bluuebunny/crossref_metadata_2025_split huggingface dataset:
The application of aqueous two-phase partition to the study of chick limb mesenchymal diversification
Authors: Cottrill C. P. , Sharpe Paul T. , Wolpert Lewis 
Published: April 2021

ABSTRACT
A technique which identifies cells differing in surface character, aqueous two-phase partition using thin-layer countercurrent distribution (TLCCD), has been used to study differentiation and pattern formation in the developing chick limb bud.
The TLCCD profiles of cell populations, derived from various regions of morphologically undifferentiated mesenchyme from three different stages of limb development, have been compared.
At no stage, or location, has the population been found to be homogeneous. Cells from progress zones and more proximal regions could all be resolved into several populations. The populations from progress zones at three different developmental stages were qualitatively similar but differed in the proportions of cells in each. The most striking differences in cell populations were those obtained from the most proximal region of the limb, closest to the flank, which represents the developmentally most advanced region.
The regeneration of double dorsal and double ventral limbs in the axolotl
Authors: Burton Rosemary , Holder Nigel , Jesani P. 
Published: April 2021

ABSTRACT
Surgically made double dorsal and double ventral upper arms, comprising double extensor and double flexor muscles respectively, were amputated immediately following operation; both limb types regenerated. In terms of skeletal anatomy, a range of limb types was found. These included four-digit limbs of normal cartilage pattern, and hypomorphic limbs having from one to three digits.
All of the double dorsal and the majority of the double ventral limbs were symmetrical in the dorsal–ventral axis. This was detected by analysing their muscle patterns at carpal and midforearm level, and muscle and epidermal characteristics in the metacarpal region are discussed in terms of the significance of healing time and stump pattern on the regenerative ability of surgically created limb regions.
Focusing on spindle poles
Authors: Compton Duane A. 
Published: April 2021

ABSTRACT
Spindle poles are discernible by light microscopy as the sites where microtubules converge at the ends of both mitotic and meiotic spindles. In most cell types centrosomes are present at spindle poles due to their dominant role in microtubule nucleation. However, in some specialized cell types microtubules converge into spindle poles in the absence of centrosomes. Thus, spindle poles in centrosomal and acentrosomal cell types are structurally different, and it is this structural dichotomy that has created confusion as to the mechanism by which microtubules are organized into spindle poles. This review summarizes a series of recent articles that begin to resolve this confusion by demonstrating that spindle poles are organized through a common mechanism by a conserved group of noncentrosomal proteins in the presence or absence of centrosomes.
A novel taxol-induced vimentin phosphorylation and stabilization revealed by studies on stable microtubules and vimentin intermediate filaments
Authors: Vilalta Patricia M. , Zhang Liping , Hamm-Alvarez Sarah F. 
Published: April 2021

ABSTRACT
To understand how protein phosphorylation modulates cytoskeletal organization, we used immunofluorescence microscopy to examine the effects of okadaic acid, a serine/threonine protein phosphatase inhibitor, and taxol, a microtubule-stabilizing agent, on stable (acetylated and detyrosinated) microtubules, vimentin intermediate filaments and other cytoskeletal elements in CV-1 cells. Okadaic acid caused major changes in both stable microtubules and vimentin intermediate filaments, but through independent mechanisms. At 300 nM, okadaic acid caused apparent fragmentation and loss of stable microtubules which was not prevented by prior exposure to K252a. In contrast, major reorganization of vimentin intermediate filaments elicited at 750 nM okadaic acid was prevented by prior exposure to K252a. Taxol pretreatment blocked the effects of okadaic acid on stable microtubules and vimentin intermediate filaments. Recent reports have revealed that taxol can activate cellular signal transduction pathways in addition to its known ability to promote microtubule stabilization, so the possibility that taxol-resistance of vimentin intermediate filaments to okadaic acid was through a microtubule-independent mechanism involving direct phosphorylation of intermediate filament proteins was explored. Vimentin immunoprecipitation from cytoskeletal extracts from 32P-labeled cells revealed that taxol (4 µM, 1 or 2 hours) caused about a 2-fold increase in vimentin phosphorylation. This phosphorylation was recovered exclusively in cytoskeletal vimentin, in contrast to the increased phosphorylation of soluble and cytoskeletal vimentin caused by exposure to 750 nM okadaic acid. Phosphorylation of soluble and cytoskeletal vimentin from cells exposed to taxol (4 µM, 1 hour) then okadaic acid (750 nM, 1 hour) was comparable to taxol-treatment alone. These findings demonstrate a novel new activity of taxol, induction of vimentin phosphorylation, that may impact on vimentin organization and stability.
Characterisation of two articulins, the major epiplasmic proteins comprising the membrane skeleton of the ciliate Pseudomicrothorax
Authors: Huttenlauch Irm , Peck Robert K. , Plessmann Uwe , Weber Klaus , Stick Reimer 
Published: April 2021

ABSTRACT
Most protists possess a unique membrane skeleton, the epiplasm, which is involved in pattern forming processes of the cell cortex and functions in maintaining cell shape. Articulins, a novel class of cytoskeletal proteins, are major constituents of the epiplasm. We have isolated cDNAs encoding the two major articulins of the ciliate Pseudomicrothorax dubius. Peptide sequence data confirm the identity of the cloned cDNAs encoding articulins 1 and 4. With the data presented here sequence information for all major articulins of ciliates as well as the distantly related euglenoids is available. Sequence comparison of the two newly characterised ciliate articulins with the previously determined sequences of p60, a minor articulin of the same species, and the two euglenoid articulins reveals general sequence principles and uncovers new features of this protein family. The hallmark of articulins is a central core domain of repetitive motifs of alternating valine and proline residues, the VPV-motif. These VPV-motif repeats are either 12-residues, or in some places, six residues long. Positively and negatively charged residues segregate in register with valine and proline positions. The VPV-motif is unique to articulins. The terminal domains flanking the core are generally hydrophobic and contain a series of hexa- or heptapeptide repeats rich in glycine and hydrophobic residues. The sequences of these short repeats are very similar in articulins of the same species but are not conserved between euglenoids and ciliates.
Human colonic cancer cells synthesize and adhere to laminin-5. Their adhesion to laminin-5 involves multiple receptors among which is integrin α2β1
Authors: Orian-Rousseau Véronique , Aberdam Daniel , Rousselle Patricia , Messent Anthea , Gavrilovic Jelena , Meneguzzi Guerrino , Kedinger Michèle , Simon-Assmann Patricia 
Published: April 2021

ABSTRACT
In the mature gut, laminin-5 is expressed at the basal aspect of the differentiating epithelial cells. In vitro, we show that three more or less differentiated human colonic cancer HT29 cell lines produce and deposit laminin-5; they predominantly synthesize and secrete the 440 kDa form of laminin-5 that comprises the unprocessed 155 kDa γ2 chain, as determined by immunoprecipitation analysis. In contrast, the highly differentiated colon carcinoma Caco-2 cells produce almost no laminin-5. Using anti-integrin antibodies, we show that adhesion of the two colonic cancer cell lines to laminin-5 is mediated by multiple integrin receptors including those for α3β1, α6β1 and α6β4 integrins like in other cell types. In addition, the implication of integrin α2β1 in this adhesion process is demonstrated for the first time. This has been shown by cell adhesion inhibition experiments, solid phase assays and confocal analysis. Together with previous in situ observations, these data provide a baseline knowledge for the understanding of the regulation of laminin-5 in normal and pathological intestine.
Physical and Chemical Properties of Rubber-Like Elastic Fibres From the Octopus Aorta
Authors: Shadwick Robert E. , Gosline John M. 
Published: April 2021

ABSTRACT
We investigated the physical and chemical properties of highly extensible elastic fibres from the octopus aorta. These fibres are composed of an insoluble rubber-like protein which we call the octopus arterial elastomer. The amino acid composition of this protein is different from that of other known protein rubbers, being relatively low in glycine and high in acidic and basic residues. Up to extensions of 50%, mechanical data from native elastic fibres fit a theoretical curve for an ideal Gaussian rubber with elastic modulus G = 4·65 × 105 Nm−2, and this is unchanged by prolonged exposure to formic acid. Thermoelastic tests on this protein indicate that the elastic force arises primarily from changes in conformational entropy, as predicted by the kinetic theory of rubber elasticity. Analysis of the non-Gaussian behaviour of the elastic fibres at extensions greater than 50% suggests that the molecular chains in this octopus protein are somewhat less flexible than those in resilin or elastin. Some speculations on the molecular design of these protein rubbers are made.
Differential In Vivo Sensitivity of Melanophores and Xanthophores To Catecholamines in Winter Flounder (Pseudopleuronectes Americanus Walbaum) Integumentary Patterns
Authors: Burton D. 
Published: April 2021

ABSTRACT
The catecholamines, adrenalin, dopamine and noradrenalin induce differential aggregation of melanophores in black-adapted winter flounder, Pseudopleuronectes americanus, paralleling patterning responses to albedo change. These differential responses to catecholamines suggest that the patterning mechanism in this species is largely dependent on a balance between neural aggregating and dispersing elements. The α-adrenoceptor agonist phenylephrine evokes paling in all pattern components in black-adapted flounder, whilst the α-adrenoceptor antagonist phentolamine darkens white-adapted flounders. The α-adrenoceptor agonist iso proterenol and the α-adrenoceptor antagonist propranalol have no effect on chromatophores of white-adapted flounder, but induce pallor in black-adapted flounder, which is interpreted as non specific. Noradrenalin elicits patterning responses in chromatically decentralized flounder, although the duration of pallor is shorter. The xanthophores, which are dispersed by a pituitary factor, will aggregate in response to high catecholamine doses.
Can A Shore Crab See A Star?
Authors: Doujak F. E. 
Published: April 2021

ABSTRACT
The absolute-intensity threshold of the optokinetic response in the crab Leptograpsus variegatus was measured using a moving continuous monochromatic point source. The results are compared to the photoreceptor responses of the same animal (Doujak, 1984), to determine the photoreceptor signal for the same behavioural threshold stimuli. Optokinetic eye movements demonstrate that at the peak of spectral sensitivity (499 nm), the minimum intensity of light the animal can detect is 4·0 ± 1·5 × 105 photons cm−2 s−1 (mean ± S.D., N = 18) incident on the eye, which is equivalent to a photon flux of about 6 photons facet−1 s−1. Comparison of behavioural and electrophysiological studies shows that at the above behavioural thresholds, the retinula cells respond with a train of discrete membrane depolarizations (bumps). The mean bump rate recorded in retinula cells at the absolute-intensity threshold of the optokinetic response to a moving point source is 22 ± 5 bumps min−1 (mean ± S.D., N= 6). Optokinetic experiments reveal an absolute sensitivity of the crab’s apposition eye to a point source that is only about 900 times less sensitive than the human eye: theoretical estimates based on quantum capture efficiency and lens size predict a much larger difference. The experimental findings provide the first definitive proof that an animal possessing a compound eye can see a star, albeit only stars of 0·5 magnitude and brighter.
Short Communication Inositol Tetrakis- And Pentakisphosphates In Gh4 Cells
Authors: Heslop J. P. , Irvine R. F. , Tashjian A. H. , Berridge M. J. 
Published: April 2021

ABSTRACT
A key question in the mechanism of hormone action is the way in which enhanced turnover of derivatives of membrane-bound phosphatidylinositol might bring about changes in cytosolic calcium. The process is known to be extremely rapid. It is probably involved, for example, in the visual pathway of Limulus (Brown et al. 1984; Fein et al. 1984) and we report here studies on a fast response to hormonal stimulation.
The Central Nervous Organization of the Motor Neurones to a Steering Muscle In Locusts
Authors: Pflüger Hans-Joachim , Elson Robert , Binkle Ulrike , Schneider Henning 
Published: April 2021

ABSTRACT
The pleuroaxillary or pleuroalar muscles of the locust (M85, Ml 14) are located in the meso- and metathoracic segments only. Each extends from the posterior face of the pleural ridge and runs dorsally and obliquely, inserting on the third axillary sclerite of the wing hinge. Each muscle consists of two distinct parts, a and b (Fig. 1). Each pleuroaxillary muscle is innervated by two motor neurones which give rise to a small and a large muscle potential in electromyogram recordings (Fig. 6E). The cell body of each neurone lies posteriorly in the ganglion and the axon runs out in nerve 4 (Figs 3–6). The two motor neurones of a particular muscle share many common morphological features (Figs 3–6). There is also clear segmental homology between the motor neurones supplying the meso- and metathoracic muscles (Fig. 3). Serial transverse sections of the motor neurones show that their arborization is confined mainly to a dorsal region of the neuropile. Some of the collaterals encompass, and terminate in, dorsal longitudinal tracts. Branching extends far anteriorly. Posteriorly, one secondary neurite runs ventrally (Figs 7, 8). A few secondary and tertiary neurites of the metathoracic pleuroaxillary motor neurones terminate within the neuropile of the first abdominal neuromere (Figs 6, 8). Additional features which distinguish these neurones from other flight motor neurones are discussed.
The Release of the Prothoracicotropic Hormonein the Tobacco Hornworm, Manduca Sexta, Iscontrolled Intrinsically by Juvenile Hormone
Authors: Rountree Dorothy B. , Bollenbacher Walter E. 
Published: April 2021

ABSTRACT
Pupal development is elicited early in the last larval instar of the tobacco hornworm, Manduca sexta (Johannson), by a precise temporal and quantitative increase in the haemolymph titre of 20-hydroxyecdysone. This increase in the titre is referred to as the pupal commitment peak, and it occurs once the titre of juvenile hormone (JH) has dropped. If the haemolymph titre of JH remains elevated at this time due to topical application of the hormone or of its analogue ZR512, commitment is delayed or inhibited in a dose-dependent manner. This delay or inhibition is due to the curtailment of the commitment peak in the ecdysteroid titre, which results from a failure of the prothoracic glands (PG) to increase the synthesis/secretion of the premoulting hormone, ecdysone. Since the PG from ZR512- and JH 1-treated larvae are capable of being activated in vitro by the prothoracicotropic hormone (PTTH), the effect of JH on the PG does not involve suppression of gland sensitivity to PTTH. The locus of the JH effect was determined to be the brain-retrocerebral complexes (Br-CC-CA), on the basis of experiments which tested the effect of implanted Br-CC-CA from pre-commitment larvae treated with JH on the occurrence of pupal commitment in head-ligated larval hosts. The implanted, JH-treated Br-CC-CA exhibited a delayed release of PTTH, and the effect was at concentrations of JH that were physiological. These results argue that JH functions to control the time during the last larval instar when pupal commitment occurs by dictating when PTTH will undergo gated release.
The Activity of A Steering Muscle in Flying Locusts
Authors: Elson Robert , Pflüger Hans-Joachim 
Published: April 2021

ABSTRACT
The pleuroaxillary muscle of a forewing (M85) or hindwing (M114) in the locust is supplied by two motor neurones. Each of the two motor neurones innervates a different part of the muscle. Single impulses in these motor neurones produce small twitches in the muscle which tetanize at about 30 Hz. At the wingbeat frequency they show considerable tonic tension upon which ripples are superimposed, 1:1 for each stimulus pulse. During sustained, straight, tethered flight, the motor neurones spike rhythmically, producing one (less often two) spike(s) per wingbeat in the first half of each downstroke. At the end of flight, when the wing is folded, a high-frequency, unpatterned burst of spikes occurs. During flight-like motor activity where rhythmic sensory feedback is reduced, the pleuroaxillary muscle of a hindwing spikes throughout the ‘wingbeat’ cycle, with little sign of rhythm. The forewing muscle, M85, responds to imposed rolling during flight by advancing the timing of its spike, increasing the number of spikes at each wingbeat, and recruiting a second motor unit on the side which is rotated downwards; converse changes occur on the side that is rolled upwards. The magnitude of the time-shift response in M85 depends on the angular position of the locust about the roll axis. The hindwing muscle shows similar changes in the number of spikes and in recruitment. Motor neurones of both the forewing and hindwing muscles can spike in response to imposed rolling in locusts that are not flying. Excitation increases on the side that is rolled down. The response to angular movement about the roll axis is primarily phasic and is dependent on visual cues. It is concluded that these muscles take part in steering behaviour during corrective reactions. Activation is increased on the side where more lift must be produced. Similar changes of activity in these muscles may play a role in active steering manoeuvres.
Flight Physiology of Intermediate-Sized Fruit Bats (Pteropodidae)
Authors: Carpenter Roger E. 
Published: April 2021

ABSTRACT
Up to eight physiological parameters were measured on members of four species of fruit bats with a size range of 0·188–0·650 kg as they flew in a wind tunnel. Regression lines were calculated for the relationships between body masses of bats and their power inputs (P,), heart and respiratory rates. These were compared to similar relationships for flying birds.
Respiratory evaporation dissipated only 10% of the heat produced. At ambient temperatures (T,) above 15°C, heat loss was facilitated by vasodilation of feet and wing membranes, but this mechanism became less effective at high Ta when thermal differential between wings and air was reduced. Bats are apparently unable to increase greatly their respiratory evaporation, and overheated at T, of 25–30°C. At low Ta, the flight ability of two bats was reduced, suggesting that reduced coordination or even freezing of wings might be a general problem for bats flying at Ta close to 0°C.
The endurance of three bats was so much greater near the middle of their speed ranges that the maximum flight distances ought to be achieved at these velocities, even though the cost of transport would be lower at higher speeds. Endurance at an airspeed was proportional to the relative power input (P1/Pi,min) raised to the power of –7·45; flying at a speed that raised P1/Pi.min by 10 % reduced endurance by half.
The Action of Hanson’s Thymus Extract on the Mouse
Authors: Lafon M. 
Published: April 2021

ABSTRACTIn a recent paper Hanson (1934) described important results as to the effect of extracts of the thymus gland on growth and morphological differentiation. In his experiments, albino rats from an inbred strain were daily injected during a long period with a thymic extract, the preparation of which is fully described by him in a previous paper (1930). Four successive generations were bred, the young being treated from the 16th day, and the treatment continuously applied even during pregnancy. Comparison with the controls shows a striking acceleration of growth, quite conspicuous from the growth curves, an earlier appearance of such morphological changes as the growth of the hair and the teeth, the opening of the eyes and the ears, and an earlier sexual maturation, as manifested by the external descent of the testes and the opening of the vagina. The injections have a cumulative effect, the results being most striking in the F2 animals, with a slight increase of effect through the following generations. The average time for the opening of the vagina may be reduced, from the 60th to 70th day in the controls, to the 18th to 19th day in F4, the appearance of the hair from the 14th to 17th day to the 3rd day.
Spinal Reflexes of the Dogfish, Scyllium Canicula
Authors: Gray J. , Sand A. 
Published: April 2021

ABSTRACT
In a previous paper (Gray and Sand, 1936) the persistent swimming rhythm of the spinal dogfish was described, and an account was given of experiments which demonstrate that the locomotory rhythm is determined by the intrinsic activity of the spinal cord without the participation of proprioceptor arcs. In the course of this work it became evident that the rhythmic activity of the spinal dogfish can be modified in various ways by external mechanical stimulation. These responses present a relatively simple pattern of reflex behaviour, their number is strictly limited, and they are uniformly reproducible. For these reasons, although our experiments raise a number of physiological questions which our data cannot answer, we have thought it worth while to record these phenomena in the present communication.
The Growth and Morphology of Fibro-BlastsIn Vitroin Relation to Certain Properties of the Plasma Coagulum1
Authors: Jacoby Fritz 
Published: April 2021

ABSTRACTBy placing blood plasma coagula containing growing cultures (fibroblasts from chick embryo) in a vertical position (vertical cultures) certain physical and quantitative chemical alterations of the medium occur under the influence of gravity; the effects of these upon the growth, morphology and products of differentiation (fibre formation) of the cultures are described. In vertical cultures the normal circular shape of the cell colony remains undisturbed, indicating that neither gravity nor a gradient of metabolites seems to play a role controlling the direction of movement of fibroblastic cells. Vertical cover-slip cultures show a greater radial extension (outgrowth) than the horizontal controls, apparently due to increased cell migration rather than to augmented cell division. Vertical cultures of fibroblasts, both on cover-slips and in flasks, do not show the usual appearance of visible fat droplets. If fat appears at all in vertical cultures a fat-free sector can sometimes be observed in the lower half of the culture. Flattening of the coagulum retards but does not prevent the appearance of visible fat in normal cultures. Under certain conditions the appearance of fat is an indicator of reduced activity since activity of fibroblastic cells (growth by migration) can be increased by preventing the accumulation of fat droplets in them. The latent period of offspring of a 10-day-old fat-free vertical culture is shortened as compared with that of offspring of the very fatty horizontal control of the same age. The greater activity observed in the vertical cover-slip cultures is apparently due to the non-appearance of fat. Vertical cover-slip cultures after three days’ cultivation show a slightly stronger formation of argyrophil fibres in the outer growth zone than the controls, but culture pairs fixed at a later time show no appreciable difference in fibre formation.