bluuebunny/crossref_metadata_2025_split huggingface dataset:
Compaction of the mouse embryo: an analysis of its components
Authors: Pratt H. P. M. , Ziomek C. A. , Reeve W. J. D. , Johnson M. H. 
Published: April 2021

ABSTRACTA variety of agents (viz.: cytochalasin D, colcemid, cytochalasin D + colcemid, Ca2+-free medium, 7-ketocholesterol, cholesterol, concanavalin A, anti-embryonal carcinoma antiserum and tunicamycin) which modify the cell membrane and/or cytoskeleton were used to investigate the molecular and cellular basis of the intercellular and intracellular components of compaction and analyse the relationships between them. It was found that the individual components could be selectively dissociated from one another. Cell flattening and close intercellular apposition were the most sensitive features and affected by the majority of agents. Tight junctions did not form in the absence of intercellular apposition, however an apparently normal degree of intercellular apposition did not necessarily lead to the assembly of these junctions. Polarization of individual blastomeres, as assessed by the reorganization of the cell surface, was the component most resistant to experimental intervention since it occurred in the presence of all agents used, though it was modified by some of them. The results are discussed in terms of the molecular and cellular events underlying polarization, intercellular apposition and tight junction formation as well as the significance of these events for normal blastocyst formation.
Behaviour of annulate lamellae during the maturation of oocytes in the newt, Cynops pyrrhogaster
Authors: Imoh Hiroshi 
Published: April 2021

ABSTRACT
The distribution of annulate lamellae, electron-dense masses, rough endoplasmic reticulum, and Golgi complexes in longitudinal sections of newt oocytes at several stages of progesterone-induced maturation was recorded with an electron microscope equipped with a drawing device. Annulate lamellae in full-grown oocytes occur in close contact with electron-dense masses and the nuclear envelope and elsewhere. Stacks of annulate lamellae increase in number for 6 h after progesterone treatment. Meanwhile, they segregate into three groups. The largest group, comprising about 75 % of total stacks, forms a row parallel to and just beneath the oocyte cortex of both the animal and vegetal hemispheres, a second group is distributed in the middle area of the vegetal hemisphere, and a third group appears near the yolk-free cytoplasm formed at the vegetal side of the germinal vesicle during the maturation. About 6 h after progesterone treatment the annulate lamellae begin to disappear at their places of localization and none is found a few hours after germinal vesicle breakdown. No immediate fine-structural change in the cortical area follows the disappearance of subcortical annulate lamellae. The possible origins and fates of annulate lamellae in the maturing newt oocytes are discussed.
The effects of partial hypoblast removal on the cell morphology of the epiblast in the chick blastoderm
Authors: Vanroelen CH. , Verplanken P. , Vakaet L. C. A. 
Published: April 2021

ABSTRACTThe hypoblast of early-primitive-streak-stage chick blastoderms was partially removed. This experiment provokes a reaction in the epiblast which curls up and becomes even at its ventral surface. The basal lamina underlying the epiblast is also dependent upon the presence of hypoblast. During culture after partial hypoblast removal, active hypoblast wound healing is observed. Where the hypoblast underlies the epiblast again, the effects of the removal disappear and normal development proceeds. The results suggest that the normal epiblast morphology is dependent upon the presence of hypoblast. This influence of hypoblast on epiblast is thought to be concerned with the morphology of the epiblast and not directly with its morphogenesis.
Differentiation of fibre types in an extraocular muscle of the rat
Authors: Nag Asish C. , Cheng Mei 
Published: April 2021

ABSTRACTMammalian extraocular muscles possess greater variation in structural and physiological properties than any other muscle. The superior rectus muscle of the adult rat contains five morphological fibre types. The differentiation of the muscle into these fibre types in embryonic and postnatal rats were studied by light and electron microscopy, and the distribution of each developing fibre type with its distinctive features was mapped. The muscle of the 18-day embryos did not display the specific structural fibre types that were observed in the adult muscle. Newborn rat muscle exhibited some differentiation that included scattered smalldiameter fibres with large myofibrils (fibre type ‘B’). As development proceeded, another small-diameter fibre type with small myofibrils (fibre type ‘A’) appeared in the 6-day post-natal rat muscle. By the end of the first week of development neuromuscular junctions were in evidence in these two fibre types. Postsynaptic folds were rare in the large-fibril fibre, and folds were extensive in the small-fibril fibre. The medium-(fibre type ‘C’) and large-diameter (fibre type ‘D’) fibres were fully differentiated with small myofibrils and abundant sarcoplasmic reticulum (SR) by the second week of the development. SR was most abundant in the large-diameter fibre, which constituted the predominant global fibre type in the adult muscle. The postsynaptic folds in the neuromuscular junctions of these two fibre types were highly developed, although the innervation did not extend widely in the global region of the muscle. The last fibre type (fibre type ‘E’) was fully differentiated with the largest myofibrils, a small amount of SR, and simple neuromuscular junction by the third week of the postnatal development. The superior rectus muscle of the four-week-old rat was differentiated with all fibre types present in the adult muscle. During the third to sixth, and final, week of development, the other types described above exhibited extensive differentiation of characteristic structural features.
Visuotectal projections following temporary transplantation of embryonic eyes to the body inXenopus laevis
Authors: Munro N. S. , Beazley L. D. 
Published: April 2021

ABSTRACTEye anlagen of Xenopus laevis at stages 22 – 26 were transplanted, 180° rotated, into the flank of similarly staged embryos and 24 – 36 h later were placed into the orbits of final hosts at stages 32 – 36. After metamorphosis visuotectal projections were mapped electrophysiologically. In one series, eyes were normally oriented in the final host and visuotectal projections were found to be normal. A second series, in which eyes were placed in a rotated orientation in the final host, had developed rotated projections. The results suggest that at stage 22 the eye already contained positional information in terms of the organization of central connections which was not overridden by cues from surrounding tissue on the flank or in the final host orbit. Earlier experiments by Hunt and Jacobson (1972), which indicated that body tissues impose positional information on the developing eye between stages 29 and 31, are discussed in relation to the present study.
Germ line ofTetrodontophora bielanensis(Insecta, Collembola). Ultrastructural study on the origin of primordial germ cells
Authors: Klag Jerzy 
Published: April 2021

ABSTRACTIn the early embryo of Tetrodontophora bielanensis (up to the stage of 500 blastomeres) nuage granules occur in two different locations: (1) in areas where the invaginating cleavage furrows have pushed fragments of the oosome into the yolk mass, and (2) in the oosome proper. In the first areas the granules are few in number and certain cells that have enclosed them in their cytoplasm eventually degenerate. The remaining cells arising in these areas are devoid of any nuage granules and differentiate into yolk cells. A different situation is observed in the other areas, where certain cells resulting from tangential divisions of the superficial blastomeres contain many nuage granules and represent primordial germ cells (PGCs). The incipient PGCs differ from the other cells of the embryo in possessing nuage granules associated with mitochondria and in lacking any annulate lamellae.
Motor projection patterns to the hind limb of normal and paralysed chick embryos
Authors: Laing N. G. 
Published: April 2021

ABSTRACTCounts were made of the number of motoneurons innervating the hind limbs of 10-day normal and paralysed chick embryos whose right hind limb buds had been subjected to varying degrees of amputation prior to innervation. The number of motoneurons on the intact sides of the paralysed embryos was found to be similar to the number present in normal embryos prior to the major period of motoneuron death. Since it has previously been shown that paralysis does not increase the number of motoneurons generated, this means that normal motoneuron death was largely prevented in the paralysed embryos.There were differences in the distributions of motoneurons in the rostrocaudal axis of the spinal cord between normal and paralysed embryos. Therefore, cell death does not eliminate a uniform fraction of motoneurons throughout the rostrocaudal extent of the chick embryo lumbar lateral motor column. It is also argued that there are differences in the relative contribution of the various lumbosacral levels to different parts of the limb, e.g. the shank, before and after the period of cell death.In both normal and paralysed embryos there was a linear relationship between the volume of limb muscle which developed after amputation and the number of motoneurons surviving in the spinal cord. There was no evidence of a ‘compression’ of motoneurons into the remaining muscle either after amputation alone or after amputation combined with paralysis. Motoneurons are therefore rigidly specified for certain parts of the limb.The relationship between motoneuron number and muscle volume on the amputated side differed from that of the intact side. For a similar increase in muscle volume there was a smaller increase in motoneuron number on the intact sides. This suggested a parallel to the paradoxically small increase in motoneuron number that occurs on the addition of a supernumerary limb.
The Effects of Trypan Blue on Chick Embryos Cultured in vitro
Authors: Mulherkar Leela 
Published: April 2021

ABSTRACT
Chick embryos at the primitive-streak or early head-process and at the medullary-plate stages were treated with Trypan blue during culture in vitro. The dye produced many abnormalities such as malformation of somites, shortening of the axis, the formation of large blisters on the embryo, and delayed heart flexure. In some specimens notochord failed to form and a median somite strand was found in these cases.
The Occurrence and Morphogenesis of Melanocytes in the Connective Tissues of the PET/MCV Mouse Strain1
Authors: Nichols Stuart E. , Reams Willie M. 
Published: April 2021

ABSTRACT
Mice of the PET/MCV strain are characterized by having melanocytes scattered in the connective tissues of most of the body. The ‘internal’ pigment cells generally first appear in fetuses as spherical melanocytes which later produce branches and lay down melanin. By contrast, pigment cells within the skin branch prior to the onset of melanogenesis. Spherical melanocytes of the serosae of the PET/MCV mouse proliferate within the coelomic lining of host chick embryos. However, the degree of proliferation and spread is considerably less than that of melanoblasts under similar conditions. Under the conditions of experimental grafting, both spherical ‘internal’ melanocytes and melanoblasts from the dermis showed a similar pattern of differentiation. The time at which donor melanocytes produce branches within the host chick embryos is in accord with their location and the specific time expected of the host and not of the donor. The data suggest that the branching of a pigment cell is evoked by a morphogenic substance which is produced by certain tissues of the body, particularly by the epidermis. The effect, at least with regard to the mouse and chick, is not species specific, since grafted mouse pigment cells react in keeping with the chick environment.
A propos du raccourcissement de la ligne primitive du blastoderme du Poulet
Authors: Vakaet L. 
Published: April 2021

ABSTRACT
Fragments of chick blastoderm containing the posterior two-thirds or two-fifths of the primitive streak have been cultured, using Spratt’s explantation and carbon particle marking techniques. The stage of embryo at operation ranged from full primitive streak to headfold. Under these circumstances a forward movement was observed in the posterior half of the primitive streak, giving rise after 15 hours of cultivation to an anterior median protrusion which contains structures plainly derived from the primitive streak (fig. 1) or even a distribution of cell-strands recalling axial organs (fig. 2). After 40 hours of cultivation a tail-bud may arise, obviously without any contribution from the node of Hensen. We therefore suggest that the shortening of the streak should not be considered merely as a regression but as the consequence of three simultaneous and integrated movements: (a) regression of the node and anterior half of the Streak; (b) a general epibolic movement of the whole blastoderm; (c) a forward movement of the posterior part of the streak, most marked at the posterior end, for which the name of ‘posterior node’ is proposed.
The Functional Differentiation of the Small Intestine
Authors: Moog Florence , Ortiz Evelina 
Published: April 2021

ABSTRACT
The development of the duodenal epithelium of the foetal guinea-pig from the 29th day in utero to 3 weeks after birth has been studied by histochemical and quantitative biochemical techniques. The growth of the adrenal glands has also been studied. Alkaline phosphatase accumulates in the striated border of the epithelial cells as the definitive villi are cut out of a mass of epithelium that occludes the intestinal lumen at early stages. The villi are completed early in the 7th week, and phosphatase activity, measured against phenylphosphate, reaches its maximal value at 49 days. The activity against beta-glycerophosphate does not rise in parallel with that against phenylphosphate. The ratio of amount of phosphorus liberated from phenylphosphate to amount liberated from beta-glycerophosphate is significantly higher at 45 days than at 31 or 60 days. At the time of alkaline phosphatase accumulation and later, the epithelial cells are choked with glycogen and appear vacuolated when stained by any technique that does not demonstrate glycogen. During the last week in utero glycogen seems to be used up, and it is not found in the new-born duodenum. Total nitrogen concentration does not increase until after 60 days in utero. In the same period granular basophilic cytoplasm begins to replace the vacuoles predominant in earlier stages. The results suggest that the end of the 6th and the beginning of the 7th prenatal weeks constitutes a critical period for the functional differentiation of the foetal duodenal epithelium. Other authors have shown that the same period is critical for the differentiation of the cerebral cortex and the lungs. The adrenal glands achieve their maximal relative weight at the middle of the 5th week. The cortex is large at this time, and is rich in sudanophilic substances. It appears capable of secreting during the critical period described above. A difference in relative weight of male and female adrenals appears first at 45 days. Comparison of patterns of duodenal differentiation in the guinea-pig, chick embryo, and mouse indicates that the chemical and structural similarity of mature intestinal epithelia is arrived at by different developmental pathways.
Respiratory Levels in Mature Sea-urchin Eggs
Authors: Gonse Pierre H. 
Published: April 2021

ABSTRACTA study of the respiratory capacity of unfertilized and fertilized eggs of Strongylocentrotus purpuratus was undertaken in a variety of suspending media such as sea-water, coelomic plasma, sucrose, and KC1. The action of glucose, succinate, and dinitrophenol on the respiration of intact eggs and homogenates of eggs was reported. In this manner it was possible to define a number of relative levels of respiration. By suspending intact eggs in sucrose or by homogenization it was possible to decrease the difference in respiratory levels between fertilized and unfertilized eggs. By employing a rapid homogenization technique two levels of respiration could be distinguished: an initial rapid rate which progressively decreases over a 20-minute interval, followed by the establishment of a constant rate of respiration at a lower level. These results are discussed with regard to the problem of the metabolic changes which take place upon fertilization.
Rôle inducteur du mésoderme dans la différenciation précoce du bourgeon de membre chez l’embryon de Poulet
Authors: Kieny Madeleine 
Published: April 2021

ABSTRACTMesoderm from the presumptive anlage of the limb-bud (stages 15–16 and 17 of Hamburger & Hamilton) or mesoderm from a very young limb-bud (stages 17–18) was separated from its ectoderm with trypsin or versene and grafted into the area pellucida of an embryo of 15–23 somites (stages 12–14). The mesoderm was placed in contact with the region of the somatopleure which normally gives rise to the flank of the embryo between the wing and the leg. After the action of the trypsin solution, the mesoderm elicited the outgrowth of a supernumerary limb in only one case out of 59 (Plate 1, fig. 3). After the action of the versene, the implanted mesoderm induced an extra limb in 22 cases out of 54 (Plate 1, figs. 4, 5, 6, 7). The inductive capacity was retained after the mesoderm had been chopped to small pieces before grafting (Plate 2, figs. 9, 10). All induced limbs grew outwards and were situated in the same plane as the limbs of the host embryo. They were all covered by host epidermis. Control grafts of mesoderm on chorio-allantoic membrane only formed amorphous cartilaginous masses ; their development was in no case greater than their prospective value (Plate 2, fig. 11). The host flank ectoderm, under the influence of the grafted mesoderm, formed an ectodermal ridge possessing the same properties as the ectodermal ridge of a normal limb-bud (text-fig. 1; Plate 2, fig. 14). It is concluded that the limb-bud mesoderm is the primary inductor of the limb.
In vitro development of isolated ectoderm from axolotl gastrulae
Authors: Slack Jonathan M. W. 
Published: April 2021

ABSTRACT
The development of ectoderm isolated from the animal pole of axolotl gastrulae is monitored by light microscopy, electron microscopy and analysis of newly synthesized proteins, glycoproteins and glycolipids. When control embryos are undergoing neurulation it is shown that the explants autonomously begin to express epidermal markers and do not express mesodermal markers. However the results suggest that not all the cells become epidermal and electron microscope examination shows that only the outer layer does so, the inner cells remaining undifferentiated.
Regeneration and pattern formation in planarians I. The pattern of mitosis in anterior and posterior regeneration in Dugesia (G) tigrina, and a new proposal for blastema formation
Authors: Saló Emili , Baguñà Jaume 
Published: April 2021

ABSTRACT
Mitotic activity during regeneration in the planarian Dugesia (G) tigrina shows a biphasic pattern, with a first maximum at 4–12 h, a second and higher maximum at 2–4 days, and a relative minimum in between. The first peak is mainly due to pre-existing G2 cells entering mitosis shortly after cutting, whereas the second maximum is due to cells that divide after going through the S period from the onset of regeneration.
From a spatial point of view, the highest mitotic values are found in stump (postblastema) regions near the wound (0–300 μm), though regions far from it also show increased mitotic values but always lower overall values. As regeneration continues the postblastema maximum shifts slightly to more proximal regions. In contrast, no mitosis has been found within the blastema, even though the number of blastema cells increases steadily during regeneration. These results suggest that blastema in planarians forms through an early accumulation of undifferentiated cells at the wound boundary, and grows by the continuous local migration of new undifferentiated cells from the stump to the base of blastema.
The results obtained demonstrate that blastema formation in planarians occurs through mechanisms somewhat different to those shown to occur in the classical epimorphic models of regeneration (Annelida, Insecta, Amphibia), and suggest that planarian regeneration could represent an intermediate stage between morphallactic and epimorphic modalities of regeneration.
Heat shock – a comparison of Drosophila and yeast
Authors: Lindquist Susan 
Published: April 2021

ABSTRACT
When cells or whole organisms are exposed to temperatures slightly above their optimum for growth, they respond by synthesizing a small group of proteins, called the heat shock proteins (hsps), which help protect them from the toxic effects of heat. The same set of proteins can also be induced by a wide variety of other stresses including exposure to ethanol, heavy metal ions, and inhibitors of respiratory metabolism. Their induction is apparently a very general reaction to adverse conditions. (See Schlessinger, Ashburner & Tissieres, 1982, for review.)
Photoregulation of the biosynthesis of ribulose bisphosphate carboxylase
Authors: Ellis R. John , Gallagher Thomas F. , Jenkins Gareth I. , Lennox C. Ruth 
Published: April 2021

ABSTRACT
Chloroplast development in higher plants is light dependent, and is accompanied by the synthesis of chlorophyll and the accumulation of many chloroplast polypeptides. There is a 100-fold greater content of the photosynthetic enzyme, ribulose-l,5-bisphosphate carboxylase-oxygenase, in light-grown seedlings of Pisum sativum than in dark-grown seedlings. Following the illumination of dark-grown seedlings, there is a parallel increase in the content of both the mRNA and the polypeptide of the small subunit of the carboxylase; this subunit is a product of the nuclear genome. The increases in the mRNA and the polypeptide of the large subunit, which is a product of the chloroplast genome, show less synchronicity. Studies with isolated leaf nuclei show that the increase in small subunit mRNA is mediated primarily at the level of transcription. Three distinct effects of light on transcription of small subunit genes have been found; a rapid (∽1 h) burst, followed by a decline, when etiolated plants are first exposed to light; a slow (∽36h) development of the competence to transcribe rapidly after the initial burst; rapid (∽20 min) switches in both directions when fully greened plants are exposed to light-dark transitions.
On the crawling of cells
Authors: Oster George F. 
Published: April 2021

ABSTRACT
Motile cells moving in vitro do so via a characteristic motile appendage, the lamellipod, a broad, flat region of the cell cytoplasm which extends ahead of the moving cell, and which is devoid of organelles. I describe here a mechanochemical model for how the lamellipod propels the cell forward. The propulsive force for the spreading of the lamella derives from the swelling pressure of the cytogel within the lamellipod. A local change in ionic conditions -caused by a leak through the leading membrane -activates solating factors, which upsets the equilibrium between the gel osmotic pressure and its elasticity. Subsequently, regelling and contraction pull the cell forward. The model is in accordance with a diverse array of experimental observations on cell motility, and suggests a common physical mechanism underlying a variety of cell motility phenomena.