bluuebunny/crossref_metadata_2025_split huggingface dataset:
MED14 and MED1 Differentially Regulate Target-Specific Gene Activation by the Glucocorticoid Receptor
Authors: Chen Weiwei , Rogatsky Inez , Garabedian Michael J. 
Published: October 2005

AbstractThe Mediator subunits MED14 and MED1 have been implicated in transcriptional regulation by the glucocorticoid receptor (GR) by acting through its activation functions 1 and 2. To understand the contribution of these Mediator subunits to GR gene-specific regulation, we reduced the levels of MED14 and MED1 using small interfering RNAs in U2OS-hGR osteosarcoma cells and examined the mRNA induction by dexamethasone of four primary GR target genes, interferon regulatory factor 8 (IRF8), ladinin 1, IGF-binding protein 1 (IGFBP1), and glucocorticoid-inducible leucine zipper (GILZ). We found that the GR target genes differed in their requirements for MED1 and MED14. GR-dependent mRNA expression of ladinin 1 and IRF8 required both MED1 and MED14, whereas induction of IGFBP1 mRNA by the receptor was dependent upon MED14, but not MED1. In contrast, GILZ induction by GR was largely independent of MED1 and MED14, but required the p160 cofactor transcriptional intermediary factor 2. Interestingly, we observed higher GR occupancy at GILZ than at the IGFBP1 or IRF8 glucocorticoid response element (GREs). In contrast, recruitment of MED14 compared with GR at IGFBP1 and IRF8 was higher than that observed at GILZ. At GILZ, GR and RNA polymerase II were recruited to both the GRE and the promoter, whereas at IGFBP1, RNA polymerase II occupied the promoter, but not the GRE. Thus, MED14 and MED1 are used by GR in a gene-specific manner, and the requirement for the Mediator at GILZ may be bypassed by increased GR and RNA polymerase II occupancy at the GREs. Our findings suggest that modulation of the Mediator subunit activities would provide a mechanism for promoter selectivity by GR.
Codependence of Growth Hormone-Responsive, Sexually Dimorphic Hepatic Gene Expression on Signal Transducer and Activator of Transcription 5b and Hepatic Nuclear Factor 4α
Authors: Holloway Minita G. , Laz Ekaterina V. , Waxman David J. 
Published: October 2005

AbstractTargeted disruption of the signal transducer and activator of transcription 5b gene (STAT5b) leads to decreased expression in male mouse liver of a male-predominant cytochrome (Cyp) 2d protein, whereas female-predominant Cyp2b proteins are increased. Presently, we characterize the effects of STAT5b deficiency on 15 specific, individual Cyp RNAs and other sexually dimorphic liver gene products. All seven male-specific RNAs investigated were decreased to normal female levels in STAT5b-deficient male liver, whereas five of eight female-specific RNAs, designated class I female genes, were increased in expression up to 200-fold or more. STAT5b deficiency had a much more modest effect on the expression of these genes in females. Hypophysectomy and GH replacement studies demonstrated positive GH pulse regulation of all seven male RNAs and negative GH pulse regulation of class I, but not class II, female RNAs in wild-type, but not in STAT5b-deficient, male mice. A majority of the sex-specific genes responded in parallel to the loss of STAT5b and the loss of hepatocyte nuclear factor 4α, indicating that both transcription factors are essential and suggesting they may coregulate sexually dimorphic liver gene expression. Continuous GH treatment of intact male mice, which overrides the endogenous male, pulsatile plasma GH pattern, down-regulated all seven male RNAs and induced expression of the five class I female RNAs within 4–7 d; however, induction of class II female RNAs was delayed until d 7–14. Given the slow responses of all 15 genes to changes in plasma GH status, GH regulation of sex-specific Cyp expression is proposed to be indirect and mediated by STAT5b- and hepatocyte nuclear factor 4α-dependent factors that may include repressors of female-specific Cyps and other targets of GH action.
Effects of intake rate on energy expenditure, somatic repair and reproduction of zebra finches
Authors: Wiersma Popko , Verhulst Simon 
Published: October 2005

SUMMARY
Understanding the effect of food availability on food requirements is critical when linking food availability e.g. to reproduction or habitat selection. Decreasing intake rate (intake per unit foraging effort) can be expected to increase daily energy expenditure (DEE), due to increased foraging costs. However, all the studies we could find that have tested this hypothesis(with one exception) found DEE to be constant or decreasing when intake rate was experimentally decreased. This may be due to the design of the reward schedule, which can be fixed (e.g. 20 units effort required for each reward)or variable (e.g. each unit effort rewarded with probability 1/20). Most studies used fixed reward rates, but foraging motivation is generally higher for variable reward rates, and the only study in which animals increased DEE when intake rate decreased used variable reward rates. To assess the generality of this result, we exposed zebra finches Taeniopygia guttata to different intake rates using variable reward rates.We decreased intake rate by mixing 25 g of seeds with 0, 25 or 75 g of chaff. With increasing chaff/seed ratio the time spent foraging increased from 6% to 27%, but this was insufficient to compensate for the lower intake rate,because DEE decreased by 6.6%. Body mass was independent of chaff/seed ratio. Effects of intake rate on foraging time and DEE were stronger at lower temperatures, when DEE was higher. The decrease in DEE in adverse conditions raises the question of what prevents such behaviour in benign circumstances.
We hypothesize that energy is saved at the expense of `condition', and we tested this hypothesis in two ways. Firstly, we tested the effect of intake rate on the replacement of two plucked tail feathers (a form of somatic repair). Replacement feathers were shorter when intake rate was low,indicating an effect of intake rate on somatic repair ability. Secondly, we tested for carry-over effects of intake rate on reproduction, by giving pairs the opportunity to reproduce with access ad libitum to food after feeding on one of the three chaff/seed ratios for 6 weeks. The interval until laying the first egg increased with decreasing intake rate in the preceding 6 weeks. The effects of intake rate on somatic maintenance and reproduction may explain why birds sustained higher metabolic rates than apparently necessary,but the physiological mechanisms determining the optimal metabolic rate remain to be discovered.
Metabolic adjustments to increasing foraging costs of starlings in a closed economy
Authors: Wiersma Popko , Salomons H. Martijn , Verhulst Simon 
Published: October 2005

SUMMARY
Knowledge of the physiological consequences of variation in food availability may be essential for understanding behavioural and life history responses to such variation. To study the physiological consequences of food availability animals are generally subjected to caloric restriction or starvation, thereby reducing the upper limit to the energy budget. The relevance of this approach to free-living animals is questionable, however,because under natural conditions low food availability often results in higher foraging costs, and everything else remaining equal this results in a higher energy budget. We manipulated food availability by varying the foraging costs and studied effects on daily energy expenditure (DEE) and energy allocation of captive starlings Sturnus vulgaris. Birds in a closed economy earned their food by flying between two perches 5 m apart. The probability of a reward was set at three different levels, thereby creating a `poor',`intermediate' and `rich' environment. Compared with the rich environment,birds flew 4 times more (2.3 h per day) in the poor environment, and increased DEE by 43% to 220 kJ day-1 (3.7×BMR), within the range of free-living parents rearing young. To our knowledge this is the first study to show an increase in DEE with decreasing food availability. Body mass, basal metabolic rate (BMR) and pectoral muscle size were reduced in the poor environment. Nocturnal energy expenditure was further reduced by reaching BMR earlier in the night. Calculations show that the energy demands in the poor environment could not be met with the flight costs of 20.5 W that we measured previously in a rich environment. Flight costs derived indirectly from the energy budget were lower, at 17.5 W, probably due to lower body mass. By reducing body mass by 20%, and economising during sleep, the birds achieved savings of 37% in their DEE. Without these savings, a DEE substantially higher than measured in free-living parents rearing young would be required to remain in energy balance. Surprisingly little data exist to verify whether free-living animals use the same tactics to survive periods with low food availability.
Calcium-activated potassium channel of the tobacco hornworm,Manduca sexta: molecular characterization and expression analysis
Authors: Keyser Matthew R. , Witten Jane L. 
Published: October 2005

SUMMARYLarge-conductance calcium- and voltage-gated potassium channels (BK or Slowpoke) serve as dynamic integrators linking electrical signaling and intracellular activity. These channels can mediate many different Ca2+-dependent physiological processes including the regulation of neuronal and neuroendocrine cell excitability and muscle contraction. To gain insights into the function of BK channels in vivo, we isolated a full-length cDNA encoding the alpha subunit of a Slowpoke channel from the tobacco hornworm, Manduca sexta (msslo). Amino acid sequence comparison of the deduced Manduca protein revealed at least 80%identity to the insect Slo channels. The five C-terminal alternative splice regions are conserved, but the cloned cDNA fragments contained some unique combinations of exons E, G and I. Our spatial profile revealed that transcript levels were highest in skeletal muscle when compared with the central nervous system (CNS) and visceral muscle. The temporal profile suggested that msslo expression is regulated developmentally in a tissue- and regional-specific pattern. The levels of msslo transcripts remain relatively constant throughout metamorphosis in the CNS, transiently decline in the heart and are barely detectable in the gut except in adults. A dramatic upregulation of msslo transcript levels occurs in thoracic but not abdominal dorsal longitudinal body wall muscles (DLM), suggesting that the msSlo current plays an important role in the excitation or contractile properties of the phasic flight muscle. Our developmental profile of msslo expression suggests that msSlo currents may contribute to the changes in neural circuits and muscle properties that produce stage-specific functions and behaviors.
Cryoprotection by urea in a terrestrially hibernating frog
Authors: Costanzo Jon P. , Lee Richard E. 
Published: October 2005

SUMMARYThe role of urea as a balancing osmolyte in osmotic adaptation is well known, but this `waste product' also has myriad other functions in diverse taxa. We report that urea plays an important, previously undocumented role in freezing tolerance of the wood frog (Rana sylvatica), a northern woodland species that hibernates terrestrially in sites where dehydration and freezing may occur. Wood frogs inhabiting an outdoor enclosure accumulated urea to 65 mmol l-1 in autumn and early winter, when soil moisture was scarce, but subsequently urea levels fell to ∼2 mmol l-1 as the availability of environmental water increased. Laboratory experiments showed that hibernating R. sylvatica can accumulate at least 90 mmol l-1 urea under relatively dry, warm conditions. During experimental freezing, frogs synthesized glucose but did not accumulate additional urea. Nevertheless, the concentrations of urea and glucose in some tissues were similar. We tested urea's efficacy as a cryoprotectant by measuring lysis and lactate dehydrogenase (LDH) leakage in samples of R. sylvaticaerythrocytes frozen/thawed in the presence of physiological levels of urea or other osmolytes. In conferring protection against freeze/thaw damage, urea was comparable to glycerol and as good as or better than glucose, cryoprotectants found in freeze-tolerant frogs and other animals. Urea treatment also improved the viability of intact tissues frozen in vitro, as demonstrated by post-thaw measures of metabolic activity and LDH leakage. Collectively, our findings suggest that urea functions both as an osmoprotectant and a cryoprotectant in terrestrially hibernating amphibians.
Does swarming cause honey bees to update their solar ephemerides?
Authors: Towne William F. , Baer Christopher M. , Fabiny Sarah J. , Shinn Lisa M. 
Published: October 2005

SUMMARYSpatial orientation in the social insects offers several examples of specialized learning mechanisms that underlie complex learning tasks. Here we study one of these systems: the processes by which honey bees update, or fail to update, their memories of the sun's daily pattern of movement (the solar ephemeris function) in relation to the landscape. Specifically, we ask whether bees that have initially learned the solar ephemeris function relative to a conspicuous treeline at their natal site can later realign the ephemeris to a differently oriented treeline. We first confirm and clarify an earlier finding that bees transplanted passively (by being carried) do not re-learn the solar ephemeris in relation to the new treeline. When they cannot detect the sun directly, as on overcast days, these transplanted bees use a solar ephemeris function appropriate for their natal site, despite days or weeks of experience at the new site. We then ask whether bees put through a swarming process as they are transplanted are induced to re-learn the solar ephemeris function at the new site, as swarming is a natural process wherein bees transplant themselves. Most of the swarmed bees failed to re-learn, even though they did extensive learning flights (in comparison with those of non-swarmed controls)as they first emerged from the hive at the new site. We hypothesize that the bees' representation of the solar ephemeris function is stored in an encapsulated cognitive module in which the ephemeris is inextricably linked to the reference landscape in which it was learned.
Miniaturization (0.2 g) and evaluation of attachment techniques of telemetry transmitters
Authors: Naef-Daenzer B. , Früh D. , Stalder M. , Wetli P. , Weise E. 
Published: October 2005

SUMMARY
We have developed a miniaturized very high frequency (VHF) transmitter design for radio-tagging small animals. The average mass of the circuitry is 0.084 g (range 0.081-0.087), hence, with the smallest power cell, complete tags weigh 0.2 g and have a life of 18-22 days. We further demonstrate that with such small tags the technique of attaching the device to the animal's body strongly affects the effective radiated power, and thus transmission ranges. Ideally the attachment couples the electronics to the animal's body as a ground plane for improved radiation. The transmitter allows the application of radio-tracking to be expanded to new taxa whose spatial behaviour and population dynamics are largely unknown, for example arthropods, reptiles or amphibians. The new design is also suitable for miniature implants and signal modulation with sensors.
Ionoregulatory changes in different populations of maturing sockeye salmonOncorhynchus nerkaduring ocean and river migration
Authors: Shrimpton J. M. , Patterson D. A. , Richards J. G. , Cooke S. J. , Schulte P. M. , Hinch S. G. , Farrell A. P. 
Published: October 2005

SUMMARYWe present the first data on changes in ionoregulatory physiology of maturing, migratory adult sockeye salmon Oncorhynchus nerka. Fraser River sockeye were intercepted in the ocean as far away as the Queen Charlotte Islands (∼850 km from the Fraser River) and during freshwater migration to the spawning grounds; for some populations this was a distance of over 700 km. Sockeye migrating in seawater toward the mouth of the Fraser River and upriver to spawning grounds showed a decline in gill Na+,K+-ATPase activity. As a result, gill Na+,K+-ATPase activity of fish arriving at the spawning grounds was significantly lower than values obtained from fish captured before entry into freshwater. Plasma osmolality and chloride levels also showed significant decreases from seawater values during the freshwater migration to spawning areas. Movement from seawater to freshwater increased mRNA expression of a freshwater-specific Na+,K+-ATPase isoform(α1a) while having no effect on the seawater-specific isoform(α1b). In addition, gill Na+,K+-ATPase activity generally increased in active spawners compared with unspawned fish on the spawning grounds and this was associated with a marked increase in Na+,K+-ATPase α1b mRNA. Increases in gill Na+,K+-ATPase activities observed in spawners suggests that the fish may be attempting to compensate for the osmotic perturbation associated with the decline in plasma chloride concentration and osmolality.
Path integration in a three-dimensional maze: ground distance estimation keeps desert ants Cataglyphis fortis on course
Authors: Grah Gunnar , Wehner Rüdiger , Ronacher Bernhard 
Published: October 2005

SUMMARY
In this study, we investigate the ability of desert ants to gauge the ground distances of sloped sections in a three-dimensional (3D) outbound path. Ground distance estimation, as opposed to a simple measurement of walking distances, is a necessary prerequisite for precise path integration in undulating terrain. We trained ants to visit a feeder along a path that included an angular turn as well as a `hill', resulting in an outbound path with a distinct 3D structure. We then observed the ants' return path in a test field on level ground. From the angles of the ants' return path on the test field one can infer which property of the hill segment was fed into the ants'path integration module, the actual walking distance or the ground distance. The results show clearly that it is the ground distance that Cataglyphis fortis feeds into its path integrator, and suggest that the ants are able to keep an accurate home vector also in hilly terrain.
Oxygen delivery to the fish eye: Root effect as crucial factor for elevated retinalPO2
Authors: Waser W. , Heisler N. 
Published: October 2005

SUMMARYAlthough the retina has one of the highest metabolic rates among tissues,certain teleost fishes lack any vascular supply to this organ which, in combination with the overall thickness of the organ, results in extremely long diffusion distances. As the only way to compensate for these obstacles, oxygen partial pressure (PO2) in the eyes of such fish is elevated far above atmospheric values. Although not supported by any direct evidence, the enhancement of PO2 is considered to be related to the Root effect, the release upon acidification of Hb-bound O2 into physical dissolution, possibly supported by counter-current multiplication similar to the loop of Henle.The present study evaluates the magnitude of intraocular PO2 enhancement under tightly controlled physiological conditions, to directly confirm the involvement of the Root effect on intraocular PO2 in the retina of rainbow trout Oncorhynchus mykiss. Intraocular PO2 was determined with special polarographic microelectrodes inserted into the eye. PO2profiles established in vivo by driving electrodes through the entire retina yielded average PO2 values between 10 mmHg (1.3 kPa) at the inner retinal surface and 382 mmHg (50.9 kPa) close to the outer retinal limit (Bruch's membrane). According to estimates on the basis of the diffusion distances determined from sections of the retina(∼436 μm at the site of PO2 measurement)and literature data on specific oxygen consumption, the in vivodetermined values would be sufficient to cover the oxygen demand of the retina with some safety margin.For a clear and direct in-tissue-test as to the involvement of the Root effect, an isolated in vitro eye preparation was established in order to avoid the problem of indirect blood supply to the eye from the dorsal aorta only via the pseudobranch, a hemibranch thought to modulate blood composition before entry of the eye. Any humoral effects (e.g. catecholamines)were eliminated by perfusing isolated eyes successively with standardized red blood cell (RBC) suspensions in Ringer, using trout (with Root) and human(lacking any Root effect) RBC suspension. To optimize perfusate conditions for maximal Root effect, the Root effect of trout RBCs was determined in vitro via graded acidification of individual samples equilibrated with standardized gas mixtures. During perfusion with trout RBC, PO2 at the outer retinal limit was 99 mmHg(13.2 kPa), but fell by a factor of 3.3 upon perfusion with human RBC in spite of higher total oxygen content (TO2 2.8 for trout vs 3.9 mmol l-1 for human RBC). Upon reperfusion with trout RBC, PO2 was restored immediately to the original value. This regularly observed pattern indicated a highly significant difference (P=0.003) between perfusion with trout (with Root effect;high retinal PO2) and perfusion with human (no Root effect; low retinal PO2) RBC suspension,thus clearly demonstrating that the Root effect is directly involved and a crucial prerequisite for the enhancement of PO2in the retina of the teleost eye.
Ontogenetic development of locomotion in small mammals - a kinematic study
Authors: Schilling Nadja 
Published: October 2005

SUMMARYComparative studies of locomotion indicate that limb design and performance are very similar in adult mammals of small to medium size. The present study was undertaken to test whether basic therian limb pattern is present during postnatal development. Kinematic data were collected from juveniles of two eutherian species in a cross-sectional study, using cinevideography. The tree shrew Tupaia glis and the cui Galea musteloides were selected because of their different reproductive strategies, which could result in differences in the development of locomotor abilities. The aims of this study were to describe the process by which young animals develop the adult pattern of locomotion and the extent to which this process varies in two species with very different postnatal ontogenies.Despite their different life histories, the development of kinematic parameters in the altricial tree shrew and the precocial cui are surprisingly similar. General limb design, performance, and timing of segment and joint movements in the young animals were similar to adults in both species, even from the first steps. Touch-down of the forelimb occurred at the position below the eye in all individuals and limb position was highly standardized at touch-down; no major changes in segment and joint angles were observed. Significant changes occurred at lift-off. With increasing body mass, limb segments rotated more caudally, which resulted in larger limb excursions and relatively longer steps. Developmental changes in locomotor abilities were similar in both species; only the time necessary to reach the adult performance was different. Despite the widely assumed maturity of locomotor abilities in precocial young, the first steps of the cui juveniles were not similar to the movements of adults. The adult locomotor pattern was reached within the first postnatal week in the cui and by the time they leave the nest in the tree shrew (39 days after birth; individual P39).These results suggest that during the evolution of precocial development only processes independent of exercise or gravity can be shifted into the intrauterine period. However, development of locomotor ability dependents on exercise, and adjustments and training occur during growth. Therefore, only the time necessary to reach maturity was clearly shortened in the precocial juvenile relative to the ancestral altricial condition.