bluuebunny/crossref_metadata_2025_split huggingface dataset:
The degree of determination of the early embryo of Schistocerca gregaria (Forskål) (Orthoptera: Acrididae)
Authors: Moloo S. K. 
Published: April 2021

ABSTRACT
The degree of determination of the young embryo of S. gregaria has been investigated using ligation, thermocautery and centrifugation techniques. From the overall results, it is suggested that the early development of the embryo is mediated by two physiological centres.
The formation of the germ rudiment is controlled by an activation centre located in the periplasm round the posterior end of the egg. This centre is already present at the zygote nucleus stage and is essential during the very early cleavage period.
The differentiation of the germ band is induced by the activity of a second centre, the differentiation centre, located in the presumptive thorax. It apparently becomes established at least by the late blastoderm stage and its activity continues during the period of germ-band formation.
During the late cleavage and early blastoderm stages, the egg is labile and the embryo is therefore able to normalize its development after part or parts of the germinal Anlage have been cauterized, removed or displaced.
The differentiation centre completes its functions by the beginning of gastrulation. Thereafter, the embryo is determined.
The embryo can regulate its size at least up to the gastrulation stage provided that a certain minimum amount of usable yolk is available.
The development of the serosa is not under the control of either centre. This structure seems to be capable of regeneration providing that a part of the extra-embryonic blastoderm remains intact.
Accelerating effect of hydrocortisone on the keratinization of chick embryonic skin growing in a chemically defined medium
Authors: Sugimoto Masanobu , Endo Hiroyoshi 
Published: April 2021

ABSTRACT
In an attempt to examine histologically, chemically and biochemically the effect of hydrocortisone in a minimal concentration on keratinization of 13-day chick embryonic shank skin, a simple replicate culture method (‘Millipore’ filter-roller-tube method) was devised to cultivate rather large pieces of the skin in a chemically defined medium, BGJb supplemented with ascorbate.
Hydrocortisone added in a minimal concentration of 0·001 μg/ml produced a heavily cornified eosinophilic layer over the epidermis after 4 days’ cultivation, whereas in the absence of the steroid no sign of cornification could be found during culture.
Determination of total protein and analysis of amino acid composition of whole protein of the epidermis indicated that hydrocortisone accelerated epidermal cornification as compared with in ovo development.
Pregnenolone and progesterone showed no effect on the in vitro keratinization of the epidermis and deoxycorticosterone gave a slight effect: thus the cornification-accelerating effect of hydrocortisone seems to be attributable to its glucocorticoid activity.
Further evidence for the sorting out of cells in the differentiation of the cellular slime mold Dictyostelium discoideum
Authors: Bonner J. T. , Sieja T. W. , Hall E. M. 
Published: April 2021

ABSTRACT
The observation of Takeuchi’s that the denser cells of Dictyostelium discoideum tend to sort out towards the anterior end of the migrating slug (and the lighter cells towards the posterior end) has been confirmed using spore size as a method of identifying cells populations. A fraction of the anterior and posterior ends of a slug are isolated and allowed to fruit; their spores are then measured. The same is done for preaggregation cells which have been separated into heavy and light fractions, using Takeuchi’s technique of centrifugation of the cells in a dextrin solution equal to the mean specific gravity of the cells. Invariably, in three experiments with different strains of D. discoideum, the spores derived from dense cells corresponded perfectly with spores derived from the anterior cells of the slug, and a similar correspondence was found between spores derived from light cells and posterior slug cells. Contrary to a previous view (Bonner, 1959), cell size did not always correlate with position; in one strain the anterior cells were larger, in the other two they were smaller.
Spotting genes and internal pigmentation patterns in the mouse
Authors: Deol M. S. 
Published: April 2021

ABSTRACT
Hereditary white spotting in the mouse may be caused by genes at over a dozen loci. It is thought that some genes achieve their effects by acting through the melanoblasts, and others by acting through the host tissue. The genes mi, Miwh, Wv and s are believed to belong to the former category. But it is not known how the abnormality of the melanoblasts is transformed into the spotting patterns observed. According to one view, the capacity of the melanoblasts to respond to some melanogenesis-promoting factor in the host tissues is impaired, and as all melanoblasts are affected about equally, the pattern depends on normal variations in the distribution of this factor in the host tissue. According to another, a proportion of the melanoblasts are ‘preprogrammed’ to die before differentiation. Both views are largely based on studies on the coat. It was thought that an investigation of the spotting patterns in the choroid, the Harderian gland and the inner ear might throw fresh light on the problem. This was carried out in the genotypes + /mi, Miwh+, Wv/+, Wv/Wv and s/s. The results provide strong support for the view that all melanoblasts are affected and the host tissue plays an important role in determining the pattern of spotting. However, there appear to be some indications that all melanoblasts may not be affected to the same degree.
The growth of the retina in Xenopus laevis: an autoradiographic study
Authors: Straznicky K. , Gaze R. M. 
Published: April 2021

ABSTRACT
The growth of the retina has been studied in Xenopus by use of autoradiography with tritiated thymidine. At the time when retinal polarization first occurs (around stage 30) there are only some 20 ganglion cells across the retinal equator and the rest of the retina develops later, by annular addition of cells at the ciliary margin. This process continues beyond metamorphosis.
Cytoplasmic DNA and basic protein synthesis in Megalobatrachus davidianus oocytes
Authors: Kong Y. C. , Lau I. F. , Lam W. L. , Choy C. M. 
Published: April 2021

ABSTRACT
Mature Megalobatrachus oocytes contain 43 μg DNA per oocyte, as compared with 250 pg DNA in a hepatocyte of the same animal. Megalobatrachus oocytes respond to CdR treatment by an increased incorporation of [3H]lysine into basic proteins associated with ooplasmic particles, with an optimal CdR concentration at 2 mM. The nucleolus is the most active site of [3H]lysine incorporation. It is suggested that CdR-stimulated basic protein synthesis is a common biochemical event during amphibian oogenesis. The dose response to CdR treatment may be a function of the c-DNA content or c-DNA synthesis potential in the ooplasm.
The control of cell adhesion in a morphogenetic system
Authors: Curtis A. S. G. , Vyver Gyséle van de 
Published: April 2021

ABSTRACT
A new general type of morphogenetic process has been revealed by experiments on the phenomenon of non-coalescence between different strain types (alpha and delta) in the sponge Ephydatia fluviatilis. The question investigated was whether any process of cell adhesion was responsible for the phenomenon. Preliminary results suggested that the cells might show specific adhesion but further results indicated that a more complex system existed. Each strain produces a soluble factor that increases the adhesiveness of homologous cells but decreases that of cells of heterologous strains. The adhesion of cells, even in the presence of these factors, is non-specific but the factors specifically control adhesion and determine its quantitative value. The adsorption of the factors to the cells was tested for with inconclusive results. Heterologous factors may irreversibly alter a cell’s adhesiveness. It is shown that this system, particularly by reason of its negative effect on adhesiveness, (a) accounts adequately for the phenomenon of non-coalescence, (b) provides a model system for many forms of morphogenesis and (c) allows many apparently contradictory results obtained by other workers to be reconciled.
The activities of three enzymes of haem synthesis during hepatic erythropoiesis in the mouse embryo
Authors: Freshney R. I. , Paul J. 
Published: April 2021

ABSTRACT
Aminolaevulinate synthetase, aminolaevulinate dehydratase, and haem synthetase, three enzymes which may have a regulatory role in haem synthesis, have been determined in liver extracts from different foetal stages of the mouse.
Haemoglobin synthesis increases rapidly from early on the 14th day, after fertilization, to reach a maximum late on the 15th day. Aminolaevulinate synthetase reaches a maximum on the 14th day, 24 –36 h before the peak of haemoglobin synthesis, aminolaevulinate dehydratase on the 15th day, about 12 h before the peak of haemoglobin synthesis, and haem synthetase on the 17th day. Maximal activity of aminolaevulinate synthetase and aminolaevulinate dehydratase is of only a few hours’ duration. Throughout embryonic development the activities of all three enzymes are higher than in the adult liver.
The absence of a correlation of enzyme activity with foetal liver cell population changes implies that fluctuations in enzyme activity cannot be explained solely by changes in the proportions of different cell types. The high levels of activity relative to those of adult liver may be related to the high proportion of erythroid cells in the foetal liver.
It is concluded that these enzymes are unlikely to form rate-limiting steps during the increase in haemoglobin synthesis between 14 and 15 days.
A comparison of certain isozyme patterns in lobeless and normal embryos of the snail, Ilyanassa obsoleta
Authors: Freeman Sallie B. 
Published: April 2021

ABSTRACT
A study was made of the emergence of certain enzymes during the embryogenesis of Ilyanassa. Lobeless and normal embryos were compared in order to determine the effect of polar lobe removal on subsequent molecular developments. Polyacrylamide gel electro-phoresis in capillary tubes, a technique requiring only small numbers of embryos, was used to obtain the isozyme patterns of alkaline phosphatases and of esterases. It was found that lobe removal interfered with the emergence of normal isozyme patterns of alkaline phosphatase and esterase during development. Certain bands of enzyme activity were severely reduced or absent while others appeared to be normal. The results provide further evidence that the influence of the polar lobe on development is of a specific nature.
Transient inhibition of DNA synthesis by methotrexate, in the rat embryo and foetus
Authors: Berry C. L. 
Published: April 2021

ABSTRACT
Massive doses of methotrexate, a folic acid inhibitor, followed by folinic acid, the specific antagonist, have been used to produce a period in which the embryo and foetus are exposed to tetrahydrofolate deficiency with subsequent inhibition of DNA synthesis. The effects of this inhibition vary at different stages of gestation, and in late foetal life provide a useful method of inducing a delay in the appearance of vertebral body ossification centres. This defect is rapidly repaired, although there may be permanent sequelae. It is hoped that this technique will be useful in the study of cellular events in ‘catch-up’ growth.
Induction d’un pharynx supplémentaire par des incisions répétées chez la planaire Dugesia lugubris O. Schmidt
Authors: Schilt J. 
Published: April 2021

ABSTRACT
The induction of a supernumerary pharynx in a planarian
Incisions are made in the prepharyngeal region of Dugesia lugubris. These incisions are repeated every day.
When the nerve trunks are regularly cut, a supernumerary pharynx may appear at the level of the incisions, on condition that these incisions are far enough from the origin of the host pharynx.
However, even at large distances, the pharyngeal region exerts an inhibitory effect on the regeneration of such a pharynx: 20 days are necessary for its differentiation, and it is always smaller than the host pharynx.
It seems that the nerve trunks play, one way or another, a role in the induction of the supernumerary pharynx, but it cannot be determined what role they play. The nature of inhibition is not certain.
These results are compared to those obtained by other authors.
Differentiation of chick embryo somites in chorioallantoic culture
Authors: O’hare M. J. 
Published: April 2021

ABSTRACT
An analysis was made of the differentiative capabilities of somites isolated from all regions of stage-8 (4-somite) to stage-18 (36-somite) chick embryos, with particular reference to the incidence of spontaneous chondrogenesis. A chorioallantoic grafting technique with Millipore filter as a graft vehicle was employed.
The youngest somites which spontaneously differentiated cartilage were the anterior somites of stage 11. Cartilage obtained from grafts of stage 8–10 anterior somites was probably derived from lateral rather than somite mesoderm. Younger, posterior somites consistently failed to differentiate cartilage in spite of the demonstrable viability of the grafts, as evidenced by the appearance of other differentiated derivatives.
Increasing the number of non-chondrifying somites grafted, from 4 to 16, did not result in their spontaneous chondrification when all such somites were derived from the same 4-somite region of embryos of the same stage.
All embryos from stage 12 to stage 18 showed a gradient of chondrogenic potential along the somite axis, with anterior somites always showing a higher incidence of cartilage than posterior somites of the same stage.
Bone and striated muscle derived from somite mesoderm, ganglion cells derived from trunk neural crest, and nephric tubules derived from nephrotome cells were also found in the grafts. Each differentiated type showed a distinct pattern of incidence along the somite axis. The incidences of nephric tubules and ganglion cells were unrelated to those of the differentiated derivatives of somite mesoderm, suggesting that the results reflect true differences of intrinsic differentiative potential.
Culture organotypique de glandes génitales de Téléostéens
Authors: Remacle C. , Demal J. 
Published: April 2021

ABSTRACT
Histological examination of gonads from teleosts, cultivated in vitro on an agar medium containing glucose and chick embryo extract shows the continuation of the germinal activity for at least 21 days. The influence of different factors: stage of maturation at the time of explantation, quantity of nutrient available, and transfer on fresh media are checked. The best results are obtained for ovaries containing only young oocytes, i.e. before any vitellogenesis or when it has just started, and for testes in which spermatogenesis is well advanced, i.e. when there are numerous spermatozoa. Results do not seem to be improved by frequent transfers.
First attempts of association with pituitary gland or gonads of the opposite sex are reported.
The biochemistry of differentiation of mouse trophoblast: studies on polyploidy
Authors: Barlow Peter W. , Sherman Michael I. 
Published: April 2021

ABSTRACT
Trophoblast development in utero in the first half of gestation is accompanied by a rise in the ploidy levels in giant cell nuclei. Giant cells constitute up to one-third of the trophoblast population over this period. The expression of polyploidy is independent of the maternal environment; the extent of polyploidy and the degree to which trophoblast develops morphologically under various conditions appear to be related. The following events are not necessary for the initiation of polyploidization in trophoblast: (a) hatching from the zona pellucida, (b) oestrogen sensitization, (c) implantation, (d) postimplantation changes in topology. That earlier developmental events such as the formation of the blastocoel cavity may in some way trigger polyploidization of trophoblast is not inconsistent with the studies described.
Preimplantation differentiation in the mouse egg as revealed by microinjection of vital markers
Authors: Wilson I. B. , Bolton Eleanor , Cuttler Rosemary H. 
Published: April 2021

ABSTRACT
A microinjection technique has been devised for labelling individual blastomeres of preimplantation mouse embryos with a marker drop of inert silicone fluid placed in the cytoplasm either at the periphery of the egg or at the interface between two blastomeres (i.e. centrally). The following observations were made on blastocysts which developed from injected eggs: (1) All drops derived from peripheral injections (at two-cell to morula stage) were found exclusively in the trophoblast.(2) Drops injected centrally at two-four-cell stages have been found in both the trophoblast and inner cell mass.(3) Peripheral labelling of one or both members of a pair of eggs (four-cell to morula) fused into a chimaeric blastocyst yielded markers in both trophoblast and inner cell mass.
No evidence was found of inherent bilateral symmetry or polarity in the cleaving egg. The results indicate that physico-chemical positional effects determine whether a cell will differentiate into trophoblast or inner cell mass.
The results are discussed in the light of current hypotheses relating to early embryonic differentiation in the mammal, and it is suggested that cleavage occurs without spatial disturbance of the cytoplasmic pattern of the egg so that its cortical region is converted directly to the outer cells of the morula and hence to the trophoblast.
Sex differentiation of germ cells in the teleost, Oryzias lalipes, during normal embryonic development
Authors: Satoh Noriyuki , Egami Nobuo 
Published: April 2021

ABSTRACT
Mitotic and meiotic activities of germ cells during early development in the medaka, Oryzias latipes, are dealt with in this report.
Primordial germ cells were obviously distinguishable from somatic cells 3 days after fertilization and began to proliferate about 7 days after fertilization. The mean number of primordial germ cells increased during a period of 7–10 days after fertilization, reaching about 90 immediately before hatching.
Newly hatched fry could be classified into two types according to the number and the nucleic activity of germ cells in the gonadal rudiment. One type consisted of fry containing about 100 germ cells and no cells in the meiotic prophase. In the other type of fry the number of germ cells increased by mitotic divisions and some of the cells began to enter into the meiotic prophase. During the course of further development the fry of the former type differen tiated into males and the latter into females.
Therefore it can be concluded that the morphological sex differentiation of germ cells occurs at the time of hatching. However, no sexual differences in the histological structure of somatic elements in the gonad are observable at that time.
The effects of minute direct electrical currents on cultured chick embryo trigeminal ganglia
Authors: Sisken Betty F. , Smith Stephen D. 
Published: April 2021

ABSTRACT
The effects of low levels of electric current were determined on organ cultures of 6- to 19-day-old chick embryo trigeminal ganglia. Current levels ranged from 0 00115 to 11·5 nA/ mm2; the time of electrical treatment varied from 2 h to 96 h.
Low levels of electricity were found to have at least three major effects on this system of mixed cellular types:
Outgrowth of nerve fibers from the explant was enriched. This resulted in a greater number of fibers which were longer and more highly branched than those in control cultures. Survival of neurons within the original explanted ganglion was enhanced by treatment with electricity. The presence of healthy neurons was found in 93·1% of the treated cultures and in 53·5% of untreated cultures. Neurons, fibers and non-neural cells were stimulated to grow in the direction of the cathode. The rate of cathodal migration was calculated to be 0·1 mm/h (2·4 mm/day) in an explant from 12-day-old embryo.
No differences were observed between surviving treated and control cultures in histochemical tests for acetycholinesterase.
A similarity between the action of low levels of electrical current and nerve growth factor (NGF) is suggested.
Organogenesis in Cephalopoda: further evidence of blastodisc-bound developmental information
Authors: Marthy H.-J. 
Published: April 2021

ABSTRACT
The basic mechanisms of organ differentiation in the Cephalopod embryo (telolecithal egg, discoidal cleavage) are studied. The results of ligation experiments, performed in early cleavage stages, confirm earlier conclusions of the author, drawn from transplantation/ explantation and heat-shock experiments. The developmental information for cellular differentiation is shown to reside in the blastodisc; the yolk syncytium, in which a large part of the original egg cortex is incorporated, acts as nutritive substrate for the cellular material involved in organogenesis.
On the basis of these results, Arnold’s induction model supposing an undisplaceable determining informational pattern laid down in the uncleaved egg cortex must be rejected.
Morphogenesis in Micrasterias: I. Tip growth
Authors: Lacalli T. C. 
Published: April 2021

ABSTRACT
Observations on lobe growth in the lateral wings of the developing primary cell wall in the desmid Micrasterias rotata are reported and discussed. Patterns of incorporation of methyl-[3H]-methionine and C-1-[3H] glucose into the primary wall as revealed in autoradiograms indicate that formation of the new wall is concentrated at the tips of lobes. Patterns follow the predictions of Robertson’s model for tip growth in fungal hyphae; thus they link growth in M. rotata lobes with mechanisms of cell elongation found in other cells. Damage done to selected regions of the cell surface with a laser microbeam demonstrates that only certain regions are required for continued growth and morphogenesis while much of the surface plays only a passive role. In growth stages at which lobes are already well defined (stage 4 and later) continued growth of each lobe requires the participation of an area no more than 4–5 μm in diameter, here termed a singularity, at its tip. At early stages (prior to stage 3) singularities per se cannot be demonstrated. At these stages the capacity to initiate lobes and hence to form singularities is not fixed at specific points, but is distributed over an area of the surface no less than 10 μm in diameter. Singularities, by their persistence and repeated duplication, are directly responsible for the spatial form of the two lateral wings.
Ultrastructural studies of t
w32
/t
w32 mouse embryos
Authors: Hillman Nina , Hillman Ralph 
Published: April 2021

ABSTRACT
Homozygous tw32/tw32 mouse embryos, obtained from both spontaneously ovulated and superovulated T+/tw32 females mated to T+/tw32 males, have a lethal period which extends from the 8-12 cell stage to the late morula stage. Most of the homozygous mutant embryos die at the early morula stage and are characterized by excessive amounts of cytoplasmic lipid, mitochondrial abnormalities, binucleated cells and nuclear lipid droplets. The excessive cytoplasmic lipid and nuclear lipid droplets distinguish 35-50% of the embryos (presumably tw32 homozygotes) from their litter-mates prior to the lethal period. The remainder of the distinguishing characteristics appear in the later (8-cell to late morula) tw32/tw32embryos in frequencies high enough to be considered phenotypic expressions of the mutant genome. The present study indicates that the non-complementary tw32 and t12 alleles are in fact separate T locus recessive alleles.