bluuebunny/crossref_metadata_2025 huggingface dataset:
Involvement of RelA-Associated Inhibitor in Regulation of Trophoblast Differentiation via Interaction with Transcriptional Factor Specificity Protein-1
Authors: Minekawa Ryoko , Sakata Masahiro , Okamoto Yoko , Hayashi Masami , Isobe Aki , Takeda Takashi , Yamamoto Toshiya , Koyama Masayasu , Ohmichi Masahide , Tasaka Keiichi , Imai Kenichi , Okamoto Takashi , Murata Yuji
Published: September 2007

Glucose transporter-1 (GLUT1), one of the key functional indicators of placental differentiation, has an important role in placental glucose transport. We previously showed that the protein levels of GLUT1 and nuclear transcription factor specificity protein-1 (Sp1) in rat choriocarcinoma cells (Rcho-1 cells) decreased during the differentiation of these cells to giant cells. We also showed that Sp1 was involved in the regulation of GLUT1 gene expression during this process. RelA-associated inhibitor (RAI) is an inhibitor of nuclear factor-κB that was identified by a yeast two-hybrid screen and is preferably expressed in human placenta and heart. RAI was also found to interact with Sp1 and exert an inhibitory effect against the DNA-binding activity of Sp1. We first show here that RAI mRNA expression increased as gestation proceeded and that RAI was localized mainly in the syncytiotrophoblast throughout pregnancy. The chloramphenicol acetyltransferase activity assay in Rcho-1 cells revealed that cotransfection of RAI expression vector resulted in decreased activity of the rat GLUT1 promoter but not in that of a mutated rat GLUT1 promoter lacking the Sp1 binding site. Furthermore, the protein level of RAI increased during differentiation. In addition, transfection of RAI expression vector promoted the morphological differentiation of Rcho-1 cells, and RAI knockdown using RAI-specific small interfering RNA reveals inhibitory effects on the morphological differentiation, as assessed by photomicroscopy. Taken together, these findings suggest that RAI may be involved in the regulation of trophoblast differentiation via interaction with Sp1.
Immunocytochemical and Phylogenetic Analyses of an Arginine Vasotocin-Dependent Aquaporin, AQP-h2K, Specifically Expressed in the Kidney of the Tree Frog, Hyla japonica
Authors: Ogushi Yuji , Mochida Hiroshi , Nakakura Takashi , Suzuki Masakazu , Tanaka Shigeyasu
Published: September 2007

Water movement occurs across the plasma membrane of various cells of animals, plants, and microorganisms through specialized water-channel proteins called aquaporins (AQPs). We have identified a new member of the amphibian AQP family, AQP-h2K, from the kidneys of Hyla japonica. This protein consists of 280 amino acid residues with two NPA (Asn-Pro-Ala) sequence motifs and a mercury-sensitive cysteine residue just upstream from the second NPA motif. There are two putative N-linked glycosylation sites at Asn-120 and Asn-128 and one protein kinase A phosphorylation site at Ser-262. The AQP-h2K protein was specifically expressed in the apical membrane and/or cytoplasm of principal cells in the kidney collecting ducts. After stimulation with arginine vasotocin, it was translocated from the cytoplasmic pool to the apical membrane. Phylogenetic analysis of AQP proteins from anurans and mammals identified six clusters of anuran AQPs: types 1, 2, 3, and 5 and two anuran-specific types, designated a1 and a2. The cluster AQPa2 contains Hyla AQP-h2 and AQP-h3, which are expressed in the anuran urinary bladder and ventral pelvic skin. AQP-h2K belongs to the type 2, together with mammalian (human and mouse) AQP2, suggesting that AQP-h2K is an anuran ortholog of the neurohypophysial hormone-regulated mammalian AQP2 and that the AQP2 molecule is already present in the anuran mesonephros.
Neonatal Lipopolysaccharide Exposure Exacerbates Stress-Induced Suppression of Luteinizing Hormone Pulse Frequency in Adulthood
Authors: Li X. F. , Kinsey-Jones J. S. , Knox A. M. I. , Wu X. Q. , Tahsinsoy D. , Brain S. D. , Lightman S. L. , O’Byrne K. T.
Published: September 2007

Early life exposure to immunological challenge has programming effects on the adult hypothalamo-pituitary-adrenocortical axis stress responsivity, and stress is known to suppress GnRH pulse generator activity, especially LH pulses. We investigated the effects of neonatal exposure to endotoxin on stress-induced suppression of pulsatile LH secretion and the involvement of corticotropin-releasing factor (CRF) receptor mechanisms in adult rats. Pups at 3 and 5 d of age were administered lipopolysaccharide (LPS, 50 μg/kg, ip). At 12 wk of age, they were ovariectomized and implanted with sc 17β-estradiol capsules and iv cannulas. Blood samples (25 μl) were collected every 5 min for 5 h for LH measurement. After 2 h of sampling, rats were given LPS (25 μg/kg, iv). CRF and CRF-R1 and CRF-R2 receptor mRNA was determined by RT-PCR in medial preoptic area (mPOA) micropunches collected at 3 h after LPS administration. There was no difference in basal LH pulse frequency between neonatal LPS- and neonatal saline-treated controls. However, neonatal endotoxin-treated rats exhibited a significantly greater LPS stress-induced suppression of LH pulse frequency. Basal mPOA CRF-R1 expression was unchanged in neonatal LPS- and neonatal saline-treated rats. However, CRF-R1 expression was significantly increased in response to LPS stress in neonatal LPS-treated animals but not in neonatal saline-treated controls. CRF and CRF-R2 expression was unchanged in all treatment groups. These data demonstrate that exposure to bacterial endotoxin in early neonatal life programs long-term sensitization of the GnRH pulse generator to the inhibitory influence of stress in adulthood, an effect that might involve up-regulation of CRF-R1 expression in the mPOA.
Tumor Necrosis Factor-α-Induced Anterior Pituitary Folliculostellate TtT/GF Cell Uncoupling Is Mediated by Connexin 43 Dephosphorylation
Authors: Meilleur Mélissa-Anne , Akpovi Casimir D. , Pelletier R.-Marc , Vitale María Leiza
Published: September 2007

The anterior pituitary folliculostellate (FS) cells are key elements of the paracrine control of the pituitary function. These cells are the source and the target of growth factors and cytokines, and are connected to other pituitary cells via Cx43-mediated gap junctions. Here, we show that acute treatment of the FS TtT/GF cell line with TNF-α caused a transient cell uncoupling that was accompanied by the dephosphorylation of Cx43 in Ser368. These TNF-α-evoked effects were dependent on protein phosphatase 2A (PP2A) and protein kinase C (PKC) activities. TNF-α did not affect total cell Cx43-PP2A catalytic subunit interaction, but it did induce PP2A catalytic subunit recruitment to the Triton X-100 insoluble subcellular fraction, in which Cx43-gap junction plaques are recovered. This recruitment temporally coincided with Cx43 phosphorylated in Ser368-Cx43 dephosphorylation. Cx43 did not interact with the conventional PKC-α, but it did interact with the atypical PKC-ζ. Moreover, this interaction was weakened by TNF-α. Cx43 dephosphorylation in Ser368 was followed by the tyrosine phosphorylation of the protein. The temporary closure of gap junctions during acute TNF-α challenge may constitute a protective mechanism to limit or confine the spread of inflammatory signals among the FS cells.
Leptin Sensitivity in the Developing Rat Hypothalamus
Authors: Carlo A.-S. , Pyrski M. , Loudes C. , Faivre-Baumann A. , Epelbaum J. , Williams L. M. , Meyerhof W.
Published: September 2007

In adults, the adipocyte-derived hormone, leptin, regulates food intake and body weight principally via the hypothalamic arcuate nucleus (ARC). During early postnatal development, leptin functions to promote the outgrowth of neuronal projections from the ARC, whereas a selective insensitivity to the effects of leptin on food intake appears to exist. To investigate the mechanisms underlying the inability of leptin to regulate food intake during early development, leptin signaling was analyzed both in vitro using primary cultures of rat embryonic ARC neurones and in vivo by challenging early postnatal rats with leptin. In neuronal cultures, despite the presence of key components of the leptin signaling pathway, no detectable activation of either signal transducer and activator of transcription 3 or the MAPK pathways by leptin was detected. However, leptin down-regulated mRNA levels of proopiomelanocortin and neuropeptide Y and decreased somatostatin secretion. Leptin challenge in vivo at postnatal d (P) 7, P14, P21, and P28 revealed that, in contrast to adult and P28 rats, mRNA levels of neuropeptide Y, proopiomelanocortin, agouti-related peptide and cocaine- and amphetamine-regulated transcript were largely unaffected at P7, P14, and P21. Furthermore, leptin stimulation increased the suppressor of cytokine signaling-3 mRNA levels at P14, P21, and P28 in several hypothalamic nuclei but not at P7, indicating that selective leptin insensitivity in the hypothalamus is coupled to developmental shifts in leptin receptor signaling. Thus, the present study defines the onset of leptin sensitivity in the regulation of energy homeostasis in the developing hypothalamus.
Contributions of Intracellular Loops 2 and 3 of the Lutropin Receptor in Gs Coupling
Authors: Angelova Krassimira , Fanelli Francesca , Puett David
Published: September 2007

A number of amino acids essential for Gs coupling, i.e. hot spots, were identified after in vitro Ala-scanning mutagenesis of the cytosolic extensions of helices 3, 5, and 6 and of intracellular loops 2 and 3 (IL2 and IL3) of the human LH receptor (LHR). Consistent with the results of in vitro experiments involving ligand binding and ligand-mediated signaling in transiently transfected human embryonic kidney 293 cells, computational modeling of the isolated receptor and of the receptor-G protein complexes suggests an important role of the cytosolic extension of helix 3 and the N-terminal portion of the IL2 in Gsα interaction, whereas the contribution of IL3 is marginal. Mapping the hot spots into the computational models of LHR and the LHR-Gs complexes allowed for a distinction between receptor sites required for intramolecular structural changes (i.e. I460, T461, H466, and I549) and receptor sites more likely involved in G protein recognition (i.e. R464, T467, I468, Y470, Y550, and D564). The latter sites include the highly conserved arginine of the (E/D)R(Y/W) motif, which is therefore likely to be a receptor recognition point for Gs rather than a switch of receptor activation. The results of in vitro and in silico experiments carried out in this study represent the first comprehensive delineation of functionality of the individual residues in the intracellular domains of LHR and establish potential switches of receptor activation as well as a map of the primary receptor recognition sites for Gs. A novel way to consider constitutively active mutants was inferred from this study, i.e. receptor states with improved complementarity for the G protein compared to the wild-type receptor.
Polycomb group proteins function in the female gametophyte to determine seed development in plants
Authors: Leroy Olivier , Hennig Lars , Breuninger Holger , Laux Thomas , Köhler Claudia
Published: September 2007

Polycomb group (PcG) proteins are evolutionary conserved proteins that stably maintain established transcriptional patterns over cell generations. The FERTILIZATION INDEPENDENT SEED (FIS) PcG complex from plants has a similar composition to the Polycomb repressive complex 2 from animals. Mutations in FIS genes cause parent-of-origin-dependent seed abortion. Every seed inheriting a mutant fis allele from the mother is destined to abort,regardless of the presence of a wild-type paternal allele. We tested in Arabidopsis whether the parent-of-origin-dependent seed abortion caused by lack of the FIS subunit MSI1 is caused by parental imprinting of the MSI1 gene. Our data show that MSI1 is not an imprinted gene and that early paternal MSI1 expression is not sufficient to rescue msi1 mutant seeds. By contrast, expression of MSI1 in msi1 female gametophytes is necessary to restore normal seed development, strongly arguing that the female gametophytic effect of fis mutants is caused by a functional requirement for an intact FIS complex in the female gametophyte. Thus, FIS-mediated expression patterns established in the female gametophyte can impact on seed development,establishing fis mutants as true female gametophytic maternal-effect mutants.
Collaboration between Smads and a Hox protein in target gene repression
Authors: Walsh Christopher M. , Carroll Sean B.
Published: September 2007

Hox proteins control the differentiation of serially iterated structures in arthropods and chordates by differentially regulating many target genes. It is yet unclear to what extent Hox target gene selection is dependent upon other regulatory factors and how these interactions might affect target gene activation or repression. We find that two Smad proteins, effectors of the Drosophila Dpp/TGF-β pathway, that are genetically required for the activation of the spalt (sal) gene in the wing,collaborate with the Hox protein Ultrabithorax (Ubx) to directly repress sal in the haltere. The repression of sal is integrated by a cis-regulatory element (CRE) through a remarkably conserved set of Smad binding sites flanked by Ubx binding sites. If the Ubx binding sites are relocated at a distance from the Smad binding sites, the proteins no longer collaborate to repress gene expression. These results support an emerging view of Hox proteins acting in collaboration with a much more diverse set of transcription factors than has generally been appreciated.
The endocytic control of JAK/STAT signalling in Drosophila
Authors: Devergne Olivier , Ghiglione Christian , Noselli Stéphane
Published: September 2007

Domeless (Dome) is an IL-6-related cytokine receptor that activates a conserved JAK/STAT signalling pathway during Drosophila development. Despite good knowledge of the signal transduction pathway in several models, the role of receptor endocytosis in JAK/STAT activation remains poorly understood. Using both in vivo genetic analysis and cell culture assays, we show that ligand binding of Unpaired 1 (Upd1) induces clathrin-dependent endocytosis of receptor-ligand complexes and their subsequent trafficking through the endosomal compartment towards the lysosome. Surprisingly, blocking trafficking in distinct endosomal compartments using mutants affecting either Clathrin heavy chain, rab5, Hrs or deep orange led to an inhibition of the JAK/STAT pathway, whereas this pathway was unchanged when rab11 was affected. This suggests that internalization and trafficking are both required for JAK/STAT activity. The requirement for clathrin-dependent endocytosis to activate JAK/STAT signalling suggests a model in which the signalling `on' state relies not only on ligand binding to the receptor at the cell surface, but also on the recruitment of the complex into endocytic vesicles on their way to lysozomes. Selective activation of the pool of receptors marked for degradation thus provides a way to tightly control JAK/STAT activity.
Plasticity of HP1 proteins in mammalian cells
Authors: Dialynas George K. , Terjung Stefan , Brown Jeremy P. , Aucott Rebecca L. , Baron-Luhr Bettina , Singh Prim B. , Georgatos Spyros D.
Published: September 2007

We have compared the distribution of endogenous heterochromatin protein 1 (HP1) proteins (α, β and γ) in different epithelial lines, pluripotent stem cells and embryonic fibroblasts. In parallel, we have interrogated assembly and dynamics of newly expressed HP1-GFP proteins in cells lacking both HP1α and HP1β alleles, blocked at the G1-S boundary, or cultured in the presence of HDAC and HAT inhibitors. The results reveal a range of cell type and differentiation state-specific patterns that do not correlate with `fast' or `slow' subunit exchange in heterochromatin. Furthermore, our observations show that targeting of HP1γ to heterochromatic sites depends on HP1α and H1β and that, on an architectural level, HP1α is the most polymorphic variant of the HP1 family. These data provide evidence for HP1 plasticity under shifting microenvironmental conditions and offer a new conceptual framework for understanding chromatin dynamics at the molecular level.
Variant-specific patterns and humoral regulation of HP1 proteins in human cells and tissues
Authors: Ritou Eleni , Bai Maria , Georgatos Spyros D.
Published: September 2007

We have examined the occurrence and distribution of HP1α and HP1β under in vivo, ex vivo and in vitro conditions. Consistent with a non-essential role in heterochromatin maintenance, both proteins are diminished or undetectable in several types of differentiated cells and are universally downregulated during erythropoiesis. Variant-specific patterns are observed in almost all human and mouse tissues examined. Yet, the most instructive example of HP1 plasticity is observed in the lymph nodes, where HP1α and HP1β exhibit regional patterns that are exactly complementary to one another. Furthermore, whereas HP1α shows a dispersed sub-nuclear distribution in the majority of peripheral lymphocytes, it coalesces into large heterochromatic foci upon stimulation with various mitogens and IL-2. The effect of inductive signals on HP1α distribution is reproduced by coculture of immortalized T- and B-cells and can be confirmed using specific markers. These complex patterns reveal an unexpected plasticity in HP1 variant expression and strongly suggest that the sub-nuclear distribution of HP1 proteins is regulated by humoral signals and microenvironmental cues.
Orientation towards prey in antlions: efficient use of wave propagation in sand
Authors: Fertin Arnold , Casas Jérôme
Published: September 2007

Substrate-borne vibration for locating mates, predators and prey is widespread in the animal kingdown. Antlion larvae dig funnel-shaped traps to catch ants and they are totally immersed in dry sand. We used a playback setup reproducing an ant walking on sand to clearly demonstrate that antlions use sand-borne vibrations to locate their prey. Half the tested animals moved towards the stimulus source. The shoot angle of sand tossing was very close to the target angle, indicating excellent ability to perceive stimulus direction. We also discuss orientation mechanisms in sand, a medium with highly unusual wave propagation properties.
Metabolic and digestive response to food ingestion in a binge-feeding lizard, the Gila monster (Heloderma suspectum)
Authors: Christel C. M. , DeNardo D. F. , Secor S. M.
Published: September 2007

The gastrointestinal tract possesses the capacity to change in form and function in response to fasting and feeding. Such plasticity can be dramatic for species that naturally experience long episodes of fasting between large meals (e.g. sit-and-wait foraging snakes, estivating anurans). By contrast,for active foraging species that feed more frequently on smaller meals,gastrointestinal responses are more modest in magnitude. The Gila monster Heloderma suspectum is an active foraging lizard that feeds infrequently on meals weighing up to one-third of its body mass. Additionally,Gila monsters possess a species-specific salivary peptide, exendin-4, which may be involved in the regulation of metabolic and digestive performance. To investigate the adaptive postprandial response of Gila monsters and the potential regulatory role of exendin-4, we measured metabolic and intestinal responses to feeding in the presence or absence of circulating exendin-4. Following the consumption of rodent or egg meals equivalent to 10% of lizard body mass, metabolic rates peaked at 4.0- to 4.9-fold of standard metabolic rates and remained elevated for 5–6 days. Specific dynamic action of these meals (43–60 kJ) was 13–18% of total meal energy. Feeding triggered significant increases in mucosal mass, enterocyte width and volume,and the upregulation of d-glucose uptake rates and aminopeptidase-N activity. Total intestinal uptake capacity for l-leucine, l-proline and d-glucose were significantly elevated within 1–3 days after feeding. Whereas the absence of circulating exendin-4 had no impact on postprandial metabolism or the postprandial response of intestinal structure and nutrient uptake, it significantly increased intestinal aminopeptidase-N activity. Within the continuum of physiological responses to feeding and fasting, Gila monsters occupy an intermediate position in experiencing moderate, though significant, regulation of intestinal performance with feeding.
Is basal metabolic rate influenced by age in a long-lived seabird, the snow petrel?
Authors: Moe Børge , Angelier Frédéric , Bech Claus , Chastel Olivier
Published: September 2007

Ageing is associated with a decline in basal metabolic rate (BMR) in many species, including humans. The evolutionary and physiological causes underlying the relationship between age and BMR are poorly understood. Studies of procellariiform seabirds may provide valuable insight because they have a longer maximum lifespan than expected from their body size and rates of energy metabolism. Such studies are rare, however, because there are few populations with a high proportion of individuals of known age.

We performed a cross-sectional study of energy metabolism in relation to age in a long-lived seabird, the snow petrel Pagodroma nivea. In an Antarctic population that has been subject to a long-term research program,including annual banding of chicks since 1963, we measured BMR of individuals aged between 8 and 39 years. We show that the BMR of the snow petrel does not decrease with increasing age. BMR seems to be sustained at a fixed level throughout the investigated age-span.

We review this result in light of the disposable soma theory of ageing, and we discuss whether species-specific relationships between age and basal metabolic rate can be related to differences in maximum lifespan.
Rapid assimilation of yolk enhances growth and development of lizard embryos from a cold environment
Authors: Storm Melissa A. , Angilletta Michael J.
Published: September 2007

Selection for rapid growth and development in cold environments results in a geographic pattern known as countergradient variation. The eastern fence lizard, Sceloporus undulatus, exhibits countergradient variation in embryonic growth and development along latitudinal clines. To identify the proximate causes of countergradient variation, we compared the energy budgets of embryos from a cold environment (Virginia) and a warm environment (South Carolina) during development at a realistic thermal cycle. The difference in mean egg size between populations was controlled by removing yolk from large eggs and performing a sham manipulation on other eggs. Respiration was measured every 4 days throughout 48 days of incubation. After this period,eggs were dissected and the energy contents of embryos and yolk were determined by calorimetry. As expected from previous experiments, embryos from Virginia reached a more advanced stage of development and deposited more energy within tissues than embryos from South Carolina. The greater absorption of yolk by embryos from Virginia was associated with a higher rate of respiration. Assimilation of yolk by rapidly growing embryos could reduce growth or survival after hatching. Such costs might explain the maintenance of countergradient variation in S. undulatus.
Efficiency of labriform swimming in the bluegill sunfish (Lepomis macrochirus)
Authors: Jones Emily A. , Lucey Kaitlyn S. , Ellerby David J.
Published: September 2007

Bluegill sunfish (Lepomis macrochirus) swim in the labriform mode at low speeds, generating lift and thrust by beating their pectoral fins. The maximal power output available from the two largest pectoral fin adductor and abductor muscles, constituting half of the total pectoral girdle muscle mass,was measured in vitro and used to estimate the muscle mechanical power output during maximal labriform swimming (Pmech;0.15–0.21 W kg–1 body mass). Respirometry was used to estimate the total metabolic power input (Ptotal; 0.95 W kg–1 body mass) and the metabolic power available to the active muscle mass (Pmuscle; Ptotalminus standard metabolic rate, 0.57 W kg–1 body mass) at this swimming speed. Drag measurements made on towed, dead fish were used to estimate the mechanical power required to overcome body drag(Pdrag; 0.028 W kg–1 body mass). Efficiency estimates based on these data fell into the following ranges:overall swimming efficiency(ηgross=Pmech/Ptotal),0.16–0.22; muscle efficiency(ηmuscle=Pmech/Pmuscle),0.26–0.37; and propeller efficiency(ηprop=Pdrag/Pmech),0.15–0.20. Comparison with other studies suggests that labriform swimming may be more efficient than swimming powered by undulations of the body axis.
Chronic electrical stimulation drives mitochondrial biogenesis in skeletal muscle of a lizard,Varanus exanthematicus
Authors: Schaeffer Paul J. , Nichols Scott D. , Lindstedt Stan L.
Published: September 2007

We investigated the capacity for phenotypic plasticity of skeletal muscle from Varanus exanthematicus, the savannah monitor lizard. Iliofibularis muscle from one leg of each lizard was electrically stimulated for 8 weeks. Both stimulated and contralateral control muscles were collected and processed for electron microscopy. We used stereological analysis of muscle cross-sections to quantify the volume densities of contractile elements, sarcoplasmic reticulum, mitochondria and intracellular lipids. We found that mitochondrial volume density was approximately fourfold higher in the stimulated muscle compared to controls, which were similar to previously reported values. Sarcoplasmic reticulum volume density was reduced by an amount similar to the increase in mitochondrial volume density while the volume density of contractile elements remained unchanged. Intracellular lipid accumulation was visibly apparent in many stimulated muscle sections but the volume density of lipids did not reach a significant difference. Although monitor lizards lack the highly developed aerobic metabolism of mammals, they appear to possess the capacity for muscle plasticity.
Regulation of glycogen metabolism in gills and liver of the euryhaline tilapia (Oreochromis mossambicus) during acclimation to seawater
Authors: Chang Joshua Chia-Hsi , Wu Su-Mei , Tseng Yung-Che , Lee Yi-Chun , Baba Otto , Hwang Pung-Pung
Published: September 2007

Glucose, which plays a central role in providing energy for metabolism, is primarily stored as glycogen. The synthesis and degradation of glycogen are mainly initialized by glycogen synthase (GS) and glycogen phosphorylase (GP),respectively. The present study aimed to examine the glycogen metabolism in fish liver and gills during acute exposure to seawater. In tilapia(Oreochromis mossambicus) gill, GP, GS and glycogen were immunocytochemically colocalized in a specific group of glycogen-rich (GR)cells, which are adjacent to the gill's main ionocytes, mitochondrion-rich(MR) cells. Na+/K+-ATPase activity in the gills, protein expression and/or activity of GP and GS and the glycogen content of the gills and liver were examined in tilapia after their acute transfer from freshwater(FW) to 25‰ seawater (SW). Gill Na+/K+-ATPase activity rapidly increased immediately after SW transfer. Glycogen content in both the gills and liver were significantly depleted after SW transfer, but the depletion occurred earlier in gills than in the liver. Gill GP activity and protein expression were upregulated 1–3 h post-transfer and eventually recovered to the normal level as determined in the control group. At the same time, GS protein expression was downregulated. Similar changes in liver GP and GS protein expression were also observed but they occurred later at 6–12 h post-transfer. In conclusion, GR cells are initially stimulated to provide prompt energy for neighboring MR cells that trigger ion-secretion mechanisms. Several hours later, the liver begins to degrade its glycogen stores for the subsequent energy supply.
Differences in membrane acyl phospholipid composition between an endothermic mammal and an ectothermic reptile are not limited to any phospholipid class
Authors: Mitchell Todd W. , Ekroos Kim , Blanksby Stephen J. , Hulbert Anthony J. , Else Paul L.
Published: September 2007

This study examined questions concerning differences in the acyl composition of membrane phospholipids that have been linked to the faster rates of metabolic processes in endotherms versus ectotherms. In liver, kidney, heart and brain of the ectothermic reptile, Trachydosaurus rugosus, and the endothermic mammal, Rattus norvegicus, previous findings of fewer unsaturates but a greater unsaturation index (UI) in membranes of the mammal versus those of the reptile were confirmed. Moreover, the study showed that the distribution of phospholipid head-group classes was similar in the same tissues of the reptile and mammal and that the differences in acyl composition were present in all phospholipid classes analysed, suggesting a role for the physical over the chemical properties of membranes in determining the faster rates of metabolic processes in endotherms. The most common phosphatidylcholine (PC) molecules present in all tissues (except brain) of the reptile were 16:0/18:1, 16:0/18:2, 18:0/18:2,18:1/18:1 and 18:1/18:2, whereas arachidonic acid (20:4), containing PCs 16:0/20:4, 18:0/20:4, were the common molecules in the mammal. The most abundant phosphatidylethanolamines (PE) used in the tissue of the reptile were 18:0/18:2, 18:0/20:4, 18:1/18:1, 18:1/18:2 and 18:1/20:4, compared to 16:0/18:2, 16:0/20:4, 16:0/22:6, 18:0/20:4, 18:0/22:6 and 18:1/20:4 in the mammal. UI differences were primarily due to arachidonic acid found in both PC and PEs, whereas docosahexaenoic acid (22:6) was a lesser contributor mainly within PEs and essentially absent in the kidney. The phospholipid composition of brain was more similar in the reptile and mammal compared to those of other tissues.
The ontogeny of fin function during routine turns in zebrafishDanio rerio
Authors: Danos Nicole , Lauder George V.
Published: September 2007

Zebrafish Danio rerio exhibit spontaneous, routine turns as part of their normal foraging behavior from the early free-swimming stage to adulthood. Given the importance of this behavior and its pervasiveness during zebrafish life history, the functional requirements of routine turning should play an important role in development. Conversely, the ontogeny of turning performance should reflect morphological development. In this paper we analyze the kinematics of routine turning during ontogeny in zebrafish and compare the scaling of turning kinematics to predictions from two existing models. Twenty-nine fish ranging in size from 0.38 to 1.97 cm in fork length(FL) were filmed at 1000 frames s–1 while performing routine turns. Images were analyzed using image cross-correlation to calculate body and fin velocities. We performed piecewise linear regression to identify variables that do not have a constant rate of change across ontogeny and found that two variables, turn angle and angular velocity, have a transition in slope at a body size of approximately 1 cm. Other variables show a constant positive (pectoral and caudal fin velocity, turn duration), negative (body curvature) or zero (head velocity) rate of change across ontogeny. We interpret these trends in light of morphological changes over ontogeny as well as relevant hydrodynamic conditions. We also compare the slope of the log-transformed variables to predictions from two scaling models of change in function with increasing size. We find mixed support for both models with no single model being better at predicting a single type of variable such as linear velocities. We conclude that morphological development of the paired and median fins and of the skeleton, is an important factor in determining the performance of routine turning over ontogeny. Three-dimensional kinematics and ecological behavior information will further elucidate the ontogenetic patterns observed here.
Timing is everything: coordination of strike kinematics affects the force exerted by suction feeding fish on attached prey
Authors: Holzman Roi , Day Steven W. , Wainwright Peter C.
Published: September 2007

During aquatic suction feeding, the predator opens its mouth and rapidly expands its buccal cavity, generating a flow field external to the mouth. The rapid expansion of the buccal cavity produces high fluid velocities and accelerations that extend only a short distance from the mouth (about half of one mouth diameter), and only persist for several milliseconds. Therefore, the predator must precisely time its strike to locate the prey within the narrow region of high flow, during the brief period when flow is at its peak. With flow being the agent for transferring force to the prey, the predator may enhance these forces by producing higher water velocities and faster acceleration at the mouth, but also through increasing the strike's accuracy,i.e. locating the prey closer to the mouth at the instant of peak flow speed. The objectives of this study were to directly measure forces exerted by bluegill Lepomis macrochirus on their prey and to determine how bluegill modify force output. Bluegill were offered ghost shrimp tethered to a load cell that recorded force at 5000 Hz, and feeding sequences were synchronously recorded using 500 Hz video. Peak forces exerted on attached 20 mm shrimp ranged from 0.005 N to 0.506 N. In accordance with the short duration of the strikes (average time to peak gape of ∼13 ms), the forces recorded were brief (∼12 ms from initiation to peak force), and force magnitude declined rapidly after peak force. Statistical analysis indicated that rate of buccal expansion, and prey size, but not strike initiation distance, significantly affected peak force. These observed variables were used with results from flow visualization studies to estimate the flow at the prey's location, which allowed the calculation of drag, pressure gradient force and acceleration reaction force. The relationship between these calculated forces and the measured forces was strong, indicating that the model can be used to estimate forces from strike kinematics. This model was then used to study the effects of strike initiation distance on peak force and on the rate of increasing force. Comparisons of model output to empirical results indicated that bluegill time their strike so as to exert an average of∼70% of the peak possible force on the prey, and that the observed strike initiation distance corresponded to the distance that maximized modeled force on an attached prey. Our results highlight the ability of bluegill to produce high forces on their prey, and indicate that precision and visual acuity play important roles in prey acquisition, beyond their recognized role in prey detection.
Heavy metal detoxification in crustacean epithelial lysosomes: role of anions in the compartmentalization process
Authors: Sterling Kenneth M. , Mandal Prabir K. , Roggenbeck Barbara A. , Ahearn Sean E. , Gerencser George A. , Ahearn Gregory A.
Published: September 2007

Crustacean hepatopancreatic lysosomes are organelles of heavy metal sequestration and detoxification. Previous studies have shown that zinc uptake by lysosomal membrane vesicles (LMV) occurred by a vanadate- and thapsigargin-sensitive ATPase that was stimulated by a transmembrane proton gradient established by a co-localized V-ATPase associated with this organelle. In the present study, hepatopancreatic LMV from the American lobster Homarus americanus were prepared by standard centrifugation methods and 65Zn2+, 36Cl–, 35SO42– and 14C-oxalate2– were used to characterize the interactions between the metal and anions during vesicular detoxification events. Vesicles loaded with SO42– or PO43– led to a threefold greater steady-state accumulation of Zn2+ than similar vesicles loaded with mannitol,Cl– or oxalate2–. The stimulation of 65Zn2+ uptake by intravesicular sulfate was SO42– concentration dependent with a maximal enhancement at 500 μmol l–1. Zinc uptake in the presence of ATP was proton-gradient enhanced and electrogenic, exhibiting an apparent exchange stoichiometry of 1Zn+/3H+. 35SO42– and 14C-oxalate2– uptakes were both enhanced in vesicles loaded with intravesicular Cl– compared to vesicles containing mannitol, suggesting the presence of anion countertransport. 35SO42– influx was a sigmoidal function of external [SO42–] with 25 mmol l–1 internal [Cl–], or with several intravesicular pH values (e.g. 7.0, 8.0 and 9.0). In all instances Hill coefficients of approximately 2.0 were obtained, suggesting that 2 sulfate ions exchange with single Cl– or OH– ions. 36Cl– influx was a sigmoidal function of external[Cl–] with intravesicular pH of 7.0 and 9.0. A Hill coefficient of 2.0 was also obtained, suggesting the exchange of 2 Cl– for 1 OH–. 14C-oxalate influx was a hyperbolic function of external [oxalate2–] with 25 mmol l–1 internal [Cl–], suggesting a 1:1 exchange of oxalate2– for Cl–. As a group,these experiments suggest the presence of an anion exchange mechanism exchanging monovalent for polyvalent anions. Polyvalent inorganic anions(SO42– and PO43–) are known to associate with metals inside vesicles and a detoxification model is presented that suggests how these anions may contribute to concretion formation through precipitation with metals at appropriate vesicular pH.
In vivored blood cell sickling and mechanism of recovery in whiting,Merlangius merlangus
Authors: Koldkjær Pia , Berenbrink Michael
Published: September 2007

Haemoglobin concentrations in vertebrate red blood cells are so high that in human sickle cell disease a single surface amino acid mutation can result in formation of large insoluble haemoglobin aggregates at low oxygen levels,causing peculiar cell deformations or `sickling'. This may cause vascular occlusion and thereby severe pain, organ failure and death. Here, using light and transmission electron microscopy, we demonstrate extensive in vivo sickling of whiting red blood cells after capture stress without any apparent haemolysis and show its subsequent recovery. We show exceptionally high cooperative proton binding during the sickling process in vitroand identify the reduction of extracellular pH below resting values as the primary cause for in vivo sickling, although the response is modulated to a lesser extent also by oxygen tension. Using isotope tracer fluxes, we further show that β-adrenergic hormones, which are released under capture stress, activate a powerful endogenous Na/H exchanger in these fish red blood cells, which is known to elevate intracellular pH.β-adrenergic treatment further leads to a marked reduction of acid-induced in vitro sickling, which is impaired when Na/H exchange is inhibited by amiloride. We propose that this mechanism protects red blood cells of some fishes against the problem of haemoglobin aggregation and red blood cell sickling, except under most severe acidosis. This system offers a unique example of how, over evolutionary time, nature may have overcome what is still a deadly disease in humans.
Nitric oxide formation from nitrite in zebrafish
Authors: Jensen Frank B.
Published: September 2007

Nitrite is a potential nitric oxide (NO) donor and may have important biological functions at low concentrations. The present study tests the hypothesis that nitrite accumulation across the gills in fish will cause a massive NO production from nitrite. Zebrafish were exposed to three different nitrite levels for variable time periods, and changes in blood nitrosylhemoglobin (HbNO), methemoglobin (metHb), oxygenated hemoglobin(oxyHb) and deoxygenated hemoglobin (deoxyHb) were evaluated by spectral deconvolution. Blood HbNO (a biomarker of internal NO production) was low in controls, increased to a stable level around 3.7% of total Hb in fish exposed to 0.6 mmol l–1 nitrite, and to 12.1% (at day 2) in fish exposed to 2 mmol l–1 nitrite. The very high HbNO levels testify to an extensive conversion of nitrite to NO. With deoxyHb-mediated reduction of nitrite being a major NO-producing mechanism, the data reveal the significance of this mechanism, when hemoglobin cycles between full and intermediate oxygen saturations in the arterial–venous circulation. Fish exposed to 0.6 mmol l–1 nitrite for up to 5 days could be divided into responding (with elevated metHb) and non-responding individuals. Exposure to 2 mmol l–1 nitrite caused a time-dependent increase in metHb to 59% of total Hb within 2 days. Taking HbNO into account,the functional (potential O2 carrying) Hb was reduced to 29% at this stage. Total blood [Hb] was also significantly decreased. In spite of the reduced blood O2 capacitance, and the possibility that excess NO may inhibit mitochondrial respiration, whole animal routine oxygen consumption was not depressed.
FoxK1splice variants show developmental stage-specific plasticity of expression with temperature in the tiger pufferfish
Authors: Fernandes Jorge M. O. , MacKenzie Matthew G. , Kinghorn James R. , Johnston Ian A.
Published: September 2007

FoxK1 is a member of the highly conserved forkhead/winged helix (Fox)family of transcription factors and it is known to play a key role in mammalian muscle development and myogenic stem cell function. The tiger pufferfish (Takifugu rubripes) orthologue of mammalian FoxK1(TFoxK1) has seven exons and is located in a region of conserved synteny between pufferfish and mouse. TFoxK1 is expressed as three alternative transcripts: TFoxK1-α, TFoxK1-γ and TFoxK1-δ. TFoxK1-α is the orthologue of mouse FoxK1-α, coding for a putative protein of 558 residues that contains the forkhead and forkhead-associated domains typical of Fox proteins and shares 53% global identity with its mammalian homologue. TFoxK1-γ and TFoxK1-δ arise from intron retention events and these transcripts translate into the same 344-amino acid protein with a truncated forkhead domain. Neither are orthologues of mouse FoxK1-β. In adult fish, the TFoxK1 splice variants were differentially expressed between fast and slow myotomal muscle, as well as other tissues, and the FoxK1-α protein was expressed in myogenic progenitor cells of fast myotomal muscle. During embryonic development, TFoxK1 was transiently expressed in the developing somites, heart,brain and eye. The relative expression of TFoxK1-α and the other two alternative transcripts varied with the incubation temperature regime for equivalent embryonic stages and the differences were particularly marked at later developmental stages. The developmental expression pattern of TFoxK1 and its localisation to mononuclear myogenic progenitor cells in adult fast muscle indicate that it may play an essential role in myogenesis in T. rubripes.
RNA-specific ribonucleotidyl transferases
Authors: Martin Georges , Keller Walter
Published: September 2007

RNA-specific nucleotidyl transferases (rNTrs) are a diverse family of template-independent polymerases that add ribonucleotides to the 3′-ends of RNA molecules. All rNTrs share a related active-site architecture first described for DNA polymerase β and a catalytic mechanism conserved among DNA and RNA polymerases. The best known examples are the nuclear poly(A) polymerases involved in the 3′-end processing of eukaryotic messenger RNA precursors and the ubiquitous CCA-adding enzymes that complete the 3′-ends of tRNA molecules. In recent years, a growing number of new enzymes have been added to the list that now includes the “noncanonical” poly(A) polymerases involved in RNA quality control or in the readenylation of dormant messenger RNAs in the cytoplasm. Other members of the group are terminal uridylyl transferases adding single or multiple UMP residues in RNA-editing reactions or upon the maturation of small RNAs and poly(U) polymerases, the substrates of which are still not known. 2′-5′Oligo(A) synthetases differ from the other rNTrs by synthesizing oligonucleotides with 2′-5′-phosphodiester bonds de novo.
Conformational energy and structure in canonical and noncanonical forms of tRNA determined by temperature analysis of the rate of s4U8–C13 photocrosslinking
Authors: Huggins Wayne , Shapkina Tatjana , Wollenzien Paul
Published: September 2007

Bacterial tRNAs frequently have 4-thiouridine (s4U) modification at position 8, which is adjacent to the C13-G22-m7G46 base triple in the elbow region of the tRNA tertiary structure. Irradiation with light in the UVA range induces an efficient photocrosslink between s4U8 and C13. The temperature dependence of the rate constants for photocrosslinking between the s4U8 and C13 has been used to investigate the tRNA conformational energy and structure in Escherichia coli tRNAVal, tRNAPhe, and tRNAfMet under different conditions. Corrections have been made in the measured rate constants to compensate for differences in the excited state lifetimes due to tRNA identity, buffer conditions, and temperature. The resulting rate constants are related to the rate at which the s4U8 and C13 come into the alignment needed for photoreaction; this depends on an activation energy, attributable to the conformational potential energy that occurs during the photoreaction, and on the extent of the structural change. Different photocrosslinking rate constants and temperature dependencies occur in the three tRNAs, and these differences are due both to modest differences in the activation energies and in the apparent s4U8–C13 geometries. Analysis of tRNAVal in buffers without Mg2+ indicate a smaller activation energy (∼13 kJ mol−1) and a larger apparent s4U8–C13 distance (∼12 Å) compared to values for the same parameters in buffers with Mg2+ (∼26 kJ mol−1 and 0.36 Å, respectively). These measurements are a quantitative indication of the strong constraint that Mg2+ imposes on the tRNA flexibility and structure.
Substrate specificity and properties of the Escherichia coli 16S rRNA methyltransferase, RsmE
Authors: Basturea Georgeta N. , Deutscher Murray P.
Published: September 2007

The small ribosome subunit of Escherichia coli contains 10 base-methylated sites distributed in important functional regions. At present, seven enzymes responsible for methylation of eight bases are known, but most of them have not been well characterized. One of these enzymes, RsmE, was recently identified and shown to specifically methylate U1498. Here we describe the enzymatic properties and substrate specificity of RsmE. The enzyme forms dimers in solution and is most active in the presence of 10–15 mM Mg2+ and 100 mM NH4Cl at pH 7–9; however, in the presence of spermidine, Mg2+ is not required for activity. While small ribosome subunits obtained from an RsmE deletion strain can be methylated by purified RsmE, neither 70S ribosomes nor 50S subunits are active. Likewise, 16S rRNA obtained from the mutant strain, synthetic 16S rRNA, and 3′ minor domain RNA are all very poor or inactive as substrates. 30S particles partially depleted of proteins by treatment with high concentrations of LiCl or in vitro reconstituted intermediate particles also show little or no methyl acceptor activity. Based on these data, we conclude that RsmE requires a highly structured ribonucleoprotein particle as a substrate for methylation, and that methylation events in the 3′ minor domain of 16S rRNA probably occur late during 30S ribosome assembly.