Rainbow trout eyed-stage embryos demonstrate melatonin rhythms under light-dark conditions as measured by a newly developed time-resolved fluoroimmunoassay

Involvement of melatonin in transducing moon-related signals into the reproductive network of the female honeycomb grouper Epinephelus merra

Most groupers (genus Epinephelus) inhabiting tropical and subtropical waters exhibit lunar-related reproductive cycles. Their gametes develop synchronously toward and are released around the species-selected moon phase. Periodical changes in cues from the moon are likely used as zeitgeber, and the hypothalamic-pituitary-gonadal (HPG) axis may be activated after cues are perceived by the sensory organ and transduced as internal signals. The objective of this study was to examine weekly changes in mRNA expression profiles of gonadotropin-releasing hormones (gnrh1 and gnrh2) and the β-subunit of gonadotropins (fshβ and lhβ) during the spawning season (May to June) of the female honeycomb grouper Epinephelus merra, which spawns around the full moon period. When mature females were collected based on the lunar cycle, the gonadosomatic index peaked around the full moon. Ovarian histology revealed that oocytes laden with yolk developed toward the full moon and, subsequently, ovulatory follicles appeared around the last quarter moon, confirming lunar-related spawning with a full moon preference. Real-time quantitative polymerase chain reaction analyses revealed high abundances of fshβ and lhβ toward the first quarter moon, whereas concentrations of gnrh1 and gnrh2 increased around the last quarter moon and the first quarter moon, respectively, suggesting that transcription levels of these hormones fluctuate with the lunar cycle. The measurement of melatonin in the eye around the new moon and the full moon revealed that the ocular melatonin content was higher around the new moon than around the full moon, suggesting that the honeycomb grouper can perceive changes in moonlight. In addition, implantation of an osmotic pump containing melatonin into the body cavity of E. merra reduced the transcription levels of gonadotropins, suggesting that melatonin negatively affects hormonal synthesis at the HPG axis. We concluded that melatonin plays an essential role in transducing periodical changes in moonlight and that decreases in melatonin levels from the new moon to the full moon activate the HPG axis for entrainment of gonadal development and spawning.

Effects of Moonlight Exposure on Plasma Melatonin Rhythms in the Seagrass Rabbitfish, Siganus Canaliculatus

Influences of light-dark (LD) cycle and moonlight exposure on plasma melatonin rhythms in the seagrass rabbitfish, Siganus canaliculatus, a lunar synchronized spawner, were determined by time-resolved fluoroimmunoassay (TR-FIA). When the fish were exposed to a natural LD (12:12) cycle, plasma melatonin levels exhibited a clear daily rhythm, with higher levels at midnight and lower levels during the day. These rhythms were not evident under either constant light (LL) or constant dark (DD) conditions. Plasma melatonin levels under LL condition were low and high under DD condition. These results indicate that plasma melatonin rhythms are driven by LD cycle in this species. When the fish were exposed to the 4 lunar phases, plasma melatonin levels around the new moon were significantly higher than during the first quarter moon and the full moon. Exposure to experimentalnewmoonand full moonconditions caused significant increases and decreases of plasma melatonin levels, respectively. The synchronous rhythmicity of melatonin levels in the plasma support the hypothesis that the seagrass rabbitfish perceives moonlight intensity and responds with secretion of melatonin into the bloodstream.

A simple, specific high-throughput enzyme-linked immunosorbent assay (ELISA) for quantitative determination of melatonin in cell culture medium

A simple, specific, high-throughput enzyme-linked immunosorbent assay (ELISA) for quantitative determination of melatonin was developed for directly measuring melatonin in cell culture medium with 10% FBS. This assay adopts a commercial monoclonal melatonin antibody and melatonin-HRP conjugate, so it can be applied in multiple labs rapidly with low cost compared with commercial RIA and ELISA kits. In addition, the procedure is much simpler with only four steps: 1) sample/conjugate incubation, 2) plate washing, 3) TMB color reaction and 4) reading of results. The standards of the assay cover a wide working range from 100 pg/mL to 10 ng/mL. The sensitivity was 68 pg/mL in cell culture medium with 10% FBS and 26 pg/mL in PBS with as little as 25 μL sample volume. The recovery of melatonin from cell culture medium was 101.0%. The principal cross-reacting compound was 5-methoxytryptophol (0.1%). The variation coefficients of the assay, within and between runs, ranged between 6.68% and 15.76% in cell culture medium. The mean linearity of a series diluted cell culture medium sample was 105% (CV=5%), ranging between 98% and 111%, y=5.5263x+0.0646, R(2)=0.99. The assay enables small research and teaching labs to reliably measure this important neurohormone.

Developmental and light-entrained expression of melatonin and its relationship to the circadian clock in the sea anemone Nematostella vectensis

Background

The primary hormone of the vertebrate pineal gland, melatonin, has been identified broadly throughout the eukaryotes. While the role for melatonin in cyclic behavior via interactions with the circadian clock has only been reported in vertebrates, comparative research has shown that the transcription-translation loops of the animal circadian clock likely date to the cnidarian-bilaterian ancestor, leaving open significant questions about the evolutionary origin of melatonin signaling in circadian behavior by interacting with the molecular clock.

Results

Expression of melatonin in adult anemones showed peak expression at the end of light period (zeitgeber time (ZT) = 12) when cultured under diel conditions, coinciding with expression of genes and enzyme activity for members of the melatonin synthesis pathway (tryptophan hydroxylase and hydroxyindol-O-methyltransferase), which also showed rhythmic expression. During embryogenesis and juvenile stages, melatonin showed cyclic oscillations in concentration, peaking in midday. Spatial (in situ hybridization) and quantitative (real-time PCR) transcription of clock genes during development of N. vectensis showed these ‘clock’ genes are expressed early in the development, prior to rhythmic oscillations, suggesting functions independent of a function in the circadian clock. Finally, time-course studies revealed that animals transferred from diel conditions to constant darkness lose circadian expression for most of the clock genes within 4 days, which can be reset by melatonin supplementation.

Conclusions

Our results support an ancient role for melatonin in the circadian behavior of animals by showing cyclic expression of this hormone under diel conditions, light-dependent oscillations in genes in the melatonin synthesis pathway, and the function of melatonin in initiating expression of circadian clock genes in the cnidarian N. vectensis. The differences in expression melatonin and the circadian clock gene network in the adult stage when compared with developmental stages of N. vectensis suggests new research directions to characterize stage-specific mechanisms of circadian clock function in animals.

Moonlight affects mRNA abundance of arylalkylamine N-acetyltransferase in the retina of a lunar-synchronized spawner, the goldlined spinefoot

Melatonin synthesis in the pineal gland and retina shows a rhythmic fashion with high levels at night and is controlled by a rate-limiting enzyme, arylalkylamine N-acetyltransferase (AANAT). A previous study revealed that moonlight suppresses the plasma melatonin levels of the goldlined spinefoot (Siganus guttatus), which exhibits a lunar cycle in its reproductive activity and repeats gonadal development toward and spawning around the first quarter moon. Whether the retina of this species responds to moonlight is unknown. To clarify the photoperceptive ability of this species, we aimed to clone the full-length cDNA of Aanat1 (sgAanat1) from the retina and examine its transcriptional pattern under several daylight and moonlight regimes. The full-length sgAanat1 cDNA (1,038 bp) contained a reading frame encoding a protein of 225 amino acids, which was highly homologous to AANAT1 of other teleosts. Reverse transcription-polymerase chain reaction (PCR) analysis revealed that among the tissues tested, sgAanat1 fragments were expressed exclusively in the retina. Real-time quantitative PCR analysis revealed that sgAanat1 fluctuated with high abundance at night under light-dark cycle and at subjective night under constant darkness, but not under constant light. These results suggest that sgAanat1 is regulated by both the external light signal and internal clock system. The abundance of sgAanat1 in the retina was higher at the culmination time around new moon than full moon phase. Additionally, exposing fish to brightness around the full moon period suppressed sgAanat1 mRNA abundance. Thus, moonlight is perceived by fish and has an impact on melatonin fluctuation in the retina.

Measurement of melatonin in body fluids: standards, protocols and procedures

BACKGROUND AND PURPOSE

The circadian rhythm of melatonin in saliva or plasma, or of the melatonin metabolite 6-sulfatoxymelatonin (a6MTs) in urine, is a defining feature of suprachiasmatic nucleus (SCN) function, the body's endogenous oscillatory pacemaker. The primary objective of this review is to ascertain the clinical benefits and limitations of current methodologies employed for detection and quantification of melatonin in biological fluids and tissues.

DATA IDENTIFICATION

A search of the English-language literature (Medline) and a systematic review of published articles were carried out.

STUDY SELECTION

Articles that specified both the methodology for quantifying melatonin and indicated the clinical purpose were chosen for inclusion in the review.

DATA EXTRACTION

The authors critically evaluated the methodological issues associated with various tools and techniques (e.g. standards, protocols, and procedures).

RESULTS OF DATA SYNTHESIS

Melatonin measurements are useful for evaluating problems related to the onset or offset of sleep and for assessing phase delays or advances of rhythms in entrained individuals. They have also become an important tool for psychiatric diagnosis, their use being recommended for phase typing in patients suffering from sleep and mood disorders. Additionally, there has been a continuous interest in the use of melatonin as a marker for neoplasms of the pineal region. Melatonin decreases such as found with aging are or post pinealectomy can cause alterations in the sleep/wake cycle. The development of sensitive and selective methods for the precise detection of melatonin in tissues and fluids has increasingly been shown to have direct relevance for clinical decision making.

CONCLUSIONS

Due to melatonin's low concentration, as well as the coexistence of numerous other compounds in the blood, the routine determination of melatonin has been an analytical challenge. The available evidence indicates however that these challenges can be overcome and consequently that evaluation of melatonin's presence and activity can be an accessible and useful tool for clinical diagnosis.

Dopaminergic activity in the brain of a tropical wrasse in response to changes in light and hydrostatic pressure

Many tropical wrasses show a daily pattern of spawning with gamete release typically near daytime high tide. The environmental cues the fish obtains from day-night and tidal cycles to ensure spawning synchrony and how those cues are transduced, however, are not fully understood. To gain insight into these issues, the involvement of monoamines in mediating endogenous day-night and tidal rhythms in the threespot wrasse, Halichoeres trimaculatus, were examined. Levels of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC, a metabolite of DA), serotonin (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA, a metabolite of 5-HT) in the brain of the fish were measured with high-performance liquid chromatography and electrochemical detection. DOPAC and the metabolic rate of DA activity (DOPAC/DA) were found to increase during the day and decrease during the night for fish held under a natural photoperiod. Fish acclimated to a 12:12 light-dark cycle and to constant dark conditions exhibited similar changes, whereas fish acclimated to constant light conditions exhibited little or no change. Intraperitoneal injection of melatonin resulted in a significant reduction in DOPAC/DA. Furthermore, DOPAC/DA was significantly lower in fish held at 3m compared to 0m depth, suggesting that hydrostatic pressure influences DA metabolic rate. These results indicate that light and hydrostatic pressure control dopaminergic turnover in the brain of threespot wrasse. Day-night and tidal changes in these two factors therefore may be the main environmental cues the fish uses to synchronize its spawning activity.

Melatonin concentrations during larval and postlarval development of gilthead sea bream Sparus auratus: more than a time-keeping molecule?

In this study, melatonin (MEL) and thyroxine (T(4)) concentrations were measured during larval and postlarval development of gilthead sea bream Sparus auratus Hormones were measured in whole bodies of larvae or the head and trunk of postlarvae after 67 days of exposure to constant light, 24L:0D, constant darkness, 0L:24D or 12L:12D and in the plasma of 6 month juveniles kept under the 12L:12D, 0L:24D and 24L:0D regimes. High MEL concentrations in larvae suggested a distinct role of MEL in early organogenesis and development of S. auratus. In larvae, the gastro-intestinal tract seemed to be an important extrapineal and extraretinal source of MEL. No endogenous rhythm of MEL synthesis was demonstrated in 67 day larvae; however, in 6 month juveniles, it was evident. At early ontogenesis of S. auratus, the role of MEL is probably related mostly to the control of development and protection against free radicals, whereas its action as a time-keeping molecule develops later. The increase in T(4) concentration during the S. auratus larva-juvenile transition, i.e. between 50 and 70 days post-hatch, which was observed concurrently with the decrease of MEL concentration, may suggest an inverse relationship between T(4) and MEL.

Profiling of melatonin in the model tomato (Solanum lycopersicum L.) cultivar Micro-Tom

Melatonin exists in a considerable variety of plant species. However, the physiological roles of melatonin in plants are not well understood. In this study, the distribution and accumulation of melatonin during leaf and fruit development were analyzed in Micro-Tom, a model cultivar of tomato (Solanum lycopersicum L.). Melatonin was extracted using an acetone-methanol method and measured by enzyme-linked immunosorbent assay. Melatonin was detected in leaves, stems, roots, flowers, fruits, seedlings and seeds in the range of 1.5-66.6 ng/g fresh weight, with seeds containing the highest concentration of melatonin. In fruits and leaves, melatonin concentrations varied depending on the developmental stage, suggesting that melatonin controls some of the processes involved in plant maturation.

Melatonin and its synthesizing enzymes (arylalkylamine N-acetyltransferase-like and hydroxyindole-O-methyltransferase) in avian eggs and early embryos

The presence of melatonin and the enzymes (transcripts and activities) involved in its synthesis, i.e. arylalkylamine N-acetyltransferase (AA-NAT) and hydroxyindole-O-methyltransferase (HIOMT), was investigated in the eggs and early embryos of Japanese quail at Hamburger-Hamilton stages 1-10. Melatonin was present in the egg yolk (approximately 70 pg/g) and albumen (approximately 20 pg/g). The average content of melatonin was approximately 416 pg/egg. AA-NAT and HIOMT transcripts were present in the oocytes, blastoderms, and ovarian follicles. AA-NAT-like and HIOMT activities were detected in quail egg yolk. The activity of AA-NAT in yolk was comparable with that found in the pineal gland when calculated per milligram of yolk or pineal gland, but was significantly lower when re-calculated per milligram of protein in the yolk or pineal gland. AA-NAT-like activity was also identified in the ovarian follicles. Low HIOMT activity was detected in yolk, but not in the ovarian follicle. Both enzymes were essentially absent from early embryos although some residual activities, probably of yolk origin, were present in the stage 1 embryo. Melatonin and all the constituents needed for its synthesis (serotonin, AA-NAT and HIOMT activities) are contained within the avian yolk and could be used by the embryo from the very beginning of its development. The role of extrapineal melatonin in early avian development may be in protecting the embryo from the action of free radicals formed during intensive embryonic metabolism and/or it may participate (together with serotonin) in a 'diffuse neuroendocrine system' acting at early developmental stages, before differentiation of the nervous system.

Profiles of alpha-melanocyte-stimulating hormone in the Japanese flounder as revealed by a newly developed time-resolved fluoroimmunoassay and immunohistochemistry

Profiles of alpha-melanocyte-stimulating hormone (alpha-MSH) in the Japanese flounder were examined by a newly developed time-resolved fluoroimmunoassay (TR-FIA) and immunohistochemistry. A TR-FIA for alpha-MSH was newly developed, and its levels in the pituitary gland and plasma of Japanese flounder reared in a white or black tank for 5 months were compared. A competitive assay using two antibodies was performed among secondary antibodies in the solid phase, alpha-MSH antibodies, samples, and europium-labeled Des-Ac-alpha-MSH. The sensitivity of the assay, defined as twice the standard deviation at a zero dose, was 0.98 ng/ml (49 pg/well). The intra- and interassay coefficients of variation of the assay were 8.8% (n=8) and 17.3% (n=5), respectively, at about 50% binding. Cross-reactivities of Des-Ac-alpha-MSH and Di-Ac-alpha-MSH were about 100%. Cross-reactivities of adrenocorticotropic hormone, salmon gonadotropin-releasing hormone (sGnRH), and chicken GnRH-II were less than 0.2%, and that of melanin-concentrating hormone was less than 2.0% at 50% binding. Displacement curves of serially twofold-diluted hypothalamus extract, pituitary gland extract, and plasma extract of Japanese flounder with the assay buffer were parallel to the alpha-MSH standard curve. Moreover, displacement curves of serially twofold-diluted hypothalamus and/or pituitary gland extract of masu salmon, goldfish, red seabream, Japanese eel, tiger puffer, and barfin flounder with the assay buffer were also parallel to the alpha-MSH standard. In Japanese flounder, total immunoreactive (ir)-alpha-MSH levels in the pituitary gland were lower in the black tank, whereas those in the plasma tended to be higher in the black tank, suggesting that the synthesis and release of alpha-MSH are higher in the black tank. alpha-MSH-ir cells were detected in the pars intermedia and a small part of the pars distalis of the pituitary gland. alpha-MSH-ir cell bodies were located in the basal hypothalamus and alpha-MSH-ir fibers were distributed not only in the hypothalamus but also in the telencephalon, midbrain, cerebellum, and medulla oblongata, suggesting that alpha-MSH functions as a neuromodulator in the brain.

A direct influence of moonlight intensity on changes in melatonin production by cultured pineal glands of the golden rabbitfish, Siganus guttatus

Rabbitfish are a restricted lunar-synchronized spawner that spawns around a species-specific lunar phase. It is not known how the fish perceive changes in cues from the moon. One possible explanation is that rabbitfish utilize changes in moonlight intensity to establish synchrony. The purpose of the present study was to examine whether or not the pineal gland of the golden rabbitfish can directly perceive changes in moonlight intensity. Isolated pineal glands were statically cultured under natural or artificial light conditions and melatonin secreted into the culture medium was measured using a time-resolved fluoroimmunoassay. Under an artificial light/dark cycle, melatonin secretion significantly increased during the dark phase. Under continuous light conditions, melatonin secretion was suppressed, while culture under continuous dark conditions seemed to duplicate melatonin secretion corresponding to the light/dark cycle in which the fish were acclimated. When cultured pineal glands were kept under natural light conditions on the dates of the full and the new moon, small amounts of melatonin were secreted at night. Moreover, exposure of cultured pineal glands to artificial and natural light conditions resulted in a significant decrease of melatonin secretion within 2 hr. These results suggest that the isolated pineal gland of golden rabbitfish responds to environmental light cycles and that 'brightness' of the night moon has an influence on melatonin secretion from the isolated pineal gland.

Transition from embryonic to adult transcription pattern of serotonin N-acetyltransferase gene in avian pineal gland

The study reports the change of transcription pattern of serotonin N-acetyltransferase gene and melatonin receptor genes during ontogenesis of the avian pineal gland. The RT-PCR technique was used to investigate the expression of the arylalkylamine N-acetyltransferase (AA-NAT) and melatonin receptor genes during development of the pineal glands isolated from Japanese quail (Coturnix coturnix japonica) embryos incubated from 3 days on until hatching (17 days), and in some organs (pineal, brain hemisphere, eye, leg, heart) of the 3-day-old quail embryo. It was shown that two phases of AA-NAT expression are observed during pineal gland development. The first, embryonic-type phase, lasts from the beginning until 7-10 days of incubation, and is marked by the presence of two RT-PCR products for AA-NAT: the shorter mature form without intron (238 bp), and the longer form (323 bp) containing an unprocessed intron of 85 bp. The second, adult-type phase is characterized by the presence of a single mature transcript, containing no intron; it starts from 7 to 10 days of incubation and lasts until hatching and in the adult pineal. The duration of this transition time from the embryonic to the adult transcription pattern in the quail pineal gland from 7 to 10 days of incubation we attribute to asynchronic embryo development, because quail chicks usually hatch between the 16th and 19th day of incubation. Analysis of the AA-NAT protein sequences for chick and quail (GeneBank accession no. U 46 502 and AF 007 068, respectively) revealed their perfect homology with the part of protein read from the sequence present in the adult-type phase of the pineal gland (the RT-PCR product of 238 bp). The presence of the intron (in the 323 bp RT-PCR product, accession no. AY 197 460) in the embryonic-phase of the pineal gland changes the reading frame of the mRNA sequence and the hypothetical resulting protein loses its homology with the chick and quail AA-NAT enzyme starting with 105th amino acid of the complete chick AA-NAT protein comprising 205 amino acids (accession no. U 46 502). In the whole embryos at stages 1-8 (according to the Hamburger-Hamilton classification) both RT-PCR products with and without intron were consistently found, and individual tissues from 3-day-old embryos also produced two AA-NAT products, i.e., the expression was of the embryonic-type. At the time of transition from the embryonic to the adult AA-NAT transcription pattern, in 7-11-day-old embryos, all three melatonin receptor transcripts (mel-1a, mel-1b, and mel-1c) were observed in the pineals, without consistent modifications of the band intensity. In the adult pineal, a single mature AA-NAT transcript was present as well as all three melatonin receptor transcripts, usually with preferential expression of the mel-1a band. The transition time from the embryonic to adult AA-NAT expression pattern coincides well with the acquisition of functional activity and the appearance of melatonin synthesis in the embryonic pineal reported for chicken, as related to quail. We suggest that the change in transcription pattern of the AA-NAT gene may reflect another, still unknown mechanism of regulating AA-NAT activity during ontogenesis, at the level of mRNA processing, whose specificity (or not) for embryonic development we wish to establish in the future.

Embryonic and post-embryonic expression of arylalkylamine N-acetyltransferase and melatonin receptor genes in the eye and brain of chum salmon (Oncorhynchus keta)

Melatonin and arylalkylamine N-acetyltransferase (AANAT), the rate-limiting enzyme in melatonin synthesis, have taken on special importance in vertebrate circadian biology. Recent identification of genes encoding two AANAT (AANAT(1) and AANAT(2)) and two subtypes of melatonin receptor (Mel-R; Mel(1a) and Mel(1b)) in several fish species has led to rapid advances in characterizing the physiological roles of melatonin. In the present study, partial cDNAs encoding these four genes were cloned from the eye and brain of chum salmon (Oncorhynchus keta). Based on the nucleotide sequences, we developed highly sensitive real-time PCR systems for these four mRNAs. The development of daily rhythmicity in AANAT(1), AANAT(2), Mel(1a), and Mel(1b) transcript levels was examined in the eye and brain of chum salmon during embryonic and post-embryonic stages (from day -9 to day +180). In a parallel experiment, ocular and brain melatonin levels were measured by radioimmunoassay. Parallelism in developmental changes and in circadian rhythms of AANAT mRNAs and melatonin levels in the eye and the brain supports a hypothesis that the developmental increases of nocturnal melatonin levels results partly from the elevated transcription of AANAT genes. Moreover, abundant expression of AANAT and Mel-R mRNAs in the optic tectum, thalamus, hypothalamus, cerebellum, and eye indicates possible roles of melatonin in visual processing and neuroendocrine regulation, through which melatonin might be involved in migratory behavior of chum salmon.

Perception and possible utilization of moonlight intensity for reproductive activities in a lunar-synchronized spawner, the golden rabbitfish

Rabbitfishes are known to spawn synchronously around the species-specific lunar phase. It is considered that they perceive and utilize cues from the moon in order to be synchronized gonadal development and spawning with the lunar cycle. Using the golden rabbitfish, Siganus guttatus, which spawns synchronously around the first quarter moon during the reproductive season, we measured the fluctuation of melatonin levels and examined the response of the fish to moonlight intensity. Daily fluctuation of melatonin concentration in the blood of golden rabbitfish showed low levels during daytime and high levels during night-time, suggesting that melatonin functions in the perception and utilization of photoperiod. Plasma melatonin concentration at the new moon was higher than that at the full moon. When the fish were exposed to moonlight at midnight of the both moon phases, the melatonin concentrations decreased to the control levels. These results show that the fish possibly perceive moonlight intensity and plasma melatonin fluctuates according to 'lightness' at a point of night. At the first spawning period (experiment was started one month before the spawning), the fish reared under natural conditions spawned at the expected spawning dates, whereas the fish reared under the constant darkness and lightness of night did not spawn. At the second spawning period (experiment was started 2 weeks before the spawning), the fish reared under the conditions of natural and constant darkness of night spawned but not that of constant lightness of night. It is possible that night conditions are related to synchronous gonadal development and spawning in the golden rabbitfish.

Daily variations in melatonin binding sites in the masu salmon brain

Daily variations in melatonin binding sites in the brain of underyearling masu salmon Oncorhynchus masou were examined by radioreceptor assay using 2-[125I]iodomelatonin as the radioligand. Fish were reared under a natural photoperiod in July and sampled eight times at 3 h intervals from 12:00 to 09:00 h. Plasma melatonin levels showed robust daily rhythms in both precocious males and immature females, with high and low levels during night and day, respectively. The affinity (Kd) and density (Bmax) of melatonin binding sites in the brain also showed similar variations. There were significant positive correlations between the plasma melatonin levels and the Kd or the Bmax in immature females and between the Kd and Bmax values in both precocious males and immature females. These results indicate that melatonin binding sites in the brain showed daily variations under a natural photoperiod in masu salmon.

Presence and developmental regulation of serotonin N-acetyltransferase transcripts in oocytes and early quail embryos (Coturnix coturnix japonica)

By RT-PCR two transcripts for arylalkylamine N-acetyltransferase (AA-NAT; serotonin N-acetyltransferase; EC 2.3.1.87), the key enzyme in melatonin synthesis, were found, for the first time, in the oocytes and blastoderms from freshly laid eggs (323- and 238-bp RT-PCR products), and one (238-bp product) in the pineal gland of Japanese quail (Coturnix coturnix japonica). The two products differed by an intron of 85-bp present in the 323-bp band and absent from the 238-bp band. The identity of the products was confirmed by restriction analysis and sequencing. The ratio of the 323:238-bp bands changed during oogenesis from approximately 17:1 in small 3-mm oocytes to approximately 4:1 in immature vitellogenic oocytes and approximately 1:1 in mature, preovulatory oocytes; it was reversed to approximately 0.2:1 in blastoderms from fertile freshly laid eggs, corresponding to embryo of approximately 40,000 cells. It is proposed that the longer 323-bp product, containing an intron, represents a translationally inactive form of the transcript, stored in maternal RNA. The shorter 238-bp product lacking an intron may represent the mature active AA-NAT mRNA found in the pineal gland and in early embryos, and-to a lower proportion-in older oocytes. These data constitute the first direct proof of an intron sequence in maternal RNA of avian oocyte. It is possible that differential processing of the immature mRNA is part of a transcriptional regulation mechanism of AA-NAT activity. A possible role of extrapineal melatonin in early avian development is discussed.