The present study thus provides new insights into the physiological changes associated with long-term exposure to light or darkness, in which the expression levels of various clock gene mRNAs are modulated, reproductive hormones are increased, and the antioxidant enzyme system is ameliorated as mechanisms of adaptation to chronic circadian disruption.

Role of preovulatory concentrations of estradiol on timing of conception and regulation of the uterine environment in beef cattle

The ability to induce ovulation with an injection of GnRH facilitated the development of fixed-time artificial insemination (AI) protocols. However, animals that exhibit estrus prior to fixed-time AI have greater pregnancy success. Thus, the objectives of the present experiments were to determine the impact of estrus expression prior to fixed-time AI on timing of conception and to characterize the role of preovulatory estradiol in regulating changes in expression of uterine genes. In experiment 1, data were collected from 4,499 beef cows inseminated by fixed-time AI in 31 different herds. Animals that did not conceive to AI but exhibited estrus before timed-AI were more likely to conceive during cycle 1 after AI, and overall conceived earlier in the breeding season compared to animals that did not exhibit estrus. In experiment 2, beef cows were synchronized using a fixed-time AI protocol. Uterine horn biopsies and blood samples were collected on Day 0, 5, 10, or 16. Concentrations of estradiol on Day 0 did not influence expression of progesterone receptor, ER beta, or oxytocin receptor. Increased concentrations of estradiol on Day 0 increased expression of ER alpha from Days 0 to 5 of the estrous cycle. Furthermore, cows with increased concentrations of estradiol on Day 0 had increased expression of inhibin beta A, and uterine milk protein precursor. Thus, animals that do not exhibit estrus prior to fixed-time AI had decreased breeding season pregnancy success and conceived later in the breeding season, and preovulatory concentrations of estradiol likely play a major role in this establishment of pregnancy, not only directly by regulating uterine gene expression, but also indirectly throughout the subsequent estrous cycle.

Clock genes alterations and endocrine disorders

BACKGROUND

Various endocrine signals oscillate over the 24-hour period and so does the responsiveness of target tissues. These daily oscillations do not occur solely in response to external stimuli but are also under the control of an intrinsic circadian clock.

DESIGN

We searched the PubMed database to identify studies describing the associations of clock genes with endocrine diseases.

RESULTS

Various human single nucleotide polymorphisms of brain and muscle ARNT-like 1 (BMAL1) and Circadian Locomotor Output Cycles Kaput (CLOCK) genes exhibited significant associations with type 2 diabetes mellitus. ARNTL2 gene expression and upregulation of BMAL1 and PER1 were associated with the development of type 1 diabetes mellitus. Thyroid hormones modulated PER2 expression in a tissue-specific way, whereas BMAL1 regulated the expression of type 2 iodothyronine deiodinase in specific tissues. Adrenal gland and adrenal adenoma expressed PER1, PER2, CRY2, CLOCK and BMAL1 genes. Adrenal sensitivity to adrenocorticotrophin was also affected by circadian oscillations. A significant correlation between the expression of propio-melanocorticotrophin and PER 2, as well as between prolactin and CLOCK, was found in corticotroph and lactosomatotroph cells, respectively, in the pituitary. Clock genes and especially BMAL1 showed an important role in fertility, whereas oestradiol and androgens exhibited tissue-specific effects on clock gene expression. Metabolic disorders were also associated with circadian dysregulation according to studies in shift workers.

CONCLUSIONS

Clock genes are associated with various endocrine disorders through complex mechanisms. However, data on humans are scarce. Moreover, clock genes exhibit a tissue-specific expression representing an additional level of regulation. Their specific role in endocrine disorders and their potential implications remain to be further clarified.

Flexible clock systems: adjusting the temporal programme

Under natural conditions, many aspects of the abiotic and biotic environment vary with time of day, season or even era, while these conditions are typically kept constant in laboratory settings. The timing information contained within the environment serves as critical timing cues for the internal biological timing system, but how this system drives daily rhythms in behaviour and physiology may also depend on the internal state of the animal. The disparity between timing of these cues in natural and laboratory conditions can result in substantial differences in the scheduling of behaviour and physiology under these conditions. In nature, temporal coordination of biological processes is critical to maximize fitness because they optimize the balance between reproduction, foraging and predation risk. Here we focus on the role of peripheral circadian clocks, and the rhythms that they drive, in enabling adaptive phenotypes. We discuss how reproduction, endocrine activity and metabolism interact with peripheral clocks, and outline the complex phenotypes arising from changes in this system. We conclude that peripheral timing is critical to adaptive plasticity of circadian organization in the field, and that we must abandon standard laboratory conditions to understand the mechanisms that underlie this plasticity which maximizes fitness under natural conditions.This article is part of the themed issue 'Wild clocks: integrating chronobiology and ecology to understand timekeeping in free-living animals'.

Both the Suprachiasmatic Nucleus and the Superior Ovarian Nerve Contribute to the Processes of Ovulation and Steroid Hormone Secretion on Proestrus

The aims of the present study were to analyze if the superior ovarian nerve (SON) plays a role in the neural signals from suprachiasmatic nucleus (SCN) that lead to ovulation and ovarian steroids secretion on proestrus day. Rats on proestrus day were treated at 11.00 to 11.30 or 17.00 to 17.30 hours with 1 of the 3 experimental procedures (1) unilateral or bilateral SON sectioning, (2) unilateral or bilateral injury to the SCN, or (3) unilateral injury to the SCN followed by unilateral sectioning of the SON ipsilateral to the treated SCN. Treatments were evaluated 24 hours after surgical procedures. Compared to laparotomized animals, right or bilateral SON sectioning treatment at 17.00 hours resulted in lower ovulation rates and number of ova shed by the right ovary. The ovaries of nonovulating animals showed early follicular luteinization signs and trapped ova. Bilateral SCN injury treatment at 11.00 hours resulted in anovulation; whereas right SCN injury treatment, with or without right SON sectioning, resulted in a lower number of ova shed. Injecting luteinizing hormone-releasing hormone to animals with bilateral SCN injury restored ovulation. In rats with unilateral or bilateral SON sectioning, or with injury to the SCN with or without unilateral sectioning of the SON, the effects on hormone levels depended of the hormone studied and the time of day treatment was performed. The present results suggest that on proestrus day, the role of the right or both SON in ovulation and steroid hormone secretion regulation takes place through different neuroendocrine mechanisms from SCN.

Pregnancy-induced changes in the circadian expression of hepatic clock genes: implications for maternal glucose homeostasis

Adaptations in maternal carbohydrate metabolism are particularly important in pregnancy because glucose is the principal energy substrate used by the fetus. As metabolic homeostasis is intricately linked to the circadian system via the rhythmic expression of clock genes, it is likely that metabolic adaptations during pregnancy also involve shifts in maternal circadian function. We hypothesized that maternal adaptation in pregnancy involves changes in the hepatic expression of clock genes, which drive downstream shifts in circadian expression of glucoregulatory genes. Maternal liver and plasma (n = 6-8/group) were collected across 24-h periods (0800, 1200, 1600, 2000, 0000, 0400) from C57Bl/6J mice under isoflurane-nitrous oxide anesthesia prior to and on days 6, 10, 14 and 18 of pregnancy (term = day 19). Hepatic expression of clock genes and glucoregulatory genes was determined by RT-qPCR. Hepatic clock gene expression was substantially altered across pregnancy, most notably in late gestation when the circadian rhythmicity of several clock genes was attenuated (≤64% reduced amplitude on day 18). These changes were associated with a similar decline in rhythmicity of the key glucoregulatory genes Pck1, G6Pase, and Gk, and by day 18, Pck1 was no longer rhythmic. Overall, our data show marked adaptations in the liver clock during mouse pregnancy, changes that may contribute to the altered circadian variation in glucoregulatory genes near term. We propose that the observed reduction of daily oscillations in glucose metabolism ensure a sustained supply of glucose to meet the high demands of fetal growth.

Factors affecting puberty in replacement beef heifers

Puberty is defined as when ovulation is accompanied by visual signs of estrus and subsequent normal luteal function. Age at puberty is an important trait in relation to reproductive success, productive life span, and profitability in beef operations. Although puberty and initiation of normal estrous cycles are complex events that require maturation of the hypothalamic-pituitary-ovarian axis, it has been well documented that nutrition, age, and genetics are regulators of age at puberty. However, their role is mainly as regulators of the endocrine maturation that must occur for sustained ovarian cyclicity to be initiated. Increased growth rate between 4 and 7 months of age is apparently sufficient to induce early puberty, and this increased growth rate decreased the negative feedback of estradiol on LH secretion during the prepubertal period. As puberty approaches, a progressive decrease in the negative feedback of estradiol on GnRH secretion allows increased pulse frequency of LH, thus stimulating follicular growth and increased estradiol production. In addition, expression of estrogen receptors in the anterior hypothalamus and ventromedial nucleus is negatively correlated with LH pulse frequency. Although a significant number of genes and pathways are involved in neuromaturation for the initiation of normal estrous cycles, the inhibitory effects of neuropeptide Y on GnRH/LH release appear to decrease, and the stimulatory effect of melanocyte-stimulating hormone alpha on GnRH appears to increase as puberty approaches. Thus, a thorough understanding of the metabolic and neuroendocrine changes that occur to initiate normal estrous cycles is needed to facilitate management of the important reproductive event.

Conditional Deletion of Bmal1 in Ovarian Theca Cells Disrupts Ovulation in Female Mice

Rhythmic events in female reproductive physiology, including ovulation, are tightly controlled by the circadian timing system. The molecular clock, a feedback loop oscillator of clock gene transcription factors, dictates rhythms of gene expression in the hypothalamo-pituitary-ovarian axis. Circadian disruption due to environmental factors (eg, shift work) or genetic manipulation of the clock has negative impacts on fertility. Although the central pacemaker in the suprachiasmatic nucleus classically regulates the timing of ovulation, we have shown that this rhythm also depends on phasic sensitivity to LH. We hypothesized that this rhythm relies on clock function in a specific cellular compartment of the ovarian follicle. To test this hypothesis we generated mice with deletion of the Bmal1 locus in ovarian granulosa cells (GCs) (Granulosa Cell Bmal1 KO; GCKO) or theca cells (TCs) (Theca Cell Bmal1 KO; TCKO). Reproductive cycles, preovulatory LH secretion, ovarian morphology and behavior were not grossly altered in GCKO or TCKO mice. We detected phasic sensitivity to LH in wild-type littermate control (LC) and GCKO mice but not TCKO mice. This decline in sensitivity to LH is coincident with impaired fertility and altered patterns of LH receptor (Lhcgr) mRNA abundance in the ovary of TCKO mice. These data suggest that the TC is a pacemaker that contributes to the timing and amplitude of ovulation by modulating phasic sensitivity to LH. The TC clock may play a critical role in circadian disruption-mediated reproductive pathology and could be a target for chronobiotic management of infertility due to environmental circadian disruption and/or hormone-dependent reprogramming in women.

A "Timed" Kiss Is Essential for Reproduction: Lessons from Mammalian Studies

Reproduction is associated with the circadian system, primarily as a result of the connectivity between the biological clock in the suprachiasmatic nucleus (SCN) and reproduction-regulating brain regions, such as preoptic area (POA), anteroventral periventricular nucleus (AVPV), and arcuate nucleus (ARC). Networking of the central pacemaker to these hypothalamic brain regions is partly represented by close fiber appositions to specialized neurons, such as kisspeptin and gonadotropin-releasing hormone (GnRH) neurons; accounting for rhythmic release of gonadotropins and sex steroids. Numerous studies have attempted to dissect the neurochemical properties of GnRH neurons, which possess intrinsic oscillatory features through the presence of clock genes to regulate the pulsatile and circadian secretion. However, less attention has been given to kisspeptin, the upstream regulator of GnRH and a potent mediator of reproductive functions including puberty. Kisspeptin exerts its stimulatory effects on GnRH secretion via its cognate Kiss-1R receptor that is co-expressed on GnRH neurons. Emerging studies have found that kisspeptin neurons oscillate on a circadian basis and that these neurons also express clock genes that are thought to regulate its rhythmic activities. Based on the fiber networks between the SCN and reproductive nuclei such as the POA, AVPV, and ARC, it is suggested that interactions among the central biological clock and reproductive neurons ensure optimal reproductive functionality. Within this neuronal circuitry, kisspeptin neuronal system is likely to "time" reproduction in a long term during development and aging, in a medium term to regulate circadian or estrus cycle, and in a short term to regulate pulsatile GnRH secretion.

Photoperiodic Modulation of Circadian Clock and Reproductive Axis Gene Expression in the Pre-Pubertal European Sea Bass Brain

The acquisition of reproductive competence requires the activation of the brain-pituitary-gonad (BPG) axis, which in most vertebrates, including fishes, is initiated by changes in photoperiod. In the European sea bass long-term exposure to continuous light (LL) alters the rhythm of reproductive hormones, delays spermatogenesis and reduces the incidence of precocious males. In contrast, an early shift from long to short photoperiod (AP) accelerates spermatogenesis. However, how photoperiod affects key genes in the brain to trigger the onset of puberty is still largely unknown. Here, we investigated if the integration of the light stimulus by clock proteins is sufficient to activate key genes that trigger the BPG axis in the European sea bass. We found that the clock genes clock, npas2, bmal1 and the BPG genes gnrh, kiss and kissr share conserved transcription factor frameworks in their promoters, suggesting co-regulation. Other gene promoters of the BGP axis were also predicted to be co-regulated by the same frameworks. Co-regulation was confirmed through gene expression analysis of brains from males exposed to LL or AP photoperiod compared to natural conditions: LL fish had suppressed gnrh1, kiss2, galr1b and esr1, while AP fish had stimulated npas2, gnrh1, gnrh2, kiss2, kiss1rb and galr1b compared to NP. It is concluded that fish exposed to different photoperiods present significant expression differences in some clock and reproductive axis related genes well before the first detectable endocrine and morphological responses of the BPG axis.

Early life exposure to undernutrition induces ER stress, apoptosis, and reduced vascularization in ovaries of adult rat offspring

Maternal nutritional restriction has been shown to induce impairments in a number of organ systems including the ovary. We have previously shown that maternal undernutrition induces fetal growth restriction and low birth weight, and results in an offspring ovarian phenotype characteristic of premature ovarian aging with reduced ovarian reserve. In the present study, we set out to investigate the underlying mechanisms that lead offspring of undernourished mothers to premature ovarian aging. Pregnant dams were randomized to 1) a standard diet throughout pregnancy and lactation (control), 2) a calorie-restricted (50% of control) diet during pregnancy, 3) a calorie-restricted (50% of control) diet during pregnancy and lactation, or 4) a calorie-restricted (50% of control) diet during lactation alone. The present study shows that early life undernutrition-induced reduction of adult ovarian follicles may be mediated by increased ovarian endoplasmic reticulum stress in a manner that increased follicular apoptosis but not autophagy. These changes were associated with a loss of ovarian vessel density and are consistent with an accelerated ovarian aging phenotype. Whether these changes are mediated specifically by a reduction in the local antioxidant environment is unclear, although our data suggest the possibility that ovarian melatonin may play a part in early life nutritional undernutrition and impaired offspring folliculogenesis.

Glutamate-Dependent BMAL1 Regulation in Cultured Bergmann Glia Cells

Glutamate, the major excitatory amino acid, activates a wide variety of signal transduction cascades. This neurotransmitter is involved in photic entrainment of circadian rhythms, which regulate physiological and behavioral functions. The circadian clock in vertebrates is based on a transcription-translation feedback loop in which Brain and muscle aryl hydrocarbon receptor nuclear translocator (ARNT)-like protein 1 (BMAL1) acts as transcriptional activator of others clock genes. This protein is expressed in nearly all suprachiasmatic nucleus neurons, as well as in the granular layer of the cerebellum. In this context, we decided to investigate the role of glutamate in the molecular mechanisms involved in the processes of transcription/translation of BMAL1 protein. To this end, primary cultures of chick cerebellar Bergmann glial cells were stimulated with glutamatergic ligands and we found that BMAL1 levels increased in a dose- and time dependent manner. Additionally, we studied the phosphorylation of serine residues in BMAL1 under glutamate stimulation and we were able to detect an increase in the phosphorylation of this protein. The increased expression of BMAL1 is most probably the result of a stabilization of the protein after it has been phosphorylated by the cyclic AMP-dependent protein kinase and/or the Ca(2+)/diacylglycerol dependent protein kinase. The present results strongly suggest that glutamate participates in regulating BMAL1 in glial cells and that these cells might prove to be important in the control of circadian rhythms in the cerebellum.

Circadian Clock Function in the Mammalian Ovary

Rhythmic events in the female reproductive system depend on the coordinated and synchronized activity of multiple neuroendocrine and endocrine tissues. This coordination is facilitated by the timing of gene expression and cellular physiology at each level of the hypothalamo-pituitary-ovarian (HPO) axis, including the basal hypothalamus and forebrain, the pituitary gland, and the ovary. Central to this pathway is the primary circadian pacemaker in the suprachiasmatic nucleus (SCN) that, through its myriad outputs, provides a temporal framework for gonadotropin release and ovulation. The heart of the timing system, a transcription-based oscillator, imparts SCN pacemaker cells and a company of peripheral tissues with the capacity for daily oscillations of gene expression and cellular physiology. Although the SCN sits comfortably at the helm, peripheral oscillators (such as the ovary) have undefined but potentially critical roles. Each cell type of the ovary, including theca cells, granulosa cells, and oocytes, harbor a molecular clock implicated in the processes of follicular growth, steroid hormone synthesis, and ovulation. The ovarian clock is influenced by the reproductive cycle and diseases that perturb the cycle and/or follicular growth can disrupt the timing of clock gene expression in the ovary. Chronodisruption is known to negatively affect reproductive function and fertility in both rodent models and women exposed to shiftwork schedules. Thus, influencing clock function in the HPO axis with chronobiotics may represent a novel avenue for the treatment of common fertility disorders, particularly those resulting from chronic circadian disruption.

Environmental control of biological rhythms: effects on development, fertility and metabolism

Internal temporal organisation properly synchronised to the environment is crucial for health maintenance. This organisation is provided at the cellular level by the molecular clock, a macromolecular transcription-based oscillator formed by the clock and the clock-controlled genes that is present in both central and peripheral tissues. In mammals, melanopsin in light-sensitive retinal ganglion cells plays a considerable role in the synchronisation of the circadian timing system to the daily light/dark cycle. Melatonin, a hormone synthesised in the pineal gland exclusively at night and an output of the central clock, has a fundamental role in regulating/timing several physiological functions, including glucose homeostasis, insulin secretion and energy metabolism. As such, metabolism is severely impaired after a reduction in melatonin production. Furthermore, light pollution during the night and shift work schedules can abrogate melatonin synthesis and impair homeostasis. Chronodisruption during pregnancy has deleterious effects on the health of progeny, including metabolic, cardiovascular and cognitive dysfunction. Developmental programming by steroids or steroid-mimetic compounds also produces internal circadian disorganisation that may be a significant factor in the aetiology of fertility disorders such as polycystic ovary syndrome. Thus, both early and late in life, pernicious alterations of the endogenous temporal order by environmental factors can disrupt the homeostatic function of the circadian timing system, leading to pathophysiology and/or disease.

Circadian clock control of endocrine factors

Organisms experience dramatic fluctuations in demands and stresses over the course of the day. In order to maintain biological processes within physiological boundaries, mechanisms have evolved for anticipation of, and adaptation to, these daily fluctuations. Endocrine factors have an integral role in homeostasis. Not only do circulating levels of various endocrine factors oscillate over the 24 h period, but so too does responsiveness of target tissues to these signals or stimuli. Emerging evidence suggests that these daily endocrine oscillations do not occur solely in response to behavioural fluctuations associated with sleep-wake and feeding-fasting cycles, but are orchestrated by an intrinsic timekeeping mechanism known as the circadian clock. Disruption of circadian clocks by genetic and/or environmental factors seems to precipitate numerous common disorders, including the metabolic syndrome and cancer. Collectively, these observations suggest that strategies designed to realign normal circadian rhythmicities hold potential for the treatment of various endocrine-related disorders.

Diet-induced maternal obesity alters ovarian morphology and gene expression in the adult mouse offspring

OBJECTIVE

To examine the effects of high-fat (HF) diet-induced maternal obesity on follicular population and gene expression in adult offspring ovaries.

DESIGN

Experimental mouse study.

SETTING

Laboratory.

ANIMAL(S)

Mice on HF diet.

INTERVENTION(S)

Female C57BL/6J mice were fed an HF or standard chow (C) diet 6 weeks before conception, through pregnancy and lactation. Offspring were fed the C or HF diet from weaning, creating the HF/HF, HF/C, C/HF, C/C offspring groups.

MAIN OUTCOME MEASURE(S)

Follicular counts and gene expression in adult offspring ovaries.

RESULT(S)

Prenatal exposure to maternal HF nutrition resulted in the reduction of primordial, antral, and Graafian follicle numbers in offspring ovaries (both HF/C and HF/HF). Expression levels of genes involved in apoptosis (FoXO3a), follicular growth and development (Gdf9), and circadian rhythms generation (Clock and Bmal1) were elevated in the ovaries of HF/C and HF/HF offspring, while expression of the circadian clock genes Cry1 and Per1 were lower in HF/HF ovaries.

CONCLUSION(S)

Maternal obesity during pregnancy has long-term deleterious consequences on follicular growth and development in the adult offspring ovaries, which may impact their reproductive potential.

Adolescent sleep patterns in humans and laboratory animals

This article is part of a Special Issue "Puberty and Adolescence". One of the defining characteristics of adolescence in humans is a large shift in the timing and structure of sleep. Some of these changes are easily observable at the behavioral level, such as a shift in sleep patterns from a relatively morning to a relatively evening chronotype. However, there are equally large changes in the underlying architecture of sleep, including a >60% decrease in slow brain wave activity, which may reflect cortical pruning. In this review we examine the developmental forces driving adolescent sleep patterns using a cross-species comparison. We find that behavioral and physiological sleep parameters change during adolescence in non-human mammalian species, ranging from primates to rodents, in a manner that is often hormone-dependent. However, the overt appearance of these changes is species-specific, with polyphasic sleepers, such as rodents, showing a phase-advance in sleep timing and consolidation of daily sleep/wake rhythms. Using the classic two-process model of sleep regulation, we demonstrate via a series of simulations that many of the species-specific characteristics of adolescent sleep patterns can be explained by a universal decrease in the build-up and dissipation of sleep pressure. Moreover, and counterintuitively, we find that these changes do not necessitate a large decrease in overall sleep need, fitting the adolescent sleep literature. We compare these results to our previous review detailing evidence for adolescent changes in the regulation of sleep by the circadian timekeeping system (Hagenauer and Lee, 2012), and suggest that both processes may be responsible for adolescent sleep patterns.