bluuebunny/crossref_metadata_2025 huggingface dataset:
barren inflorescence2regulates axillary meristem development in the maize inflorescence
Authors: McSteen Paula , Hake Sarah
Published: April 2021

Organogenesis in plants is controlled by meristems. Shoot apical meristems form at the apex of the plant and produce leaf primordia on their flanks. Axillary meristems, which form in the axils of leaf primordia, give rise to branches and flowers and therefore play a critical role in plant architecture and reproduction. To understand how axillary meristems are initiated and maintained, we characterized the barren inflorescence2 mutant, which affects axillary meristems in the maize inflorescence. Scanning electron microscopy, histology and RNA in situ hybridization using knotted1 as a marker for meristematic tissue show that barren inflorescence2 mutants make fewer branches owing to a defect in branch meristem initiation. The construction of the double mutant between barren inflorescence2 and tasselsheath reveals that the function of barren inflorescence2 is specific to the formation of branch meristems rather than bract leaf primordia. Normal maize inflorescences sequentially produce three types of axillary meristem: branch meristem, spikelet meristem and floral meristem. Introgression of the barren inflorescence2 mutant into genetic backgrounds in which the phenotype was weaker illustrates additional roles of barren inflorescence2 in these axillary meristems. Branch, spikelet and floral meristems that form in these lines are defective, resulting in the production of fewer floral structures. Because the defects involve the number of organs produced at each stage of development, we conclude that barren inflorescence2 is required for maintenance of all types of axillary meristem in the inflorescence. This defect allows us to infer the sequence of events that takes place during maize inflorescence development. Furthermore, the defect in branch meristem formation provides insight into the role of knotted1 and barren inflorescence2 in axillary meristem initiation.
Headless flies produced by mutations in the paralogousPax6geneseyelessandtwin of eyeless
Authors: Kronhamn Jesper , Frei Erich , Daube Michael , Jiao Renjie , Shi Yandong , Noll Markus , Rasmuson-Lestander Åsa
Published: April 2021

The two Pax6 gene homologs eyeless and twin of eyeless play decisive early roles in Drosophila eye development. Strong mutants of twin of eyeless or of eyeless are headless, which suggests that they are required for the development of all structures derived from eye-antennal discs. The activity of these genes is crucial at the very beginning of eye-antennal development in the primordia of eye-antennal discs when eyeless is first activated by the twin of eyeless gene product. This activation does not strictly depend on the Twin of eyeless protein, but is temperature-dependent in its absence. Twin of eyeless acts also in parallel to the eyeless gene and exerts functions that are partially redundant with those of Eyeless, while Eyeless is mainly required to prevent early cell death and promote eye development in eye-antennal discs.
Onset of neuronal differentiation is regulated by paraxial mesoderm and requires attenuation of FGF signalling
Authors: del Corral Ruth Diez , Breitkreuz Dorette N. , Storey Kate G.
Published: April 2021

While many neuronal differentiation genes have been identified, we know little about what determines when and where neurons will form and how this process is coordinated with the differentiation of neighbouring tissues. In most vertebrates the onset of neuronal differentiation takes place in the spinal cord in a head to tail sequence. Here we demonstrate that the changing signalling properties of the adjacent paraxial mesoderm control the progression of neurogenesis in the chick spinal cord. We find an inverse relationship between the expression of caudal neural genes in the prospective spinal cord, which is maintained by underlying presomitic mesoderm and FGF signalling, and neuronal differentiation, which is repressed by such signals and accelerated by somitic mesoderm. We show that key to this interaction is the ability of somitic mesoderm to repress Fgf8 transcription in the prospective spinal cord. Our findings further indicate that attenuation of FGF signalling in the prospective spinal cord is a prerequisite for the onset of neuronal differentiation and may also help to resolve mesodermal and neural cell fates. However, inhibition of FGF signalling alone does not promote the formation of neurons, which requires still further somite signalling. We propose a model in which signalling from somitic tissue promotes the differentiation of the spinal cord and serves to co-ordinate neural and mesodermal development.
Ontogeny of haemoglobin in the chicken
Authors: Manwell Clyde , Baker C. M. Ann , Betz T. W.
Published: April 2021

The controversy as to whether haemoglobin embryology in the chicken involves qualitative or merely quantitative changes is settled by the observation of consistent electrophoretic differences between the haemoglobins of early embryos and the haemoglobins of foetuses, chicks and adult chickens. Studies on polypeptide chain composition indicate that the multiple haemoglobins of 3-to 5-day incubation embryos are A2C2, B2C2 and D2F2. The major and minor haemoglobins of foetuses and adult chickens are A2F2 and A2E2. Thus, although embryos and adults have no haemoglobins in common, they appear to have two kinds of polypeptide chains in common, A and F. Embryos have three unique polypeptide chain types and adults have one, on the basis of differences in electrophoretic mobility. Some degree of polypeptide chain interchange occurs with at least one of the chicken haemoglobins in that one of the adult haemoglobins will hybridize with human adult haemoglobin, α 2β 2. Although two of the three 3-to 5-day chick embryonic haemoglobin components have one of their polypeptide chain types in common with the major adult haemoglobin, the oxygen equilibria and Bohr effect of adult and early embryonic haemoglobin are very different. Chick embryo haemoglobin has an extremely high oxygen affinity and a Bohr effect only two-thirds that of the adult. The haemoglobin ‘switchover’ at the end of day 5 of incubation is not paralleled by changes in erythrocyte esterases, lactate dehydrogenase or malate dehydrogenase isoenzymes.
The control of muscle and cartilage development in the chick limb: the role of differential vascularization
Authors: Caplan Arnold I. , Koutroupas Steven
Published: April 2021

The results of previous studies on the effects of nicotinamide levels on chick limb mesodermal cell expression have indicated that there may exist a metabolic gradient situated radially across the limb which has a controlling influence on whether a limb cell will differentiate into either a myogenic or chondrogenic phenotype. This study investigates the possible role of the vascular pattern in establishing such a metabolic gradient. Observations are reported which show that prospective myogenic and chondrogenic areas become differentially vascularized before the onset of molecular differentiation, thus indicating that the vascular pattern is capable of establishing metabolic gradients across the limb. Furthermore, predictions based on these results have been tested and verified in vitro. The hypothesis is presented that the spatial differentiation of cartilage and muscle in the developing chick limb is under the controlling influence of gradients of metabolic potential which can be established by the differential vascularization of the limb.
The differentiation of the chick chorionic epithelium: an experimental study
Authors: Narbaitz Roberto , Tellier Pierre P.
Published: April 2021

An electron microscopical study of the chorionic epithelium under two different experimental situations was conducted in order to gain knowledge on the mechanisms controlling the differentiation of ‘calcium-absorbing’ cells. In chorioallantoic membranes from 10-day-old embryos cultured on a semi-synthetic medium, the chorion became avascular but ‘calcium-absorbing’ cells differentiated, showing that the differentiation of these cells is not dependent on the vascular changes which in vivo occur simultaneously.

The number of ‘calcium-absorbing’ cells was much larger in the explants cultured on parathyroid hormone-enriched medium than in controls, indicating that the hormone is capable of stimulating their differentiation. Since it is known that parathyroid glands are active at the time in which ‘calcium-absorbing’ cells normally appear, our results suggest that the hormone may be the normal inductor of their differentiation.

Finally, a small number of ‘calcium-absorbing’ cells differentiated in vivo in a portion of chorion which had been artificially separated from the shell membranes, showing that their differentiation does not depend on the proximity of the external source of calcium.
Origine des ceintures scapulaires et pelviennes chez l’embryon d’oiseau
Authors: Chevallier Alain
Published: April 2021

The development and the origin of the pectoral and pelvic girdles have been studied in bird embryos by homo- or heterotopic transplantations of somitic and somatopleural mesoderm.

Experiments consisted in implanting a piece of somitic or of somitic and somatopleural mesoderm obtained from a 2-to 2 · 5-day quail or chick embryo into a chick host of equal age.

Results showed that the scapula derives from the somitic mesoderm, while clavicle, coracoid, sternum and pelvic girdle originate from the somatopleural mesoderm.

The longitudinal span of the territories of the various skeletal elements, expressed as the number of the corresponding somites, was found to be as follows: scapula 15 – 24, clavicle 10 – 15, coracoid .15 – 17, sternum 12 – 26, and pelvic girdle 26 – 32.

It was also demonstrated that both somitic and somatopleural mesoderm are regionalized as early as 2 days of incubation, prior to somitic segmentation, with respect to their ability to give rise to the skeletal elements of the girdles.

These results were compared to those acquired previously concerning the other morphogenetic potentialities (vertebrae, ribs, limb musculature, dorsal plumage) of the para-axial and lateral mesoderm.
Bristle patterns and compartment boundaries in the tarsi ofDrosophila
Authors: Lawrence Peter A. , Struhl Gary , Morata Gines
Published: April 2021

We describe cell lineage of the tarsus of wild-type Drosophila. Large Minute+ clones were made to map the position of the antero-posterior compartment boundary in all three tarsi. The tarsus is mirror symmetric, but the compartment boundary does not coincide with the mirror plane. This boundary runs along the dorsal and the ventral rows of bristles which are immediately posterior to the mirror plane; elements in these rows being made by both anterior and posterior polyclones. The provenance of bristles and bracts suggests that the bristle cells move into their final positions. The homoeotic mutation engrailed affects only the posterior compartments of all three tarsi. The mutations bithorax and postbithorax affect only the anterior and posterior compartments of the third legs, respectively, transforming them into homologous compartments of the second leg. These results support the selector gene model of development (Garcia-Bellido, 1975) and emphasize that collaboration between polyclones is important in pattern formation.
Experimental analysis of control mechanisms in somite segmentation in avian embryos.: I. Reduction of material at the blastula stage in Coturnix coturnix japonica
Authors: Veini Marianne , Bellairs Ruth
Published: April 2021

The blastulae of unincubated eggs of the quail, Coturnix coturnix japonica, have been bisected in ovo, using the technique of Lutz (1949). Some embryos were harvested after 24 h and found to possess two primitive streaks. Most were fixed at 48 h or 72 h. Some were found to have regulated to form almost normal single axes, whilst others had developed into duplicitas anterior embryos, separate twins or collided axes. All three types of twinned embryos were smaller than the control embryos. The number of somites was not however reduced in the shorter embryos. This finding corresponds with a similar result obtained by Cooke (1975) who reported that if a Xenopus blastula is reduced in size, it nevertheless develops the correct number of somites.

The quail however adjusts the shape of the individual somites so that they fit into the reduced body length, whereas Xenopus reduces the size of somites. No miniaturized somites were ever seen in these quail embryos.

As a result of the present experiments, it was concluded that the length of incubation time does not directly control the rate of somite formation, because different numbers of somites were found in twins which possessed identical genomes and had developed in almost the same environment for identical periods. In addition, the size of the area pellucida does not appear to control somite formation. Probably, the most important influence is the regression of the node.
The mechanism of feather pattern development in the chick: I. The time of determination of feather position
Authors: Davidson Duncan
Published: April 2021

A regular array of feather primordia covers chick dorsal skin in vivo. The pattern develops over a period of 2 days as a morphogenetic wave sweeps across either side of the back of the chick, forming successive anteroposterior rows of primordia.

This paper describes a new method for the culture of chick skin which allows the development of large areas of the feather pattern to be investigated experimentally. Skin is cultured on a substratum of hydrated collagen; since the collagen is transparent, feather primordium development can be observed in detail.

The new method has been used to investigate the problem of when the positions of feathers are determined. I show that during the time when the first few rows of primordia are forming, skin taken from just lateral to the most recently formed row can be caused to form an increased number of primordia per row by stretching it anteroposteriorly. This result indicates that the positions of feathers are determined sequentially along an invisible wave which moves just ahead of the visible wave of primordium morphogenesis.
X-chromosome instability in pluripotential stem cell lines derived from parthenogenetic embryos
Authors: Robertson E. J. , Evans M. J. , Kaufman M. H.
Published: April 2021

The karyotype of six pluripotential stem cell lines derived from haploid and two additional lines derived from diploid parthenogenetic embryos is described. All these lines are diploid and possess a normal autosomal complement. The stage at which diploidization of the haploid cells occurs is not yet known. The XX-chromosome complement in these lines is unstable, although in two haploid-derived lines and one diploid-derived line many normal XX-bearing cells are found in early cultures. All of the lines so far examined either become XO (rarely), or a single X chromosome shows a deletion in the distal region. The extent of this deletion varies between lines, but the position of the breakpoint appears to be constant for a given line. We suggest that these cytogenetic findings raise the possibility that a single deletion event occurring at an early stage during the isolation of these lines may confer a selective advantage to those cells carrying the deleted X chromosome.
The development of facial motoneurones in the mouse — neuronal death and the innervation of the facial muscles
Authors: Ashwell K. W. , Watson C. R. R.
Published: April 2021

The relationship between neuronal death and the formation of patterned connections was studied in the facial neuromuscular system of foetal, neonatal, and adult mice. The facial neuromuscular system was selected because two large, widely separated, facial muscles (the nasolabial and posterior auricular muscles) are innervated by clearly separated parts of the the facial motor nucleus in the adult mouse. The number of motorneurones in the facial nucleus was counted in Nissl-stained sections at different stages of development. Over 6400 neurones were present in the facial nucleus at day 17 p.c. (post-coitum). After day 17 p.c. the number of neurones fell rapidly and only 2000 cells remain in the adult nucleus. This represents a loss of 68 %, most of which occurs between days 18 and 20 p.c. Neurones with pyknotic nuclei are seen on day 17p.c. and are most numerous on day 18p.c. This leads us to believe that the fall in neurone numbers is due to cell death.

Indirect evidence provided by acetylcholinesterase histochemistry (time of earliest reaction in the facial muscles) and horseradish peroxide (HRP) tracing studies (time of earliest transport) indicate that facial motorneurone axons innervate the facial musculature before the period of cell death: diffuse acetylcholinesterase activity first appeared inthe auricular muscles at day 15 p.c. and in the nasolabial muscles at day 17 p.c. ; retrograde transport of HRP from the auricular and nasolabial muscles to the facial nucleus cannot be reliably demonstrated before day 17 p.c.

We assessed the topography of early facial neuromuscular innervation by making HRP injections into nasolabial and posterior auricular muscles of embryonic and neonatal mice. Injections of HRP at day 17 p.c. (the day before cell loss commenced) showed that the nasolabial muscle and posterior auricular muscles were innervated by the same subnuclei of the facial nucleus as in the adult - except that there was a small number (1-5 %) of labelled cells located in parts of the nucleus not consistent with the adult innervation pattern. These data indicate that, except for a small number of neurones, topographically organized connections in the facial neuromuscular system are established before the period of cell death. We conclude that motoneurone cell death does not play a major role in the establishment of topographically organized connections in this system.
Synthesis of globin chains in the erythropoietic sites of the early chick embryo
Authors: Fucci L. , Cirotto C. , Tomei L. , Geraci G.
Published: April 2021

The synthesis of globins in the chick embryo before the onset of circulation has been studied in situ by specific immunofluorescence labelling of embryonic sections and by labelling newly synthesized proteins in ovo and in vitro in embryonic explants with [3Hjleucine.

The presence of major primitive haemoglobins is observed by 28 h of incubation. The minor primitive haemoglobins become detectable by immunofluorescence after 40 h of development, shortly before the onset of circulation. 3H-labelling shows that one definitive a chain is synthesized, though in low concentration, from the initial globin detection. The other definitive a chain is observed in embryos of at least 40 h of development. The relative concentration of the two definitive α chains changes rapidly with development indicating a specific mechanism of regulation.

An erythropoietic site is observed in the wall of the dorsal aorta in embryos of about 45–50 h of development. From the initial detection, those cells contain all four primitive embryonic haemoglobins, in contrast to what is observed for the cells of the blood islands.
The form and structure of supernumerary hindlimbs formed following skin grafting and nerve deviation in the newt Triturus cristatus
Authors: Reynolds Susan , Holder Nigel , Fernandes Manuel
Published: April 2021

The results of a series of skin grafting experiments performed on the hindlimb of the newt Triturus cristatus are described. In an attempt to limit the position of origin and the complexity of supernumerary limb outgrowths four experimental features were varied. These were 1) size of skin grafts; 2) their position of origin; 3) the position to which they were grafted; and 4) the presence or absence of nerves of two different sizes at the graft site. The degree of distal outgrowth and the pattern of the supernumerary structures in the anterior to posterior and dorsal to ventral axes were assessed. The results are discussed in terms of the control of pattern regulation in localized populations of limb blastema cells.
Autonomous cortical activity in mouse eggs controlled by a cytoplasmic clock
Authors: Waksmundzka Małgorzata , Krysiak Elżbieta , Karasiewicz Jolanta , Czołowska Renata , Tarkowski Andrzej K.
Published: April 2021

Mouse eggs of Swiss albino origin, both parthenogenetic and fertilized, were bisected into nucleate (NHs) and anucleate halves (AHs) and observed in vitro (semicontinuous observations) for up to 40 h for possible manifestations of cortical activity. Three experimental groups were studied: (1) Non-fertilized eggs activated 17h after administration of hCG with a heatshock and bisected 4h later. (2) Non-fertilized eggs first bisected, and the resulting sister halves activated 17 h after administration of hCG with ethyl alcohol. (3) In vivo fertilized eggs bisected 27 h after administration of hCG into an AH and a binucleate half. Parthenogenetic eggs (intact, zona-free, and incompletely bisected), and fertilized eggs collected 17, 20, and 27 h after administration of hCG were also studied.

In the middle of the first cell cycle the cell surface in all types of cells studied changed from smooth to slightly undulate. In nucleate cells the surface deformations lasted for several hours and disappeared shortly before the first mitosis. In contrast, in AHs the indentations of the cell surface deepened, and developed into manifold furrows, thus leading to fragmentation. However, in 20 % of AHs fragmentation was partially or completely reversed. The incidence and the intensity of fragmentation were lower, and its reversibility was more common in AHs carrying the 2nd polar body. We suggest that the interphase nucleus, i.e. the pronucleus in whole eggs and NHs, and the 2nd polar body nucleus (if 2nd polary body is attached to an AH) exerts a moderating effect on cortical activity. However, the initiation of cortical activity is nucleus-independent, as shown by the behaviour of AHs separated before activation. We believe that the observed phenomena reflect autonomous cortical activity which is regulated by a cytoplasmic clock.
Mutational analysis of patterning of oral structures in Tetrahymena: I. Effects of increased size on organization
Authors: Frankel Joseph , Jenkins Leslie M. , Bakowska Julita , Nelsen E. Marlo
Published: April 2021

The oral apparatus (OA) of the ciliated protozoan Tetrahymena thermophila consists of four ordered arrays of ciliary units. In wild-type cells, these arrays are constant in spatial organization and vary little in size except during extreme starvation. Recessive mutations at five gene loci are known to increase the size of the OA. They do this by increasing the length of the ciliary arrays, without affecting their width and often without increasing their number beyond the usual four. Comparison of the oral arrays over a large range of sizes has revealed: (1) that the lengths of the anterior two of three parallel arrays (membranelles) are rather tightly coordinated; (2) that the specific basal body configurations resulting from remodelling of the membranelles are only slightly affected by large changes in lengths of membranelles; and (3) that the third membranelle is restricted to a nearly constant length, except in the very largest OAs in which the structure is lengthened but interrupted by a gap in the middle. This gap may reveal the spatial extent of a putative zone of basal body regression. These phenomena are not specific to any of the genotypes utilized in this investigation; the effect of the mutations is to loosen quantitative restrictions and thus reveal underlying associations and constraints.
Size regulation in the mouse embryo
Authors: Rands G. F.
Published: April 2021

The development of mouse embryos formed by the aggregation of four 8-cell-stage eggs was analysed in comparison with control single embryos. The analysis revealed that: Quadruple aggregates undergo size regulation over several days, starting before implantation and being completed by 6·5 days post coitum.The attainment of recognizable postimplantation morphological stages is independent of size.Regulation is not brought about by disproportionate alterations in the size of the internal cavities.Regulation in both inner cell mass (ICM) and trophectoderm derivatives is completed between 5·5 and 6·5 days post coitum.Despite the abnormal proportions of ICM and trophectoderm in quadruple blastocysts, the proportions of the tissues derived from them are already normal by 5·5 days.

The possibility that down regulation in size of aggregate embryos occurs as a consequence of limited nutrient supply is discussed.
Basal laminar thinning in branching morphogenesis of the chick lung as demonstrated by lectin probes
Authors: Gallagher Betty C.
Published: April 2021

Three lectins, wheat germ agglutinin (WGA), soybean agglutinin (SBA) and Ricinis communis agglutinin I (RCA), were used to study the basement membrane of developing chick lungs. Thinning of the basement membrane at the tips of newly formed bronchi was visualized with all three lectins, but was particularly evident using SBA. Control sections established the ability of the lectins to stain hyaluronic acid and chondroitin sulphate. Neuraminidase, bovine testes hyaluronidase and Streptomyces hyaluronidase removed some of the staining, but none were able to affect the staining of the basement membrane. Possible explanations for this are discussed in the text. Incorporation of [3H]thymidine is enhanced at the tips relative to the interbud area in stage-30 lungs, extending previous studies on stage-26 lungs. Evidence has been presented here which demonstrates that mechanisms of morphogenesis used in avian embryos are similar to those already elucidated in work on mammalian embryos.
Analysis of the cytosolic proteins of chick embryo gonads by two-dimensional gel electrophoresis
Authors: Samsel J. , Lorber B. , Petit A. , Weniger J.-P.
Published: April 2021

Gonads and mesonephros dissected from normal chick embryos, as well as a blood sample, were labelled in vitro with [35S]methionine and [14C]leucine. The patterns of cytosolic protein synthesis of the different tissues were analysed using two-dimensional (2-D) polyacrylamide gel electrophoresis. Three developmental stages, i.e. 8, 12 and 17 days of incubation, were investigated.

Five sex-specific proteins were detected in the male and two in the female. In the testis, only one protein is already present at the 8-day stage. In the ovary, one protein exists since the 8-day stage, but it is also synthesized in the mesonephros. The second ovary-specific protein appeared only at the 12-day stage.
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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

In 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.