bluuebunny/crossref_metadata_2025_split huggingface dataset:
Identification and distribution of gap junctions in the mesoderm of the developing chick limb bud
Authors: Kelley Robert O. , Fallon John F. 
Published: April 2021

ABSTRACT
Sub-ridge, core, anterior and posterior borders of mesoderm were dissected from stages 22-24 chick wing buds to investigate whether structures for intercellular coupling develop between mesenchymal cells. Fine structure was examined using techniques of transmission electron microscopy, freeze-fracture and scanning electron microscopy. Gap (communicating) junctions which were observed between mesenchymal cells of all limb bud regions were distributed between apposed cell bodies, points of contact between cell processes and other cell bodies, and between contacting tips of slender cell projections. In addition, particularly in the sub-ridge region, filopodia were observed to extend through the intercellular matrix to contact other cells several micrometers distant.
The observations reported in this paper show that mesodermal cells throughout the limb have the structural capability for electrotonic and metabolic coupling during a critical period of morphogensisis in the avian limb. Whether intercellular signals which are thought to be transmitted through gap junctions are active in normal limb development remains to be investigated.
The development of projections and connections from transplanted locust sensory neurons
Authors: Anderson Hilary 
Published: April 2021

ABSTRACT
Neurons innervating wind-sensitive hairs on the locust head form characteristic projections and connections within the CNS. These depend on intrinsic properties of the epidermis from which the hair and its neuron are formed (Anderson & Bacon, 1979; Bacon & Anderson, 1984). To investigate further these intrinsic properties and also extrinsic factors involved in guiding axon growth and determining synaptic connectivity, pieces of epidermis from the head were transplanted to the posterior head, prothorax, or mesothorax. Thus wind-sensitive neurons developing from the grafts were caused to grow into foreign parts of the CNS.
The neuronal projections from the graft hairs were examined by filling the axons with cobalt, and their connectivity with an identified interneuron, the Tritocerebral Commissure Giant, was examined by recording electrophysiologically the activity of the interneuron during stimulation of the graft hairs.
The results show that 1) the neuronal projections are confined to one tract, the median ventral tract, and to one arborization area, the ventral association centre, in all ganglia; 2) in all ganglia, neurons from different epidermal regions preserve their location-specific properties of forming ipsilateral or additional contralateral projections; 3) the extent of their projection in the CNS is not interpretable in terms of intrinsic instructions only; 4) in foreign ganglia, they fail to form connections with their normal target interneuron.
On the Normal and Abnormal Development of the Feather
Authors: Cohen J. , ’Espinasse Paul G. 
Published: April 2021

ABSTRACT
A brief résumé is given of previous views of feather development. It is here emphasized that the collar is not to be regarded as producing a feather, but that it is in its entirety transformed into a feather and so is lost each time a feather is plucked. The culture of collar fragments is described. Many cultures produced apparently normal barbs and barbules without any process resembling concrescence. It is concluded that the only movement of tissue which occurs during the transformation of a collar into a feather is along the generators of the feather cylinder. The growth process concerned in the transformation of collar into feather is thus an essentially simple one of elongation such that distal collar becomes distal feather and proximal collar becomes proximal feather. It is the original length from distal collar to proximal collar that increases to become the whole length of the feather. Thus the structure of a particular feather may be projected back in a simple manner and the structure of the collar which it once was can be deduced. The collar, however, is indeed produced from the papillar ectoderm and the manner of its production is considered as a topological problem. A feather with a distal abnormality but which is normal proximally, resulting from a collar that is abnormal distally but normal proximally, may be repeated. The papilla in this case must return to a condition of abnormality after producing the normal proximal part of each such collar in order subsequently to produce another collar with a similar abnormality distally. From the results of papilla transplant experiments described here and from those reported from other workers, it is deduced that the manner of the production of a collar from a papilla involves a preferential growth of dorsal ectodermal tissue : tissue which was dorsal on the papilla grows over the top and down the ventral side of the dome produced at the top of the healing papilla. Some evidence is presented that this occurs both when a pin-feather is plucked and when a feather matures normally by closure of its inferior umbilicus. ‘Longitudinal’ and ‘transverse’ chimaerae, double feathers and feathers with defective apices, and their repetition, are considered and explained in terms of our views.
An Analysis of the Postgastrula Differentiation of the Hypomere
Authors: Finnegan Cyril V. 
Published: April 2021

ABSTRACTWhen a small mass of hypomeric mesoderm is cultured in vitro within an ectodermal ball (M series) the splanchnic portion is collected in the centre and some haematopoiesis (erythropoiesis) occurs. In explants from post-stage 18 explants, cultured beyond two weeks, granulopoiesis was found in a differentiating reticulo-endothelium. When a group of endoderm cells were added to the explanted hypomere (M+E series) the younger postgastrula stages (stages 13–18) now demonstrated a histogenesis similar to the older stages in the M series (above), while the poststage 18 explants undergo a similar histogenesis but more rapidly than in the previous series. Some of these older-stage explants gave evidence Of axial orientation in the splanchnic mesoderm. When the mass of hypomere was increased (2M series) a large amount of peritoneum and endothelium was produced in all explants along with the usual erythropoietic area. No reticulo-endothelium or granulopoiesis appeared. The explants from the older donors (stages 17–20) frequently indicated an axial pattern in the splanchnic mesoderm. When groups of endoderm cells were added to the increased mass of hypomere (2M+E series) the early postgastrula explants (stages 13–16) evidenced an axial pattern for the first time in the endothelial-haematopoietic histogenesis of the splanchnic mesoderm. Again, no reticulo-endothelium with granulopoiesis was observed. Analysis of mitotic counts in the various explants indicated that the endoderm was influencing differentiation rather than growth (i.e. cell-division). Similarly, the increase in mass of hypomere appeared to influence differentiation and also to stabilize growth. The experimental results are considered to further indicate the synergistic role of the endoderm in the histogenesis of the splanchnic hypomere.
Influence inductrice de l’encéphale et de la chorde sur la morphogenèse du squelette cranien chez l’embryon de Poulet
Authors: Schowing par Jean 
Published: April 2021

ABSTRACT
De nombreux auteurs, parmi lesquels Parker (1876) et de Beer (1937), ont étudié et décrit le développement de la tête chez l’embryon d’Oiseau. C’est en 1933 que P. Ancel et Ét. Wolff ont inauguré l’analyse expérimentale des facteurs qui président à l’organogenèse embryonnaire chez le Poulet. Les travaux d’Ét. Wolff (1936) sur les bases de la tératogénèse expérimentale chez les Vertébrés amniotes ont incité d’autres collaborateurs à des recherches sur la morphogenèse des différents organes de l’embryon.
Experimental Investigations of Morphogenesis in the Growing Antler
Authors: Goss R. J. 
Published: April 2021

ABSTRACT
Investigations of the morphogenesis of antler growth have been undertaken in the sika deer (Cervus nippon). Operations were performed on the left antlers, while the intact right antlers served as controls. Amputation of the terminal centimetre of growing antlers seriously impedes further development except for the production of an abortive outgrowth from the stump. By contrast, transverse amputation through the middle of the pedicle is followed by normal antler formation. Removal of the entire pedicle permits antler development to occur, although at a retarded rate. Therefore, antlerforming potentiality resides in the growing tips of the elongating antler as well as in the tissues of the entire pedicle. The extent of morphogenetic regulation for defects surgically inflicted on the antler bud or pedicle depends on the age of the antler and the location of the injury. Excision of the posterior halves of 1-inch antler buds results in corresponding deficiencies in the antlers produced. The same injury to an extremely rudimentary bud, however, is followed by considerable regulation, and removal of the posterior half of the pedicle prior to shedding of the old antler has no effect on the normal development of the resulting antler. Ablation of anterior or median halves of pedicles likewise causes no morphogenetic abnormality, but if the lateral half of the pedicle is removed no antler develops. The importance of the lateral half of the antler-forming structure is further illustrated by the fact that a complete and normal antler can grow from just the lateral half of a pedicle or of a 1-inch antler bud. The morphogenetic field of the antler can give rise to double antlers if bisected longitudinally; transverse subdivision, however, does not alter subsequent normal production of a single antler. It is proposed that a relationship between the initial mass of antler-forming material and the degree of morphogenetic expression may possibly exist.
miRNA interplay: mechanisms and consequences in cancer
Authors: Hill Meredith , Tran Nham 
Published: April 2021

ABSTRACT
Canonically, microRNAs (miRNAs) control mRNA expression. However, studies have shown that miRNAs are also capable of targeting non-coding RNAs, including long non-coding RNAs and miRNAs. The latter, termed a miRNA:miRNA interaction, is a form of self-regulation. In this Review, we discuss the three main modes of miRNA:miRNA regulation: direct, indirect and global interactions, and their implications in cancer biology. We also discuss the cell-type-specific nature of miRNA:miRNA interactions, current experimental approaches and bioinformatic techniques, and how these strategies are not sufficient for the identification of novel miRNA:miRNA interactions. The self-regulation of miRNAs and their impact on gene regulation has yet to be fully understood. Investigating this hidden world of miRNA self-regulation will assist in discovering novel regulatory mechanisms associated with disease pathways.
DMM Outstanding Paper Prize 2020 winner: Sarah Colijn
Authors: Hackett Rachel 
Published: April 2021

ABSTRACT
Disease Models & Mechanisms (DMM) is delighted to announce that the winner of the DMM Prize 2020 is Sarah Colijn, for her paper entitled ‘Cell-specific and athero-protective roles for RIPK3 in a murine model of atherosclerosis’ (Colijn et al., 2020b). The prize of $1000 is awarded to the first author of the paper that is judged by the journal's editors to be the most outstanding contribution to the journal that year. To be considered for the prize, the first author must be a student or a postdoc of no more than 5 years standing.
The effects of starvation and light on intra-mitochondrial granules in Physarum Polycephalum
Authors: Nicholls T. J. 
Published: April 2021

ABSTRACT
The presence of spherical or rod-shaped, electron-dense particles was noted within the mitochondrial cristae of Physarum polycephalum plasmodia. When sporulation was stimulated by starvation and subsequent illumination it was found that the numbers of such particles present per mitochondrion increased during the starvation phase, reaching a maximum after about 4 days, and then decreased rapidly during exposure of the plasmodium to light. Few particles were present in the mitochondria of spores. It is suggested that the particles may be similar to the mitochondrial granules of other organisms in providing a repository of calcium, which in Physarum is deposited in the capillitium during sporulation.
Surface extensions on bhk cells grown in monolayers and agar suspension
Authors: Tuffery A. A. 
Published: April 2021

ABSTRACT
Three types of surface extensions found on a subline of BHK cells capable of growing in agar are described.
These are:Microvilli-borne on the cell surface, lacking rigid cores, found on trypsinized cells and on cells growing in solid tissue type growth;Microspikes-borne on the cell margins, containing rigid cores, found on spread, attached cells, but not trypsinized cells or cells growing in solid tissues;Retraction fibrils-coreless ‘passive’ cell extensions drawn out distally as motile cells move across a surface.
Microvilli also seem to be associated with micropinocytic vesicles. It is suggested that microvilli on tissue cells in vitro may be homologous with the cell membrane interdigitations found in, for example, gut epithelium, and possibly also with the microvilli of brush borders. Their association with these structures suggests they may play a role in producing a local environment near the cell membrane in which micropinocytosis may function more effectively.
An inhibitor present in calf serum which prevents growth of BHK21 cells in suspension culture
Authors: Otsuka H. 
Published: April 2021

ABSTRACT
BHK21 cells do not form colonies in soft agar suspension culture in the presence of calf serum; but if swine serum is used instead they do so. In methylcellulose suspension culture supplemented with calf serum the cells synthesize very little RNA or DNA, but if swine serum is used there is a marked increase of syntheses. Calf serum was found to contain an inhibitor which prevents the induction, but not the continuation, of RNA and DNA synthesis in BHK21 cells. In contrast the growth of polyoma-virus-transformed cells is not affected by this serum inhibitor which has been partially purified from calf serum by ammonium sulphate precipitation followed by Sephadex G-200 column chromatography.
Brain extracellular space and membrane morphology variations with preparative procedures
Authors: Schultz R. L. , Karlsson U. L. 
Published: April 2021

ABSTRACT
When considering extracellular space and plasma membrane structure in the brain, duration of postfixation in osmium tetroxide and embedding procedure are equally as important as the dehydrating agent employed. The use of ethanol instead of acetone for dehydration does not adequately explain the finding of a 5–30 nm space instead of apposed membranes. In this investigation it was found that postfixation for 3 h stabilized the tissue sufficiently so that ethanol or acetone dehydration followed by Vestopal W, Epon 812, or Araldite 502 embedding produced similar results, and apposed, triple-layered plasma membranes were prevalent. In contrast, when postfixed for a shorter time, namely 90, 45 or 30 min, ethanol dehydration followed by Epon embedding resulted in the common ‘20-ntn ‘extracellular space and only partially triple-layered plasma membranes. The same tissue dehydrated with acetone and Vestopal embedded looked much like the equivalent 3-h postfixed material, i.e. it had apposed, triple-layered plasma membranes. When acetone dehydration and Epon embedding, or ethanol dehydration and Vestopal embedding were used with tissue of short postfixation time, the results were comparable. Apposed membranes interspersed with erratic amounts of extracellular space were common and plasma membranes tended to show an indistinct outer leaflet. Taken together the results indicate that the presence of apposed triple-layered plasma membranes is at least as valid as the common finding of a 20-nm space and partially tri-laminar membranes.
The effect of 6-hydroxydopamine on nerves in the rat upper urinary tract
Authors: Gosling J. A. , Dixon J. S. 
Published: April 2021

ABSTRACT
The effect of a single large dose of 6-hydroxydopamine (6-OHDA) on adrenergic nerves in the rat upper urinary tract has been investigated by both light and electron microscopy. Reduction in the intensity of fluorescent catecholamine-containing nerves was seen 1–2 h after drug treatment. At 3–5 h, fluorescing nerves were absent from all preparations. Forty-eight hours after injection fine catecholamine-containing nerves could not be detected, although a few large nerves adjacent to vessels and in the adventitia of the upper urinary tract were associated with increased fluorescence. Using the electron microscope, axons related to smooth muscle were seen to be swollen and contained aggregations of small (50 nm diameter) granulated vesicles and electron-dense material 3–6 h after drug treatment. Other axons contained damaged mitochondria and were devoid of neurofilaments and neurotubules. Normal axons were also seen, some of which contained accumulations of small (50 nm diameter) agranular vesicles and occasional large (100 nm diameter) granulated vesicles. In the submucosa, damaged axons were observed lying close to, or occasionally running between, basal epithelial cells. Axons containing electron-dense clumps of synaptic vesicles were not observed in this situation. Normal axons containing accumulations of small agranular vesicles were identified, some of which were closely related to damaged axon profiles. Forty-eight hours after the drug treatment, some axons related to smooth muscle cells contained accumulations of electron-dense material. All other axons in the wall of the upper urinary tract appeared normal. These results are discussed in relation to the distribution of various types of autonomic nerve in the upper urinary tract.
Cellular junctions in the tunicate heart
Authors: Lorber V. , Rayns D. G. 
Published: April 2021

ABSTRACT
The cell membranes of the tunicate heart exhibit an abundance of macular close junctions (also referred to as gap junctions or nexuses), distributed more or less randomly over the intercellular surfaces, and a system of zonal tight junctions limited to the cell borders adjacent to the epicardial surface. Three-dimensional images of these structures are displayed by the freeze-etch technique. In sectioned tissue, lanthanum appears to be excluded from the tight junctions, but is present in the close junctions. The presence of a primitive intercalated disk is suggested.
Cell electrophoresis of the cellular slime mould Dictyostelium Discoideum: II. relevance of the changes in cell surface charge density to cell aggregation and morphogenesis
Authors: Lee K.-C. 
Published: April 2021

ABSTRACT
The reduction in the cell surface charge density of Dictyostelium discoideum during differentiation has been studied by the technique of cell electrophoresis. It was abolished under conditions in which cell aggregation was inhibited (e.g. low temperature, the presence of actinomycin D or cycloheximide). In the presence of nutrients incapable of supporting growth, cell aggregation occurred without a reduction in surface charge density. Cell adhesion in these aggregates was impaired, and a reduction in surface charge density appeared to be necessary for further development.
Brief treatment of exponential phase and aggregating cells with agents which disaggregate slugs failed to alter their electrophoretic mobilities. Low concentrations of magnesium chloride caused extensive agglutination, especially in aggregating cell suspensions, but little change in their electrophoretic mobilities. Magnesium chloride could agglutinate cells by association with cell surface components undetectable by cell electrophoresis. This, together with immunological evidence from other workers, supports the possibility of involvement of specific surface macromolecules in cellular slime mould aggregation. It was concluded that changes in surface charge density, though important for cell adhesion and morphogenesis, cannot account for all aspects of cell interactions in D. discoideum.
Characterization of dna-bound histone in the cells of the avian erythropoietic series
Authors: Appels R. , Wells J. R. E. , Williams A. F. 
Published: April 2021

ABSTRACT
The distribution of DNA-bound histone from purified cell populations of the avian erythroid cell series was studied to examine the possible relationship between these molecules and the in vivo activity of cells. High-resolution polyacrylamide gel electrophoresis of histones indicated that the 3 main cell types, namely, erythrocytes (inactive in macromolecular synthesis), polychromatic erythrocytes (active in RNA and protein synthesis) and erythroblasts (dividing cells) all contained the same histone components. This result is contrary to previous reports that the f2c histone (characteristic of avian erythroid cells) was absent from erythroblasts; in addition it does not support the proposition that dividing cells contain a uniqueμ histone component. Quantitation of histone analyses showed that erythroblasts contain relatively less f2c histone than the non-dividing cells of the series and that there was a slight redistribution ofμ histone components between polychromatic and mature erythrocytes.
Spindle shape changes as an indicator of force production in crane-fly spermatocytes
Authors: Lafountain J. R. 
Published: April 2021

ABSTRACT
Changes in spindle shape during the first and second meiotic divisions in living Nephrotoma suturalis spermatocytes have been studied and recorded cinematographically with phase-contrast, Nomarski differential interference, and polarization microscopy. With the Nomarski system 2 classes of discrete spindle filaments (new terminology) have been observed: continuous filaments that extend between the poles and appear to form a cage-like framework within which the chromosomes move, and kinetochore filaments which are attached to the chromosomes at their kinetochores and converge toward the poles. Spindle deformation occurs in a manner consistent with the hypothesis that whatever tensile forces are transmitted by the kinetochore filaments are balanced by compressive forces acting on the cage-like framework of continuous filaments causing them to become splayed. Just when these forces would be expected to reach a maximum, kinetochore filaments undergo a noticeable increase in contrast. It has not been determined whether this change represents a crowding of linear elements or addition of dry mass to a constant number of linear elements.
Structure and coiling of the stalk in the peritrich ciliates Vorticella and Carchesium
Authors: Amos W. B. 
Published: April 2021

ABSTRACT
The stalk of Carchesium and Vorticella coils by the action of a contractile organelle. The organelle lies within a thread of cytoplasm which is encased in a complex extracellular tube. Study with the light microscope and the electron microscope suggests that the structure of the tube and the course of the organelle determine the form of the coiling. The contractile organelle contains a system of interconnected membranous tubules and the cytoplasm around it also contains membranous saccules. Both tubules and saccules extend along the length of the stalk.