Ultradian oscillation in expression of four melatonin receptor subtype genes in the pineal gland of the grass puffer, a semilunar-synchronized spawner, under constant darkness

Melatonin receptor gene expression as well as melatonin synthesis and secretion activities were examined in the pineal gland of the grass puffer, which exhibits unique lunar/tidal cycle-synchronized mass spawing: spawning occurs before high tide on the day of spring tide during spawing season. Melatonin synthesizing activity was assessed by the abundance of arylalkylamine N-acetyltransferase 2 (AANAT2) mRNA. The amount of aanat2 mRNA was low during light phase and initiated to increase after the light was turned off. The secretion of melatonin from primary pineal organ culture was stimulated after the light was turned off and ceased immediately after the light was turned on. The expression levels of four melatonin receptor subtype genes (mel 1a 1.4, mel 1a 1.7, mel1b, and mel1c) showed synchronous variations, and the levels tended to be high during the dark phase under light/dark conditions. These results suggest that the action of melatonin on the pineal gland is highly dependent on light and photoperiod, possibly with stronger action during night time. Under constant darkness, the expression of four melatonin receptor subtype genes showed unique ultradian oscillations with the period of 14.0-15.4 h, suggesting the presence of a circatidal oscillator in the pineal gland. The present results indicate that melatonin may serve local chronobiological functions in the pineal gland. These cyclic expressions of melatonin receptor genes in the pineal gland may be important in the control of the lunar/tidal cycle-synchronized mass spawning in the grass puffer.

Synthesis of DNA fragments containing 2′-deoxy-4′-selenonucleoside units using DNA polymerases: comparison of dNTPs with O, S and Se at the 4′-position in replication

The first synthesis of 4′-selenoDNA was achieved using 4′-selenothymidine triphosphate by taking advantage of its bioequivalence against DNA polymerases.

Differential expression patterns of PQRFamide peptide and its two receptor genes in the brain and pituitary of grass puffer during the reproductive cycle

Pain-modulatory neuropeptides, PQRFamide (PQRFa) peptides, have recently been implicated in the regulation of reproduction in fish. As a first step toward investigating the role of PQRFa peptides on reproductive function in the grass puffer Takifugu niphobles, which is a semilunar spawner, we cloned genes encoding PQRFa peptide precursor (pqrfa) and its two types of receptors (pqrfa-r1 and pqrfa-r2), and examined changes in their expression levels in the brain and pituitary over several months during the reproductive cycle. The grass puffer PQRFa peptide precursor of 126 amino acid residues contains two putative PQRFa peptides, PQRFa-1 and PQRFa-2, which correspond to NPFF and NPAF in other vertebrates, respectively. The grass puffer PQRFa-R1 and PQRFa-R2 consist of 426 and 453 amino acid residues, respectively, and contain distinct characteristics of G-protein coupled receptors. These three genes were exclusively expressed in the brain and pituitary. The expression levels of pqrfa and pqrfa-r1 were significantly increased during the late stage of sexual maturation, but low in the spawning fish just after releasing sperms and eggs. Therefore, the grass puffer PQRFa peptide may have a role in the late stage of sexual maturation before spawning via PQRFa-R1. In contrast, the pqrfa-r2 expression showed maximum levels in the spawning fish and in the post-spawning period. The present results provide fundamental data suggesting that the grass puffer PQRFa peptide may have multiple roles in the control of reproduction that are dependent on the reproductive stages.

Diurnal and circadian oscillations in expression of kisspeptin, kisspeptin receptor and gonadotrophin-releasing hormone 2 genes in the grass puffer, a semilunar-synchronised spawner

In seasonally breeding animals, the circadian and photoperiodic regulation of neuroendocrine system is important for precisely-timed reproduction. Kisspeptin, encoded by the Kiss1 gene, acts as a principal positive regulator of the reproductive axis by stimulating gonadotrophin-releasing hormone (GnRH) neurone activity in vertebrates. However, the precise mechanisms underlying the cyclic regulation of the kisspeptin neuroendocrine system remain largely unknown. The grass puffer, Takifugu niphobles, exhibits a unique spawning rhythm: spawning occurs 1.5-2 h before high tide on the day of spring tide every 2 weeks, and the spawning rhythm is connected to circadian and lunar-/tide-related clock mechanisms. The grass puffer has only one kisspeptin gene (kiss2), which is expressed in a single neural population in the preoptic area (POA), and has one kisspeptin receptor gene (kiss2r), which is expressed in the POA and the nucleus dorsomedialis thalami. Both kiss2 and kiss2r show diurnal variations in expression levels, with a peak at Zeitgeber time (ZT) 6 (middle of day time) under the light/dark conditions. They also show circadian expression with a peak at circadian time 15 (beginning of subjective night-time) under constant darkness. The synchronous and diurnal oscillations of kiss2 and kiss2r expression suggest that the action of Kiss2 in the diencephalon is highly dependent on time. Moreover, midbrain GnRH2 gene (gnrh2) but not GnRH1 or GnRH3 genes show a unique semidiurnal oscillation with two peaks at ZT6 and ZT18 within a day. The cyclic expression of kiss2, kiss2r and gnrh2 may be important in the control of the precisely-timed diurnal and semilunar spawning rhythm of the grass puffer, possibly through the circadian clock and melatonin, which may transmit the photoperiodic information of daylight and moonlight to the reproductive neuroendocrine centre in the hypothalamus.

Accumulation of organotins in wharf roach (Ligia exotica Roux) and its ability to serve as a biomonitoring species for coastal pollution

In this study, we measured the accumulation of tributyltin (TBT) in wharf roach (Ligia exotica Roux) and examined the species' ability to be used for TBT biomonitoring in coastal environments. In an exposure test, wharf roach were exposed to TBT via diet for 2d. TBT was accumulated in wharf roach, and its metabolite dibutyltin was detected. The concentrations of these compounds gradually decreased during the depuration period, but they were still detected 12d after exposure ceased (TBT 290±140ng/g; dibutyltin 1280±430ng/g). The biological half-life of TBT in wharf roach was estimated to be about 4d. In a field study conducted in 2011-2012, wharf roach were collected from 15 coastal sites in Japan and 3 sites in Manado, Indonesia. TBT was detected in both Japanese and Indonesian samples. The highest concentration of TBT was found in wharf roach collected at Bitung ferry port, Manado (57.9±16.5ng/g), which is close to a shipyard, and the highest concentration at a Japanese site was 12.3±6.2ng/g. Thus, we were able to detect organotins in the coastal environments by testing wharf roach, suggesting that L. exotica might serve as a good bioindicator for monitoring organotin pollution.

Hypothalamic brain-derived neurotrophic factor regulates glucagon secretion mediated by pancreatic efferent nerves

Understanding the molecular mechanism of the regulation of glucagon secretion is critical for treating the dysfunction of α cells observed in diabetes. Glucagon-like peptide (GLP)-1 analogues reduce plasma glucagon and are assumed to contribute to their action to lower blood glucose. It has previously been demonstrated that the central administration of brain-derived neurotrophic factor (BDNF) improves glucose metabolism by a mechanism independent of feeding behaviour in obese subjects. Using male rats, we examined whether BDNF influences glucagon secretion from α cells via the the central nervous system. We investigate whether: (i) the central infusion of BDNF stimulates glucagon and/or insulin secretion via the pancreatic efferent nerve from the hypothalamus; (ii) the intraportal infusion of GLP-1 regulates glucose metabolism via the central and peripheral nervous system; and (iii) BDNF receptor and/or BDNF-positive fibres are localised near α cells of islets. The portal glucagon level decreased with the central administration of BDNF (n = 6, in each; P < 0.05); in contrast, there was no significant change in portal insulin, peripheral glucagon and insulin levels with the same treatment. This reduction of glucagon secretion was abolished by pancreatic efferent denervation (n = 6, in each; P < 0.05). In an immunohistochemical study, pancreatic α cells were stained specifically with BDNF and tyrosine-related kinase B, a specific receptor for BDNF, and α cells were also co-localised with BDNF. Moreover, intraportal administration of GLP-1 decreased glucagon secretion, as well as blood glucose, whereas it increased the BDNF content in the pancreas; these effects were inhibited with the central infusion of BDNF antibody (n = 6, in each; P < 0.05). BDNF and GLP-1 affect glucose metabolism and modulate glucagon secretion from pancreatic α cells via the central and peripheral nervous systems.

Molecular neuroendocrine basis of lunar-related spawning in grass puffer

Grass puffer, Takifugu niphobles, exhibits unique spawning behavior: it spawns on beach in semilunar cycles during spring tide in early summer. The fish aggregate at certain seashore locations several hours before high tide every two weeks. To explore the molecular and neuroendocrine mechanisms underlying the regulation of the lunar-related spawning rhythm, seasonal and cyclic variations in gene expression for hypothalamic neuropeptides related to reproduction were examined by quantitative real-time PCR. The expression levels of genes for gonadotropin-releasing hormone, kisspeptin, LPXRFamide peptide and PQRFamide peptide in the hypothalamus varied differently depending on reproductive stage and gender, suggesting their specific roles in reproduction. In the spawning period, the expression levels of LPXRFamide peptide and its receptor genes showed diurnal and circadian variations in association with the expression of four subtypes of melatonin receptor genes. Together with the nocturnal secretion of melatonin from the pineal gland, melatonin may play an important role in transmitting the photoperiodic information of moonlight to the reproductive neuroendocrine center in the hypothalamus of grass puffer.

Computer-Aided Diagnosis Scheme for Detection of Unruptured Intracranial Aneurysms in MR Angiography

The detection of unruptured intracranial aneurysms is a major subject in magnetic resonance angiography (MRA) images. However,it is difficult for radiologists to detect small aneurysms on the maximum intensity projection (MIP) images, because adjacent vessels overlap with the aneurysm. The purpose of this study was to develop an automated computerized detection of aneurysms in order to assist radiologists' interpretation as a "second opinion." The vessels were first segmented from background by use of gray-level thresholding and region growing technique. The gradient concentrate (GC) filter was then applied to the segmented vessels for enhancement of aneurysm. The initial aneurysm candidate was identified in the GC image with a gray level threthold. For removal of false positives (FPs), we determined three features, i.e.,size,sphericity, and mean value of GC image in each of the candidate regions. Finally, the rule-based schemes with these features and quadratic discriminant analysis were applied for distinction between aneurysms and FPs. The sensitivity of our method for detection of aneurysms was 100% (7/7) with 1.85 FPs per patient. With our computerized scheme, all aneurysms were detected correctly with low FP rates, and would be useful in assisting radiologists for identifying correct aneurysms and for reducing the interpretation time.

Identification and gene expression analyses of ghrelin in the stomach of Pacific bluefin tuna (Thunnus orientalis)

Full length cDNA and gene encoding ghrelin precursor and mature ghrelin peptide were identified from the stomach of Pacific bluefin tuna, Thunnus orientalis, which has unique metabolic physiology and high commercial value at fishery markets. Quantitative expression analysis was conducted for the gastric ghrelin and pepsinogen 2 genes during the early stage of somatic growth from the underyearling to yearling fish. The full length cDNA of bluefin tuna ghrelin precursor has a length of 470bp and the deduced precursor is composed of 107 amino acids. The ghrelin gene is 1.9kbp in length and has a 4 exon-3 intron structure. The major form of mature ghrelin in the stomach was an octanoylated 20-amino acid peptide with C-terminal amidation, while overall 12 different forms of ghrelin peptides, including short form of 18-amino acid peptide and seven kinds of acyl modifications were identified. The expression profiles of the gastric ghrelin and pepsinogen 2 genes showed no significant changes related to the early growth stages. The present results suggest that digestive physiology has already been functional in this growth stage of the juvenile bluefin tuna and ghrelin may have a role in the sustained digestive and metabolic activities.