bluuebunny/crossref_metadata_2025_split huggingface dataset:
Localisation and interaction of the protein components of the yeast 2µ circle plasmid partitioning system suggest a mechanism for plasmid inheritance
Authors: Scott-Drew Suzanna , Murray James A. H. 
Published: April 2021

ABSTRACT
Replicating plasmids are highly unstable in yeast, because they are retained in mother cells. The 2µ circle plasmid overcomes this maternal inheritance bias by using a partitioning system that involves the plasmid encoded proteins Rep1p and Rep2p, and the cis-acting locus STB. It is thus widely exploited as a cloning vehicle in yeast. However, little is known about the cellular or molecular mechanisms by which effective partitioning is achieved, and models of both free diffusion and plasmid localisation have been proposed. Here we show that Rep1p and Rep2p proteins interact to form homo- and hetero-complexes in vitro. In vivo, Rep1p and Rep2p are shown to be nuclear proteins, exhibiting sub-nuclear concentration in distinct foci. The number of foci appears constant regardless of plasmid copy number and cell ploidy level. Before cell division, the number of foci increases, and we observe approximately equal allocation of foci to mother and daughter cell nuclei. We show that whereas Rep2p expressed alone is found exclusively in the nucleus, Rep1p requires the presence of Rep2p for effective nuclear localisation. High levels of 2µ plasmid induce a multiple-budded elongated cell phenotype, which we show can be phenocopied by overexpression of both REP1 and REP2 together but not alone. Taken together, these results suggest that Rep1p and Rep2p interact in vivo, and occupy defined nuclear sites that are allocated to both mother and daughter nuclei during division. We propose a model for 2µm plasmid partitioning based on these results, involving the association of plasmid DNA with specific, segregated subnuclear sites.
Actin microfilaments control the MHC class II antigen presentation pathway in B cells
Authors: Barois Nicolas , Forquet Frédérique , Davoust Jean 
Published: April 2021

ABSTRACT
Newly synthesised major histocompatibility complex class II molecules associate with invariant chains (Ii) to form nonameric complexes. These complexes are transported to endosomes, where proteolytic enzymes generate αβ class II dimers associated with nested Ii-derived peptides. These peptides are then exchanged with antigen peptide, and mature class II molecules reach the cell surface. The role of the actin cytoskeleton in the transport and maturation of class II molecules has not been studied. We show here that upon treatment with cytochalasin D (cyto D), the rate of Ii degradation is drastically reduced in B cells. Cyto D treatment also leads to a delayed appearance of stable forms of class II molecules, and a reduced presentation efficiency of antigen determinants requiring newly synthesised class II molecules. Under such conditions, we found that invariant chain fragments and class II molecules are accumulated in early and late endosomal compartments, whereas the leupeptin protease inhibitor induces their accumulation in lysosomal compartments. The addition of cyto D to leupeptin blocks the delivery of class II/invariant chain complexes to lysosomes, and further inhibits degradation of Ii. The dynamics of the actin cytoskeleton can therefore control the meeting point between newly synthesised class II molecules and lysosomal proteases, involved in Ii degradation and antigen peptide loading.
Nuclear import of protein kinase C occurs by a mechanism distinct from the mechanism used by proteins with a classical nuclear localization signal
Authors: Schmalz Dirk , Hucho Ferdinand , Buchner Klaus 
Published: April 2021

ABSTRACT
Protein kinase C does not have any known nuclear localization signal but, nevertheless, is redistributed from the cytoplasm to the nucleus upon various stimuli. In NIH 3T3 fibroblasts stimulation with phorbol ester leads to a translocation of protein kinase C α to the plasma membrane and into the cell nucleus. We compared the mechanism of protein kinase C α’s transport into the nucleus with the transport mechanism of a protein with a classical nuclear localization signal at several steps. To this end, we comicroinjected fluorescently labeled bovine serum albumin to which a nuclear localization signal peptide was coupled, together with substances interfering with conventional nuclear protein import. Thereafter, the distribution of both the nuclear localization signal-bearing reporter protein and protein kinase C α was analyzed in the same cells. We can show that, in contrast to the nuclear localization signaldependent transport, the phorbol ester-induced transport of protein kinase C α is not affected by microinjection of antibodies against the nuclear import factor p97/importin/karyopherin β or microinjection of non-hydrolyzable GTP-analogs. This suggests that nuclear import of protein kinase C α is independent of p97/ importin/karyopherin β and independent of GTP. At the nuclear pore there are differences between the mechanisms too, since nuclear transport of protein kinase C α cannot be inhibited by wheat germ agglutinin or an antibody against nuclear pore complex proteins. Together these findings demonstrate that the nuclear import of protein kinase C α occurs by a mechanism distinct from the one used by classical nuclear localization signal-bearing proteins at several stages.
Three distinct steps in transport of vesicular stomatitis virus glycoprotein from the ER to the cell surface in vivo with differential sensitivities to GTPγS
Authors: Pepperkok Rainer , Lowe Martin , Burke Brian , Kreis Thomas E. 
Published: April 2021

ABSTRACT
Microinjected GTPγS revealed three distinct steps in the exocytic transport of the temperature sensitive glycoprotein of vesicular stomatitis virus (ts-O45-G) from the ER to the cell surface in intact Vero cells. While COPII dependent export of ts-O45-G from the ER is blocked in cells injected with recombinant protein of a dominant mutant of SAR1a (SAR1a[H79G]) inhibited in GTP hydrolysis, neither injected GTPγS nor antibodies against β-COP (anti-EAGE) interfere with this transport step significantly. In contrast, transport to the Golgi complex is blocked by 5ø µM GTPγS, a dominant mutant of ARF1 (ARF1[Q71L]) inhibited in GTP hydrolysis, or microinjected anti-EAGE, but injected Sar1a[III9G]p has no effect. Microinjection of GTPγS or expression of ARF[Q71L] rapidly induces accumulation of COPI coated vesicular structures lacking ts-O45-G. Finally, transport of ts-O45-G from the trans -Golgi network (TGN) to the cell surface is inhibited only by high concentrations of GTPγS (500 µM). Interestingly, this step is only partially brefeldin A sensitive, and injected antibodies against β-COP and p200/myosin II, a TGN membrane associated protein, have no effect. These data provide first strong in vivo evidence for at least three distinct steps in the exocytic pathway of mammalian cells regulated by different sets of GTPases and coat proteins. COPII, but not COPI, is required for ER export of ts-O45-G. COPI plays a role in subsequent transport to the Golgi complex, and a so far unidentified GTPγS sensitive coat appears to be involved in transport from the TGN to the cell surface.
Radial F-actin arrays precede new hypha formation in Saprolegnia: implications for establishing polar growth and regulating tip morphogenesis
Authors: Bachewich Catherine , Heath; I. Brent 
Published: April 2021

ABSTRACT
The roles of cortical F-actin in initiating and regulating polarized cell expansion in the form of hyphal tip morphogenesis were investigated by analyzing long term effects of F-actin disruption by latrunculin B in the oomycete Saprolegnia ferax, and detecting localized changes in the cortical F-actin organization preceding hyphal formation. Tubular hyphal morphology was dependent on proper F-actin organization, since latrunculin induced dose-dependent actin disruption and corresponding changes in hyphal morphology and wall deposition. With long incubation times (1 to 3 hours), abundant subapical expansion occurred, the polar form of which was increasingly lost with increasing actin disruption, culminating in diffuse subapical expansion. These extreme effects were accompanied by disorganized cytoplasm, and novel reorganization of microtubules, characterized by star-burst asters. Upon removing latrunculin, hyperbranching produced abundant polar branches with normal F-actin organization throughout the colony. The results are consistent with F-actin regulating polar vesicle delivery and controlling vesicle fusion at the plasma membrane, and suggest that F-actin participates in establishing polar growth. To test this idea further, we utilized the hyperbranching growth form of Saprolegnia. Early during the recovery time, prior to multiple branch formation, radial arrays of filamentous F-actin were observed in regions with no detectable surface protrusion. Their locations were consistent with those of the numerous branches that formed with longer recovery times. Similar radial arrays preceded germ tube formation in asexual spores. The arrays were important for initiating polar growth since the spores lost their ability to polarize when the F-actin was disrupted with latrunculin, and increased isometrically in size rather than producing germ tubes. Therefore, F-actin participates in initiating tip formation in addition to its previously demonstrated participation in maintenance of hyphal tip growth. The cortical location and radial organization of the arrays suggest that they recruit and stabilize membrane-bound and cytosolic factors required to build a new tip.
An Analysis of Branchial Ammonia Excretion in the Freshwater Rainbow Trout: Effects of Environmental Ph Change and Sodium Uptake Blockade
Authors: Wright P. A. , Wood C. M. 
Published: April 2021

ABSTRACT
Short-term treatments (3 h) designed to change the relative NH3 and NH4+ (ΔNH4+) gradients and sodium transport (JNa) across the gills were employed to analyse the normal mechanism(s) of branchial ammonia excretion in trout acclimated to fresh water of pH ≃8·0. Control occurred in the absence of, or against, an apparent gradient, while ΔNH4+ was positive. Severe acid exposure (pH = 4·06) raised and ΔNH4+, abolished , and reduced by 28%, while moderate acidity (pH = 6·64), which also elevated had no significant influence on and . Severe alkaline exposure (pH = 9·4) raised ΔNH4+, reduced to a very negative value, and decreased and by equ1molar amounts, representing 55% and 80% of control levels respectively. Moderate alkalinity (pH = 8·69) had similar effects on and , but reduced and by only ∼25%. The sodium transport inhibitor amiloride (10−4moll −1 in the external water, pH ≃8·0) had very similar effects to pH = 4·06 on both and , but did not alter or . The results discount the quantitative importance of NH4+ diffusion and favour a flexible combination of NH3 diffusion and Na+/NH4+ exchange as the major mechanisms of , with the latter dominating under the particular control conditions of the present study.
Insect Cardioactive Peptides: I. Distribution and Molecular Characteristics of two Cardioacceleratory Peptides in the Tobacco Hawkmoth, Manduca Sexta
Authors: Tublitz Nathan J. , Truman James W. 
Published: April 2021

ABSTRACT
Using an in vitro heart bioassay, the pharmacological and biochemical properties of two cardioactive peptides derived from neural tissues of the moth, Manduca sexta, were analysed.
Gel filtration of ventral nerve cords (VNC) from pharate adults identified two cardioacceleratory peptides (CAP1 and CAP2) with apparent molecular weights of 1000 and 500 Da, respectively. Both CAPs were localized to the abdominal perivisceral organs, the major neurohaemal release sites in the insect VNC. Pulse application of CAP1 or CAP2 on the in vitro Manduca heart produced a dose-dependent increase in rate but had no effect on beat amplitude. The threshold dose for the action of each peptide on the isolated heart bioassay was less than 0·05 abdominal nerve cord equivalents.
Both CAPs were present in the pharate adult VNC of several other Lepidopteran species. Neither CAP1 nor CAP2 was detected in the prepupal VNC of Manduca sexta.
Effects of Body Temperature on Respiration, Blood Gases and Acid-Base Status in the Turtle Chrysemys Picta Bellii
Authors: Glass M. L. , Boutilier R. G. , Heisler N. 
Published: April 2021

ABSTRACT
Freshwater turtles (Chrysemys picta bellii Gray) were acclimated to temperatures of 5, 10, 20 and 30°C for at least 12 days, and pulmonary ventilation, oxygen uptake and arterial pH, and were determined in completely unrestrained specimens. Oxygen uptake increased overproportionately (6·7-fold) as compared to pulmonary ventilation (, 4·4-fold) when the temperature increased from 10 to 30°C. The observed rise in arterial from 13 (5 °C) to 32 mmHg (30°C) was the result of a decrease in , whereas an increase of arterial from 12Torr at 5°C to about 60Torr at 20 and 30°C mainly resulted from the effects of intracardiac blood shunting combined with temperature-dependent shifts of the oxygen dissociation curve. Arterial pH fell with rising temperature significantly less (ΔpH/Δt = −0·010U/°C) than required for constant relative alkalinity and for constant dissociation of imidazole. The changes of cerebrospinal fluid pH with temperature, calculated from the mean arterial values, were even smaller [ΔpH/Δtcsf = −0·008). It is concluded that the observed temperature dependence of the acid-base status is not in agreement with the alphastat hypothesis.
Unilateral Ciliary Reversal and Motor Responses During Prey Capture by the Ctenophore Pleurobrachia
Authors: Tamm Sidney L. , Moss Anthony G. 
Published: April 2021

ABSTRACT
High-speed cinematography of feeding Pleurobrachia revealed a stereotyped sequence of ciliary motor responses underlying the feeding behaviour of this ctenophore. Prey capture by a tentacle first elicited high frequency beating in all comb rows, propelling the animal forward at a rapid speed for several seconds. This was followed by a brief period of inactivity on some or all comb rows. Then comb rows adjacent to the catching tentacle beat in the reverse direction, causing the ctenophore to spin rapidly toward this side and sweeping the prey-catching tentacle to the opened mouth, which bent towards it. After engulfing the prey, the animal slowly swam forward to re-set the relaxed tentacles as à fishing net. The patterns, timing, onset and coordination of these ciliary responses particularly the unilateral reversal of comb rows on the catching side, are analysed with respect to possible conducting pathways mediating this behaviour.
The Effects of Temperature Acclimation on the Resting Membrane of Skeletal Muscle Fibres from Green Sunfish
Authors: Klein M. G. , Prosser C. L. 
Published: April 2021

ABSTRACT
Conductive properties of muscle fibres from green sunfish (Lepomis cyanellus) acclimated to different temperatures were examined. The relative membrane permeability to chloride and potassium ions, PCI/PK, measured at acclimation temperature, was approximately 7·0 after acclimation at 25 °C and 1·3 after acclimation at 7°C. This difference was due to a six-fold reduction in the membrane chloride conductance upon acclimation to 7 °C as compared to 25 °C-acclimated fibres. Mean (±S.E.M.) values of the chloride conductance were 554 + 68μS cm−2 in warm-acclimated sunfish, and 75 ± 9μ.Scm−2 in cold-acclimated sunfish. Membrane capacitance also differed significantly between the two acclimation groups.
When the temperature was varied acutely, the magnitude of the chloride conductance exhibited a maximum Q10 of only 1·9, compared with a Q10 of 3·0 associated with acclimation. Upon transferring 25 °C-acclimated sunfish to holding tanks at 7 °C, the total membrane resistance exhibited a sigmoidal increase over about 14 days, and a steady membrane capacitance was achieved in about 10 days. For 7°C-acclimated sunfish, transferred to 25 °C, resistance showed a sigmoidal decrease over 10 days and capacitance was steady after 8 days. The results indicate that thermal acclimation of the muscle membrane involves cellular regulatory processes which underlie significant changes in the electrical properties of the fibre.
Swimming In The Pteropod Mollusc, Clione Limacina: I. Behaviour and Morphology*
Authors: Satterlie Richard A. , Labarbera Michael , Spencer Andrew N. 
Published: April 2021

ABSTRACT
In the pteropod mollusc Clione limacina (Phipps), swimming is accomplished through alternate dorsal and ventral flexions of a pair of strongly muscularized wing-like parapodia (wings). Wing musculature is arranged in seven muscle groups. The two outermost dorsal and ventral groups produce the bending movements of swimming. The three inner muscle groups include longitudinal and transverse wing retractors and dorso-ventral muscles. The overall muscle arrangement is similar to that of the generalized mollusc foot.
During hovering locomotion the wings pronate on downstroke and supinate on upstroke to produce a maximal angle of attack of 42° for both phases. Wing tips nearly touch or overlap in the saggital plane at the extreme of each half-cycle. High speed movie analysis of hovering swimming indicates that upstroke and downstroke are nearly symmetrical. It is suggested that wings produce lift in both wing phases.
We estimate from wing dimensions and velocity measurements that the Reynolds number of the wings is approximately 200. A novel lift-generating mechanism, similar to the ‘clap-and-fling’ of insects, may be utilized by the Clione wing to generate lift throughout the wing cycle despite the reversal of wing movement in each half-stroke.
Identification of Neurones Containing Cardio-Acceleratory Peptides (Caps) in the Ventral Nerve Cord of the Tobacco Hawkmoth, Manduca Sexta
Authors: Tublitz Nathan J. , Truman James W. 
Published: April 2021

ABSTRACT
The abdominal ganglion neurosecretory cells responsible for the synthesis and release of two insect neurohormones, cardioacceleratory peptides 1 and 2 (CAP1 and CAP2), from the perivisceral organs (PVOs) have been identified in the tobacco hawkmoth, Manduca sexta. Previous work established the existence of two groups of abdominal ganglion cell bodies with axons projecting to the PVO: four laterally-situated pairs and five pairs lying on the midline (Taghert & Truman, 1982b). Micro dissection and bioassay of various parts of an abdominal ganglion revealed that CAP activity was greatest in the medial portion of the ganglion, the portion containing the 10 midline neurones. Six of the 10 midline neurosecretory cells, the new midline bilateral (MB) cells, appeared to differentiate post-embryonically, commencing differentiation late in the last larval instar and reaching maturity midway through adult development. The development of the new MB cells was mirrored by the accumulation of CAP activity in the abdominal nerve cord. Not present in measurable amounts in larvae, CAP activity was first detectable a few days after pupation and reached maximal levels midway through adult development. CAP-like bioactivity was collected from the PVO in response to antidromic stimulation of the nerve containing the new MB axons. No CAP-like bioactivity was detected in those preparations in which the new MB axons were severed or in which other nerves were stimulated. Intracellular stimulation of a new MB neurone evoked the release from the PVO of measurable levels of CAP bioactivity. It was shown that this stimulation-evoked, cardioacceleratory activity was sensitive to protease treatment, and was released only from the cell that was stimulated. On the basis of these experiments, it was concluded that the CAPs are synthesized and secreted from the new MB cells.
Short Communication Urea Efflux From the Squalus Acanthias Pup: the Effect of Stress
Authors: Evans David H. , Kormanik Gregg A. 
Published: April 2021

ABSTRACT
The extremely high concentration of urea found in elasmobranch blood (approx. 400 mmol 1–1) is secondary to nearly complete reabsorption (90–95%) of this solute in the renal tubules (Forster, 1967), and a branchial urea permeability which is approximately 1% that of the toad bladder (&lt;10 × 10–8cm s–1, Payan, Goldstein & Forster, 1973). Evans, Oikari, Kormanik & Mansberger (1982) have recently shown that the premature spiny dogfish (Squalus acanthias) pup is capable of osmoregulation in sea water, despite an initial reduction in plasma urea concentration (13% in 3 days). This fall could have been secondary to a reduced synthetic rate, or caused by an increased efflux across surfaces such as the gills, renal and/or rectal gland epithelia, or yolk sac. The present study was therefore undertaken to measure the rate of urea efflux from intact spiny dogfish pups, and to determine the effect of stress on that efflux. Stress was induced by the experimentally common procedure of handling, MS-222 anaesthesia, and weighing.
Angiotensin II Can Initiate Contact-Rehydration in Terrestial Slugs
Authors: Makra Martha E. , Prior David J. 
Published: April 2021

ABSTRACT
Moist-skinned terrestrial animals such as snails and slugs are highly susceptible to desiccation. It has been shown that active slugs can lose up to 35% of their initial body weight (%IBW) within 2-3 h (Dainton, 1954; Prior, Hume, Varga & Hess, 1983). They can, however, rapidly recover from dehydration by integumental absorption of water while in contact with a moist substrate (Burton, 1966; Prior, 1982, 1984). This process of contact-rehydration involves an increase in the epithelial paracellular permeability of the foot and is mediated by a well regulated behavioural sequence (Prior, 1982, 1984; Prior & Uglem, 1984). Contact-rehydration is initiated when slugs have been dehydrated to the threshold level of 60–70% IBW. They move onto a moist surface and assume a characteristic flattened posture while water is absorbed through the foot. They remain in this posture until enough water has been absorbed to achieve their rehydration set-point (93·6 ± 12·2% IBW for Limax maximus;Prior, 1984). Once rehydrated, the slugs move off the moist surface and come to rest on a dry surface, thus terminating the behaviour.
A Rotating Respirometer to Monitor Voluntary Activity and Associated Exchange of Respiratory Gases in the Land Hermit Crab (Coenobita Compressus)
Authors: Wheatly Michèle G. , McMahon Brian R. , Burggren Warren W. , Pinder Alan W. 
Published: April 2021

ABSTRACT
A rotating respirometer was designed which enabled respiratory gas exchange in the land hermit crab Coenobita compressas to be correlated with voluntary submaximal sustained pedestrian activity. In the laboratory, crabs remained spontaneously active for up to 150 min, maintaining velocities of 0·6 cm s−1. Comparable activity patterns were observed in the field. Quiescent O2 uptake increased logarithmically as a function of load rating of the adopted molluscan shell. Steady-state and were measured after 30 min of spontaneous activity and both increased linearly with velocity. There was good correspondence between Y-intercept values and those measured in inactive crabs. At the mean locomotory speed, and were increased 3·4-fold and 2·6-fold respectively above settled rates. Minimum and gross energetic cost of transport were estimated and compared with values in the literature. and returned to settled levels within the first hour of recovery. The activity profile and concomitant changes in gas exchange are discussed in the context of acquisition of the shell-dwelling habit.