bluuebunny/crossref_metadata_2025_split huggingface dataset:
The single CH domain of calponin is neither sufficient nor necessary for F-actin binding
Authors: Gimona Mario , Mital Renu 
Published: April 2021

ABSTRACT
Calponins have been implicated in the regulation of actomyosin interactions in smooth muscle cells, cytoskeletal organisation in nonmuscle cells, and the control of neurite outgrowth. Domains homologous to the amino-terminal region of calponin have been identified in a variety of actin cross-linking proteins and signal transduction molecules, and by inference these ‘calponin homology (CH) domains’ have been assumed to participate in actin binding.
We here report on the actin binding activities of the subdomains of the calponin molecule. All three mammalian isoforms of calponin (basic h 1, neutral h2 and acidic) possess a single CH domain at their amino terminus as well as three tandem repeats proximal to the carboxyl terminus. Calponin h2 differs, however, from h 1 in lacking a consensus actin-binding motif in the region 142-163, between the CH domain and the tandem repeats, which in h 1 calponin can be chemically cross-linked to actin. Despite the absence of this consensus actin-binding motif, recombinant full-length h 2 calponin co-sediments in vitro with F-actin, suggesting the presence of another bindingsite in the molecule. It could be shown that this binding site resides in the C-terminal tandem repeats and not in the CH domain. Thus, constructs of h 2 calponin bearing partial or complete deletions of the triple repeated sequences failed to co-localise with actin stress fibres despite the presence of a CH domain. Deletion of the acidic carboxyl terminus, beyond the repeats, increased actin binding, suggesting that the carboxy-terminal tail may modulate actin association. Results obtained from transient transfections of amino- and carboxy-terminal truncations in h 1 calponin were consistent with the established location of the actin binding motif outside and carboxy-terminal to the CH domain, and confirm that the presence of a single CH domain alone is neither sufficient nor necessary to mediate actin binding. Instead, the carboxy-terminal tandem repeats of h 1 and h 2 calponin are shown to harbour a second, independent actin binding motif.
A rod end deletion in the intermediate filament protein nestin alters its subcellular localization in neuroepithelial cells of transgenic mice
Authors: Marvin Martha J. , Dahlstrand Jonas , Lendahl Urban , McKay Ronald D. G. 
Published: April 2021

ABSTRACT
Neuroepithelial and radial glial cells span between the ventricular and the pial surfaces of the neural tube and express two intermediate filaments (IFs), nestin and vimentin, which form a filamentous network throughout the length of the cells. In this report we study the polymerization characteristics of nestin and examine how mutations affect the assembly and localization of the nestin protein in cultured cells and in the developing CNS of transgenic mice. A wild-type rat nestin gene transfected into the IF-free SW13 cell line failed to assemble into a filamentous network but was incorporated into the existing IF network of a subclone expressing vimentin, demonstrating that nestin requires vimentin for proper assembly. In transgenic mice, rat nestin formed a network indistinguishable from that formed by endogenous nestin and vimentin, but a mutant form lacking five amino acids at the carboxy terminus of the rod domain was largely restricted to the pial endfeet. Since nestin mRNA is localized to the pial endfoot region we propose that both transgenes are translated there, but that the wild-type protein is preferentially incorporated into the IF network. These observations provide evidence for hierarchical assembly and a complex organization of the IF network along the ventricular-pial axis in the early CNS.
Functional association of nuclear protein 4.1 with pre-mRNA splicing factors
Authors: Lallena Marĺa-José , Martĺnez Concepción , Valcárcel Juan , Correas Isabel 
Published: April 2021

ABSTRACT
Protein 4.1 is a multifunctional polypeptide that links transmembrane proteins with the underlying spectrin/actin cytoskeleton. Recent studies have shown that protein 4.1 is also present in the nucleus, localized in domains enriched in splicing factors. Here we further analyze the relationship between protein 4.1 and components of the splicing machinery. Using HeLa nuclear extracts capable of supporting the splicing of pre-mRNAs in vitro, we show that anti-4.1 antibodies specifically immunoprecipitate pre-mRNA and splicing intermediates. Immunodepletion of protein 4.1 from HeLa nuclear extracts results in inhibition of their splicing activity, as assayed with two different pre-mRNA substrates. Coprecipitation of protein 4.1 from HeLa nuclear extracts with proteins involved in the processing of pre-mRNA further suggests an association between nuclear protein 4.1 and components of the splicing apparatus. The molecular cloning of a 4.1 cDNA encoding the isoform designated 4.1E has allowed us to show that this protein is targeted to the nucleus, that it associates with the splicing factor U2AF35, and that its overexpression induces the redistribution of the splicing factor SC35. Based on our combined biochemical and localization results, we propose that 4.1 proteins are part of nuclear structures to which splicing factors functionally associate, most likely for storage purposes.
Membrane recruitment of Rac1 triggers phagocytosis
Authors: Castellano Flavia , Montcourrier Philippe , Chavrier Philippe 
Published: April 2021

ABSTRACT
Rac1 is a Rho-family GTP-binding protein that controls lamellipodia formation and membrane ruffling in fibroblasts. Recently, Rac1 and Cdc42, another member of the Rho-family, have been shown to regulate Fc receptor-mediated phagocytosis in macrophages by controlling different steps of membrane and actin dynamics leading to particle engulfment. Here, we investigated the function of Rac1 using a membrane recruitment system that mimics phagocytosis. Recruitment of an activated Rac1 protein to the cytoplasmic domain of an engineered membrane receptor by using rapamycin as a bridge induces ingestion of latex beads bound to the receptor. Rac1-mediated bead uptake depends on actin polymerisation since actin filaments accumulate at the bead/membrane binding sites and internalisation is inhibited by cytochalasin D. Internalisation is also abolished upon substitution of Phe37 to Leu in the Rac1 effector region. Our results indicate that by promoting actin polymerisation at particle attachment sites, Rac1 by acting through specific downstream effectors induces plasma membrane remodeling that allows particle internalisation in a membrane-enclosed phagosome.
Temperature Regulation Of Honey Bees (Apis Mellifera) Foraging In The Sonoran Desert
Authors: Cooper Paul D. , Schaffer William M. , Buchmann Stephen L. 
Published: April 2021

ABSTRACT
A heat budget for foraging honey bees (Apis mellifera L.) indicated that at 30-35 °C all bees are in positive heat balance during flight. Observations of honey bees returning to their hives at high ambient temperatures support the conjecture that honey bees regulate head and thorax temperatures at high Ta by regurgitating droplets of honey stomach contents which are then evaporated. The proportion of returning bees with a droplet on the tongue increased with increasing shade temperature (Ts), from essentially no bees at 20°C to 40% of returning bees at 40°C. Pollen foragers carry relatively little fluid during the hottest periods, and pollen foraging decreased at high ambient temperatures. Thoracic temperatures of pollen collectors are significantly higher than thoracic temperatures of water and nectar gatherers at 40°C (46·13 vs 44°C). Additionally, water and nectar foragers with extruded droplets have slightly cooler heads and thoraces (38·94 and 43·22°C) than bees not extruding droplets (40·28 and 44·18°C). Wingloading and thoracic temperatures of bees are inversely correlated at high ambient temperatures (35 °C) and this is probably caused by a higher propensity of heavier bees to extrude fluid, thus reducing thoracic temperature.
Intrapulmonary Chemoreceptor Control of Ventilatory Movements in the Self-Ventilating Chicken
Authors: Barnas G. M. , Burger R. E. 
Published: April 2021

ABSTRACT
The importance of intrapulmonary chemoreceptors (IPC), sensitive to in the lung, in the control of ventilatory movements is yet to be demonstrated in the self-ventilating bird. We distinguished between the effects of on IPC and on extrapulmonary CO2-sensitive receptors (EPC) in anaesthetized cockerels by denervating IPC in the right lung, ligating the left pulmonary artery and changing . Left IPC were thus exposed to a combination of from inspired gas and dead space, while EPC were exposed to greatly increased arterial resulting from the ventilation-perfusion inequality. At OTorr , steady state ventilatory depth and frequency did not change (P&gt;0·5) after the ligation, although rose by 12·2 ± 1·7 Torr. After the ligation, ventilatory movements were more sensitive to increasing Pico,- Tracheostomy, which results in a greater decrease in in the innervated lung after ligation, produced greater effects. We conclude that these responses were due to the strong controlling influence of IPC on ventilatory movements in the self-ventilating cockerel.
Influence of Coxa-Thorax Joint Receptors on Retractor Motor Output During Walking in Carausius Morosus
Authors: Graham D. 
Published: April 2021

ABSTRACT
The coxal leg-stump of a stick insect was rotated about the coxa-thorax joint, by means of a pen-motor, while the animal walked on a self-propelled double treadwheel. Motor activity in the retractor muscles of the legs was recorded for standing and walking animals with the stump of either the middle or hind leg moved forward and backward in a trajectory similar to that used in a walking step.
In a standing animal the movement of either leg evokes a weak resistance reflex. If the animal walks with the middle leg-stump held still, then short and weak motor bursts are generated with the periodicity of the walking legs. Front and hind legs alternate in a manner typical of the middle leg amputee and the retractor muscle of the amputated leg is most active during the power stroke of the leg behind.
When a middle leg-stump is moved at a different frequency from that of the walking legs, the motor output to the retractor is strongly modulated and depends on the relative timing of the stump and the walking legs.
Rearward movement of the hind leg-stump, during walking, is always accompanied by strong motor output in the retractor muscle. In addition, forward movement in this leg-stump produces a resistance reflex similar to that produced in the standing animal.
Oxygen Acquisition of the Reedfish, Erpetoichthys Calabaricus
Authors: Pettit Michael J. , Beitinger Thomas L. 
Published: April 2021

ABSTRACT
In normoxic water at 25 °C, the reedfish (Erpetoichthys calabacicus) can breathe in both air and water, although water is the primary source of oxygen. This pattern of oxygen partitioning is altered by a number of factors. Increases in metabolic costs (e.g. locomotor activity) and decreases in aquatic oxygen concentration are met by increases in aerial oxygen uptake.
Reedfish acclimated to 33 °C have increased lung breathing compared with fish acclimated to 25°C. Also, activity stimulates lung breathing more at 33 °C than at 25 °C. Unexpectedly, weight-specific oxygen uptake rates of reedfish at these two temperatures were not significantly different. In-creased lung-breathing compensates for changes in locomotor activity, dissolved oxygen and temperature, allowing reedfish to meet their overall oxygen requirements.
Exposure of reedfish to six different combinations of oxygen and carbon dioxide indicated that lung ventilation frequencies were more labile than gill ventilation frequencies. The maximum change in lung ventilation rates was 849% above controls whereas the largest change in gill ventilation frequency was 27%. Exposure of reedfish to hyperoxia significantly de-pressed both gill and lung ventilation. Hypercapnic gases stimulated gill ventilation at both low (0·5%) and high (5%) concentrations; however, lung ventilation was only stimulated at the higher carbon dioxide concentration. The observed depression of gill ventilation frequencies in reedfish exposed to combinations of hypercapnic and hypoxic gases indicates that the inhibitory effect of low oxygen on gill ventilation dominates the stimulatory effect of hypercapnia. Overall, these data suggest that oxygen exerts a stronger influence in the control of respiration than carbon dioxide in this air-and water-breathing fish.
Reedfish survived out of water for 6 and 8 h at 25 °C without obvious ill effects. Oxygen consumption rates of these fish were significantly less than those of similar sized reedfish measured in water at either 25 or 33°C. The respiratory physiology of the reedfish frees it from aquatic oxygen constraints and allows it to tolerate at least short-term terrestrial exposures.
Coactivating Influences Between Neighbouring Legs in Walking Insects
Authors: Cruse H. 
Published: April 2021

ABSTRACT
When the movement of one leg of a walking stick insect is interrupted during the power stroke, the force developed by other legs is increased. This effect is shown to occur between all orthogonal nearest-neighbour legs except for the two hind legs. Such effects do not occur between diagonal or next nearest-neighbour pairs. The possible function of these ‘coactivating’ influences is assumed to be to enable the animal to increase the total force propelling the body.
Strain Gauge Measurement Of Mesokinetic Movement In The LizardVaranusExanthematicus
Authors: Smith Kathleen K. , Hylander William L. 
Published: April 2021

ABSTRACTSingle-element strain gauges were placed across the mesokinetic joint of the skull of the savanna monitor lizard, Varanus exanthematicus Bose, in order to document the extent and timing of mesokinetic movement. In addition, rosette strain gauges were placed on various points .of the palatomaxillary segment. Strain recordings and simultaneous cineradiographic films or videotapes were taken during normal feeding activities, including the strike, prey manipulation, ingestion and pharyngeal compression. Tensile strain, indicating lowering (retraction) of the palato-maxillary segment, was observed during all stages of feeding. Compressive strain, indicating lifting (protraction) of the palato-maxillary segment, generally appeared briefly in the strike and during pharyngeal compression. Maximum tensile strains were always larger than maximum compressive strains within each sequence. The highest levels of tensile strain occurred during prey manipulation periods, which were characterized by isometric biting. Strain on the palato-maxillary segment revealed a pattern of timing similar to the one at the mesokinetic joint, although strain levels were at least an order of magnitude lower. These data directly contradict conventional models of the function of the kinetic skull in lizards. We conclude that the kinetic apparatus in lizards is not a mechanism for actively moving the palato-maxillary unit and is therefore not a mechanism for increasing gape or actively controlling upper jaw movements.
Properties of the Chloride Conductance Associated with Temperature Acclimation in Muscle Fibres of Green Sunfish
Authors: Klein M.G. 
Published: April 2021

ABSTRACT
Characteristics of the anion conductance of muscle fibres from green sunfish have been determined. The membrane conductance of fibres from sunfish acclimated to 25 and 7 °C was linearly related to the extracellular chloride concentration. The chloride conductance exhibited a pH dependence which was adequately described by the titration of an acidic site with a pKa of 5·3 in 25 °C-acclimated fibres and 6·4 in 7°C-acclimated fibres.
The anion current-voltage (I-V) relationship of warm-acclimated fibres exhibited constant-field rectification, while the I-V relationship of cold-acclimated fibres was linear. In Ringer solutions containing elevated calcium concentrations (33 and 115 mmol l−1), the I-V relationship of warm-acclimated fibres was similar to the control situation. However, the I-V relationship of cold-acclimated fibres showed a calcium concentration-dependent curvature in the direction expected for constant-field rectification. The voltage-dependence of the time constant of chloride current inactivation was shifted along the voltage axis by about 40 mV in the negative direction in 7°C-acclimated fibres as compared to 25°C-acclimated fibres. The results can be adequately described by a model of constant-field rectification with the inclusion of a term for the membrane surface potential. A simple hypothesis which can qualitatively account for many of these observations is that temperature acclimation alters the density of fixed negative surface charges in the vicinity of chloride channels.
An Improved Chamber for the Short-Circuiting of Epithelia
Authors: Dow Julian A. T. , Harvey William R. , Wolfersberger Michael G. , Boyes Bruce 
Published: April 2021

ABSTRACT
Since the pioneering work of Ussing & Zerahn (1951), the design of short-circuit apparatus has been modified only slightly. Such chambers generally consist of two halves, between which the epithelium is stretched. The assembly is clamped together and filled with saline, which is circulated in each half chamber by gas lift pumps, usually connected to the main chamber with plastic pipes. There are two current electrodes, one at each end of the chamber, and -usually -two voltage-sensing electrodes close to the tissue. The current passed through the chamber is adjusted until the p.d. between the sensing electrodes becomes zero. Under such conditions, only actively transported ions move across the tissue, and the short-circuit current is a precise measure of the net flux of charged species. Short-circuiting is thus a method of choice for investigating transport phenomena in epithelia.
Pattern and Reset Analysis of the Gastric Mill Rhythm in a Spiny Lobster, Panulirus Interruptus
Authors: Russell David F. 
Published: April 2021

ABSTRACT
The burst pattern of the gastric mill rhythm was studied by varying its cycle period in in vitro preparations comprising the stomatogastric (STG), oesophageal and (paired) commissural ganglia. Reset tests using intracellular polarization of identified STG neurones showed that the CI, LC, GP and GM cells can all strongly affect the cycle period, and therefore apparently play a role in generating the gastric rhythm. Variation in the cycle period could be obtained by: (i) cutting certain input nerves; (ii) relative coordination between the gastric and oesophageal rhythms; or (iii) intracellular polarization of identified STG cells, especially the LC motoneurone. Variation in the cycle period by any of these means showed that the gastric pattern (in such preparations) comprises two basic alternating phases: a variable-duration ‘powerstroke’ and a constant-duration ‘returnstroke’. The powerstroke is taken to include bursts in the LC, GP and GM motoneurones (since they evoke closing of the gastric mill teeth and mastication of food), along with the interburst intervals of the other cells. The durations of all these events co-varies over a large range, as a linear function of the cycle period. The activity level of neurones bursting during the powerstroke is directly proportional to their burst length, and hence appears to be a basic parameter affecting the cycle period. The returnstroke is taken to include bursts in the CP, AM and LG motoneurones (since they evoke opening and resetting of the gastric mill teeth), along with the interburst intervals of the powerstroke cells. All these events tended to assume a fixed duration. The two-part gastric mill pattern can be analogized to other two-part rhythms, e.g. for terrestrial locomotion, in which the load-bearing phase has a variable duration and accounts for most of the variation in the cycle period whereas the unloaded phase tends to assume a constant duration.
Neural Basis of Teeth Coordination During Gastric Mill Rhythms in Spiny Lobsters, Panulirus Interruptus
Authors: Russell David F. 
Published: April 2021

ABSTRACT
Motoneurones that drive the closing of the lateral teeth during gastric mill rhythms in spiny lobsters start firing before the motoneurones that drive the medial tooth powerstroke. This has the expected behavioural interpretation that the lateral teeth must close on a food particle before the medial tooth is pulled across it. The neural basis of the teeth coordination was examined. Experiments were made during gastric rhythms in in vitro preparations comprising the stomatogastric, oesophageal and (paired) commissural ganglia. Identified neurones in the stomatogastric ganglion were polarized to study their functional effects on the phasing and amplitude of bursts in other cells. Evoked firing of the lateral teeth closer motoneurones (especially LC) would evoke a discharge in the medial tooth powerstroke (GM) motoneurones, and suppress the firing of the medial tooth returnstroke (CP) motoneurone. Therefore the coordination pathway starts directly with the lateral teeth closer motoneurones. 4. The CI interneurone was found to be an important link in the coordination pathway. It exerted opposite effects on the medial tooth motoneurones, suppressing firing of the powerstroke GM cells while evoking bursts in the returnstroke CP cell. CI affected other features of the pattern as well. Non-spiking inhibition from the lateral teeth closer motoneurones (LC and GP) to the lateral teeth opener motoneurones (LGs) was found to occur conjointly with spike-mediated IPSPs. Hyperpolarization of the LC, GP or CI neurones could temporarily abolish the gastric rhythm, but bursting in some or all of the other cells would eventually return, although in some cases the phase pattern was altered. It appears that no individual neurone in the gastric network is necessary for rhythm production. The coordination system can be viewed as several ‘levels’ of synaptic connections, each level being redundant and synergistic with the others.
Flight Energetics of Euglossine Bees in Relation to Morphology and Wing Stroke Frequency
Authors: Casey Timothy M. , May Michael L. , Morgan Kenneth R. 
Published: April 2021

ABSTRACT
Mass-specific oxygen consumption of euglossine bees during free hovering flight is inversely related to body mass, varying from 66mlO2g−1h−1 in a 1−0·10 bee to 154mlO2g−1h−1 in a 0·10-g bee. Individuals of Eulaema and Eufreisea spp. have smaller wings and higher wing stroke frequency and energy metabolism at any given mass than bees of Euglossa spp. or Exaerete frontalis. Calculated aerodynamic power requirements represent only a small fraction of the energy metabolism, and apparent flight efficiency [aerodynamic power (= induced + profile power)/power input] decreases as size declines. If efficiency of flight muscle = 0·2, the mechanical power output of hovering bees varies inversely with body mass from about 480 to 1130 W kg−1 of muscle. These values are 1·9 to 4·5 times greater than previous predictions of maximum mechanical power output (Weis-Fogh & Alexander, 1977; see also Ellington, 1984c). Mass-specific energy expenditure per wing stroke is independent of body mass and essentially the same for all euglossines. Differences in energy metabolism among bees having similar body mass is primarily related to differences in wing stroke frequency. Scaling of energy metabolism in relation to mass is generally similar to the relationship for sphingid moths despite the fact that bees have asynchronous flight muscle whereas moths have synchronous muscle.