bluuebunny/crossref_metadata_2025 huggingface dataset:
Behaviour of annulate lamellae during the maturation of oocytes in the newt, Cynops pyrrhogaster
Authors: Imoh Hiroshi
Published: April 2021

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

The 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

Mammalian 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

Eye 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

In 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

Counts 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

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

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

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

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

A 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

Mesoderm 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

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

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

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

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

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.
Chromosomal changes associated with changes in development
Authors: Bostock Christopher J.
Published: April 2021

In the past there has been a tendency to dwell on aspects of chromosomes which stress constancy of structure, number and content; even to the extent of dismissing exceptions as ‘aberrations’ or ‘oddities’. It is now becoming clear that genomes can be quite plastic, and that structural changes to chromosomes are an important and often necessary part of normal differentiation and development. Elimination of whole chromosome sets or defined portions of genomes is not uncommon and selective gene amplification has been shown to be part of normal development in both protozoa and higher organisms. Chromosomal rearrangements are now a well-documented feature of normal development of, for example, B- and T-lymphocytes and trypanosomes. Transposable elements, whose mobility may not be part of normal developmental processes, can have marked effects on development if their transposition takes them to developmentally important genes. This article reviews some of the structural changes that occur during normal development, and discusses some of the consequences for development when the mechanisms which bring about these rearrangements go wrong.
A programme for the construction of a lambda phage
Authors: Brammar W. J. , Hadfield C.
Published: April 2021

Infection of a sensitive host by the lambdoid coliphages can cause death of the bacterial cell by lysis or can lead to a lysogenic cell, with the viral DNA stably integrated into the host chromosome. These alternative responses both require the coordination of several host and phage functions, and lambda infection follows a well controlled developmental plan. The lytic and lysogenic pathways of lambdoid infection are reviewed, with emphasis on the variety of control mechanisms involved in the commitment to a particular pathway.
The cellular dynamics of pattern formation in the eye of Drosophila
Authors: Tomlinson Andrew
Published: April 2021

The establishment and early development of the ommatidial bundles in the presumptive eye of Drosophila have been investigated using electron microscopic serial sectioning. A progression of developmental stages has been characterized. Initially simple, symmetrically constructed bundles develop into asymmetrical, more complex constructions. Computer graphic reconstruction has been used to show the three-dimensional structure of the various ommatidial bundles. Autoradiography has been used to locate the position of a region of cell division which is intimately associated with the formation of the ommatidial bundles.
Neural induction: embryonic determination elicits full expression of specific neuronal traits
Authors: Duprat A. M. , Kan P. , Gualandris L. , Foulquier F. , Marty J. , Weber M.
Published: April 2021

In Pleurodeles waltl, the early neuronal differentiation of precursor cells from late gastrula stage has been studied by culture in vitro from either isolated neural plate (NP) or isolated neural fold (NF).

The aim of this study was to delineate the information acquired by ectodermal target cells during neural induction. By culturing these cells in vitro either with or without the underlying chordamesoderm, we showed that in the absence of chordamesodermal influence such NP or NF cells exhibited a high degree of biochemical and morphological differentiation as revealed by the synthesis and the storage of neurotransmitters, the activity of specific enzymes, as well as by the expression of neuronal markers: specific changes in cell surface carbohydrates, tetanus toxin binding sites and neuro filament polypeptides. Remarkable changes in the cell adhesive properties were the first events observed in the different central (NP) and peripheral (NF) types.

In cocultures the chordamesodermal cells exert a beneficial influence on this differentiation, specially increasing acetylcholine synthesis. There are some differences between central (NP) or peripheral (NF) neuroblast response to this further notochord or mesodermal influence.
Recent advances in our understanding of the temporal control of early embryonic development in amphibians
Authors: Satoh Noriyuki
Published: April 2021

Recent studies on temporal control of early amphibian development are reviewed. It is becoming clear that the development of an embryo is not timed by a single clock set in motion at fertilization, instead each developmental event seems to be timed by its own clock-like mechanism. The timing of developmental events is rigidly determined within embryonic cells, and usually can not be altered experimentally. One exception, however, is the timing of midblastula transition in amphibian embryos; recent studies have shown that its timing is regulated by the nucleocytoplasmic ratio. Several developmental events, particularly those associated with transcriptional activities, require DNA replication prior to their occurrence, suggesting an intimate relationship between DNA replication cycles and their onset. On the other hand, there are many other developmental events where timing is not controlled by the number of cell divisions, DNA replication cycles, or the nucleocytoplasmic ratio. Cytoplasmic machinery with autonomous oscillatory properties is thought to be involved in the timing of these events.
Single cell analysis of commitment in early embryogenesis
Authors: Heasman Janet , Snape Alison , Smith Jim , Wylie Christopher C.
Published: April 2021

Fate maps of amphibian embryos tell us the destination of certain areas at later stages of development. After studying Vogt’s fate maps, Spemann wrote (in 1938) that “the question which at once calls for an answer is whether this pattern of presumptive primordia in the beginning gastrula is the expression of a real difference of these parts, whether they are already more or less predestined or ‘determined’ for their ultimate fate, or whether they are still indifferent and will not receive their determination until a later time.” Until recently answers to this question have relied upon explant experiments, which indicate that by the late blastula stage ectoderm, mesoderm and endoderm regions are distinctly determined. By using a method involving single cell labelling and transplantation, it is now possible to pinpoint more accurately the time during early embryogenesis at which individual blastomeres become committed. In the vegetal pole, determination towards endoderm is a gradual process beginning during the middle blastula stage (stage 8) and completed by the beginning of gastulation (stage 10). This method offers the possibilities of comparing the committed and the uncommitted state and studying at a molecular level the mechanisms of cell determination.
Inductive interactions in early amphibian development and their general nature
Authors: Nieuwkoop P. D.
Published: April 2021

After a short discussion on cell interactions in general and inductive interactions in particular, the almost completely epigenetic nature of amphibian development is emphasized.

In the symmetrized egg undergoing cleavage a large-scale inductive interaction occurs which leads to the formation of the meso-endoderm. Meso-endoderm formation gives rise to the morphogenic process of gastrulation. In the ensuing triple-layered embryo inductive interactions are strongly enhanced. The following large-scale inductive interaction leads to the formation of the neural anlage. This is again followed by the morphogenetic process of neurulation or neural tube formation. Subsequent interactions between the germ layers of the triple-layered embryo give rise to the formation of the regional pattern of organ anlagen. Finally, the most promising approaches to the nature of inductive interactions for mesoderm and endoderm formation are discussed.
Towards understanding paternal extragenic contributions to early amphibian pattern specification: the axolotl ts—1 gene as a model system
Authors: Malacinski George M. , Barone Dorothy
Published: April 2021

As a model system for understanding the role sperm extragenic components might play in early embryogenesis the genetics and phenotype of the ts—1 axolotl (Ambystoma mexicanum) mutant gene are reviewed. That mutant gene displays parental effects. It exhibits both maternal (egg-mediated) as well as paternal (sperm-mediated) phenotypic effects. A variety of possible modes of action of the ts—1 gene are reviewed. Comparisons of various precedents to the ts—1 genetic data are made. In addition, novel models which account for the ts—1 phenotypic data are presented.
The Development of the Phagocytic Activity of the Reticulo-endothelial System in the Chick
Authors: Kent Rosalind
Published: April 2021

The embryonic development of the ability of some cells to undertake ex-tensive phagocytosis has been studied in the chick embryo using the particulate materials ‘Thorotrast’ and colloidal silver (Ag110). Extensive phagocytosis of Thorotrast particles by the embryo chick and the young chicken takes place in the liver and spleen and to some extent in the lung, bone-marrow, and areolar connective tissue of the mesenteries and body-wall, uptake in the latter being more evident in cases of larger doses. In addition, the embryo chick takes up Thorotrast in the mesodermal part of the yolk-sac wall. In the embryo chick rapid and extensive uptake of particulate matter does not occur until the main centres of the reticulo-endothelial system have been differentiated. Particles taken up by the yolk-sac wall of the embryo chick disappear after hatching. The exact mechanism involved has not yet been established.
The Onset and Maturation of the Graft versus Host Reaction in Chickens
Authors: Solomon J. B.
Published: April 2021

The increase in wet weight of the host spleen following implantation of competent chick, juvenile or adult chicken spleen has been shown to be paralleled by increases in dry weight and in content of RNA, DNA, and protein. No increase in the spleen-weights of the hosts was found when non-competent spleen cells from chick embryos or 1-day-old chicks were used as donor. The onset of immunological competence with respect to this transplantation reaction has been shown to occur at about 5 days post-hatching when the spleens were implanted into embryos at 8 days of incubation and the host spleens removed 10 days later. The ability of chicken spleen cells to evoke hepatomegaly and splenomegaly of the embryo hosts increased with age and was greatest after 21 weeks of age. Sometimes a reduction in whole body-weight of the embryo hosts also occurred. Although no sex differences in host spleen-weight were observed when 8– 15-day-old male chick spleens were used as grafts, a significant increase in female host liver- and spleen-weights (compared with those of the male hosts) was noted when 8–21-day-old female chick spleens were used as grafts. Spleen cells from male chickens of 6–17-weeks old did not produce much greater splenomegaly than those from young chicks and there were no sex differences between the host embryo spleen-weights. However, when female spleen tissue from 6-to 20-week-old chicks was used as graft a significant increase in the hepatomegaly and splenomegaly of the female hosts above those in the male hosts was observed. No sex differences were obtained in embryo host spleen-weights when small implants of adult male or female spleen cells were used as grafts. Thymus, liver, and bone-marrow from competent donors have been found to be nearly as effective as spleen in producing splenomegaly of the embryo hosts.
The Two-gradient Hypothesis in Primary Induction. The Combined Effect of Two Types of Inductors Mixed in Different Ratios
Authors: Saxén Lauri , Toivonen Sulo
Published: April 2021

On the basis of certain earlier suggestions made by Lehmann (1950) and Yamada (1950), together with our own experimental data, a modification of the two-gradient hypothesis of primary induction was presented by us some years ago (Toivonen & Saxén, 1955). Subsequently, this theory has often been referred to, accepted or criticized, and even misunderstood. There may thus be reasons for discussing it in the light of some recent experimental data.
The Differential Growth-response of Embryonic Chick Limb-bone Rudiments to Triiodothyronine in vitro
Authors: Lawson Kirstie
Published: April 2021

The growth of the tibia and radius from 6-to 10-day-old embryos was estimated from the increase in the total nitrogen content of the rudiments. A comparison of the specific growth rates of eight limb bones showed that the bones could be arranged in the following order of diminishing specific growth rate: tibia, third metatarsus, femur, ulna, humerus, third metacarpus, radius, fourth metacarpus. If the small bones were arranged in order of the percentage growth of their rudiments in vitro, the sequence found in various media was the same as that of their specific growth rates in vivo. A comparison of the growth-promoting properties of various biological media showed that the best growth and differentiation occurred on a plasma and embryo extract clot. The growth-promoting properties of the extract were greatly enhanced in a plasma clot with which the fibroblasts of the explant, through their abundant outgrowth, were in intimate contact. In the absence of extract there was no difference between the growth of rudiments in contact with the clot or supported by lens paper floating on serum. The order of a series of bones arranged according to their growth response to T3 in a medium of plasma and embryo extract was the same as their order when arranged according to their specific growth rate in vivo: the growth of potentially fast-growing bones was reduced by T3, that of slowly growing bones was increased. The growth rates in vitro of different rudiments were varied by altering either the composition of the medium or the incubation temperature, but the rudiments continued to respond differentially to T3. The characteristic differences in the relative growth of the different bones when not treated with T3 were maintained under these conditions.
Les effets de la succion de l’un des deux premiers blastomères de l’œuf de Grenouille (Rana temporariaetRana escalenta)
Authors: Milaire par J.
Published: April 2021

La destruction d’un blastomère au début de la segmentation de l’œuf d’Amphibien est l’une des plus anciennes opérations de l’embryologie expérimentale. Après les premières tentatives de Roux, A. Brachet (1904) répéta cette expérience en détruisant au moyen d’une aiguille chauffée, l’un des deux premiers blastomères de l’œuf de grenouille rousse. Les résultats obtenus ont conduit l’auteur à démontrer le développement normogénétique du blastomère sain et à établir l’existence d’une relation constante entre le plan de symétrie bilatérale de l’œuf fécondé et celui de l’embryon quelle que soit l’orientation du premier plan de segmentation.
Transfer of Primordial Germ-cells in Xenopus laevis
Authors: Blackler A. W. , Fischberg M.
Published: April 2021

A technique is described whereby the so-called primordial germ-cells of X. laevis, together with some accompanying non-germinal cells, may be grafted from one embryo to another at the neurula stage. A nuclear marker enabled graft cells to be identified. Some cells from the graft migrate into the host gonads and there form functional gametes. It is concluded that primordial germ-cells actually exist in neurula stages, that these cells are probably identical with the so-called primordial germ-cells described in histological studies, and that they are directly ancestral to at least some of the definitive eggs and sperm.
The Arrangement of Bristles inDrosophila1
Authors: Smith J. Maynard , Sondhi K. C.
Published: April 2021

The bristles of Drosophila fall into two classes, the microchaetes which are small, numerous, and which vary in number from individual to individual, and the macrochaetes, which are larger, fewer in number, and constant in arrangement within a species, although many mutants which alter their number are known. Variations in the arrangement of macrochaetes in populations of D. subobscura homozygous for the mutant ocelli-less are interpreted in terms of variations in a ‘prepattern’ determining the positions of the bristles, and of the competence of cells to respond to this prepattern by forming bristles. A process whereby such a prepattern may develop is described. It is argued that the arrangement of the microchaetes is determined by a similar process, differing only in that it is less accurately regulated. Mechanisms which may increase the accuracy of prepattern formation are discussed.
The contribution of the primitive streak to the somites in the avian embryo
Authors: Ooi V. E. C. , Sanders E. J. , Bellairs R.
Published: April 2021

Chick embryos were removed from the egg at stages 6–11 and explanted in culture. The greater part of the postnodal primitive streak of each embryo was replaced with a similar region taken from a corresponding quail embryo. The reciprocal experiment was also carried out, chick primitive streak being grafted in place of quail. After further incubation, the grafted primitive streak cells were found to contribute to lateral plate mesoderm, somites and intermediate cell mass. In an additional series of experiments, the postnodal primitive streak was extirpated and the embryo allowed to heal without a graft being inserted; after further incubation, many more somites formed in these embryos. It is concluded therefore that the contribution of cells from the primitive streak shown in the first experiment may not be essential for somite formation. It is suggested moreover that two major morphogenetic movements are taking place simultaneously in the mesoderm during this period: one is the mediolateral migration of cells after ingression through the streak, whilst the other is an anteroposterior movement associated with regression.
A study on the pattern of prospective somites in the presomitic mesoderm of mouse embryos
Authors: Tam P. P. L.
Published: April 2021

Consistently six to seven somites were formed in explants of presomitic mesoderm of 8·5-day to 11·5-day mouse embryos and this number correlated well with the number of somitomeres previously identified in the same tissue by stereo SEM (Tam, Meier & Jacobson, 1982). During this period of development, the size of the presomitic mesoderm varied up to two-fold but the number of prospective somites remained unchanged. This pattern in the presomitic mesoderm was stable with respect to the number and the position of somites that were formed, the cranio-caudal sequence and the rate of segmentation. The prospective somite also went through an orderly sequence of expansion and cellular rearrangement prior to segmentation. During the differentiation of the presomitic mesoderm, somites were formed at the expense of somitomeres, suggesting that the somitomere was a morphological manifestation of the prospective somite.
Chimaerism of primordial germ cells in the early postimplantation mouse embryo following microsurgical grafting of posterior primitive streak cells in vitro
Authors: Copp Andrew J. , Roberts Heather M. , Polani Paul E.
Published: April 2021

A microsurgical grafting technique has been used to introduce primordial germ cell (PGC) precursors into intact primitive-streak-stage mouse embryos in vitro. Operated embryos were cultured for 36–40 h and then analysed by a combined histochemical and autoradiographic method. PGC chimaerism occurred in embryos that received grafts of caudal primitive streak cells but not adjacent embryonic endoderm or anterolateral ectoderm/mesoderm cells. Graft-derived PGCs were found to be migrating through the gut endoderm alongside host-derived PGCs in approximately half of the chimaeric embryos whereas in the other 50 % of cases PGCs remained at the site of grafting in association with graft-derived somatic cells. A similar pattern of somatic chimaerism was produced by primitive streak and anterolateral ectoderm/mesoderm grafts: the allantois was colonized predominantly, with, in addition, formation of amnion, surface ectoderm and caudal mesoderm in a few embryos. The majority of embryonic endoderm grafts failed to incorporate into host embryos and formed yolk-sac-like vesicles.

The findings of this study indicate that (a) PGCs originate from the embryonic ectoderm via the primitive streak during development of the mouse embryo, and (b) anterolateral ectoderm and mesoderm cells are unable to form PGCs after heterotopic grafting to the posterior primitive streak site. The combined microsurgical and embryo culture methods provide an experimental system for the analysis of PGC development in intact mouse embryos.
Timekeeping by frog embryos, in normal development and after heat shock
Authors: Elsdale Tom , Davidson Duncan
Published: April 2021

Timekeeping refers to the uniformity of development in time. The precision of timekeeping is measured by the extent to which embryos, within an initially synchronous population, come to diverge in the course of their development. Divergence is measured as the variation in the stage of development reached between embryos allowed to develop for a fixed period of time. The lower the variation the better the timekeeping. Divergence among frog embryos that started development at the same time is hardly measurable after approx. 100 h of development. This striking uniformity indicates good timekeeping. Timekeeping is not impaired among the survivors following heat shocks that retard development and disturb and curtail morphogenesis. The immediate effect of heat shock is a stoppage of development, the duration of which is the same for all embryos in the same treatment batch. The embryos react to heat shock by rescheduling their development with the interpolation of a rest, the duration of which is controlled to the same precision as normal development. The postponement of development, without impairment of timekeeping, implies dis-engagement of the processes of morphogenesis from, and their subsequent re-engagement with, an enduring ratedetermining activity unaffected by heat shock. We have searched for embryos whose rate of development was disturbed by heat shock to run slower or faster than the norm. We have found none. It seems that the (temperature-compensated) rate of development is invariant up to the moment of failure, or a change is immediately lethal.
Induction of myofibrillogenesis in cardiac lethal mutant axolotl hearts rescued by RNA derived from normal endoderm
Authors: Davis Lynn A. , Lemanski Larry F.
Published: April 2021

A strain of axolotl, Ambystoma mexicanum, that carries the cardiac lethal or c gene presents an excellent model system in which to study inductive interactions during heart development. Embryos homozygous for gene c contain hearts that fail to beat and do not form sarcomeric myofibrils even though muscle proteins are present. Although they can survive for approximately three weeks, mutant embryos inevitably die due to lack of circulation. Embryonic axolotl hearts can be maintained easily in organ culture using only Holtfreter’s solution as a culture medium. Mutant hearts can be induced to differentiate in vitro into functional cardiac muscle containing sarcomeric myofibrils by coculturing the mutant heart tube with anterior endoderm from a normal embryo. The induction of muscle differentiation can also be mediated through organ culture of mutant heart tubes in medium ‘conditioned’ by normal anterior endoderm. Ribonuclease was shown to abolish the ability of endoderm-conditioned medium to induce cardiac muscle differentiation. The addition of RNA extracted from normal early embryonic anterior endoderm to organ cultures of mutant hearts stimulated the differentiation of these tissues into contractile cardiac muscle containing well- organized sarcomeric myofibrils, while RNA extracted from early embryonic liver or neural tube did not induce either muscular contraction or myofibrillogenesis. Thus, RNA from anterior endoderm of normal embryos induces myofibrillogenesis and the development of contractile activity in mutant hearts, thereby correcting the genetic defect.
Haemocytes secrete basement membrane components in embryonic locusts
Authors: Ball Eldon E. , Couet Heinz Gert de , Horn Peggy L. , Quinn Joan M. A.
Published: April 2021

Several monoclonal antibodies raised against a glycoprotein-enriched fraction of adult muscle membranes of Locusta migratoria selectively stain particles within haemocytes and basement membrane in developing locust embryos. Haemocytes containing immunoreactive particles are found associated with areas where basement membrane is being laid down. The underlying ectoderm does not show immunoreactivity. We conclude that haemocytes contribute to basement membrane formation in embryonic locusts.