Expression of type II iodothyronine deiodinase marks the time that a tissue responds to thyroid hormone-induced metamorphosis in Xenopus laevis

The thyroid gland synthesizes thyroxine (T4), which passes through the larval tadpole's circulatory system. The enzyme type II iodothyronine deiodinase (D2) converts thyroxine (T4) to the active hormone 3,5,3'-triiodothyronine (T3) in peripheral tissues. An early response to thyroid hormone (TH) in the Xenopus laevis tadpole is the stimulation of cell division in cells that line the brain ventricles, the lumen of the spinal cord, and the limb buds. These cells express constitutively high levels of D2 mRNA. Exogenous T4 induces early DNA synthesis in brain, spinal cord, and limb buds as efficiently as T3. The deiodinase inhibitor iopanoic acid blocks T4- but not T3-induced cell division. At metamorphic climax, both TH-induced cell division and D2 expression decrease in the brain. Then D2 expression appears in late-responding tissues including the anterior pituitary, the intestine, and the tail where cell division is reduced or absent. Therefore, constitutive expression of D2 occurs in the earliest target tissues of TH that will grow and differentiate, while TH-induced expression of D2 takes place in late-responding tissues that will remodel or die. This pattern of constitutive and induced D2 expression contributes to the timing of metamorphic changes in these tissues.     

Inhibition of type I and type II iodothyronine deiodinase activity in rat liver, kidney and brain produced by selenium deficiency.

Selenium deficiency for periods of 5 or 6 weeks in rats produced an inhibition of tri-iodothyronine (T3) production from added thyroxine (T4) in brain, liver and kidney homogenate. This inhibition was reflected in plasma T4 and T3 concentrations, which were respectively increased and decreased in selenium-deficient animals. Although plasma T4 levels increased in selenium-deficient animals, this did not produce the normal feedback inhibition on thyrotropin release from the pituitary. Selenium deficiency was confirmed in the animals by decreased selenium-dependent glutathione peroxidase (Se-GSH-Px) activity in all of these tissues. Administration of selenium, as a single intraperitoneal injection of 200 micrograms of selenium (as Na2SeO3)/kg body weight completely reversed the effects of selenium deficiency on thyroid-hormone metabolism and partly restored the activity of Se-GSH-Px. Selenium administration at 10 micrograms/kg body weight had no significant effect on thyroid-hormone metabolism or on Se-GSH-Px activity in any of the tissues studied. The characteristic changes in plasma thyroid-hormone levels that occurred in selenium deficiency appeared not to be due to non-specific stress factors, since food restriction to 75% of normal intake or vitamin E deficiency produced no significant changes in plasma T4 or T3 concentration. These data are consistent with the view that the Type I and Type II iodothyronine deiodinase enzymes are seleno-enzymes or require selenium-containing cofactors for activity.     

Molecular cloning and daily variations of the <Emphasis Type="Italic">Period</Emphasis> gene in a reef fish <Emphasis Type="Italic">Siganus guttatus</Emphasis>

As the first step in understanding the molecular oscillation of the circa rhythms in the golden rabbitfish Siganus guttatus—a reef fish with a definite lunar-related rhythmicity—we cloned and sequenced a Period gene (rfPer). The rfPer gene contained an open reading frame that encodes a protein consisting of 1,452 amino acids; this protein is highly homologous to PER proteins of vertebrates including zebrafish. Phylogenetic analyses indicated that the rfPER protein is related to the zebrafish PER1 and PER4. The expression of rfPer mRNA in the whole brain, retina, and liver under light/dark (LD) conditions increased at 06:00 h and decreased at 18:00 h, suggesting that its robust circadian rhythm occurs in neural and peripheral tissues. When daily variation in the expression in rfPer mRNA in the whole brain and cultured pineal gland were examined under LD conditions, similar expression patterns of the gene were observed with an increase around dawn. Under constant light condition, the increased expression of rfPer mRNA in the whole brain disappeared around dawn. The present results demonstrate that rfPer is related to zPer4 and possibly zPer1. The present study is the first report on the Period gene from a marine fish.     

Multi-annual changes in the parasite communities of rabbitfish Siganus rivulatus (Siganidae) in the Gulf of Aqaba, Red Sea

The parasite communities of the rabbitfish, Siganus rivulatus, were used to track multi-annual changes in the northern Gulf of Aqaba, Red Sea, in an environment subjected to ongoing anthropogenic impact. Parasitological data from these fish were collected from 1998 to 2000, with spring and fall samplings at three locations: at a coral reef (OBS), at a sandy beach area (NB) and at a mariculture cage farm (FF). These data were compared with data from 1995–1997 as well as data collected during 1981–1985 at the coral reef sampling site. The data analyses indicate that the ratio between heteroxenous and monoxenous parasite species declined significantly at all sites between 1995–1997 and 1998–2000. During the same period, the species richness of monoxenous parasites increased significantly at all sites. The species richness of heteroxenous parasites decreased significantly at the coral reef site, but remained steady at the other two sites. This coincided with a significant increase in the prevalence of monogeneans at the OBS and FF sites and a significant decrease in the prevalence of digeneans at the FF and NB sites. The decline in the abundance of the latter, specifically of Opisthogonoporoides sp. and Gyliauchen sp., was even more significant when compared with the 1981–1985 data. The prevalence of other gut helminths, namely the digenean Hexangium sigani and the nematodes Cucullanus sigani and Procamallanus elatensis, however, showed a significant increase over the same period. Analysis of the species richness and diversity indices of the parasite communities did not reveal conspicuous differences. These, however, did become apparent when heteroxenous and monoxenous members of particular taxa were analyzed separately. Therefore, when using parasite assemblages to detect ecological changes, it is essential to analyze not only at the community level, but also to consider separate components of particular parasitic groups. Communicated by H. von Westernhagen, A. Diamant     

Comparison of the circadian eclosion rhythm between non-diapause and diapause pupae in the onion fly,Delia antiqua

The influence of pupal diapause on adult eclosion rhythm of Delia antiqua was investigated. When non-diapause and diapause pupae were exposed to various photoperiods at 15, 20 and 25 °C, both of them emerged as adults close to the light-on time, but the phase of eclosion varied with photoperiod and temperature. Moreover, there was a significant difference in the eclosion time between non-diapause and diapause pupae; the eclosion peak of diapause pupae was earlier than that of non-diapause pupae. When non-diapause and diapause pupae were transferred to constant darkness (DD) after having experienced LD 12:12 at 15, 20 and 25 °C, both showed circadian rhythmicity in eclosion. Although the free-running period (τ) decreased slightly as temperature increased in both non-diapause and diapause pupae, the latter tended to show shorter τ than the former. This observation suggests that the observed difference in eclosion time in LD cycles between non-diapause and diapause pupae is due to differences in τ.     

Seasonal change in the locomotor activity rhythm of the medaka,Oryzias latipes

A group of the medaka,Oryzias latipes (Cyprinodontidae, orange-red variety, 25 males and 25 females), was kept in an aquarium, which was placed outdoors under natural conditions from December 1984 to January 1986. Locomotor activity at three layers (upper, middle, and lower layers) was recorded with a phototransistor system in each season. In summer, the fish showed typical diurnal activity at all three layers and the activity was greater than in other seasons. However, in autumn and winter, the fish became less active and showed relatively high activity at night at the upper or middle layer and diurnal activity at the lower layer. Nocturnal activity seemed to appear when the water temperature was decreased and the photoperiod was shortened. A free-running activity rhythm was also recorded under continuous darkness (DD) in each season; however, the fish showed clear free-running activity rhythms under DD only in summer.     

Diet and habitat use of frillneck lizards in a seasonal tropical environment

A population of frillneck lizards, Chlamydosaurus kingii, was monitored by mark-recapture and telemetry over a 2 year period in Kakadu National Park. The aims of the study were to document changes in diet, growth, condition and habitat use between the wet and dry seasons of northern Australia, in light of recent research examining seasonal variation in the physiology of this species. Frillneck lizards feed on a diverse range of invertebrates in both seasons, even though there is a substantial reduction in food avail-ability in the dry season. Harvester termites from the genus Drepanotermes constitute a major component of the diet, and the prevalence of termites in the diet of sedentary foragers in a tropical environment is unusual. Adult male body condition remained relatively stable throughout the year, but females experienced considerable variation. These differences are attributed to different reproductive roles of the sexes. Growth in C. kingii was restricted to the wet season, when food availability was high, and growth was minimal in the dry season when food availability was low. The method used in catching lizards was an important factor in determining seasonal habitat use. Telemetered lizards selected a significantly different distribution of tree species than was randomly available, and they selected significantly larger tree species during the dry season. Lizards spotted along roadsides showed little seasonal variation in the selection of tree species or tree sizes. The results suggest a comprehensive change in the ecology of this species, in response to an annual cycle of low food and moisture availability, followed by a period with few resource restrictions.     

Interacting effect of thermoperiod and photoperiod on the eclosion rhythm in the onion fly, Delia antiqua supports the two-oscillator model

Daily light and temperature cycles entrain adult eclosion rhythms in many insect species, but little is known about their interaction. We studied this problem in the onion fly, Delia antiqua. Pupae were subjected to various combinations of a photoperiod of 12L:12D and thermoperiods. The thermoperiods consisted of 12 h warm phase (W) and 12 h cool phase (C), giving a mean temperature of 25 °C with different temperature steps of 8, 4 and 1 °C. As the phase relation of the two Zeitgebers was varied, the phase of eclosion rhythm was shifted, depending on the phase angle with the light cycle and the amplitude of the temperature cycle. When the temperature step in the thermoperiod was 8 °C (WC 29:21 °C), the eclosion rhythm was entrained mainly to thermoperiod rather than photoperiod. In the regime with a 4 °C temperature step (WC 27:23 °C), both thermoperiod and photoperiod affected eclosion rhythm, and a phase jump of the eclosion rhythm occurred when the warm phase of thermoperiod was delayed 15-18 h from light-on. In regimes with a 1 °C temperature step (WC 25.5:24.5 °C), the eclosion rhythm was completely entrained to photoperiod. The observed interacting effect of light and temperature cycle on the eclosion rhythm in D. antiqua can be explained by the two-oscillator model proposed by Pittendrigh and Bruce (1959).     

Expression of cadherin10, a type II classic cadherin gene, in the nervous system of the embryonic zebrafish

Cadherins are cell surface adhesion molecules that play important roles in development of tissues and organs. In this study, we analyzed expression pattern of cadherin10, a member of the type II classic cadherin subfamily, in the embryonic zebrafish using in situ hybridization methods. cadherin10 message (cdh10) is first and transiently expressed by the notochord. In the developing nervous system, cdh10 was first detected in a subset of the cranial ganglia, then in restricted brain regions and neural retina. As development proceeds, cdh10 expression domain and/or expression levels increased in the embryonic nervous system. Our results show that cdh10 expression in the zebrafish developing nervous system is both spatially and temporally regulated.     

三唑磷、氟虫腈及其复配剂对四种miRNAs在斑马鱼组织中表达的影响

MicroRNAs(miRNAs)是一类长约22 nt的非编码小RNA,在基因表达中起重要调控作用.已有研究表明,农药三唑磷和氟虫腈能影响斑马鱼全鱼组织中部分miRNAs的正常表达,但未见对miRNA表达的组织特异性的研究.本研究采用荧光定量PCR技术研究了经三唑磷微乳剂、氟虫腈微乳剂及其复配剂处理后,四种miRNA(...     

Expression of nuclear hormone receptors, their coregulators and type I iodothyronine 5'-deiodinase gene in mammary tissue of nonlactating and postlactating rats

The aim of the study was to test the hypothesis that expression of retinoid receptors (RARalpha, RARbeta, RARgamma), rexinoid receptors (RXRalpha, RXRbeta), thyroid hormone receptors (TRalpha, TRbeta), estrogen receptors (ERalpha, ERbeta), nuclear receptor coregulators (N-CoR, SRC-1, SMRT), and in addition type I iodothyronine 5'-deiodinase (5'-DI), EGFR and erb-B2/neu would be different in mammary postlactating tissue in comparison with that of nonlactating mammary gland. Using RT-PCR, we have shown that expression of RARalpha, RXRalpha,TRalpha, ERalpha,ERbeta,N-CoR, SRC-1, SMRT and EGFR in rat was significantly increased in postlactating mammary gland when compared to that of nonlactating mammary tissue. Postlactating mammary glands were found to express all RAR and RXR subtypes studied when compared to nonlactating mammary tissues that express exclusively RARalpha and RXRalpha subtypes. Enhanced expression of a number of nuclear hormone receptors, their coregulators in mammary tissue of postlactating rats in comparison with nonlactating animals identify a potential role for retinoid, thyroid and estrogen signalling pathways also after lactation period.     

Daily Behavioral Rhythmicity and Organization of the Suprachiasmatic Nuclei in the Diurnal Rodent,Lemniscomys barbarus

Wheel‐running activity was recorded in Lemniscomys barbarus exposed to different lighting conditions. This rodent shows rhythmic locomotor activity under natural twilight‐light/dark (LD) as well as squared‐LD cycles. A mean of 77% of the activity occurred during the light phase. Under different controlled photoperiods, the quantity of daily locomotor activity was relatively stable except for a lower level in the shortest photoperiod tested (LD 06∶18). The duration of the active phase tended to increase with the duration of the light phase, especially in the longer photoperiods. Whatever the lighting conditions, Lemniscomys barbarus started running before lights‐on and stopped after lights‐off. The phase angle of activity offset relative to lights‐off was stable in each squared‐photoperiod, whereas the phase angle of activity onset relative to lights‐on was significantly the highest under the shortest photoperiods. Recording of activity under constant lighting conditions showed that the daily rhythm of locomotor activity is fundamentally circadian. The endogenous period was slightly<24 h (mean=23.8 h) in permanent darkness and>24 h (mean=24.5 h) in continuous light. Re‐entrainment of the locomotor activity rhythm after a 6 h phase advance or delay requires only four days on average. Moreover, the phase‐responses curve to a 30 min light pulse (200 lux) in Lemniscomys barbarus kept in constant dark reveals large phase shifts according to circadian times (CT). With CT0 being defined as the onset of daily activity, maximum phase delay and advance shifts were observed at CT11 (Δ Ψ=‐5.7 h±2.3 h) and CT21 (Δ Ψ =4.9±1.2 h), respectively. Interestingly, the phase‐response curve to light did not show any dead zone. Immunohistochemical staining of the suprachiasmatic nuclei indicates that arginine vasopressin‐immunoreactive cell bodies and fibers delimited a dorsal subregion that extends laterally and medially. The ventral subregion is rich in vasoactive intestinal peptide‐immunoreactive neurones overlapping a smaller area containing gastrin‐releasing peptide‐expressing cells and receives numerous fibers labeled with neuropeptide Y antibody. The results of this study clearly demonstrate that Lemniscomys barbarus is a diurnal species highly sensitive to the shifting effects of light. Overall, this rodent can be considered a new and interesting model for circadian rhythm neurobiology.     

Robustness of Circadian Timing Systems Evolves in the Fruit Fly Drosophila melanogaster as a Correlated Response to Selection for Adult Emergence in a Narrow Window of Time

Robustness is a fundamental property of biological timing systems that is likely to ensure their efficient functioning under a wide range of environmental conditions. Here we report the findings of our study aimed at examining robustness of circadian clocks in fruit fly Drosophila melanogaster populations selected to emerge as adults within a narrow window of time. Previously, we have reported that such flies display enhanced synchrony, accuracy, and precision in their adult emergence and activity/rest rhythms. Since it is expected that accurate and precise circadian clocks may confer enhanced stability in circadian time-keeping, we decided to examine robustness in circadian rhythms of flies from the selected populations by subjecting them to a variety of environmental conditions comprising of a range of photoperiods, light intensities, ambient temperatures, and constant darkness. The results revealed that adult emergence and activity/rest rhythms of flies from the selected stocks were more robust than controls, as they displayed enhanced stability under a wide variety of environmental conditions. These results suggest that selection for adult emergence within a narrow window of time results in the evolution of robustness in circadian timing systems of the fruit fly D. melanogaster. (Author correspondence: vsharma@jncasr.ac.in or vksharmas@gmail.com)     

Circadian and seasonal variation of the body temperature of sheep in a tropical environment

Nychthemeral and annual rhythms of the rectal temperature were determined for Corriedale sheep in a tropical climate. The minimum rectal temperature averaged 39.55° C at 0500 hours in summer, and 38.87° C at 0600 hours in winter. The maximum was 40.03° C in summer (1700 hours) and 39.33° C in winter (1830 hours). Annual cycle of the rectal temperature showed a minimum in July and maximum in December.     

Expression of HSP 70 and its mRNAS during ischemia-reperfusion in the rat bladder

HSP 70 is an important protein that repairs damaged tissue after injury. In the present study, we investigated the expression of HSP 70 and its mRNAs during ischemia-reperfusion in the rat bladder. Rat abdominal aorta was clamped with a small clip to induce ischemia-reperfusion injury in the bladder dome. Male Wistar rats, 8 weeks old, were divided into six groups: controls, 30-min ischemia, 30-min ischemia and 30-, 60-minute, 1- and 7-day reperfusion, groups A, B, C, D, E, and F, respectively. In functional studies, contractile responses to carbachol were measured in these groups. The expression of HSP 70-1/2 mRNAs was quantified using a real-time PCR method, and that of HSP 70 proteins was measured using ELISA in the bladders. In the functional study, Emax values of carbachol to bladders in the A, B, C, D, E and F groups were 9.3 +/- 1.3, 7.9 +/- 1.7, 4.3 +/- 0.8, 4.2 +/- 0.7, 4.5 +/- 0.6, and 8.1 +/- 1.2 g/mm2, respectively. In the control group, the expression of HSP 70-1/2 mRNA was detected, and the expression of HSP 70-1 mRNAs was significantly higher than that of HSP 70-2 mRNAs in each group. The expression of HSP 70-1 mRNA increased in groups B and C, but decreased in groups D, E, and F. The expression of HSP 70-2 mRNA in group C was significantly higher than that of groups A, D, E, and F. The expression of HSP 70-1/2 mRNAs after 1 day or 1 week of reperfusion was similar to control levels. The expression of HSP 70 proteins was increased shortly after the expression of their mRNAs. The expression of HSP 70 after 1 day or 1 week of reperfusion was almost identical to control levels. Our data indicate that contractile responses of the bladder were decreased by ischemia reperfusion, and that expression of HSP 70 and its mRNAs appeared to increase after a short period of the insult.