Circadian clocks and the measurement of daylength in seasonal reproduction

Effect of active immunization with OPN5 on follicular development and egg production in quail under different photoperiods

OPN5 is one of the main deep brain photoreceptors (DBPs), converting photoperiodic information into neuroendocrine signals to regulate reproduction in birds. This study investigated the mechanism of OPN5-mediated photoperiodic regulation of reproduction by active immunization against OPN5. 96 female quail were divided into OPN5-immunized and control group under the same photoperiod: 16 L:8 D (d 1 to d 35), 8 L:16 D (d 36 to d 70) and 12 L:12 D (d 71 to d 126). OPN5-immunized group was conducted with OPN5 protein vaccination and control group was given a blank vaccine. Samples were collected on d 1, d 30, d 60, and d 126. Results showed switching photoperiod to 8 L:16 D decreased the laying rate, GSI%, numbers of YFs and WFs, serum levels of PRL, P4 and E2, and pituitary PRL and TSHβ protein expressions in both groups (P < 0.05). Whereas the OPN5-immunized group exhibited higher laying rates than the control group (P < 0.05). The control group showed reduced GnRHR and TSHβ gene expressions in the pituitary and increased GnIH and DIO3 transcript and/or protein abundance in the hypothalamus. (P < 0.05). The OPN5-immunized group had lower DIO3 expression at both mRNA and protein levels. (P < 0.05). Switching photoperiod from 8 L:16 D to 12 L:12 D increased the laying rates, GSI%, numbers of YFs and WFs, serum levels of PRL, and PRL protein expression in both groups (P < 0.05), and the responses were more pronounced in OPN5-immunized group (P < 0.05). In contrast to the control group, quail with OPN5-immunization had higher OPN5 and DIO2 transcript and/or protein levels but lower DIO3 expressions in the hypothalamus along the transition photoperiods (P < 0.05). The results revealed that OPN5 responds to photoperiod transition, and its activation mediates related signaling to up-regulate TSH-DIO2/DIO3 pathway and VIP-PRL secretion to prime quail reproductive functions.

The Royal Zoological Society of Scotland's Approach to Assessing and Promoting Animal Welfare in Collaboration with Universities

Good zoos have four aims-to conserve species, educate the public, engage in research, and provide recreation-all of which can only be achieved when underpinned by high animal welfare standards. In this paper, we share the approach that The Royal Zoological Society of Scotland's (RZSS) Edinburgh Zoo and Highland Wildlife Park take to animal welfare. We highlight the role that animal welfare research, in collaboration with universities, has had in enabling the zoo to take an evidence-based approach to welfare and to put findings into practice. We share the collaborative process through which we developed and piloted the current animal welfare assessment tools, how they were validated, and how they were tested for reliability as part of a long-term collaboration between the Royal Zoological Society of Scotland and the University of Stirling: (1) the RZSS Welfare Assessment Tool, a 50-question animal welfare assessment adapted from the British and Irish Association of Zoos and Aquariums (BIAZA) Toolkit; and (2) the Stirling Toolkit, a package of evidence-based resources for behavioural-data collection. Our aim is to facilitate standardised, evidence-based approaches to assessing animal welfare which, when finalised, can be used collaboratively across zoos.

A clock for all seasons in the subterranean

In 1976, Pittendrigh and Daan established a theoretical framework which has coordinated research on circadian clock entrainment and photoperiodism until today. The "wild clocks" approach, which concerns studying wild species in their natural habitats, has served to test their models, add new insights, and open new directions of research. Here, we review an integrated laboratory, field and modeling work conducted with subterranean rodents (Ctenomys sp.) living under an extreme pattern of natural daily light exposure. Tracking animal movement and light exposure with biologgers across seasons and performing laboratory experiments on running-wheel cages, we uncovered the mechanisms of day/night entrainment of the clock and of photoperiodic time measurement in this subterranean organism. We confirmed most of the features of Pittendrigh and Daan's models but highlighted the importance of integrating them with ecophysiological techniques, methodologies, and theories to get a full picture of the clock in the wild. This integration is essential to fully establish the importance of the temporal dimension in ecological studies and tackling relevant questions such as the role of the clock for all seasons in a changing planet.

Receptor-Mediated and Receptor-Independent Actions of Melatonin in Vertebrates

Melatonin (N-acetyl-5-methoxytryptamine) is an indolamine that is synthesized from tryptophan in the pineal glands of vertebrates through four enzymatic reactions. Melatonin is a quite unique bioactive substance, characterized by a combination of both receptor-mediated and receptor-independent actions, which promote the diverse effects of melatonin. One of the main functions of melatonin, via its membrane receptors, is to regulate the circadian or seasonal rhythm. In mammals, light information, which controls melatonin synthesis, is received in the eye, and transmitted to the pineal gland, via the suprachiasmatic nucleus, where the central clock is located. Alternatively, in many vertebrates other than mammals, the pineal gland cells, which are involved in melatonin synthesis and secretion and in the circadian clock, directly receive light. Recently, it has been reported that melatonin possesses several metabolic functions, which involve bone and glucose, in addition to regulating the circadian rhythm. Melatonin improves bone strength by inhibiting osteoclast activity. It is also known to maintain brain activity during sleep by increasing glucose uptake at night, in an insulin-independent manner. Moreover, as a non-receptor-mediated action, melatonin has antioxidant properties. Melatonin has been proven to be a potent free radical scavenger and a broad-spectrum antioxidant, even protecting organisms against radiation from space. Melatonin is a ubiquitously distributed molecule and is found in bacteria, unicellular organisms, fungi, and plants. It is hypothesized that melatonin initially functioned as an antioxidant, then, in vertebrates, it combined this role with the ability to regulate rhythm and metabolism, via its receptors.

Endocrine and molecular regulation mechanisms of follicular development and egg-laying in quails under different photoperiods

Photoperiod is a key environmental factor in regulating bird reproduction and induces neuroendocrine changes through the hypothalamic-pituitary-gonadal (HPG) axis. OPN5, as a deep-brain photoreceptor, transmits light signals to regulate follicular development through TSH-DIO2/DIO3. However, the mechanism among OPN5, TSH-DIO2/DIO3, and VIP/PRL in the HPG axis underlying the photoperiodic regulation of bird reproduction is unclear. In this study, 72 laying quails with 8-week-old were randomly divided into the long-day (LD) group [16 light (L): 8 dark (D)] and the short-day (SD) group (8 L:16 D), and then samples were collected on d 1, d 11, d 22, and d 36 of the experiment. The results showed that compared with the LD group, the SD group significantly inhibited follicular development (P < 0.05), decreased the P4, E2, LH, and PRL in serum (P < 0.05), downregulated the expression of GnRHR, VIP, PRL, OPN5, DIO2, and LHβ (P < 0.05), reduced the expression of GnRH and TSHβ (P > 0.05), and promoted DIO3, GnIH gene expression (P < 0.01). The short photoperiod downregulates OPN5, TSHβ, and DIO2 and upregulates DIO3 expression to regulate the GnRH/GnIH system. The downregulation of GnRHR and upregulation of GnIH resulted in a decrease in LH secretion, which withdrew the gonadotropic effects on ovarian follicles development. Slow down of follicular development and egg laying may also arise from lack of PRL potentiation to small follicle development under short days.

The circadian clock controls temporal and spatial patterns of floral development in sunflower

Biological rhythms are ubiquitous. They can be generated by circadian oscillators, which produce daily rhythms in physiology and behavior, as well as by developmental oscillators such as the segmentation clock, which periodically produces modular developmental units. Here, we show that the circadian clock controls the timing of late-stage floret development, or anthesis, in domesticated sunflowers. In these plants, up to thousands of individual florets are tightly packed onto a capitulum disk. While early floret development occurs continuously across capitula to generate iconic spiral phyllotaxy, during anthesis floret development occurs in discrete ring-like pseudowhorls with up to hundreds of florets undergoing simultaneous maturation. We demonstrate circadian regulation of floral organ growth and show that the effects of light on this process are time-of-day dependent. Delays in the phase of floral anthesis delay morning visits by pollinators, while disruption of circadian rhythms in floral organ development causes loss of pseudowhorl formation and large reductions in pollinator visits. We therefore show that the sunflower circadian clock acts in concert with environmental response pathways to tightly synchronize the anthesis of hundreds of florets each day, generating spatial patterns on the developing capitulum disk. This coordinated mass release of floral rewards at predictable times of day likely promotes pollinator visits and plant reproductive success.

Expression of GnIH and its effects on follicle development and steroidogenesis in quail ovaries under different photoperiods

Photoperiod is an important environmental factor that influence seasonal reproduction behavior in bird and GnIH can play a function in this process through the reproductive axis, and some studies suggest that GnIH may have a direct role at the gonadal level. To investigate the expression of GnIH and its effects on follicle development and steroidogenesis in quail ovaries under different photoperiods, 72 healthy laying quails of 8-wk-old were randomly divided into long day (LD) group [16 light (L): 8 dark (D)] (n = 36) and short day (SD) group (8L:16D) (n = 36). Samples were collected from each group on d1, d11, d22, and d36 of the experiment. The result showed that short day treatment upregulated the level of GnIH in the gonads (P < 0.05), decreased the expression level of CYP19A1,3β-HSD, StAR, LHR, and FSHR and increased the expression level of AMH, AMHR2, GDF9, and BMP15 to inhibit follicle development and ovulation, thus affecting the egg production performance of quails. In vitro culture of quail granulosa cells and treatment with different concentrations of GnIH (0, 1, 10, and 100 ng/mL) for 24 h. Result showed that GnIH inhibited the levels of FSHR, LHR, and steroid synthesis pathways in granulosa cells, upregulated the levels of AMHR2, GDF9, and BMP15. The results suggest that the inhibition of follicle development and reduced egg production in quail by short day treatment is due to GnIH acting at the gonadal level, and GnIH affected the steroid synthesis by inhibiting gonadotropin receptors.

Screening of Differentially Expressed Genes and miRNAs in Hypothalamus and Pituitary Gland of Sheep under Different Photoperiods

The reproduction of sheep is affected by many factors such as light, nutrition and genetics. The Hypothalamic-pituitary-gonadal (HPG) axis is an important pathway for sheep reproduction, and changes in HPG axis-related gene expression can affect sheep reproduction. In this study, a model of bilateral ovarian removal and estrogen supplementation (OVX + E₂) was applied to screen differentially expressed genes and miRNAs under different photoperiods using whole transcriptome sequencing and reveal the regulatory effects of the photoperiod on the upstream tissues of the HPG axis in sheep. Whole transcriptome sequencing was performed in ewe hypothalamus (HYP) and distal pituitary (PD) tissues under short photoperiod 21st day (SP21) and long photoperiod 21st day (LP21). Compared to the short photoperiod, a total of 1813 differential genes (up-regulation 966 and down-regulation 847) and 145 differential miRNAs (up-regulation 73 and down-regulation 72) were identified in the hypothalamus of long photoperiod group. Similarly, 2492 differential genes (up-regulation 1829 and down-regulation 663) and 59 differential miRNAs (up-regulation 49 and down-regulation 10) were identified in the pituitary of long photoperiod group. Subsequently, GO and KEGG enrichment analysis revealed that the differential genes and target genes of differential miRNA were enriched in GnRH, Wnt, ErbB and circadian rhythm pathways associated with reproduction. Combined with sequence complementation and gene expression correlation analysis, several miRNA-mRNA target combinations (e.g., LHB regulated by novel-414) were obtained. Taken together, these results will help to understand the regulatory effect of the photoperiod on the upstream tissues of HPG in sheep.

Daylength Shapes Entrainment Patterns to Artificial Photoperiods in a Subterranean Rodent

Photoperiodism plays an important role in the synchronization of seasonal phenomena in various organisms. In mammals, photoperiod encoding is mediated by differential entrainment of the circadian system. The limits of daily light entrainment and photoperiodic time measurement can be verified in organisms that inhabit extreme photic environments, such as the subterranean. In this experimental study, we evaluated entrainment of circadian wheel-running rhythms in South American subterranean rodents, the Anillaco tuco-tucos ( Ctenomys aff. knighti), exposed to different artificial photoperiods, from extremely long to extremely short photophases (LD 21:3, LD 18:6, LD 15:9, LD 9:15, LD 6:18 and LD 3:21). Artificial photoperiods synchronized their activity/rest rhythms and clear differences occurred in (a) phase angles of entrainment relative to the LD cycle and (b) duration of the daily activity phase α. These photoperiod-dependent patterns of entrainment were similar to those reported for epigeous species. Release into constant darkness conditions revealed aftereffects of entrainment to different photoperiods, observed in α but not in the free-running period τ. We also verified if animals coming from summer and winter natural photoperiods entrained equally to the artificial photoperiods by evaluating their phase angle of entrainment, α and τ aftereffects. To this end, experimental animals were divided into “Matching” and “Mismatching” groups, based on whether the experimental photoperiod (short-day [L < 12 h] or long-day [L > 12 h]) matched or not the natural photoperiod to which they had been previously exposed. No significant differences were found in the phase angle of entrainment, α and τ aftereffects in each artificial photoperiod. Our results indicate that the circadian clocks of tuco-tucos are capable of photoperiodic time measurement despite their natural subterranean habits and that the final entrainment patterns achieved by the circadian clock do not depend on the photoperiodic history.

Diaphorina citri Genome Possesses a Complete Melatonin Biosynthesis Pathway Differentially Expressed under the Influence of the Phytopathogenic Bacterium, Candidatus Liberibacter asiaticus

Melatonin is synthesized from the amino acid L-tryptophan via the shikimic acid pathway and ubiquitously distributed in both prokaryotes and eukaryotes. Although most of melatonin biosynthesis genes were characterized in several plants and animal species including the insect model, Drosophila melanogaster, none of these enzymes have been identified from the Asian citrus psyllid, Diaphorina citri. We used comprehensive in silico analysis and gene expression techniques to identify the melatonin biosynthesis-related genes of D. citri and to evaluate the expression patterns of these genes within the adults of D. citri with gradient infection rates (0, 28, 34, 50, 58, and 70%) of the phytopathogenic bacterium Candidatus Liberibacter asiaticus and after the treatment with exogenous melatonin. We showed that the D. citri genome possesses six putative melatonin biosynthesis-related genes including two putative tryptophan 5-hydroxylase (DcT5H-1 and DcT5H-2), a putative aromatic amino acid decarboxylase (DcAADC), two putative arylalkylamine N-acetyltransferase (DcAANAT-1 and DcAANAT-2), and putative N-acetylserotonin O-methyltransferase (DcASMT). The infection with Ca. L. asiaticus decreased the transcript levels of all predicted genes in the adults of D. citri. Moreover, melatonin supplementation induced their expression levels in both healthy and Ca. L. asiaticus-infected psyllids. These findings confirm the association of these genes with the melatonin biosynthesis pathway.

The role of astrocytes in generating circadian rhythmicity in health and disease

Evidence is accumulating that the mammalian circadian clock system is considerably more complex than previously believed, also in terms of the cell types that actually contribute to generating the oscillation within the master clock, in the suprachiasmatic nuclei of the hypothalamus. Here we review the evidence that has lead to the identification of a bona fide astrocytic circadian clock, and that of the potential contribution of such clock to the generation of circadian and seasonal rhythmicity in health and in neurodegenerative disorders. Finally, we speculate on the role of the astrocytic clock in determining some of the clinical features of hepatic encephalopathy, a reversible neuropsychiatric syndrome associated with advanced liver disease, which is characterized by transient, profound morphological and functional astrocytic abnormalities, in the absence of significant, structural neuronal changes.

Seasonal variations in photoperiod affect hepatic metabolism of medaka (Oryzias latipes)

Organisms living in temperate regions are sensitive to seasonal variations in the environment; they are known to accumulate energy as fat in their livers during the winter when days are shorter, temperatures are lower, and food is scarce. However, the effect of variations in photoperiod alone on hepatic lipid metabolism has not been well studied. Therefore, in this study, we analyzed lipid metabolism in the liver of medaka, Oryzias latipes, while varying the length of days at constant temperature. Larger amounts of fatty acids accumulated in the liver after 14 days under short‐day conditions than under long‐day conditions. Metabolome analysis showed no accumulation of long‐chain unsaturated fatty acids, but showed a significant accumulation of long‐chain saturated fatty acids. Short‐day conditions induced a reduction in the levels of succinate, fumarate, and malate in the tricarboxylic acid cycle, decreased expression of PPARα, and decreased accumulation of acylcarnitine, which suggested inhibition of lipolysis. In addition, transparent medaka fed on a high‐fat diet under short‐day conditions exhibited greater amounts of fat accumulation and developed fatty liver. The findings of our study will be useful for creating a medaka hepatic steatosis model for future studies of hepatic steatosis‐related diseases.

Molecular economy of nature with two thyrotropins from different parts of the pituitary: pars tuberalis thyroid-stimulating hormone and pars distalis thyroid-stimulating hormone

Thyrotropin (TSH) is classically known to be regulated by negative feedback from thyroid hormones and stimulated by thyrotropin-releasing hormone (TRH) from the hypothalamus. At the end of the 1990s, studies showed that thyrotroph cells from the pars tuberalis (PT) did not have TRH receptors and their TSH regulation was independent from TRH stimulation. Instead, PT-thyrotroph cells were shown to have melatonin-1 (MT-1) receptors and melatonin secretion from the pineal gland stimulates TSH-β subunit formation in PT. Electron microscopy examinations also revealed some important differences between PT and pars distalis (PD) thyrotrophs. PT-TSH also have low bioactivity in the peripheral circulation. Studies showed that they have different glycosylations and PT-TSH forms macro-TSH complexes in the periphery and has a longer half-life. Photoperiodism affects LH levels in animals via decreased melatonin causing increased TSH-β subunit expression and induction of deiodinase-2 (DIO-2) in the brain. Mammals need a light stimulus carried into the suprachiasmatic nucleus (which is a circadian clock) and then transferred to the pineal gland to synthesize melatonin, but birds have deep brain receptors and they are stimulated directly by light stimuli to have increased PT-TSH, without the need for melatonin. Photoperiodic regulations via TSH and DIO 2/3 also have a role in appetite, seasonal immune regulation, food intake and nest-making behaviour in animals. Since humans have no clear seasonal breeding period, such studies as recent ''domestication locus'' studies in poultry are interesting. PT-TSH that works like a neurotransmitter in the brain may become an important target for future studies about humans.

Expression analysis of DIO2, EYA3, KISS1 and GPR54 genes in year-round estrous and seasonally estrous rams

The expression characteristics of the hypothalamic-pituitary-gonadal (HPG) axis-related candidate genes, DIO2, EYA3, KISS1 and GPR54, were analyzed in year-round estrous rams (small-tail Han sheep, STH) and seasonally estrous rams (Sunite sheep, SNT) using qPCR. The results were as follows: DIO2 was mainly expressed in pituitary, and KISS1 was specifically expressed in hypothalamus in the two groups. However, EYA3 and GPR54 were widely expressed in the cerebrum, cerebellum, hypothalamus, pituitary, testis, epididymis, vas deferens and adrenal gland tissues in both breeds, with significant differences in the cerebellum, hypothalamus, pituitary, testis and vas deferens tissues. We speculated that DIO2 and KISS1 may have positive roles in different regions in ram year-round estrus. Moreover, the expression patterns of EYA3 and GPR54 suggested that they may regulate the estrous mode of ram via testis and vas deferens. This is the first study to systematically analyze the expression patterns of HPG axis-related genes in rams.

Circadian clock mechanism driving mammalian photoperiodism

The annual photoperiod cycle provides the critical environmental cue synchronizing rhythms of life in seasonal habitats. In 1936, Bünning proposed a circadian-based coincidence timer for photoperiodic synchronization in plants. Formal studies support the universality of this so-called coincidence timer, but we lack understanding of the mechanisms involved. Here we show in mammals that long photoperiods induce the circadian transcription factor BMAL2, in the pars tuberalis of the pituitary, and triggers summer biology through the eyes absent/thyrotrophin (EYA3/TSH) pathway. Conversely, long-duration melatonin signals on short photoperiods induce circadian repressors including DEC1, suppressing BMAL2 and the EYA3/TSH pathway, triggering winter biology. These actions are associated with progressive genome-wide changes in chromatin state, elaborating the effect of the circadian coincidence timer. Hence, circadian clock-pituitary epigenetic pathway interactions form the basis of the mammalian coincidence timer mechanism. Our results constitute a blueprint for circadian-based seasonal timekeeping in vertebrates.

Reproduction in the Eared Dove: An exception to the classic model of seasonal reproduction in birds?

In avian species living at high altitudes and latitudes, reproductive events are largely controlled by photoperiod, with changes being perceived mainly through encephalic photoreceptors located in the hypothalamus. It is known that during long day periods (reproductive periods), the information transmitted by brain photoreceptors triggers the production of thyroid hormones that regulate GnRH secretion, inducing secretion of pituitary gonadotropins. As a result, gonads develop and grow and the production of gonadal sex hormones, testosterone and estradiol increases (classic gonadal cycle). During short day periods (non-reproductive periods) on the other hand, the gonads regress, and plasma gonadal steroid levels are low. By means of this mechanism, birds synchronize their physiology and reproductive behaviors with seasonal changes in the environment. However, it appears that not all avian species comply with this general reproductive pattern. For example, the Eared Dove (Zenaida auriculata), a South American opportunistic breeding columbiform, has been reported to successfully reproduce throughout the year, making it an interesting avian system for studying the endocrine basis of avian reproduction. In view of a clear lack of seasonal variability in testicular weight and size (the classic gonadal regression/recrudescence cycle) in the male Eared Dove, we examined whether their reproductive aseasonality could be the result of being in a continuous state of reproductive preparedness. Our results show that despite the absence of a marked gonadal cycle in terms of gonadal volume, plasma testosterone levels in males were minimal during autumn-winter, reaching maximum values during spring-summer. This indicates that male gonad function is not seasonal in terms of spermatogenesis but that circulating testosterone levels are correlated with photoperiod, demonstrating an exception to the classic model of reproduction in birds.

Melatonin in the seasonal response of the aphid Acyrthosiphon pisum

Aphids display life cycles largely determined by the photoperiod. During the warm long-day seasons, most aphid species reproduce by viviparous parthenogenesis. The shortening of the photoperiod in autumn induces a switch to sexual reproduction. Males and sexual females mate to produce overwintering resistant eggs. In addition to this full life cycle (holocycle), there are anholocyclic lineages that do not respond to changes in photoperiod and reproduce continuously by parthenogenesis. The molecular or hormonal events that trigger the seasonal response (i.e., induction of the sexual phenotypes) are still unknown. Although circadian synthesis of melatonin is known to play a key role in vertebrate photoperiodism, the involvement of the circadian clock and/or of the hormone melatonin in insect seasonal responses is not so well established. Here we show that melatonin levels in the aphid Acyrthosiphon pisum are significantly higher in holocyclic aphids reared under short days than under long days, while no differences were found between anholocyclic aphids under the same conditions. We also found that melatonin is localized in the aphid suboesophageal ganglion (SOG) and in the thoracic ganglionic mass (TGM). In analogy to vertebrates, insect-type arylalkylamine N-acetyltransferases (i-AANATs) are thought to play a key role in melatonin synthesis. We measured the expression of four i-AANAT genes identified in A. pisum and localized two of them in situ in the insect central nervous systems (CNS). Levels of expression of these genes were compatible with the quantities of melatonin observed. Moreover, like melatonin, expression of these genes was found in the SOG and the TGM.

Quantitative Study of Dual Circadian Oscillator Models under Different Skeleton Photoperiods

The daily proportion of light and dark hours (photoperiod) changes annually and plays an important role in the synchronization of seasonal biological phenomena, such as reproduction, hibernation, and migration. In mammals, the first step of photoperiod transduction occurs in the suprachiasmatic nuclei (SCN), the circadian pacemaker that also coordinates 24-h activity rhythms. Thus, in parallel with its role in annual synchronization, photoperiod variation acutely shapes day/night activity patterns, which vary throughout the year. Systematic studies of this behavioral modulation help understand the mechanisms behind its transduction at the SCN level. To explain how entrainment mechanisms could account for daily activity patterns under different photoperiods, Colin Pittendrigh and Serge Daan proposed a conceptual model in which the pacemaker would be composed of 2 coupled, evening (E) and morning (M), oscillators. Although the E-M model has existed for more than 40 years now, its physiological bases are still not fully resolved, and it has not been tested quantitatively under different photoperiods. To better explore the implications of the E-M model, we performed computer simulations of 2 coupled limit-cycle oscillators. Four model configurations were exposed to systematic variation of skeleton photoperiods, and the resulting daily activity patterns were assessed. The criterion for evaluating different model configurations was the successful reproduction of 2 key behavioral phenomena observed experimentally: activity psi-jumps and photoperiod-induced changes in activity phase duration. We compared configurations with either separate light inputs to E and M or the same light inputs to both oscillators. The former replicated experimental results closely, indicating that the configuration with separate E and M light inputs is the mechanism that best reproduces the effects of different skeleton photoperiods on day/night activity patterns. We hope this model can contribute to the search for E and M and their light input organization in the SCN.

The effect of inflammation on the synthesis of luteinizing hormone and gonadotropin-releasing hormone receptor expression in the pars tuberalis of ewe during different photoperiodic conditions

The study was designed to determine the effect of endotoxin-induced inflammation on luteinizing hormone (LH) synthesis and gonadotropin-releasing hormone (GnRH) receptor expression in the pars tuberalis (PT) of ewes during anestrous season and follicular phase taking into account the time of the day. Moreover, the effect of inflammation on the release of melatonin and its type I receptor gene expression in the PT was also determined. Lipopolysaccharide administration reduced nocturnal release of melatonin only during anestrous season, but it did not influence the gene expression of melatonin type I receptor in the PT. Inflammation inhibited nocturnal increase in the gene and protein expression of LH in the PT during the follicular phase. Since in day-active species nocturnal accumulation of LH protein in the pituitary precedes the LH surge, this lowering of LH content may delay or disturb the surge occurrence. Suppression of LH secretion could have resulted from the decreased sensitivity of the PT on the action of GnRH because inflammation reduced GnRH receptor expression. The study suggests that the ability of endotoxin to suppress LH synthesis in the PT may be another mechanism by which inflammation disturbs reproductive neuroendocrine axis in seasonal breeders.

Infection with phytopathogenic bacterium inhibits melatonin biosynthesis, decreases longevity of its vector, and suppresses the free radical-defense

Vector-borne phytopathogenic bacteria may alter the reproductive fitness, survival, behavior, and metabolism of their vectors. Candidatus Liberibacter asiaticus (CLas) is associated with the Huanglongbing (also known as citrus greening disease), one of the most destructive citrus diseases worldwide, and transmitted by Asian citrus psyllid, Diaphorina citri (Insecta, Hemiptera, Liviidae). The genome sequencing of CLas revealed that it does not have the ability to synthesize tryptophan, the precursor of melatonin, and it must acquire it from its host plant or insect vector to achieve its biologic processes, such as growth and multiplication. Herein, we aimed to develop a GC-MS-SIM-based method to detect the endogenous melatonin from small insects such as D. citri, and to explore the hidden relationship between melatonin content and D. citri-adult survival. Then, we studied the ability of exogenous melatonin supplementation to reverse the negative effects of CLas-infection. Our findings showed that CLas-infection reduced the levels of melatonin and its biosynthetic genes (DcTPHs, DcAAAD, DcSNAT, and DcASMT) of D. citri compared to uninfected insects. In addition, CLas decreased the longevity of its vector, D. citri via the suppression of the free radical-defense associated genes (SODs, GSTs, PODs, and PHGPXs). On the other hand, melatonin supplementation could reverse the negative effects of CLas-infection. Melatonin supplementation enhanced the endogenous melatonin content, melatonin biosynthetic genes, free radical-defense associated genes, and the longevity of both healthy and CLas-infected D. citri. Furthermore, melatonin supplementation decreased the CLas bacterial population within the D. citri psyllids. Based on these findings, we hypothesize that melatonin plays multi-layered defensive roles in D. citri. These roles include acting as a natural antioxidant or as an antibacterial compound.

Timing as a sexually selected trait: the right mate at the right moment

Sexual selection favours the expression of traits in one sex that attract members of the opposite sex for mating. The nature of sexually selected traits such as vocalization, colour and ornamentation, their fitness benefits as well as their costs have received ample attention in field and laboratory studies. However, sexually selected traits may not always be expressed: coloration and ornaments often follow a seasonal pattern and behaviours may be displayed only at specific times of the day. Despite the widely recognized differences in the daily and seasonal timing of traits and their consequences for reproductive success, the actions of sexual selection on the temporal organization of traits has received only scant attention. Drawing on selected examples from bird and mammal studies, here we summarize the current evidence for the daily and seasonal timing of traits. We highlight that molecular advances in chronobiology have opened exciting new opportunities for identifying the genetic targets that sexual selection may act on to shape the timing of trait expression. Furthermore, known genetic links between daily and seasonal timing mechanisms lead to the hypothesis that selection on one timescale may simultaneously also affect the other. We emphasize that studies on the timing of sexual displays of both males and females from wild populations will be invaluable for understanding the nature of sexual selection and its potential to act on differences within and between the sexes in timing. Molecular approaches will be important for pinpointing genetic components of biological rhythms that are targeted by sexual selection, and to clarify whether these represent core or peripheral components of endogenous clocks. Finally, we call for a renewed integration of the fields of evolution, behavioural ecology and chronobiology to tackle the exciting question of how sexual selection contributes to the evolution of biological clocks.This article is part of the themed issue 'Wild clocks: integrating chronobiology and ecology to understand timekeeping in free-living animals'.

Cloning and expression characterization in hypothalamic Dio2/3 under a natural photoperiod in the domesticated Brandt's vole (Lasiopodomys brandtii)

The Dio2/3 gene is related to the photoperiodic response in mammals and plays an important role in the development of gonadal organs and seasonal breeding. Our previous studies have reported synchronous variations in the gonadal mass and photoperiodical transition around the summer solstice in a wild Brandt's vole population, a species with striking seasonal breeding. To investigate the role of the Dio2/3 gene in the control of seasonal breeding in this species, we cloned and characterized its expression levels by high-throughput Real-Time PCR during the period around the summer solstice. We selected a domesticated strain to ensure similar development of samples. The synchronous variation pattern between the Dio2/3 expression levels and gonadal mass around the summer solstice supports the prediction that the Dio2/3 gene plays an important role in the seasonal transition in this species. We suggest that the observed photoperiod response may be triggered by differences in the day length rather than the absolute daylength in this species. However, the similar Dio2/3 gene expression patterns but inconsistent gonadal mass patterns between the domesticated strain and the wild strain in the samples collected on Sep 8th, an absolute nonbreeding stage in the wild, lead us to speculate that the core function of the Dio2/3 gene should be restricted in response to the photoperiod rather than factors directly regulating gonadal development, and this laboratory strain could be used as an animal model to test the mechanism of environmental adaptation.

The pars tuberalis: The site of the circannual clock in mammals?

Accurate timing and physiological adaptation to anticipate seasonal changes are an essential requirement for an organism's survival. In contrast to all other environmental cues, photoperiod offers a highly predictive signal that can be reliably used to activate a seasonal adaptive programme at the correct time of year. Coupled to photoperiod sensing, it is apparent that many organisms have evolved innate long-term timekeeping systems, allowing reliable anticipation of forthcoming environmental changes. The fundamental biological processes giving rise to innate long-term timing, with which the photoperiod-sensing pathway engages, are not known for any organism. There is growing evidence that the pars tuberalis (PT) of the pituitary, which acts as a primary transducer of photoperiodic input, may be the site of the innate long-term timer or "circannual clock". Current research has led to the proposition that the PT-specific thyrotroph may act as a seasonal calendar cell, driving both hypothalamic and pituitary endocrine circuits. Based on this research we propose that the mechanistic basis for the circannual rhythm appears to be deeply conserved, driven by a binary switching cell based accumulator, analogous to that proposed for development. We review the apparent conservation of function and pathways to suggest that these broad principles may apply across the vertebrate lineage and even share characteristics with processes driving seasonal adaptation in plants.

Effect of Seasonal Change on Testicular Protein Expression in White Roman Geese

The purpose of this study was to investigate the change in protein expression in the testes of ganders at various breeding stages. A total of nine 3-year-old male White Roman ganders were used. The blood and testis samples were collected at the nonbreeding, sexual reactivation, and breeding stages for sex hormone analysis and proteomic analysis, respectively. The testicular weight and serum testosterone observed for ganders at the breeding stage were higher than those for ganders at nonbreeding and sexual reactivation stages (P < 0.05). There were 124 protein spots differentially expressed in the testes of ganders at various reproductive stages. A total of 107 protein spots of 74 proteins was identified through mass spectrometry. Most of the differentially expressed proteins were responsible for the molecular functions of protein binding (24%) and catalytic activity (16%). A functional pathway analysis suggested that proteins involved in steroidogenesis, metabolism, and spermatogenesis pathways changed in the White Roman geese at various reproductive stages. In conclusion, ganders at various reproductive stages exhibited different levels of testosterone and protein expression in the testes. The varied levels of the proteins might be essential and unique key factors in seasonal reproduction in ganders.

Diurnal and photoperiodic changes in thyrotrophin-stimulating hormone β expression and associated regulation of deiodinase enzymes (DIO2, DIO3) in the female juvenile chicken hypothalamus

Increased thyrotrophin-stimulating hormone β (TSHβ) expression in the pars tuberalis is assumed to be an early step in the neuroendocrine mechanism transducing photoperiodic information. The present study aimed to determine the relationship between long-photoperiod (LP) and diurnal TSHβ gene expression in the juvenile chicken by comparing LP-photostimulated birds with groups kept on a short photoperiod (SP) for 1 or 12 days. TSHβ expression increased by 3- and 23-fold after 1 and 12 days of LP-photostimulation both during the day and at night. Under both SP and LP conditions, TSHβ expression was between 3- and 14-fold higher at night than in the day, suggesting that TSHβ expression cycles in a diurnal pattern irrespective of photoperiod. The ratio of DIO2/3 was decreased on LPs, consequent to changes in DIO3 expression, although there was no evidence of any diurnal effect on DIO2 or DIO3 expression. Plasma prolactin concentrations revealed both an effect of LPs and time-of-day. Thus, TSHβ expression changes in a dynamic fashion both diurnally and in response to photoperiod.

Assessing enclosure design and husbandry practices for successful keeping and breeding of the Burmese brow antlered deer (Eld's deer, Rucervus eldii thamin) in European zoos

The endangered Burmese brow antlered deer (Rucervus eldii thamin) is a medium sized tropical cervid kept in a number of European zoos. Studbook data and anecdotal reports have suggested that this species suffers from poor reproductive success and relatively high neonatal mortality in captivity. Questionnaires were sent to 10 European zoos, holding 91 (20.71.0) deer, in order to record information on husbandry practices and enclosure design. Studbook analysis was performed to determine reproductive success and mortality values at each of the zoos participating in the study. Statistical analysis was carried out to identify any links between husbandry or enclosure design and the population parameters calculated from the studbook. From the nine zoos that were analyzed in this study, no significant differences were found for population parameters between male and female deer. Neonatal mortality was negatively correlated to enclosure size (in males) and enclosure cover (in females). Positive correlations were found between enclosure cover, average temperature and group size with life expectancy, and negative correlations between enclosure visibility and visitor distance with female life expectancy. These results may be useful for informing husbandry guidelines, although further research into stress responses in captivity is recommended for this species to improve their welfare.

Reproductiveaxis gene regulation during photostimulation and photorefractoriness in Yangzhou goose ganders

Background

The Yangzhou goose is a long-day breeding bird that has been increasingly produced in China. Artificial lighting programs are used for controlling its reproductive activities. This study investigated the regulations of photostimulation and photorefractoriness that govern the onset and cessation of the breeding period.

Results

Increasing the daily photoperiod from 8 to 12 h rapidly stimulated testis development and increased plasma testosterone concentrations, with peak levels being reached 2 months after the photoperiod increase. Subsequently, testicular activities, testicular weight, spermatogenesis, and plasma testosterone concentrations declined steadily and reached to the nadir at 5 months after the 12-hour photoperiod. Throughout the experiment, plasma concentrations of triiodothyronine and thyroxine changed in reciprocal fashions to that of testosterone. The stimulation of reproductive activities caused by the increasing photoperiod was associated with increases in gonadotropin-releasing hormone (GnRH), but decreases in gonadotropin-inhibitory hormone (GnIH) and vasoactive intestinal peptide (VIP) gene messenger RNA (mRNA) levels in the hypothalamus. In the pituitary gland, the levels of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) mRNA abruptly increased during the longer 12-hour photoperiod. The occurrence of photorefractoriness was associated with increased GnIH gene transcription by over 250-fold, together with increased VIP mRNA levels in the hypothalamus, and then prolactin and thyroid-stimulating hormone in the pituitary gland. FSH receptor, LH receptor, and StAR mRNA levels in the testis changed in ways paralleling those of testicular weight and testosterone concentrations.

Conclusions

The seasonal reproductive activities in Yangzhou geese were directly stimulated by a long photoperiod via upregulation of GnRH gene transcription, downregulation of GnIH, VIP gene transcription, and stimulation of gonadotrophin. Development of photorefractoriness was characterized by hyper-regulation of GnIH gene transcription in the hypothalamus, in addition of upregulation of VIP and TRH gene transcription, and that of their receptors, in the pituitary gland.

REV-ERBα regulates Fgf21 expression in the liver via hepatic nuclear factor 6

The circadian clock contributes to the timing of many body functions including metabolism and reproduction. The hepatokine fibroblast growth factor 21 (FGF21) is a critical metabolic regulator involved in modulation of fertility. Here we show that lack of the clock component REV-ERBα elevates FGF21 levels in liver and plasma. At the molecular level, REV-ERBα modulates the expression of FGF21 via the liver-specific hepatic nuclear factor 6 (HNF6). We conclude that REV-ERBα regulates metabolism and reproduction, at least in part, via regulation of Fgf21.

Summary: The hepatokine Fgf21 is transcriptionally regulated by the nuclear receptor REV-ERBα with the hepatocyte-specific factor HNF6 to regulate metabolism and fertility.

Avian biological clock - Immune system relationship

Biological rhythms in birds are driven by the master clock, which includes the suprachiasmatic nucleus, the pineal gland and the retina. Light/dark cycles are the cues that synchronize the rhythmic changes in physiological processes, including immunity. This review summarizes our investigations on the bidirectional relationships between the chicken pineal gland and the immune system. We demonstrated that, in the chicken, the main pineal hormone, melatonin, regulates innate immunity, maintains the rhythmicity of immune reactions and is involved in the seasonal changes in immunity. Using thioglycollate-induced peritonitis as a model, we showed that the activated immune system regulates the pineal gland by inhibition of melatonin production at the level of the key enzyme in its biosynthetic pathway, arylalkylamine-N-acetyltransferase (AANAT). Interleukin 6 and interleukin 18 seem to be the immune mediators influencing the pineal gland, directly inhibiting Aanat gene transcription and modulating expression of the clock genes Bmal1 and Per3, which in turn regulate Aanat.

A domestication related mutation in the thyroid stimulating hormone receptor gene (TSHR) modulates photoperiodic response and reproduction in chickens

The thyroid stimulating hormone receptor gene (TSHR) has been suggested to be a "domestication locus" in the chicken. A strong selective sweep over TSHR in domestic breeds together with significant effects of a mutation in the gene on several domestication related traits, indicate that the gene has been important for chicken domestication. TSHR plays a key role in the signal transduction of seasonal reproduction, which is characteristically less strict in domestic animals. We used birds from an advanced intercross line between ancestral Red Junglefowl (RJF) and domesticated White Leghorn (WL) to investigate effects of the mutation on reproductive traits as well as on TSHB, TSHR, DIO2 and DIO3 gene expression during altered day length (photoperiod). We bred chickens homozygous for either the mutation (d/d) or wild type allele (w/w), allowing assessment of the effect of genotype at this locus while also controlling for background variation in the rest of the genome. TSHR gene expression in brain was significantly lower in both d/d females and males and d/d females showed a faster onset of egg laying at sexual maturity than w/w. Furthermore, d/d males showed a reduced testicular size response to decreased day length, and lower levels of TSHB and DIO3 expression. Additionally, purebred White Leghorn females kept under natural short day length in Sweden during December had active ovaries and lower levels of TSHR and DIO3 expression compared to Red Junglefowl females kept under similar conditions. Our study indicates that the TSHR mutation affects photoperiodic response in chicken by reducing dependence of seasonal reproduction, a typical domestication feature, and may therefore have been important for chicken domestication.

Determination of melatonin in Acyrthosiphon pisum aphids by liquid chromatography-tandem mass spectrometry

Melatonin is a hormone mainly involved in the regulation of circadian and seasonal rhythms in both invertebrates and vertebrates. Despite the identification of melatonin in many insects, its involvement in the insect seasonal response remains unclear. A liquid chromatography tandem mass spectrometry (LC-MS/MS) method has been developed for melatonin analysis in aphids (Acyrthosiphon pisum) for the first time. After comparing two different procedures and five extraction solvents, a sample preparation procedure with a mixture of methanol/water (50:50) was selected for melatonin extraction. The method was validated by analyzing melatonin recovery at three spiked concentrations (5, 50 and 100 pg/mg) and showed satisfactory recoveries (75-110%), and good repeatability, expressed as relative standard deviation (<10%). Limits of detection (LOD) and quantitation (LOQ) were 1 pg/mg and 5 pg/mg, respectively. Eight concentration levels were used for constructing the calibration curves which showed good linearity between LOQ and 200 times LOQ. The validated method was successfully applied to 26 aphid samples demonstrating its usefulness for melatonin determination in insects. This is -to our knowledge- the first identification of melatonin in aphids by LC-MS/MS.

The Effect of a Mutation in the Thyroid Stimulating Hormone Receptor (TSHR) on Development, Behaviour and TH Levels in Domesticated Chickens

The thyroid stimulating hormone receptor (TSHR) has been suggested to be a “domestication locus” in the chicken, due to a strong selective sweep over the gene found in domesticated chickens, differentiating them from their wild ancestor the Red Junglefowl (RJF). We investigated the effect of the mutation on development (incubation time), behaviour and thyroid hormone levels in intercross chickens homozygous for the mutation (d/d), wild type homozygotes (w/w) or heterozygotes (d/w). This allowed an assessment of the effect of genotype at this locus against a random mix of RJF and WL genotypes throughout the rest of the genome, controlling for family effects. The d/d genotype showed a longer incubation time, less fearful behaviours, lower number of aggressive behaviours and decreased levels of the thyroid hormone T4, in comparison to the w/w genotype. The difference between TSHR genotypes (d/d vs. w/w) in these respects mirrors the differences in development and behaviour between pure domesticated White Leghorns and pure RJF chickens. Higher individual T3 and T4 levels were associated with more aggression. Our study indicates that the TSHR mutation affects typical domestication traits, possibly through modifying plasma levels of thyroid hormones, and may therefore have been important during the evolution of the domestic chicken.

Development, regeneration, and evolution of feathers

The feather is a complex ectodermal organ with hierarchical branching patterns. It provides functions in endothermy, communication, and flight. Studies of feather growth, cycling, and health are of fundamental importance to avian biology and poultry science. In addition, feathers are an excellent model for morphogenesis studies because of their accessibility, and their distinct patterns can be used to assay the roles of specific molecular pathways. Here we review the progress in aspects of development, regeneration, and evolution during the past three decades. We cover the development of feather buds in chicken embryos, regenerative cycling of feather follicle stem cells, formation of barb branching patterns, emergence of intrafeather pigmentation patterns, interplay of hormones and feather growth, and the genetic identification of several feather variants. The discovery of feathered dinosaurs redefines the relationship between feathers and birds. Inspiration from biomaterials and flight research further fuels biomimetic potential of feathers as a multidisciplinary research focal point.

Regulation of seasonal reproduction by hypothalamic activation of thyroid hormone

Organisms living outside the tropics measure the changes in the length of the day to adapt to seasonal changes in the environment. Animals that breed during spring and summer are called long-day breeders, while those that breed during fall are called short-day breeders. Although the influence of thyroid hormone in the regulation of seasonal reproduction has been known for several decades, its precise mechanism remained unknown. Recent studies revealed that the activation of thyroid hormone within the mediobasal hypothalamus plays a key role in this phenomenon. This localized activation of the thyroid hormone is controlled by thyrotropin (thyroid-stimulating hormone) secreted from the pars tuberalis of the pituitary gland. Although seasonal reproduction is a rate-limiting factor in animal production, genes involved in photoperiodic signal transduction pathway could emerge as potential targets to facilitate domestication.

Cellular mechanisms and integrative timing of neuroendocrine control of GnRH secretion by kisspeptin

The hypothalamus integrates endogenous and exogenous inputs to control the pituitary-gonadal axis. The ultimate hypothalamic influence on reproductive activity is mediated through timely secretion of GnRH in the portal blood, which modulates the release of gonadotropins from the pituitary. In this context neurons expressing the RF-amide neuropeptide kisspeptin present required features to fulfill the role of the long sought-after hypothalamic integrative centre governing the stimulation of GnRH neurons. Here we focus on the intracellular signaling pathways triggered by kisspeptin through its cognate receptor KISS1R and on the potential role of proteins interacting with this receptor. We then review evidence implicating both kisspeptin and RFRP3--another RF-amide neuropeptide--in the temporal orchestration of both the pre-ovulatory LH surge in female rodents and the organization of seasonal breeding in photoperiodic species.

Minutes, days and years: molecular interactions among different scales of biological timing

Biological clocks are genetically encoded oscillators that allow organisms to keep track of their environment. Among them, the circadian system is a highly conserved timing structure that regulates several physiological, metabolic and behavioural functions with periods close to 24 h. Time is also crucial for everyday activities that involve conscious time estimation. Timing behaviour in the second-to-minutes range, known as interval timing, involves the interaction of cortico-striatal circuits. In this review, we summarize current findings on the neurobiological basis of the circadian system, both at the genetic and behavioural level, and also focus on its interactions with interval timing and seasonal rhythms, in order to construct a multi-level biological clock.

Avian circadian organization: a chorus of clocks

In birds, biological clock function pervades all aspects of biology, controlling daily changes in sleep: wake, visual function, song, migratory patterns and orientation, as well as seasonal patterns of reproduction, song and migration. The molecular bases for circadian clocks are highly conserved, and it is likely the avian molecular mechanisms are similar to those expressed in mammals, including humans. The central pacemakers in the avian pineal gland, retinae and SCN dynamically interact to maintain stable phase relationships and then influence downstream rhythms through entrainment of peripheral oscillators in the brain controlling behavior and peripheral tissues. Birds represent an excellent model for the role played by biological clocks in human neurobiology; unlike most rodent models, they are diurnal, they exhibit cognitively complex social interactions, and their circadian clocks are more sensitive to the hormone melatonin than are those of nocturnal rodents.

Adaptive genetic markers discriminate migratory runs of Chinook salmon (Oncorhynchus tshawytscha) amid continued gene flow

Neutral genetic markers are routinely used to define distinct units within species that warrant discrete management. Human-induced changes to gene flow however may reduce the power of such an approach. We tested the efficiency of adaptive versus neutral genetic markers in differentiating temporally divergent migratory runs of Chinook salmon (Oncorhynchus tshawytscha) amid high gene flow owing to artificial propagation and habitat alteration. We compared seven putative migration timing genes to ten microsatellite loci in delineating three migratory groups of Chinook in the Feather River, CA: offspring of fall-run hatchery broodstock that returned as adults to freshwater in fall (fall run), spring-run offspring that returned in spring (spring run), and fall-run offspring that returned in spring (FRS). We found evidence for significant differentiation between the fall and federally listed threatened spring groups based on divergence at three circadian clock genes (OtsClock1b, OmyFbxw11, and Omy1009UW), but not neutral markers. We thus demonstrate the importance of genetic marker choice in resolving complex life history types. These findings directly impact conservation management strategies and add to previous evidence from Pacific and Atlantic salmon indicating that circadian clock genes influence migration timing.

Thyroid hormone and seasonal regulation of reproduction

Organisms living outside the tropics use changes in photoperiod to adapt to seasonal changes in the environment. Several models have contributed to an understanding of this mechanism at the molecular and endocrine levels. Subtropical birds are excellent models for the study of these mechanisms because of their rapid and dramatic response to changes in photoperiod. Studies of birds have demonstrated that light is perceived by a deep brain photoreceptor and long day-induced thyrotropin (TSH) from the pars tuberalis (PT) of the pituitary gland causes local thyroid hormone activation within the mediobasal hypothalamus (MBH). The locally generated bioactive thyroid hormone, T₃, regulates seasonal gonadotropin-releasing hormone (GnRH) secretion, and hence gonadotropin secretion. In mammals, the eyes are the only photoreceptor involved in photoperiodic time perception and nocturnal melatonin secretion provides an endocrine signal of photoperiod to the PT to regulate TSH. Here, I review the current understanding of the hypothalamic mechanisms controlling seasonal reproduction in mammals and birds.

Establishment of TSH β real-time monitoring system in mammalian photoperiodism

Organisms have seasonal physiological changes in response to day length. Long-day stimulation induces thyroid-stimulating hormone beta subunit (TSHβ) in the pars tuberalis (PT), which mediates photoperiodic reactions like day-length measurement and physiological adaptation. However, the mechanism of TSHβ induction for day-length measurement is largely unknown. To screen candidate upstream molecules of TSHβ, which convey light information to the PT, we generated Luciferase knock-in mice, which quantitatively report the dynamics of TSHβ expression. We cultured brain slices containing the PT region from adult and neonatal mice and measured the bioluminescence activities from each slice over several days. A decrease in the bioluminescence activities was observed after melatonin treatment in adult and neonatal slices. These observations indicate that the experimental system possesses responsiveness of the TSHβ expression to melatonin. Thus, we concluded that our experimental system monitors TSHβ expression dynamics in response to external stimuli.

Circadian regulation of reproduction: from gamete to offspring

Few challenges are more critical to the survival of a species than reproduction. To ensure reproductive success, myriad aspects of physiology and behaviour need to be tightly orchestrated within the animal, as well as timed appropriately with the external environment. This is accomplished through an endogenous circadian timing system generated at the cellular level through a series of interlocked transcription/translation feedback loops, leading to the overt expression of circadian rhythms. These expression patterns are found throughout the body, and are intimately interwoven with both the timing and function of the reproductive process. In this review we highlight the many aspects of reproductive physiology in which circadian rhythms are known to play a role, including regulation of the estrus cycle, the LH surge and ovulation, the production and maturation of sperm and the timing of insemination and fertilisation. We will also describe roles for circadian rhythms in support of the preimplantation embryo in the oviduct, implantation/placentation, as well as the control of parturition and early postnatal life. There are several key differences in physiology between humans and the model systems used for the study of circadian disruption, and these challenges to interpretation will be discussed as part of this review.

Health consequences of circadian disruption in humans and animal models

Daily rhythms in behavior and physiology are programmed by a hierarchical collection of biological clocks located throughout the brain and body, known as the circadian system. Mounting evidence indicates that disruption of circadian regulation is associated with a wide variety of adverse health consequences, including increased risk for premature death, cancer, metabolic syndrome, cardiovascular dysfunction, immune dysregulation, reproductive problems, mood disorders, and learning deficits. Here we review the evidence for the pervasive effects of circadian disruption in humans and animal models, drawing from both environmental and genetic studies, and identify questions for future research.

Iodothyronine deiodinases: a functional and evolutionary perspective

From an evolutionary perspective, deiodinases may be considered pivotal players in the emergence and functional diversification of both thyroidal systems (TS) and their iodinated messengers. To better understand the evolutionary pathway and the concomitant functional diversification of vertebrate deiodinases, in the present review we summarized the highlights of the available information regarding this ubiquitous enzymatic component that represents the final, common physiological link of TS. The information reviewed here suggests that deiodination of tyrosine metabolites is an ancient feature of all chordates studied to date and consequently, that it precedes the integration of the TS that characterize vertebrates. Phylogenetic analysis presented here points to D1 as the oldest vertebrate deiodinase and to D2 as the most recent deiodinase gene, a hypothesis that agrees with the notion that D2 is the most specialized and finely regulated member of the family and plays a key role in vertebrate neurogenesis. Thus, deiodinases seem to be major participants in the evolution and functional expansion of the complex regulatory network of TS found in vertebrates.