bluuebunny/crossref_metadata_2025 huggingface dataset:
The development of the tectum inXenopus laevis: an autoradiographic study
Authors: Straznicky K. , Gaze R. M.
Published: April 2021

The development of the optic tectum in Xenopus laevis has been studied by the use of autoradiography with tritiated thymidine. The first part of the adult tectum to form is the rostroventral pole; cells in this position undergo their final DNA synthesis between stages 35 and 45 or shortly thereafter. Next, the cells comprising the ventrolateral border of the tectum form. These cells undergo their final DNA synthesis at or shortly after stage 45. Finally the cells comprising the dorsal surface of the adult tectum form, mainly between stages 50–55. This part of the tectum originates from the serial addition of strips of cells medially, which displace the pre-existing tissue laterally and rostrally. The formation of the tectum is virtually complete by stage 58.

The tectum in Xenopus thus forms in topographical order from rostroventral to caudomedial. The distribution of labelled cells, several stages after the time of injection of isotope, indicates that, at any one time, a segment of tectum is forming which runs normal to the tectal surface and includes all layers from the ventricular layer out to the surface. In Xenopus, therefore, the times of origin of tectal cells appear to be related not to cell type or tectal layer but to the topographical position of the cells across the surface of the tectum.
Metabolite utilization by isolated embryonic rat hearts in vitro
Authors: Cox Steven J. , Gunberg David L.
Published: April 2021

Isolated hearts from 11-, 12- and 13-day rat embryos were incubated in a simple defined salt solution to which was added a variety of single substrates. Utilization of the added substrate was determined by comparing the contractile rates of the hearts in the presence and absence of the compound being tested. Of all the compounds tested only those involved in the Embden-Meyerhof glycolytic pathway were capable of maintaining cardiac contraction at a maximum rate in the 11-day heart. This was accomplished under both aerobic and anaerobic conditions. Although glycolysis remained important, the 12- and 13-day hearts exhibited a shift in dependence towards other metabolic pathways. This conclusion was based on the observations that anaerobic glycolysis could no longer maintain maximum heart rates and that a variety of non-glycolytic compounds could be utilized for contractile activity by the 12- and 13-day organs.
An investigation of inner cell mass and trophoblast tissues following their isolation from the mouse blastocyst
Authors: Gardner R. L. , Johnson M. H.
Published: April 2021

Inner cell mass (ICM) and trophoblast were isolated from -day post-coitum mouse blastocysts by microsurgery. Trophoblastic fragments formed vesicles in culture but did not aggregate with other such fragments. They proved as effective as intact blastocysts in inducing decidua in recipient uteri, but thereafter failed to proliferate. Isolated ICMs remained as solid balls of cells that readily aggregated in pairs or groups in culture but failed to induce implantation changes in receptive uteri. Possible explanations for the failure of isolated trophoblast to proliferate after implantation are discussed. It is argued that presence of ICM tissue is necessary for trophoblast proliferation, and suggested that the ICM exerts its effect by controlling development of the ectoplacental cone.
Rôle du mésoderme somitique dans le développement du plumage dorsal chez l’embryon de Poulet:II Régionalisation du mésoderme plumigène
Authors: Mauger Annick
Published: April 2021

The role of somitic mesoderm in the development of dorsal plumage in chick embryos. II. Regionalisation

Transplantation and inversion experiments were performed on the somitic mesoderm of 2-to 2·5-day chick embryos in order to study the role of regional and axial determinations in the development of the dorsal plumage.

The transposition of a piece of somitic mesoderm from the posterior cervical region (where the spinal pteryla is narrow) to the thoraco-lumbar region (where it is wide) leads to a local and unilateral narrowing of the spinal pteryla at the operation site. Conversely, the transposition of somitic mesoderm from the thoraco-lumbar region to the posterior cervical region results in a local and unilateral widening of the spinal pteryla. Consequently at the time of operation the segmented or not yet segmented somitic mesoderm is already determined to give rise to a definite transverse level of the spinal pteryla.

The inversion of the cephalo-caudal polarity of a piece of somitic mesoderm without the ectodermal covering, or of a portion of the axial organs deprived of the overlying ectoderm has no effect on the orientation of feather filaments and feather rows. In contrast, the inversion of the cephalo-caudal polarity of a portion of the axial organs together with the overlying ectoderm results in the development of feathers growing in a cephalad direction and feather chevrons opening towards the head of the embryo.

The inversion of the dorso-ventral polarity of a piece of somitic mesoderm does not prevent the normal differentiation of feathers in the operated region.

The inversion of the medio-lateral polarity of a piece of unsegmented somitic mesoderm has little effect on the development of the spinal pteryla. On the contrary, the medio-lateral inversion of a chain of somites precludes the formation of the feathers at the level of operation.

The somitic mesoderm, even when segmented, is endowed with extensive regulative capacity of its axes, except for the medio-lateral polarity, which is fixed irreversibly at the time of segmentation. The regional determination of the feather-forming somitic mesoderm is acquired at an early stage, at any rate before segmentation. However, at a given transverse level of the cephalo-caudal axis, the somitic cells remain totipotent as concerns their histogenetic destiny (dermatome, myotome, or sclerotome) until after the onset of segmentation.
Investigation of the mode of nuclear control over protein synthesis in early development of loach and sea urchin
Authors: Krigsgaber Maya R. , Neyfakh A. A.
Published: April 2021

It is shown that in loach embryos the incorporation of precursors into protein takes place in the blastoderm cells only. The change of the rate of incorporation of labelled amino acids into protein of the blastoderm separated from the yolk at successive developmental stages reflects the changes in the level of protein synthesis in intact embryos of the same developmental stages. Typical periodic changes of the intensity of protein synthesis in early embryogenesis of the loach are detected: low incorporation of amino acids at blastula stages is followed by an increase of synthesis during gastrulation and by a decrease with the onset of organogenesis.

To study the genetic control over protein synthesis at various developmental stages of loach and sea-urchin embryos the effects of ionizing radiation and long-term treatment with actinomycin D have been examined. X-Irradiation doses produce an insignificant direct effect on protein synthesis, while radiation damage of the nuclear apparatus results in a gradual but ever increasing inhibition of protein synthesis. The inhibition of RNA synthesis with actinomycin or ionizing radiation damage of the nuclei produce essentially the same effect on the intensity of protein synthesis. Protein synthesis in androgenetic haploid hybrid embryos (loach ♀ ×goldfish ♂) and in loach androgenetic haploid embryos after producing a partial elimination of chromosomes does not differ from ‘enucleated’ loach embryos completely deprived of chromosomes. These data suggest that high-polymeric RNA formed after the elimination of some chromsomes is unable to provide a normal level of protein synthesis.

Protein synthesis is not controlled by the nuclei up to the stages of early blastula (sea urchin) and of late blastula (loach), being evidently programmed in oogenesis. To provide a rapid activation of protein synthesis in the course of gastrulation in the loach the function of the nuclei has to be realized during mid-blastula stages. An increase of the rate of the incorporation of amino acids at the stages of mesenchyme blastula in the sea urchin depends on the synthesis of RNA at the early blastula. At the same time protein synthesis during gastrulation in the loach and at mesenchyme blastula in the sea urchin is much less dependent on the simultaneous RNA synthesis. Protein synthesis at these stages seems to be provided by the long-living templates and controlled by non-gene mechanisms of the regulation of translation.

Thus early embryonic differentiation in the loach and sea-urchin development is related to the activation of protein synthesis. The latter is provided by the preceding morphogenetic nuclear function, which makes protein synthesis relatively independent of simultaneous synthesis of templates that ensures subsequent development stages.
Artificial metaplasia of pigmented epithelium into retina in tadpoles and adult frogs
Authors: Lopashov G. V. , Sologub Alla A.
Published: April 2021

The present work was aimed at investigating the possibility and conditions necessary for the artificial transformation of one tissue into another. Experiments were carried out with the pigmented epithelium of the eye in tadpoles and adult frogs of Rana temporaria. Following the removal of the mesenchyme envelopes (or their exfoliation during the experiment), pigmented epithelium transformed into retina under the influence of retina from tadpoles of the same species. This phenomenon was observed both under the cultivation of a piece of retina in a sandwich of pigmented epithelium and the transplantation of pigmented epithelium layers into the eye cavity of tadpoles. Such transformation did not occur in the absence of retinal influence. Metaplasia requires the removal of the mesenchyme envelopes, the action of the retinal agent, as well as preservation of the integrity of the pigmented epithelium layer and subsequent proliferation of its cells. The character of general control mechanisms both maintaining the stability of cell types and leading to their transformation into other cell types is discussed.
Composite eggs and Siamese twins in paedogenetic gall midges
Authors: Went Dirk F. , Camenzind René
Published: April 2021

Several types of composite eggs were found in two species of paedogenetic gall midges. One composite egg, consisting of two blastoderms, was cultured in vitro, and its development was recorded on film. Two other composite eggs were fixed in the oocyte stage; each contained two nurse chambers, two egg chambers and one oocyte nucleus. Some other ‘eggs’ are described, which consisted merely of a nurse chamber or of one or two oocytes and of the follicular epithelium. It is argued that the formation of composite eggs and incomplete eggs must be due to errors in the formation of the oocyte-nurse cell complexes.

The article also describes three Siamese twins in larval stage which were found in two paedogenetic gall-midge species. In two twins the larvae were linked posterior-posterior, while in the third they were connected anterior-anterior. It is assumed that the Siamese twin-larvae evolved from composite eggs.
Fine structure of the apical rim—mesenchyme complex during limb morphogenesis in man
Authors: Kelley Robert O.
Published: April 2021

Ultrastructure of the apical rim-basal lamina-mesenchyme complex in man duringHorizons 15-18 is correlated with the development of limbs.

Apical epithelium is a complicated tissue exhibiting surface microvilli, junctional complexes, free ribosomes, elaborate Golgi centers, glycogen and scanty granular endoplasmic reticulum. The apical rim thickens during stages 15 and 16, remaining multilayered at digital tips and thinning adjacent to zones of necrosis by stages 17 and 18. Epithelial thinning may be a response to lack of ‘maintenance factor’. A continuous basal lamina is present during these stages. Collagen-like fibrils are numerous in interdigital zones of necrosis and sparse at tips of digital blastemata. The presence of oriented microfilaments in interdigital epithelium suggests active invagination during morphogenesis of fingers in man.
Spermine is major polyamine in sea urchins: studies of polyamines and their synthesis in developing sea urchins
Authors: Manen Carol-Ann , Russell Diane H.
Published: April 2021

Polyamine synthesis and accumulation was studied in several species of developing sea urchins. Most striking is the presence in the gametes of a large amount of spermine, with low amounts of putrescine and spermidine. This contrasts with the pattern of polyamines present in both micro-organisms and mammals. Micro-organisms contain mainly putrescine and spermidine and adult mammalian tissues usually contain equimolar concentrations of spermidine and spermine.

During development (i.e. to gastrulation) there is a large increase in the spermidine concentration with relatively little change in either putrescine or spermine levels. After gastrulation, both spermidine and spermine concentrations are elevated. These new accumulations parallel the new synthesis of rRNA that occurs after gastrulation.

Enzyme activity patterns parallel the changes detected in the concentrations of the polyamines with the exception of ornithine decarboxylase activity. This exception may be due to the rapid turnover of putrescine, the precursor for the synthesis of spermidine and spermine.
The formation of the optic fibre projection after partial tectal removal in Xenopus
Authors: Straznicky K.
Published: April 2021

The formation of retinotectal connexions in Xenopus has been investigated by mapping the visual field projections of animals after various partial tectal removals.

Following removal of a sufficiently extensive piece of the left rostral, caudal, medial or lateral tectum with, in addition, section of the contralateral optic nerve, a consistent defect in the nasal, temporal, superior or inferior visual fields respectively was obtained. The various scotomas indicated that optic axons did not regenerate into the residual tectum from all regions of the retina. The conclusion drawn from the present experiments is that optic fibres tend to connect, in a residual half-tectum, only with appropriate tectal loci.
An ultrastructural and cytochemical study of developing small intestine in man
Authors: Kelley Robert O.
Published: April 2021

The observations and results of this study suggest that intestinal absorptive cells possess structural and enzymic potential for function in utero. As early as the tenth postfertilization week, microvilli are differentiated, a surface coat is elaborated, alkaline phosphatase activity is localized on microvillar borders, and colloidal particles when introduced into the gut lumen in vitro are transported in vesicles from the apical cell surface to the lamina propria via extracellular spaces. In addition, cytoplasmic lipid droplets appear after administration of corn oil by injection into the gut lumen. However, the term ‘potential’ is stressed in that one can only speculate at present on what materials are absorbed from swallowed amniotic fluid in man.
Appearance of antler pedicles in early foetal life in red deer
Authors: Lincoln G. A.
Published: April 2021

The primordial antler pedicles of red deer show a transitory enlargement in early foetal life in the male while no similar change occurs in the female. Observations on the growth rate of the reproductive tract, pituitary and adrenal glands and the content of testosterone in the gonads, indicate that the precocious development of the pedicles occurs during a phase of increased testicular activity and probably reflects a surge in testosterone secretion following sexual differentation.
The site of action of the fuzzy locus (fz) in the mouse, as determined by dermal-epidermal recombinations
Authors: Mayer Thomas C. , Mittelberger James A. , Green Margaret C.
Published: April 2021

The site of action of the mutation fuzzy (fz) was investigated by the method of dermal- epidermal recombination. Skins from 14-day mutant and normal mouse embryos were sepa- rated into dermal and epidermal components, recombined, and grown in the mouse testis for 14 days. Grafts that contained mutant epidermis as one of the components produced many abnormal hairs characteristic of fuzzy mice. There was no observable effect of the fz locus on the dermis under the conditions of this experiment.
A quantitative study of the growth and development of the ventral root in normal and experimental conditions
Authors: Prestige M. C. , Wilson Margaret A.
Published: April 2021

The development of the ventral root (VR) in Xenopus has been studied by electron microscopy. Total fibre counts, and counts of classes of fibres were made from large photomontages of the whole of VR 9 at × 15000. The total number of fibres in the root shows the same pattern of initial rise, peak, and subsequent decline that previous ventral horn (VH) cell counts had shown. The two curves overlay each other initially, but after the decline, there were apparently more cells than fibres. Promyelin and myelin formation was seen at the time of the decline. There was no evidence that dying axons had started to myelinate. In some animals the limb-bud was removed at the time of its first penetration by nerve fibres. The ventral roots developed normally for a week, but thereafter fibre loss was accentuated, advanced and more profound, so that after another week, no fibres were left. In these roots, no promyelin or myelin was formed. In other animals, it was shown that there is no evidence for collateral sprouting in the ventral roots during normal development. It is argued that the axons which die in normal development have already reached the limb-bud. The correspondence between axon and cell number is discussed.
Sex chimaerism and germ cell distribution in a series of chimaeric mice
Authors: McLaren Anne
Published: April 2021

Of 30 mice born from aggregation of embryos from a multiple recessive strain with F1 embryos carrying the contrasting alleles, 4 females and 20 males proved to be overtly chimaeric. Three XX/XX females, five XY/XY males and eight XY/XX males were identified by chromosome analysis. Thus 50% of the population analysed were sex chimaeras, and all of these developed as phenotypic males, though one showed evidence of hermaphroditism. In seven XY/XX chimaeras that bred, the genetic component undergoing spermatogenesis coincided in every case with the component identified by chromosome morphology as XY. The F1 component predominated in metaphase plates derived from cultured blood cells. Comparison with direct preparations from bone marrow suggested selection in favour of F1 cells, either through differential proliferation of stem cells in vivo or differential response to phytohaemagglutinin in vitro. In XY/XX males, the percentage of XX cells detected varied from 1% to 98% in blood, and from 0% to 80% in bone marrow. Of eight ‘single-sex’ chimaeras progeny-tested (three XX/XX, five XY/XY), only one showed evidence of a mixed population of germ cells. The proportion of the two types of progeny varied significantly from litter to litter, but was unrelated to the age of the male.
An immunofluorescent study of cornea development in the chick
Authors: Ikeda A. , Maisel H. , Waggoner D.
Published: April 2021

The developmental pattern of appearance of a structural corneal antigenic determinant was studied by immunofluorescent methods. It was first detected in the primary corneal stroma at stage 23, and thereafter spread throughout the primary and secondary stroma. This antigen was absent from Bowman’ s membrane at its initial stage of development, suggesting that this membrane is a new structure in corneal morphogenesis, and not simply a modification of the primary stroma. This study also suggests that the antigenic determinant is a carbohydrate and is secreted by the corneal epithelial cells.
Le développement du thalamus des Anoures au cours de la métamorphose
Authors: Picouet M. J.
Published: April 2021

Development of the thalamus in anurans during metamorphosis

A developmental study of the anuran diencephalon from stage 30 to 2 months after metamorphosis has been done. At stage 30 in Discoglossuspictus, the diencephalic wall is divided into a superior area and an inferior area, where two kinds of cellular migrations are described.

Comparison with the urodele diencephalon suggests that the building of a new area (area dorsolateralis) in anurans, by means of an ‘external migration’, characterizes a level of organization which is related to the optic system in Anura. During metamorphosis, optical morphogenetic influences would come from the tectum opticum to the dorsal thalamus. It is possible that the dorsal thalamus could be involved in binocular vision by way of tectofugal fibres.

Some typical anuran diencephalic nuclei (i.e. nucleus corpus geniculatum latérale) are missing or are not well differentiated (i.e. nucleus rotondus) in Discoglossus. This species gives a simplified pattern of the anuran diencephalon.
Zona pellucida denudation, blastocyst proliferation and attachment in the rat
Authors: Surani M. A. H.
Published: April 2021

The mode of zona pellucida denudation and blastocyst proliferation and attachment was investigated in Wistar rats during day 5 of pregnancy and in ovariectomized pregnant animals given 5.0 mg progesterone daily until the 10th day, when 0.2 µg oestradiol was injected together with progesterone.

During day 5 of pregnancy, when only 5 empty zonae were detected from 32 animals, zona denudation occurred by lysis, which took 6 h. Zona denudation occurred by shedding in the ovariectomized pregnant animals; 190 empty zonae were detected from 40 animals. Oestradiol administration to the experimental animals caused lysis of the shed zonae 24-30 h after oestradiol treatment.

Air-dried preparations of the embryos showed that the blastomeres proliferated exponentially from a mean of 27.52 ± 4.0 cells per embryo at 12.00 h on day 5 of pregnancy to 53.96 ± 2.58 cells per embryo at 22.00 h, with a cell doubling time of 10 h in normal animals. In the ovariectomized animals, blastocysts were arrested at about the 100-cell stage on the 10th day. Oestradiol administration to the experimental animals did not induce mitosis; the embryos implanted without further cell division.

The number of free embryos recovered declined from a mean of 12.0 per animal at 12.00 h to 4.25 per animal at 22.00 h on day 5 of pregnancy. The number of embryos recovered from the ovariectomized animals varied between one and 11 per animal .

The results show that cell division continued in embryos within ovariectomized pregnant animals in the absence of oestrogen, until about the 100-cell stage. There was no further cell division before nidation when oestradiol was administered. The empty zonae were, however, lysed between 24 and 30 h after oestradiol treatment. The zona lytic factor appears to be oestradiol dependent and of maternal origin. A causal relationship exists between zona lysis and embryo attachment, which is independent of the number of cells per blastocyst.
Marker chromosome analysis of two mouse chimaeras
Authors: Ford C. E. , Evans E. P. , Gardner R. L.
Published: April 2021

Chimaeric mice were obtained by injecting embryonic (CBA/H-T6 × PDE)F1 cells into PDE blastocysts. Three of 15 young were overt chimaeras. One female and one male chimaera survived to adulthood and after completion of test breeding, which demonstrated chimaerism in the germ cells of both, they were killed for study when aged 32 and 33 weeks respectively. Chromosome spreads were scored for the presence or absence of the T6 marker chromosome in direct preparations from bone marrow, spleen, thymus, lymph nodes, Peyer’ s patches, corneas, gut epithelium and testes. Preparations from monolayer cultures of skin, kidney, ovaiy and gut and from mitogen-stimulated blood cultures were scored in the same way.

Both components of the chimaeras were identified in every one of 53 specimens studied, some of which, such as single lymph nodes, corneas and segments of gut, may not have contained more than 105 proliferating cells. This result complements published evidence for fine-grained mixture obtained in morula-aggregation chimaeras by other methods and implies extensive cell movement during embryogenesis.

Results obtained from the lymphomyeloid tissues show a clear partition into two groups in respect of the proportions of host-type to donor-type cells identified. The one group consists of bone marrow, thymus and Peyer’ s patches, the other of spleen and lymph nodes. This result would be most simply explained in terms of two distinct stem cell pools and appears to conflict with the currently favoured hypothesis of a single stem cell pool for the whole lymphomyeloid complex located in bone marrow. Four groups of factors may, however, modify the relative representation of the two components in different lymphomyeloid sites: (1) The magnitude of embryonic founder populations. (2) Limited recruitment from the stem cell pool in post-natal life. (3) Variable size of clones produced by individual stem cells. (4) Differential cellular behaviour determined by genotypic differences.
Expression of homeotic mutations in duplicated and regenerated antennae ofDrosophila melanogaster
Authors: Gehring Walter J. , Schubiger Gerold
Published: April 2021

Three homeotic mutants, aristapedia (ssa and ssa-UCI) and Nasobemia (Ns) which involve antenna-leg transformations were analyzed with respect to their time of expression. In particular we studied the question of whether these mutations are expressed when the mutant cells pass through additional cell divisions in culture. Mutant antennal discs were cultured in vivo and allowed to duplicate the antennal anlage. Furthermore, regeneration of the mutant antennal anlage was obtained by culturing eye discs and a particular fragment of the eye disc. Both duplicated and regenerated antennae showed at least a partial transformation into leg structures which indicates that the mutant gene is expressed during proliferation in culture.
Development and differentiationin vitroofDrosophilaimaginal disc cells from dissociated early embryos
Authors: Dübendorfer Andreas , Shields Glen , Sang James H.
Published: April 2021

Embryos of Drosophila melanogaster, 6-8 h after oviposition, were dissociated and the cells cultured in vitro. Besides larval cell types, imaginal disc cells, assembled and growing in bloated monolayered vesicles, were obtained.

The cells of these vesicles become competent to differentiate adult structures when treated with a-ecdysone or ecdysterone in vitro. Recognizable patterns of the adult fly are not formed though. If metamorphosis of imaginal cell vesicles from in vitro-cultures is induced in vivo by transplantation into host larvae of various ages within the third larval instar, recognizable patterns can differentiate provided the host larva does not metamorphose prior to 2 days after transplantation. The frequency of specific patterns in the implants can be increased by providing 9 days of culture in vivo (adult host flies) before metamorphosis. Passage through the third larval instar is not essential for these cells to produce identifiable patterns since culture in adult flies alone can achieve this. The quality of the differentiated pattern is not correlated with the extent of cell proliferation in the cultured tissues.

The problem of pattern specification in vitro and in vivo is discussed.
Positional information and pattern regulation in Hydra. Dynamics of regions at the boundary
Authors: Hicklin J. , Hornbruch A. , Wolpert L.
Published: April 2021

The dynamics of boundary regions have been investigated mainly by axial grafting and with the emphasis on the head end. The time to resist inhibition of head-end formation and the ability to inhibit head-end formation have been assayed under a variety of conditions. The times increase with distance from the head end. The times required by a boundary region to acquire the inhibitory properties of a head end are longer than those required to acquire resistance to inhibition. Determination of a head end is faster at a cut surface and at higher temperatures. The results are discussed in terms of a model involving two gradients. Some anomalous results are reported.
Le rôle du système nerveux au cours de la régénération du bras chez une Etoile de mer: Asterina gibbosa Penn. (Echinoderme, Astéride)
Authors: Huet Michel
Published: April 2021

In Asterina gibbosa regeneration of a cut-off arm tip cannot occur if the radial nerve has been removed. This regeneration needs the presence of the oral nerve ring connected with the radial nerve intact up to the level of the wound tissues. The oral nerve ring can be considered as a central nervous system. Exposure of the radial nerve to irradiation induces a delay in regeneration. These data suggest there is a stimulation from the oral nerve ring up to the wound tissues. When the tissues involved in regeneration, except for the radial nerve, have been destroyed by irradiation, regeneration is inhibited. Stimulation by a healthy radial nerve is necessary to maintain differentiation and growth of the blasternal cells. The amount of blasternal growth and differentiation depends on the time when the radial nerve ceases to stimulate regeneration. The action of the nervous system is needed throughout the whole course of regeneration.
Studies of t6/t6 mouse embryos
Authors: Nadijcka Mary , Hillman Nina
Published: April 2021

The phenocritical period of the t6/t6 genome extends from the late blastocyst substages through the elongated egg-cylinder stage, whereas the lethal period begins at the short eggcylinder stage and extends through the elongated egg-cylinder stage. Most of the homozygous mouse embryos die during the short egg-cylinder stage. The viable egg-cylinder-staged t6/t6 embryos can be distinguished from their phenotypically wild-type litter-mates at both the light and electron microscopic levels. The distinguishing characteristics of these embryos are aberrantly arrangedentodermal cells,excessive cytoplasmic lipid and crystal-containing mitochondria. These same features are also characteristic of those mutant embryos which are developmentally arrested at both the short and elongated egg-cylinder stages. Over 50% of the t6/t6 embryos can be identified as early as the late blastocyst substages by the presence of large, electron-dense cytoplasmic lipid droplets.
ATP metabolism in t
n
/t
n mouse embryos
Authors: Ginsberg Leonard , Hillman Nina
Published: April 2021

Total ATP, ATP/ADP ratios, and the rates of synthesis and turnover of ATP were determined for t12-, tw32- and T+/T+-litters at the 2-cell, 4-cell, 8-cell, early morula, late morula and late blastocyst stages. The results show that tn-litters have excessive rates of ATP metabolism up to the cleavage stage immediately before the stage of lethality for most tw32/tw32embryos (early morula) and most t12/t12 embryos (late morula); mutant ATP metabolism then falls below control levels. After the death of the tn homozygotes, ATP metabolism in the tn-litters (composed of only T+/T+ and T+/tn embryos) returns to control levels. These data are discussed in relation to the phenotypes of the homozygous tn embryos.
Myogenesis in the trunk and leg during development of the tadpole of Xenopus laevis (Daudin 1802)
Authors: Muntz Louise
Published: April 2021

Xenopus embryos pass through five behavioural stages between the end of neurulation (stage 20) and the accomplishment of free swimming (stage 33). These are (I) non-motile (stage 20 – 22) when the myotome muscle begins to differentiate; (II) pre-motile (stage 22 – 24) when the first striated fibrils are visible and contractions are possible; (III) early flexure (stage 24 – 27) when reflex responses are given and peripheral nerves are present; (IV) early swimming (stage 28 – 33); and (V) free swimming (stage 32 – 46) when co-ordinated swimming is possible but the myotome muscles are still uninucleate. At the onset of metamorphosis (stage 48 – 50) the myotome muscle becomes multinucleate, possibly by fusion with satellite cells at the ends of the fibres, and has the appearance of adult skeletal muscle.

The hind limb of Xenopus passes through similar behavioural stages but at a later stage in development: (i) non-motile (stage 48 – 52) when little differentiation of the limb-bud has occurred but nerves are present; (ii) pre-motile (stage 53 – 54) when the limb trembles and muscles are just beginning to acquire striated fibrils; (iii) motile (stage 55 – 58) when the limb can make stepping movements and the muscles are striated and multinucleate; and (iv) fully functional (stage 60 – 63) when the limbs are fully differentiated. Unlike the myotome muscle the limb muscle becomes multinucleate before striated myofibrils are assembled.

By stage 60 myotome and limb muscle are similar in appearance except that the myotome muscle has larger fibres with fewer nuclei than the limb muscle.

In Xenopus, myotome and limb muscle become multinucleate at more or less the same time in the development of the tadpole. In the myotome this is long after contractility and nervous control have appeared, in the limb it precedes the formation of striated fibrils and the ability to contract. It is suggested that the difference in development of the myotome and limb muscles with respect to the stage at which they become multinucleate may be due to some substance produced just before or during metamorphosis.
Effets biologiques de solutions de protéines chromatiniennes non histoniques sur un système embryonnaire en différenciation in vitro
Authors: Mathieu C. , Duprat A. M. , Dupuy M. H. , Ferrer P. , Zalta J. P. , Beetschen J. C.
Published: April 2021

Biological effects of solutions of non-histone chromatin-associated proteins on cell differentiation in vitro

Nuclear non-histone (NNH) proteins, both chromatin-associated and otherwise, have been prepared in defined conditions, either from nuclei or from washed chromatin. When these NNH proteins are homospecific, they produce inhibitory effects on morphological differentiation of embryonic Urodelan Amphibian cells cultivated in vitro. When they are heterospecific, on the contrary, they have no action on the differentiation of those cells. It is concluded that the effects of the non-histone proteins on cell differentiation depend upon the relationship between the animal species which is used to provide the proteins and that used to provide the reactive material.
In vitro studies of limb regeneration in adult Diemictylus viridescens: Neural dependence of blastema cells for growth and differentiation
Authors: Globus Morton , Liversage Richard A.
Published: April 2021

Explants of 99 adult newt forelimb blastemata (21-to 24-day regenerates) were cultured, with and without implanted dorsal root ganglia, in modified Parker’s medium (CMRL-1415) for periods of 72 – 144 h. Growth and differentiation of the cultured blastemata were compared with ganglionated and non-ganglionated controls fixed at the start of the culture period.

The results of these experiments establish that implanted spinal ganglia are able to sustain growth and differentiation of forelimb blastemata in vitro: active proliferation amongst the blastema cells was found to be correlated with the presence of an implanted ganglion. In addition, the blastema cells exhibited a differential growth response which was most pronounced when the ganglion was eccentrically implanted 2 – 3 days before explantation of the limb regenerate.

These results suggest that a causal relationship exists between the position of the implanted ganglion and the localization of growth within the blastema. The nerve influence, believed to be mediated by a chemical factor(s), was localized in the region of the implanted neurons, indicating that a close association between the nerves and the responding blastema cells is essential for normal growth. The importance of the physical presence of nerves for the cultivation of blastemata in vitro is emphasized.
Polarity reversal in hydra by oligomycin
Authors: Hornbruch Amata , Wolpert L.
Published: April 2021

Intact hydra treated for 24 h with oligomycin gradually lose their head structures and the distal ends form feet. Grafting experiments show that the distal ends of treated animals induce proximal structures.
Positional information and pattern regulation in hydra: enzyme profiles
Authors: Baquer Najma Zaheer , McLean Patricia , Hornbruch Amata , Wolpert L.
Published: April 2021

Certain key enzymes of alternative pathways of glucose metabolism, of amino acid metabolism and of redox systems have been measured in hydra and this profile compared with mammalian differentiated tissues with a view to locating pathways of specific importance in hydra. There was a marked constant proportionality in the major part of the enzymes investigated, the profile suggested a metabolic pattern geared to utilization of amino acids as a carbon source for biosynthesis and energy production and to the production and conservation of pyruvate. The importance of conversion to ionized forms was noted. The most notable specific proportion changes were the exceptionally low lactate dehydrogenase, malic enzyme and the relatively high citrate synthase. The proximal-distal gradients in hydra were examined and these gradients suggested a switch to a more anaerobic type of metabolism and an elevation of the pentose phosphate pathway as the basal region was approached. Measurements of the formation of 14CO2 from specifically labelled glucose provided additional evidence for the functional activity and polarity of the pentose phosphate pathway in hydra. The effect of oligomycin, which can reverse polarity in hydra, had a significant effect on gradients of enzymes eliminating all except that observed for G6P dehydrogenase. The profile suggested a movement towards a more anaerobic type of metabolism, in keeping with the known biochemical action of this inhibitor. It is suggested that redox states and/or phosphorylation states may be featured in the positional information of cells in hydra.
Proportionality in the pattern of differentiation of the cellular slime mouldDictyostelium discoideumand the time of its determination
Authors: Farnsworth Paul A.
Published: April 2021

A quantitative measure of the proportionality of the pattern of cell differentiation is obtained by separating populations of fruiting bodies into stalks and spores and determining the ratio of their dry weights.

The effect of incubation temperature on the proportion of a population which becomes stalk cells is determined.

The time of determination of this proportion is then indicated by the time in the developmental sequence at which a temperature shift fails to alter it.

The results show that the temperatures of growth, aggregation and migration have no effect on the pattern of differentiation and that temperature alterations during early culmination alter the pattern of differentiation.

This result demonstrates that the pattern of differentiation is not determined during the migrating slug stage, and it is suggested that the axial inhomogeneities seen in the slug are not directly related to the terminal pattern of differentiation of the fruiting body as has been previously suggested.
On the determination of the dorso-ventral polarity inXenopus laevisembryos
Authors: Landström Ulf , Løvtrup Søren
Published: April 2021

When embryos, or dorsal or ventral half-embryos, of Xenopus laevis are subjected to unilateral restriction of oxygen supply, the posterior end will always appear at the aerobic side, while the development of the anterior end, oriented towards the anaerobic side, will be partly suppressed. The shorter the time treatment lasts, the more normal the development will be. When the restriction of oxygen effects an inversion of the dorso-ventral polarity, development is retarded, otherwise not. Measurements of oxygen consumption show a substantial reduction in the experimental embryos, as compared with normal ones. The change in oxygen consumption in inverted embryos is delayed relative to non-inverted ones, but there is no significant difference in the total consumption of oxygen. Our results support the idea that the dorso-ventral polarity is associated with a gradient in oxygen consumption, and various kinds of evidence suggest that oxygen consumption is, in part, required for the formation of Ruffini’s flask-cells, responsible for the initiation of invagination. It is suggested that the basic mechanisms involved in the determination of the normal, and the inverted, dorso-ventral polarity are fundamentally different, the latter being in fact an induction of a new polarity.
Parthenogenetic activation of mouse oocytes following avertin anaesthesia
Authors: Kaufman M. H.
Published: April 2021

Avertin anaesthesia induced mouse eggs to become activated parthenogenetically. An increasing incidence of activation was observed when females were anaesthetized 6·5, 9 and 13 h after ovulation, reaching a maximum of 45·8 %. In a spontaneously ovulating group approximately 12·5 % of all the eggs ovulated, or 27·3 % of all the eggs activated evoked a decidual response, and the presence of implanting embryos was confirmed histologically. These findings demonstrate a new and simple method of inducing post-implantation parthenogenetic development in the mouse, and stress the necessity of taking into account the possible consequences of anaesthesia in the early post-ovulatory period.
Xenopus laeviscement gland as an experimental model for embryonic differentiation
Authors: Picard J. J.
Published: April 2021

Ectoblastic cells explanted from the animal pole of young Xenopus laevis gastrulae have been cultured in vitro. When these cells were cultured for five days in standard salt solutions they formed atypical epidermis. When they were first submitted for 6 h to Holtfreter solution containing ammonium chloride and then transferred for five days in standard Barth’s solution they underwent differentiation into typical cement gland tissue.

The optimum concentration of ammonium chloride was 10 mM. Below and above this concentration the resulting cement glands had a smaller volume.

The optimum duration for the initial stimulation with 10 mM ammonium chloride in Holtfreter solution was 6 h. Shorter stimulation times produced only small cement glands. Longer initial incubations in ammonium chloride resulted in progressive dissociation of the explants.

To obtain the best differentiation into cement gland it appeared that the pH of the ammonium chloride solution should be between 7·5 and 7·7.

When the stimulation is performed under these optimum conditions the cement gland measured after five days of culture accounts for 80–90 ° % of the explanted tissue. This means that all or almost all of the competent superficial layer of the ectoblastic cells underwent differentiation into cement gland. No other differentiated tissue was observed in the explants. The cement gland is a very simple organ containing only one single cell type. The gland obtained under the described in vitro conditions is therefore proposed as an experimental model for biochemical studies on early embryonic differentiation.
Mesenchymal derivatives of the neural crest: analysis of chimaeric quail and chick embryos
Authors: Lièvre C. S. Le , Douarin N. M. Le
Published: April 2021

Interspecific grafts of neural tube and associated neural crest (NC) have been made between quail and chick embryos. Structural differences of the interphase nucleus in the two species make it possible to identify quail from chick cells in the chimaeras after Feulgen-Rossenbeck’s staining and at the electron microscope level. Owing to the stability of the natural quail nuclear marker labelling, migration pattern and developmental fate of the grafted NC cells could be followed in the host embryo. In previous work it has been demonstrated that the visceral skeleton derives entirely from NC mesenchyme and the various levels of the neural axis from which visceral cartilages and bones originate have been established. In the present work, the contribution to the lower jaw and pharynx of NC mesenchymal derivatives other than bones and cartilages has been studied. It is shown that the dermis in the face and ventrolateral side of the neck has a neural origin. The wall of the large arteries deriving from the branchial arches (systemic aorta, pulmonary arteries, brachiocephalic trunks and common carotid arteries) are entirely made up of mesectodermal cells except for the endothelial epithelium which is mesodermal in origin. The presence in the wall of the common carotid arteries of fluorogenic monoamines-containing cells is demon-strated using the formol-induced-fluorescence technique. Like the secretory cells of the carotid body, the fluorescent cells of the carotid artery wall originate from the rhomb-encephalic NC.

Connective tissue of the lower jaw, tongue and ventrolateral part of the neck originate from the neural crest. Mesectoderm participate in the formation of the glands associated with the tongue and pharynx (lingual gland, thymus, thyroid, parathyroids) giving their mesenchymal component. On the other hand, as demonstrated previously by our group, NC cells are the main cellular component of the UB since they give rise to the calcitonin-producing cells. The wall of the oesophagus and trachea is of mesodermal origin, but adipose tissue around the trachea and parasympathetic enteric ganglia of the digestive tube derives from NC. NC cells participate in the formation of striated muscles of the branchial arches and differentiate there into connective and muscle cells.

It appears from this study that the differentiating capabilities are similar in mesenchymal and mesectodermal cells with the exception of blood vessel endothelia which in our experiments are always of host origin in mesectoderm-derived tissues.

The capacity of the NC to give rise to mesenchymal derivatives is restricted to the cephalic neural axis down to the level of the 5th somite in both chick and quail embryos.
La localisation du matériel germinal dans le blastoderme non incube de l’oeuf de cane: étude à l’aide des irradiations aux rayons X
Authors: Fargeix Noël
Published: April 2021

Le problème de l’origine des cellules germinales primordiales (CGP) des Oiseaux a suscité de très nombreuses recherches tant histologiques qu’expérimentales et il est maintenant bien établi qu’à partir du stade de la ligne primitive, ces cellules sont situées, au moins pour la grande majorité d’entre elles, dans les régions antérieures et latérales de l’aire extra-embryonnaire (croissant germinal de Swift, 1914). Quant à la localisation du matériel germinal à des stades antérieurs, elle est plus difficile à préciser.
The effect of u.v. irradiation of the vegetal pole of Xenopus laevis eggs on the presumptive primordial germ cells
Authors: Züst Brigitta , Dixon K. E.
Published: April 2021

The initial effect of u.v. irradiation of the vegetal pole was to inhibit cleavage in the vegetal hemisphere although karyokinesis was not substantially affected. In this way a syncytium formed in the vegetal hemisphere which broke down into individual cells some time between morula and late blastula. The movement of the germ plasm from the peripheral cortical regions into the interior of the egg was not appreciably delayed although aggregation of the germ plasm did not take place until the individual presumptive primordial germ cells were formed when the syncytium broke down. The method of segregation of the germ plasm and formation of the presumptive primordial germ cells was therefore very different in irradiated embryos from the normal orderly processes which depend on normal cleavage patterns. After neurula, the number of presumptive primordial germ cells declined rapidly and at stage 43/44, when the genital ridges in normal embryos contain primordial germ cells, the genital ridges in irradiated embryos were sterile. These results raise the question whether derangement of the segregation of the presumptive primordial germ cells is solely responsible for the later abnormalities in the cell lineage or whether u.v. irradiation affects the germ plasm and therefore indirectly the germ cells.