bluuebunny/crossref_metadata_2025 huggingface dataset:
The guanine nucleotide exchange factor C3G is necessary for the formation of focal adhesions and vascular maturation
Authors: Voss Anne K. , Gruss Peter , Thomas Tim
Published: December 2002

The Ras signalling pathway has major roles in normal cell function and oncogenesis. C3G is a guanine nucleotide exchange factor for members of the Ras family of GTPases. We generated a mouse strain with a hypomorphicC3G allele. C3Ggt/gt mutant embryos died of vascular defects around E11.5 due to haemorrhage and vascular integrity defects. Vascular supporting cells did not develop appropriately. C3G-deficient fibroblasts responded to PDGF-BB abnormally, exhibited cell adhesion defects and lacked paxillin and integrin-β1-positive cell adhesions. In contrast, integrin-β3-positive cell adhesions formed normally. These results show that C3G is required for (1) vascular myogenesis,(2) the formation of paxillin- and integrin β1-positive, but not integrinβ3-positive, cell adhesions and (3) normal response to PDGF, necessary for vascular myogenesis.
Grainy head controls apical membrane growth and tube elongation in response to Branchless/FGF signalling
Authors: Hemphälä Johanna , Uv Anne , Cantera Rafael , Bray Sarah , Samakovlis Christos
Published: December 2002

Epithelial organogenesis involves concerted movements and growth of distinct subcellular compartments. We show that apical membrane enlargement is critical for lumenal elongation of the Drosophila airways, and is independently controlled by the transcription factor Grainy head. Apical membrane overgrowth in grainy head mutants generates branches that are too long and tortuous without affecting epithelial integrity, whereas Grainy head overexpression limits lumenal growth. The chemoattractant Branchless/FGF induces tube outgrowth, and we find that it upregulates Grainy head activity post-translationally, thereby controlling apical membrane expansion to attain its key role in branching. We favour a two-step model for FGF in branching: first, induction of cell movement and apical membrane growth, and second, activation of Grainy head to limit lumen elongation,ensuring that branches reach and attain their characteristic lengths.
DNA repair geneErcc1is essential for normal spermatogenesis and oogenesis and for functional integrity of germ cell DNA in the mouse
Authors: Hsia Kan-Tai , Millar Michael R. , King Sasha , Selfridge Jim , Redhead Nicola J. , Melton David W. , Saunders Philippa T. K.
Published: December 2002

Ercc1 is essential for nucleotide excision repair (NER) but, unlike other NER proteins, Ercc1 and Xpf are also involved in recombination repair pathways. Ercc1 knockout mice have profound cell cycle abnormalities in the liver and die before weaning. Subsequently Xpa andXpc knockouts have proved to be good models for the human NER deficiency disease, xeroderma pigmentosum, leading to speculation that the recombination, rather than the NER deficit is the key to the Ercc1knockout phenotype. To investigate the importance of the recombination repair functions of Ercc1 we studied spermatogenesis and oogenesis inErcc1-deficient mice. Male and female Ercc1-deficient mice were both infertile. Ercc1 was expressed at a high level in the testis and the highest levels of Ercc1 protein occurred in germ cells following meiotic crossing over. However, in Ercc1 null males some germ cell loss occurred prior to meiotic entry and there was no evidence that Ercc1 was essential for meiotic crossing over. An increased level of DNA strand breaks and oxidative DNA damage was found in Ercc1-deficient testis and increased apoptosis was noted in male germ cells. We conclude that the repair functions of Ercc1 are required in both male and female germ cells at all stages of their maturation. The role of endogenous oxidative DNA damage and the reason for the sensitivity of the germ cells to Ercc1deficiency are discussed.
TheDrosophilatrithorax group genetonalli(tna) interacts genetically with the Brahma remodeling complex and encodes an SP-RING finger protein
Authors: Gutiérrez Luis , Zurita Mario , Kennison James A. , Vázquez Martha
Published: December 2002

The trithorax group genes are required for positive regulation of homeotic gene function. The trithorax group gene brahma encodes a SWI2/SNF2 family ATPase that is a catalytic subunit of the Brm chromatin-remodeling complex. We identified the tonalli (tna) gene inDrosophila by genetic interactions with brahma. tnamutations suppress Polycomb phenotypes and tna is required for the proper expressions of the Antennapedia, Ultrabithorax andSex combs reduced homeotic genes. The tna gene encodes at least two proteins, a large isoform (TnaA) and a short isoform (TnaB). The TnaA protein has an SP-RING Zn finger, conserved in proteins from organisms ranging from yeast to human and thought to be involved in the sumoylation of protein substrates. Besides the SP-RING finger, the TnaA protein also has extended homology with other eukaryotic proteins, including human proteins. We show that tna mutations also interact with mutations in additional subunits of the Brm complex, with mutations in subunits of the Mediator complex, and with mutations of the SWI2/SNF2 family ATPase genekismet. We propose that Tna is involved in postranslational modification of transcription complexes.
A critical role for elastin signaling in vascular morphogenesis and disease
Authors: Karnik Satyajit K. , Brooke Benjamin S. , Bayes-Genis Antonio , Sorensen Lise , Wythe Joshua D. , Schwartz Robert S. , Keating Mark T. , Li Dean Y.
Published: December 2002

Vascular proliferative diseases such as atherosclerosis and coronary restenosis are leading causes of morbidity and mortality in developed nations. Common features associated with these heterogeneous disorders involve phenotypic modulation and subsequent abnormal proliferation and migration of vascular smooth muscle cells into the arterial lumen, leading to neointimal formation and vascular stenosis. This fibrocellular response has largely been attributed to the release of multiple cytokines and growth factors by inflammatory cells. Previously, we demonstrated that the disruption of the elastin matrix leads to defective arterial morphogenesis. Here, we propose that elastin is a potent autocrine regulator of vascular smooth muscle cell activity and that this regulation is important for preventing fibrocellular pathology. Using vascular smooth muscle cells from mice lacking elastin(Eln-/-), we show that elastin induces actin stress fiber organization, inhibits proliferation, regulates migration and signals via a non-integrin, heterotrimeric G-protein-coupled pathway. In a porcine coronary model of restenosis, the therapeutic delivery of exogenous elastin to injured vessels in vivo significantly reduces neointimal formation. These findings indicate that elastin stabilizes the arterial structure by inducing a quiescent contractile state in vascular smooth muscle cells. Together, this work demonstrates that signaling pathways crucial for arterial morphogenesis can play an important role in the pathogenesis and treatment of vascular disease.
Prey-capture success revealed by echolocation signals in pipistrelle bats (Pipistrellus pygmaeus)
Authors: Surlykke Annemarie , Futtrup Vibeke , Tougaard Jakob
Published: December 2002

Three Pipistrellus pygmaeus bats were trained to capture prey on the wing while flying in the laboratory. The bats' capture behaviour and capture success were determined and correlated with acoustic analyses of post-buzz echolocation signals. Three acoustic parameters revealed capture success: in case of success, post-buzz pauses (pbP) were longer, interpulse intervals (IPI) of the post-buzz signals were longer and, most notably, the spectra of the echolocation signals showed a number of notches that were absent after unsuccessful attempts. If the bats touched the prey without seizing it, pbP was significantly increased, but by less than was seen following a successful capture. Thus, acoustic recordings can be used to determine the outcome of a capture attempt with 72-75% correct using IPI or pbP, and with 78% correct using notches. Even more trials (>85%) were classified correctly by using the first canonical discriminant factor from principal component analysis combining the three parameters. Four types of prey were used, of 7-22 mm length and 7-240 mg mass. After successful captures, interpulse intervals, post-buzz pause and notches all depended on prey type, but not in a way that was systematically related to size, indicating that acoustic parameters cannot reveal prey size.
Tension sensitivity of the heart pacemaker neurons in the isopod crustaceanLigia pallasii
Authors: Sakurai Akira , Wilkens Jerrel L.
Published: December 2002

In the crustacean neurogenic heart, the cardiac ganglion (CG) acts as a peripherally located central pattern generator (CPG) by producing rhythmic motor output that initiates the heartbeat. In the isopod Ligia, the CG consists of six electrically coupled neurons that all function both as endogenous oscillators and as glutamatergic motoneurons innervating heart muscle. In the present study, we present several lines of evidence to suggest that the CG neurons are sensitive to passive stretch and active tension of the heart muscle. Stretching the heart wall caused a sustained decrease in the burst frequency of the CG neuron. Releasing from the stretch caused a rebound increase in burst frequency above the control rate. A brief stretch (200-300 ms duration) caused either phase advance or phase delay of the following CG bursts, depending on the timing at which the stretch was applied. Repeated brief stretches could entrain the CG bursts to either higher or lower frequencies than the free-run burst frequency. Intracellular recording from one of the CG neurons revealed that it exhibited hyperpolarization during the stretch. The stretch-induced hyperpolarization was followed by a burst discharge upon release from the stretch. With increased stretch amplitude, the amplitude of hyperpolarizing response increased and the timing of the following burst was advanced. When the myogenic activity of the heart muscle was pharmacologically isolated from the ganglionic drive by applying a glutamatergic antagonist, Joro spider toxin (JSTX), the spontaneous muscle contraction caused a hyperpolarizing deflection in the CG neuron. Under specific conditions made by JSTX and tetrodotoxin, the CG burst became entrained to the myogenic rhythm. These results suggest that the Ligia CG neurons have tension sensitivity in addition to their pacemaker and motoneuronal functions. Such multifunctional neurons may form a single neuron reflex arc inside the heart.
Proliferation of myogenic progenitor cells following feeding in the sub-antarctic notothenioid fishHarpagifer bispinis
Authors: Brodeur Julie C. , Calvo Jorge , Johnston Ian A.
Published: December 2002

Feeding metabolism and the activation of myogenic progenitor cells were investigated in the fast myotomal muscle of the sub-Antarctic fish Hapagifer bispinis acclimatized to either simulated summer (10°C; 18 h:6 h light:dark) or simulated winter (5°C; 6 h:18 h light:dark) conditions. Ingestion of a single meal equivalent to 10% and 15% of body mass in simulated winter and summer groups, respectively, resulted in an average 2.6-fold and 3.6-fold increase in oxygen consumption, declining to 75% of peak values after 63 h and 46 h. In fasted individuals, the number of myogenic progenitor cells, identified by the expression of c-met, was not significantly different between simulated summer and winter fish, representing 6.6% and 5.8% of total myonuclei, respectively. However, the number of cells expressing myogenin was higher whereas the expression of MyoD was lower in winter than in summer groups. The ingestion of a single meal under winter and summer treatment regimes resulted in a significant increase in the number of cells expressing MyoD (51% and 111%) and PCNA (88% and 140%, respectively). This was followed by an increase in the abundance of c-met (74 and 85%) and myogenin (42 and 97%, respectively) positive cells, indicating the production of new myogenic progenitor cells and the commitment to differentiation of a number of them. These results show that the proliferation of myogenic progenitor cells can be induced by feeding in teleost fishes and that temperature and photoperiod influence the expression of myogenic regulatory factors.
Differential expression of voltage-sensitive K+ and Ca2+ currents in neurons of the honeybee olfactory pathway
Authors: Grünewald Bernd
Published: December 2002

In order to understand the neuronal processes underlying olfactory learning, biophysical properties such as ion channel activity need to be analysed within neurons of the olfactory pathway. This study analyses voltage-sensitive ionic currents of cultured antennal lobe projection neurons and mushroom body Kenyon cells in the brain of the honeybee Apis mellifera. Rhodamine-labelled neurons were identified in vitro prior to recording, and whole-cell K+ and Ca2+ currents were measured. All neurons expressed transient and sustained outward K+ currents, but Kenyon cells expressed higher relative amounts of transient A-type K+ (IK,A) currents than sustained delayed rectifier K+ current (IK,V). The current density of the IK,V was significantly higher in projection neurons than in Kenyon cells. The voltage-dependency of K+ currents at positive membrane potentials was linear in Kenyon cells, but N-shaped in projection neurons. Blocking of voltage-sensitive Ca2+ currents transformed the N-shaped voltage-dependency into a linear one, indicating activation of calcium-dependent K+ currents (IK,Ca). The densities of currents through voltage-sensitive Ca2+ channels did not differ between the two neuron classes and the voltage-dependency of current activation was similar. Projection neurons thus express higher calcium-dependent K+ currents. These analyses revealed that the various neurons of the honeybee olfactory pathway in vitro have different current phenotypes, which may reflect functional differences between the neuron types in vivo.
Metabolic plasticity and critical temperatures for aerobic scope in a eurythermal marine invertebrate (Littorina saxatilis, Gastropoda: Littorinidae) from different latitudes
Authors: Sokolova Inna M. , Pörtner Hans-Otto
Published: December 2002

Effects of latitudinal cold adaptation and cold acclimation on metabolic rates and aerobic scope were studied in the eurythermal marine gastropod Littorina saxatilis from temperate North Sea and sub-arctic White Sea areas. Animals were acclimated for 6-8 weeks at control temperature (13°C) or at 4°C, and their respiration rates were measured during acute temperature change (1-1.5°C h-1) in a range between 0°C and 32°C. In parallel, the accumulation of anaerobic end products and changes in energy status were monitored. Starting from 0°C, aerobic metabolic rates of L. saxatilis rose quickly with increasing temperatures up to a point at or slightly above the respective acclimation temperature. Beyond this value, thermal sensitivity of oxygen consumption rate (V̇O2) greatly decreased in a wide, 15°C range of experimental temperatures. This change in metabolic regulation was also reflected in the activation energy of aerobic metabolism (Ea), which was approximately seven times lower at temperatures above Arrhenius breakpoint temperatures (ABTs) than at temperatures below ABTs. Warming progressively led to a discrepancy between energy demand and energy production, as demonstrated by a decrease in the levels of high-energy phosphates [phosho-L-arginine (PLA) and ATP], and resulted in the onset of anaerobiosis at critically high temperatures, indicating a limitation of aerobic scope. The comparison of aerobic and anaerobic metabolic rates in L. saxatilis in air and water suggests that the heat-induced onset of anaerobiosis is due to the insufficient oxygen supply to tissues at high temperatures. Cold acclimation led to an increase in aerobic metabolic rates and a considerable downward shift of the upper critical temperature in North Sea L. saxatilis but not in White Sea L. saxatilis. Limited metabolic plasticity in response to cold acclimation in sub-arctic White Sea snails as compared with their temperate North Sea counterparts suggests that metabolic depression occurs during overwintering under the more extreme winter conditions at the White Sea.
Fluid mechanics produces conflicting, constraints during olfactory navigation of blue crabs,Callinectes sapidus
Authors: Weissburg M. J. , James C. P. , Smee D. L. , Webster D. R.
Published: December 2002

Foraging blue crabs must respond to fluid forces imposed on their body while acquiring useful chemical signals from turbulent odor plumes. This study examines how blue crabs manage these simultaneous demands. The drag force, and hence the cost of locomotion, experienced by blue crabs is shown to be a function of the body orientation angle relative to the flow. Rather than adopting a fixed orientation that minimizes the drag, blue crabs decrease their relative angle (increase drag) when odor is present in low speed flow, while assuming a drag-minimizing posture under other conditions. The motivation for crabs to adopt an orientation with larger drag appears to relate to their ability to acquire chemical signal information for odor tracking. In particular, when orienting at a smaller angle relative to the flow direction, more concentrated odor filaments arrive at the antennules to mediate upstream movement, allowing a more useful bilateral comparison between the appendage chemosensors to be made. Blue crabs respond to conflicting demands by weighting the degree of drag minimization in proportion to the potential magnitude of the drag cost and the potential benefit of acquiring chemosensory cues. Higher flow velocity magnifies the locomotory cost of a high drag posture, thus in swift flows crabs minimize drag and sacrifice their ability to acquire olfactory cues.
Rheotaxis and prey detection in uniform currents by Lake Michigan mottled sculpin(Cottus bairdi)
Authors: Kanter Max J. , Coombs Sheryl
Published: December 2002

Lake Michigan mottled sculpin, Cottus bairdi, exhibit a lateral-line mediated, unconditioned orienting response, which is part of the overall prey capture behavior of this species and can be triggered in visually deprived animals by both live (e.g. Daphnia magna) and artificial (e.g. chemically inert vibrating sphere) prey. However, the extent to which background water motions (e.g. currents) might mask the detection of biologically significant stimuli like these is almost entirely unknown, despite the fundamental nature and importance of this question. To examine this question, the orienting response of mottled sculpin was used to measure threshold sensitivity to a nearby artificial prey (a 50 Hz vibrating sphere) as a function of background noise level (unidirectional currents of different flow velocities). Because many fish show unconditioned rheotaxis to uniform currents, we also measured the fish's angular heading relative to the oncoming flow in the absence of the signal. Frequency distributions of fish headings revealed positive rheotaxis to flows as low as 4 cm s-1 and an increasing degree of alignment with the oncoming flow as a function of increasing flow velocity. Sculpin positioned in the upstream direction were able to detect relatively weak signals (estimated to be approx. 0.001-0.0001 peak—peak cm s-1 at the location of the fish) in the presence of strong background flows (2-8 cm s-1), and signal levels at threshold increased by less than twofold for a fourfold increase in flow velocity. These results are consistent with the idea that lateral line canals behave as high-pass filters to effectively reject low frequency noises such as those caused by slow d.c. currents.
Transient peripheral warming accompanies the hypoxic metabolic response in the golden-mantled ground squirrel
Authors: Tattersall Glenn J. , Milsom William K.
Published: December 2002

The hypoxic metabolic response of mammals involves a reversible metabolic suppression, possibly brought about by a reduction in the body temperature set-point. In the present study we tested the hypothesis that this is accompanied by a transient increase in heat loss that facilitates the decline in body temperature and metabolic rate. Peripheral heat distribution was assessed using infrared thermography to measure the surface temperatures of the golden-mantled ground squirrel at three different ambient temperatures (10, 22 and 30°C). During early hypoxic exposure, surface temperatures increased dramatically in the feet, ears and nose, and this increase was more dramatic and prolonged at 22°C than at the other two temperatures. These increases were associated with a fall in metabolic rate. Following this initial increase, surface temperatures decreased back to control values, and at 10°C, the surface temperatures of the eyes and body decreased below normoxic levels. Subsequent normoxic recovery was not accompanied by transient changes in surface temperatures, despite large increases in metabolic rate associated with post-hypoxic shivering and thermogenesis. The temporal changes in surface temperature suggest that peripheral blood flow is initially increased during hypoxia, shifting heat away from the core to the periphery and thus facilitating cooling. These results are consistent with the hypothesis that hypoxia leads to a regulated fall in body temperature.
Amino acids modulate ion transport and fluid secretion by insect Malpighian tubules
Authors: Hazel Matthew H. , Ianowski Juan P. , Christensen Robert J. , Maddrell Simon H. P. , O'Donnell Michael J.
Published: December 2002

Insect haemolymph typically contains very high levels of free amino acids. This study shows that amino acids can modulate the secretion of ions and water by isolated Malpighian tubules of Rhodnius prolixus and Drosophila melanogaster. Secretion rates of Rhodnius tubules in amino-acid-free saline increase after addition of serotonin to a peak value, then slowly decline to a plateau. Addition of glutamine, glutamate or aspartate to such tubules increases secretion rates dramatically relative to the controls in amino-acid-free saline, and these increases are sustained for 1-2h. Seven other amino acids have more modest stimulatory effects, whereas lysine and arginine are inhibitory. Secreted fluid pH and Na+ concentration increase and K+ concentration decreases in response to glutamine. Pre-incubation of unstimulated tubules in saline solutions containing amino acids followed by stimulation with serotonin in amino-acid-free saline shows that the effects of amino acids far outlast the duration of exposure to them. Amino acids do not appear to be important as metabolites in Rhodnius tubules, nor do they act to draw significant amounts of water into the lumen by osmosis. Significant stimulation of fluid secretion can be achieved by physiological levels of particular amino acids, whereas those amino acids that inhibit fluid secretion only do so at concentrations much above those at which they occur naturally in the haemolymph. Secretion rates of unstimulated or stimulated Drosophila tubules are increased by pre-incubation in saline solutions containing glutamine or methionine or by continuous exposure to glutamine, methionine or tyrosine. Cysteine dramatically inhibited fluid secretion by Drosophila tubules, but only at concentrations well above the physiological range. We suggest that the amino acids probably function as compatible intracellular osmolytes that are necessary for sustained secretion at high rates by the Malpighian tubules.
Energetics of diving in macaroni penguins
Authors: Green J. A. , Butler P. J. , Woakes A. J. , Boyd I. L.
Published: December 2002

Heart rate (fH), abdominal temperature (Tab) and diving depth were measured in thirteen free-ranging breeding female macaroni penguins. Measurement of these variables allowed estimation of the mass-specific rate of oxygen consumption (V̇O2) while diving and investigation of the physiological adjustments that might facilitate the diving behaviour observed in this species. In common with other diving birds, macaroni penguins showed significant changes in fH associated with diving, and these variables accounted for 36% of the variation in dive duration. When V̇O2 was calculated for dives of different durations, 95.3% of dives measured were within the calculated aerobic dive limit (cADL) for this species. Mean fH for all complete dive cycles was 147±6 beats min-1. When this fH is used to estimate V̇O2 of 26.2±1.4 ml min-1 kg-1 then only 92.8% of dives measured were within the cADL. Significant changes in abdominal temperature were not detected within individual dives, though the time constant of the measuring device used may not have been low enough to record these changes if they were present. Abdominal temperature did decline consistently during bouts of repeated diving of all durations and the mean decrease in Tab during a diving bout was 2.32±0.2°C. There was a linear relationship between bout duration and the magnitude of this temperature drop. There was no commensurate increase in dive duration during dive bouts as Tab declined, suggesting that macaroni penguins are diving within their physiological limits and that factors other than Tab are important in determining the duration of dives and dive bouts. Lowered Tab will in turn facilitate lower metabolic rates during diving bouts, but it was not possible in the present study to determine the importance of this energy saving and whether it is occurs actively or passively.
Exposure of brown troutSalmo truttato a sublethal concentration of copper in soft acidic water: effects upon gas exchange and ammonia accumulation
Authors: Beaumont M. W. , Butler P. J. , Taylor E. W.
Published: December 2002

The present study was undertaken to answer two questions relating to the exposure of brown trout Salmo trutta to sublethal concentrations of copper and low pH (CLP) for 96h. (1) What is the effect of these pollutants on the rate of oxygen consumption (ṀO2) at different levels of exercise and (2) why does ammonia accumulate within these fish, when the low external pH should favour the diffusion of NH3 across the gills? Mean ṀO2 of fish in CLP and control (normal pH and no added copper) conditions were not significantly different from each other at any level of exercise. This suggests that exposure to CLP was not a `loading' factor at any level of activity. However, both maximum ṀO2 and critical swimming speed (Ucrit) were significantly lower in the CLP trout (5.5±1.6 mmol O2 kg-1 h-1 and 1.12±0.06 BL s-1, respectively) than in control fish (18.5±2.3 mmol O2 kg-1 h-1 and 2.04±0.11 BL s-1, respectively). There was no evidence from cardiovascular variables, such as heart rate and cardiac output, to suggest any changes in the oxygen transport system to compensate for any possible reduction in branchial gas exchange. Thus, it is suggested that oxygen exchange and transport do not limit the swimming performance of CLP trout, but that exposure to CLP reduces the maximum demand for O2, i.e. it is a limiting factor.

The accumulation of ammonia in the plasma and white muscles during exposure to CLP has already been implicated in reducing the swimming performance of brown trout. Inhibition of cortisol synthesis abolished a large proportion of the increases in both the accumulation and excretion of ammonia that occurred during the second 48 h of the exposure to CLP, but did not inhibit ammonia accumulation completely. It is suggested that CLP not only causes an increase in the rate of production of ammonia, which is enhanced when the level of cortisol starts to increase after 48 h, but that it also inhibits an excretory mechanism (most probably Na+/NH4+ exchange) that is non-obligatory under `normal' conditions (when passive diffusion is sufficient), but is required in order to respond to unusually high ammonia loads.
Forgetting and the extension of memory inLymnaea
Authors: Sangha Susan , McComb Chloe , Lukowiak Ken
Published: December 2002

Aerial respiratory behaviour in Lymnaea stagnalis was operantly conditioned using a procedure that results in long-term memory (LTM) persisting for 1 but not 3 days. By manipulating the snails' post-training environment, i.e. preventing Lymnaea from performing aerial respiratory behaviour, memory persistence was significantly extended. Memory retention, however, is only extended if snails are prevented from performing aerial respiration in the same context in which they were trained. Snails trained in the `standard' context but prevented from performing aerial respiration in the `carrot-odor' context (and vice versa) did not extend their memory. These data are consistent with the hypothesis that forgetting is due to interfering events, that occur following learning and memory consolidation.
Fine-scale patterns of odor encounter by the antennules of mantis shrimp tracking turbulent plumes in wave-affected and unidirectional flow
Authors: Mead Kristina S. , Wiley Megan B. , Koehl M. A. R. , Koseff Jeffrey R.
Published: December 2002

Many marine animals track odor plumes to their source. Although studies of plume-tracking behavior have been performed in unidirectional flow, benthic animals such as crustaceans live in coastal habitats characterized by waves. We compared signal encounters by odor-plume-tracking stomatopods (mantis shrimp) in wave-affected and unidirectional flow in a flume. Stomatopods are small enough that we can study their natural behavior in a flume. They sample odors by flicking their antennules. A thin sheet of laser light illuminating an odor plume labeled with dye [planar laser induced fluorescence (PLIF) technique] permitted us to measure the instantaneous odor concentration encountered by the animal's chemosensory organs (antennules) while it tracked the plume. We simultaneously measured behavior and the high-resolution odor signal at the spatial and temporal scale of the animal. We found that the navigating animal encountered odor filaments more often in wave-affected flow than in unidirectional flow. Odor filaments along the animals' antennules were significantly wider and of higher concentration in waves than in unidirectional flow.
K+ amino acid transporter KAAT1 mutant Y147F has increased transport activity and altered substrate selectivity
Authors: Liu Zhilin , Stevens Bruce R. , Feldman Daniel H. , Hediger Matthias A. , Harvey William R.
Published: December 2002

KAAT1, a K+-coupled, neutral amino acid transporter from larval insect midgut, differs from other members of the Na+:neurotransmitter transporter family (SNF) in two important ways: (1) it transports nutrient L-, α-amino acids, rather than neurotransmitters such as γ-aminobutyric acid (GABA), and (2) it accepts K+ as well as Na+ as a co-substrate. To determine whether the restoration of KAAT1 residues to their GABA transporter GAT1 cation-binding equivalents might abolish its K+ but not its Na+ recognition site, we constructed a multiple mutant in which nine divergent KAAT1 residues were mutated back to the conserved form of the superfamily. To investigate the amino-acid-binding site, we constructed several single mutants that had been identified in GAT1. Wild-type (WT) or mutant cRNA was injected into Xenopus oocytes and the effects of external amino acids and ions upon labeled leucine uptake and substrate-induced currents were examined.

The multiple mutant exhibited no amino-acid-induced currents, indicating that one or more of the mutated residues are crucial for function. W75L and R76E mutations in the first transmembrane helix of KAAT1 led to results equivalent to those observed in the corresponding mutants of GAT1; namely,substrate (leucine) uptake and substrate-evoked net inward current were severely curtailed. The KAAT1 A523S mutant, which corresponds to a serotonin transporter mutant that is thought to render Li+ equivalent to Na+ as a co-transported ion, functioned no differently to WT.

The effects of mutation Y147F in the third transmembrane helix of KAAT1 were dramatically different from the equivalent mutation, Y140F, in GAT1. Although kinetic characteristics, expression levels and plasma membrane localization were all similar in Y147F and WT, the Y147F mutant exhibited a sevenfold increase in labeled leucine uptake by Xenopus oocytes in Na+ buffer. This increase is in sharp contrast to the complete loss of uptake activity in the GAT1 Y140F mutant. KAAT1 Y147F also differed from WT in cation selectivity and substrate spectrum, as revealed by amino-acid-induced net inward currents that were measured with a two-electrode voltage clamp.

Amino-acid-independent currents induced by Li+ and Na+ chloride salts were observed in both WT and the Y147F mutant. The Li+-induced current was 30% higher in Y147F than in WT, whereas no substrate-independent K+-induced currents above control levels were detected either in WT or Y147F. These results suggest that transport of K+, the physiological co-substrate in insect midgut, is tightly coupled to that of amino acids in KAAT1, in contrast to the independence of cation and amino acid transport in the closely related cation amino acid transporter channel, CAATCH1.
The dependence of electrical transport pathways in Malpighian tubules on ATP
Authors: Wu Daniel S. , Beyenbach Klaus W.
Published: December 2002

The relationship between the intracellular ATP concentration[ATP]i and the electrical properties of principal cells was investigated in Malpighian tubules of the yellow fever mosquito, Aedes aegypti. Under control conditions, [ATP]i was 0.91 mmol l-1, the input resistance of the principal cell(Rpc) was 334.1 kΩ, and the basolateral membrane was marked by a large K+-conductance and a membrane voltage(Vbl) of -75.8 mV. Peritubular cyanide (CN, 0.3 mmol l-1) reduced [ATP]i to 0.08 mmol l-1 in less than 2 min; however, Vbl dropped to -8 mV and Rpc increased to 3150.8 kΩ in 8 min, while the K+-conductance of the basolateral membrane disappeared. Upon washout of CN, Vbl and Rpc returned to control values within 2 min, and the basolateral membrane recovered its K+-conductance. The recovery of normal [ATP]i took 15 min. Dose-dependence and EC50 values for the CN-inhibition of Vbl and the increase in Rpc were strikingly similar (184.0 μmol l-1 and 164.4 μmol l-1). Similar effects of metabolic inhibition were observed with dinitrophenol (DNP), but the EC50 values were 50.3 μmol l-1 and 71.7 μmol l-1 for the effects on Vbl and Rpc, respectively. Barium, a blocker of K+-channels, significantly hyperpolarized Vbl to -89.1 mV and increased Rpc to 769.4 kΩ under control conditions, but had no effects during metabolic inhibition. These results illustrate a temporal relationship between[ATP]i and electrogenic and conductive transport pathways in principal cells that is consistent with the role of ATP as an integrator of transport steps at apical and basolateral membranes of the cell. When[ATP]i drops to levels that are 10% of control, the V-type H+-ATPase is inhibited, preventing the extrusion of K+to the tubule lumen. At the same time, basolateral membrane K+-channels close, preventing the entry of K+ from the hemolymph. Intracellular K+ homeostasis is thus protected during metabolic inhibition, allowing the cell to re-establish K+transport when ATP is synthesized again.
The myoglobin gene of the Antarctic icefish, Chaenocephalus aceratus, contains a duplicated TATAAAA sequence that interferes with transcription
Authors: Small Deena J. , Moylan Thomas , Vayda Michael E. , Sidell Bruce D.
Published: December 2002

Six of the 16 known species of Antarctic icefish (family Channichthyidae) have lost the ability to express cardiac myoglobin (Mb) via at least four independent events during radiation of these species. We report here that the lesion in Chaenocephalus aceratus Mb is a duplicated TATAAAA element that blocks transcription. This lesion is distinct from those of other icefish species that do not express cardiac Mb. The C. aceratus Mb gene is nearly identical to that of Chionodraco rastrospinosus, a closely related Mb-expressing icefish species, with one exception. A 15-bp segment is present in C. aceratus but absent from C. rastrospinosus; this insertion is located 648 bp upstream from the reference transcription start site of C. rastrospinosus and includes the sequence TATAAAA, which bound HeLa cell transcription factor IID (TFIID) and icefish nuclear proteins in gel-retardation assays. Reporter constructs containing the `full-length' C. aceratus Mb promoter were not expressed in transient expression assays in oxidative skeletal muscle of live icefish. By contrast, constructs employing the nearly identical `full-length' C. rastrospinosus Mb promoter were efficiently expressed in parallel assays in the same tissue. Truncated constructs of C. aceratus Mb that did not contain the 15-bp duplication were expressed at very low levels. These data confirm a third independent mechanism of Mb loss among channichthyid species, indicate that C. aceratus aerobic muscle is capable of expressing functional Mb genes and demonstrate that duplication of the muscle-specific TATAAAA sequence in an inappropriate context can result in loss of a gene's expression, resulting in significant physiological consequences.
Nutritive metal uptake in teleost fish
Authors: Bury Nicolas R. , Walker Paul A. , Glover Chris N.
Published: December 2002

Transition metals are essential for health, forming integral components of proteins involved in all aspects of biological function. However, in excess these metals are potentially toxic, and to maintain metal homeostasis organisms must tightly coordinate metal acquisition and excretion. The diet is the main source for essential metals, but in aquatic organisms an alternative uptake route is available from the water. This review will assess physiological, pharmacological and recent molecular evidence to outline possible uptake pathways in the gills and intestine of teleost fish involved in the acquisition of three of the most abundant transition metals necessary for life; iron, copper, and zinc.
The hydrodynamics of locomotion at intermediate Reynolds numbers:undulatory swimming in ascidian larvae (Botrylloidessp.)
Authors: McHenry Matthew J. , Azizi Emanuel , Strother James A.
Published: December 2002

Understanding how the shape and motion of an aquatic animal affects the performance of swimming requires knowledge of the fluid forces that generate thrust and drag. These forces are poorly understood for the large diversity of animals that swim at Reynolds numbers (Re) between 100 and 102. We experimentally tested quasi-steady and unsteady blade-element models of the hydrodynamics of undulatory swimming in the larvae of the ascidian Botrylloides sp. by comparing the forces predicted by these models with measured forces generated by tethered larvae and by comparing the swimming speeds predicted with measurements of the speed of freely swimming larvae. Although both models predicted mean forces that were statistically indistinguishable from measurements, the quasi-steady model predicted the timing of force production and mean swimming speed more accurately than the unsteady model. This suggests that unsteady force (i.e. the acceleration reaction) does not play a role in the dynamics of steady undulatory swimming at Re≈102. We explored the relative contribution of viscous and inertial force to the generation of thrust and drag at 100<Re<102 by running a series of mathematical simulations with the quasi-steady model. These simulations predicted that thrust and drag are dominated by viscous force (i.e. skin friction) at Re≈100 and that inertial force (i.e. form force) generates a greater proportion of thrust and drag at higher Rethan at lower Re. However, thrust was predicted to be generated primarily by inertial force, while drag was predicted to be generated more by viscous than inertial force at Re≈102. Unlike swimming at high (>102) and low (<100) Re, the fluid forces that generate thrust cannot be assumed to be the same as those that generate drag at intermediate Re.
What determines the tuning of hearing organs and the frequency of calls? A comparative study in the katydid genusNeoconocephalus(Orthoptera, Tettigoniidae)
Authors: Schul Johannes , Patterson Adam C.
Published: December 2002

The calls of five syntopic species of Neoconocephalus varied significantly in their spectral composition. The center-frequency of the narrow-band low-frequency component varied from 7kHz to 15kHz among the five species. Hearing thresholds, as determined from whole nerve recordings, did not vary accordingly among the five species but were lowest in the range from 16kHz to 18kHz in all five species. Iso-intensity response functions were flat for stimulus intensities up to 27dB above threshold, indicating an even distribution of the best frequencies of individual receptor cells. At higher stimulus intensities, the intensity/response functions were steeper at frequencies above 35kHz than at lower frequencies. This suggests the presence of a second receptor cell population for such high frequencies, with 25-30dB higher thresholds. This receptor cell population is interpreted as an adaptation for bat avoidance. The transmission properties of the Neoconocephalus habitat (grassland) had low-pass characteristics for pure tones. Frequencies below 10kHz passed almost unaffected, while attenuation in excess of spherical attenuation increased at higher frequencies. Considering these transmission properties and the tuning of female hearing sensitivity, call frequencies of approximately 9-10kHz should be most effective as communication signals in this group of insects. It is discussed that the frequency of male calls is strongly influenced by bat predation and by the transmission properties of the habitat but is not strongly influenced by the tuning of the female hearing system.
Sex differences in razorbill Alca torda parent—offspring vocal recognition
Authors: Insley Stephen J. , Paredes Rosana , Jones Ian L.
Published: December 2002

We investigated differences in parent—offspring vocal recognition between males and females in a natural population of razorbills Alca torda, a long-lived and highly social species of auk (Family: Alcidae). Razorbills provide biparental care to their chicks while at the nest site, after which the male is the sole caregiver for an additional period at sea. Parent—offspring recognition in razorbills is most challenging once the chick becomes mobile, leaves the nest site and goes to sea with the male parent. It is during this period when selection pressure acting on recognition behaviour is expected to be strongest. As a result, we predicted that parent—offspring recognition would be better developed in the male parent, that is, show a paternal bias. To test this prediction we used vocal playback experiments conducted on breeding razorbills at the Gannet Islands, Labrador, Canada. We found (1) most positive responses to playbacks (vocal and phonotactic) occurred close to fledging, (2) males responded more to calls from their chicks than to calls from strange chicks, (3) females responded indifferently to calls from their own or strange chicks and (4) chicks responded more to calls from their male parent than to calls from other adult males. The results provide clear evidence of mutual vocal recognition between the male parent and the chick but not between the female parent and the chick, supporting the prediction that parent—offspring recognition is male biased in this species. Such a bias could have important social implications for a variety of behavioural and basic life history traits such as cooperation and sex-biased dispersal.
Escape manoeuvres in damsel-fly larvae: kinematics and dynamics
Authors: Brackenbury John
Published: December 2002

The kinematics and hydrodynamics of rapid escape manoeuvres executed by final-stage larvae of Enallagma cyathigerum were investigated using videography combined with a simple wake-visualisation technique. Two kinds of escape manoeuvres were identified: first, a `rapid flex', comparable with the rapid C-start of fish, and, second, a `rapid twist' that involves a helical contraction of the body inducing motion in the yaw, pitch and roll planes. In both cases, the initial flexion phase is concerned with re-orientating the body, the extensional phase with acceleration of the body in the new direction. The behaviour of the caudal fin during twist indicates considerable independence of movement and aspect control within the three constituent lobes. Dye deposited beneath the resting larvae showed a thrust jet shed into the wake at the end of the extension phase. The estimated momentum of the ring vortex containing the jet was similar to that imparted to the body at the start of the translational phase. Similarities between the swimming dynamics of damsel-fly larvae and fish are discussed, as well as the wider implications of these findings to other aquatic invertebrates whose normal, steady swimming appears to be based on unsteady manoeuvres.
Expression and localization of carbonic anhydrase and ATPases in the symbiotic tubewormRiftia pachyptila
Authors: De Cian Marie-Cécile , Andersen Ann C. , Bailly Xavier , Lallier François H.
Published: December 2002

The symbiotic tubeworm Riftia pachyptila needs to fuel its chemoautotrophic symbiotic bacteria with inorganic carbon. CO2 is transported from the surrounding water to the bacteriocytes located in the trophosome, through the branchial plume and the body fluids. Previous studies have demonstrated the implication of carbonic anhydrase (CA) and proton pumps(ATPases) at various steps of CO2 transport. The present study describes the expression pattern of cytosolic CA using an RNA probe and its histochemical and immunocytochemical localization in the trophosome and branchial plume of Riftia. Immunolocalization of V-H+ATPase and Na+K+-ATPase were also performed and related to CA localization. In the branchial plume, CA is expressed and localized in the most apical region of the branchial epithelium,close to the surrounding water. V-H+ATPase is mostly colocalized with CA and both enzymes probably allow CO2 entry against the concentration gradient while regulating intracellular pH. Na+K+-ATPase is mostly restricted to the basal part of epithelial cells and probably participates in CO2 transport to the body fluids. In the trophosome lobules, cytosolic CA is expressed and found in bacteriocytes and peritoneal cells. Hypotheses on the role of CA in bicarbonate and CO2 interconversion to fuel the symbiotic bacteria are discussed.
A comparison of visual and haltere-mediated equilibrium reflexes in the fruit flyDrosophila melanogaster
Authors: Sherman Alana , Dickinson Michael H.
Published: December 2002

Flies exhibit extraordinary maneuverability, relying on feedback from multiple sensory organs to control flight. Both the compound eyes and the mechanosensory halteres encode angular motion as the fly rotates about the three body axes during flight. Since these two sensory modalities differ in their mechanisms of transduction, they are likely to differ in their temporal responses. We recorded changes in stroke kinematics in response to mechanical and visual rotations delivered within a flight simulator. Our results show that the visual system is tuned to relatively slow rotation whereas the haltere-mediated response to mechanical rotation increases with rising angular velocity. The integration of feedback from these two modalities may enhance aerodynamic performance by enabling the fly to sense a wide range of angular velocities during flight.