bluuebunny/crossref_metadata_2025 huggingface dataset:
Les caractères de la segmentation et la détermination de la polarité dorsoventrale dans le développement de quelques Spiralia
Authors: Guerrier Pierre
Published: April 2021

Des travaux antérieurs m’ont permis de montrer que les déterminations axiales des œufs de Parascaris equorum, de Limax maximus et de Sabellaria alveolata se fixent selon un mode partiellement épigénétique au cours des premières divisions (Guerrier, 1967; 1968; 1970a, b). Le mode de segmentation inégal, particulier à l’œuf de certains Lamellibranches, permet de se demander si celui-ci n’est pas le siège d’un processus original, relevant éventuellement d’une structuration dorsale préformée au sein de l’œuf indivis. Cette hypothèse, retenue par Tyler (1930) après des études portant sur Cumingia tellinoïdes est réfutée par Pease (1940) qui, sur le même matériel, examine les effets d’une stratification des éléments endoplasmiques. Nous avons choisi d’étudier deux espèces dont les œufs, remarquablement transparents, permettent de suivre avec une très grande précision les mouvements des constituants cellulaires au cours de la segmentation. L’emploi de la compression et de la centrifugation a permis de déplacer ces constituants selon des modalités diverses et d’examiner les conséquences de ces interventions sur la morphogenèse. Nos observations nous conduisent à conclure que la fixation des principales potentialités et, en particulier, de la symétrie dorsoventrale, répond ici à un mécanisme épigénétique qui présente de nombreuses analogies avec celui que nous avons rencontré chez d’autres Spiralia.
Steroid control of the normal development of glutamine synthetase in the embryonic chick retina
Authors: Piddington R.
Published: April 2021

Glutamine synthetase (GS) activity in the neural retina of the chick embryo is inducible with corticosteroids (Moscona & Piddington, 1966; Piddington, 1967; Moscona, Saenz & Moscona, 1967; Moscona, Moscona & Saenz, 1968; Alescio & Moscona, 1969). Striking increases in retinal GS activity can be elicited with hydrocortisone in ovo days in advance of the normal rapid rise of this enzyme (Piddington & Moscona, 1967). Rapid increases in GS activity can also be induced precociously with corticosteroids in organ cultures of young retina (Piddington & Moscona, 1967; Reif-Lehrer & Amos, 1968). The natural steroids most effective in stimulating retinal GS activities in vitro are the 11β-hydroxyl steroids hydrocortisone, corticosterone and aldosterone (Moscona & Piddington, 1967; Reif-Lehrer, 1968).
Some bio-electric parameters of early Xenopus embryos
Authors: Palmer J. F. , Slack Christine
Published: April 2021

Membrane potential and resistance were measured in eggs, cleavage stages and blastulae of the South African toad Xenopus laevis, using intracellular microelectrodes.

The membrane potential increased from – 6·5 ±2 mV in eggs to –57 ±8· 0 mV at the mid-blastula stage.

The input resistance of fertile eggs ranged from 0·5 MΩ to 5 ·0 MΩ corresponding to a specific resistance of 20–200 kΩ cm2. During the first two or three division cycles the input resistance usually decreased by a factor of 2– 10 and then subsequently rose during the blastula stages from a mean value of 600 ± 100 kΩ at stage 5 to 2·0 ±0·5 MΩ at stage 8.

At all developmental stages examined, point polarization of a surface cell in the embryo by rectangular current pulses of 0·5–6 × 10−8 A produced voltage deflexions in other surface cells. This was seen even when several (7–8) cell junctions intervened between the current passing and voltage recording microelectrodes at distances of more than 1 mm. These measurements suggest that the junctional resistance is low compared with that at the surface, though the geometrical arrangement of cells is not favourable for calculation of absolute values of membrane resistance.

Current spread between cells occurred apparently less easily during mid-blastula stages than at earlier stages in development, perhaps indicating an increase in junctional resistance during development.

A comparison has been drawn between the present measurements and similar ones made in another amphibian, Triturus.
Histochemical observations on early implantation in the mouse
Authors: Smith M. S. R. , Wilson I. B.
Published: April 2021

Acid phosphatase, polysaccharide complexes and lipids were studied in the uterus and embryo of the mouse from 90 to 120 h post coitum (p.c.).

The pattern of acid phosphatase-rich vesicles (ERV) in the uterine epithelium and its manner of degeneration are discussed.

At 90 h p.c. there are large ERV in the inner cell mass indicating degenerating cells; these are not detectable at 96 h p.c.

A border of lysosomes is prominent in regions of the peripheral trophoblastic cytoplasm adjoining the epithelium at 96 h p.c. and this may be involved in membrane changes which facilitate closer contact and interactions between the embryonic and maternal cells.

Discrete aggregates of large ERV are present in the epithelium and trophoblast at sites scattered around the abembryonic region, from 96 to 104 h p.c.

From 94 to 100 h p.c. macrophage-like cells can be found in the uterine epithelium.

In the later stages of implantation, 110–120 h p.c., the pattern of acid phosphatase-rich vesicles becomes progressively more complicated with the whole of the epithelium around the blastocyst gradually becoming degenerate.
Structure and developmental tendency of the dorsal marginal zone in the early amphibian gastrula
Authors: Ikushima Nobushige , Maruyama Setsuko
Published: April 2021

The peripheral surface of a fertilized, uncleaved egg is subdivided through cleavage and is allotted to constituent cells. This is called the primary surface. In an early morula a constituent cell has two kinds of surfaces: the primary surface, and the secondary surface, which does not participate in forming the periphery of the embryo. Electron-microscopic observations showed structural differences between the two surfaces.

When the dorsal marginal zone of an early gastrula of Hynobius nebulosus is excised and immersed in Feldman’s solution, the piece can easily be separated into two layers: the outer layer, whose constituent cells are given a share of the primary surface, and the inner layer, whose constituent cells are completely covered only by the secondary surface.

Both an explanted piece of the outer layer and an intact double-layered piece show three kinds of movement: spreading, convergence followed by stretching, and spherical thickening. The inner layer is kinetically very inert, showing slight spreading and thickening.

An explanted piece of the outer layer differentiates into axial mesodermal structures, while the inner layer does not.

When a piece of either the inner or the outer layer is implanted in the blastocoel of another gastrula, it induces deuterencephalic and spino-caudal structures and seems to differentiate into axial mesodermal structures.

Differences of kinetic properties and differentiation are considered to result from the fact that the outer layer has the primary surface, while the inner layer does not.

Functional effects of the primary surface on the movement of tissues and differentiation are discussed.
The degree of determination of the early embryo of Schistocerca gregaria (Forskål) (Orthoptera: Acrididae)
Authors: Moloo S. K.
Published: April 2021

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.
Pathogenesis of preaxial polydactyly of the hand in human embryos
Authors: Yasuda Mineo
Published: April 2021

Hand plates with preaxial polydactyly from 13 human embryos of the Carnegie stages 17 – 23 were examined macro- and microscopically. Morphological features in early pathogenesis of preaxial polydactyly are (1) an abnormal extension and a delayed involution of the apical ectodermal ridge on the preaxial border of the hand plate in stages 17 and 18, (2) a precocious development of an interdigital notch between the duplicated thumbs in stages 17 and 18, and (3) bifurcation of the distal part of the first digital ray in stage 19. A disorder of the interaction between limb ectoderm and mesoderm is considered to be the pathogenetic event.
Investigation of the determinative state of the mouse inner cell mass
Authors: Rossant J.
Published: April 2021

Inner cell masses (ICMs) were dissected from and day blastocysts and cultured in contact with day morulae. Blastocysts and morulae were homozygous for different electrophoretic variants of the enzyme glucose phosphate isomerase (GPI). Aggregation of ICMs and morulae was observed, and such aggregates were able to form blastocysts in vitro and morphologically normal foetuses in utero. GPI analysis of these conceptuses revealed that most were chimaeric. However, donor ICM-type isozyme was only detected in the embryonic and extra-embryonic fractions of the chimaeras and never in the trophoblastic fraction.

Thus, ICM cells appear unable to form trophoblast derivatives even when exposed to ‘outside’ conditions as experienced by developing trophoblast cells. This is evidence that ICM cells, although not overtly differentiated, are determined by days.
Aspects of tail muscle ultrastructure and its degeneration in Rana temporaria
Authors: Fox H.
Published: April 2021

Tail muscles of larval Rana temporaria and to a lesser extent Xenopus laevis, at prometamorphosis, were investigated by light and electron microscopy. In the case of Rana their degeneration is described at metamorphic climax. The non-degenerate tail muscles of both genera are generally similar in their ultrastructure and likewise similar to those striated muscles of other adult vertebrates including amphibians. At climax tail muscles of Rana degenerate by autolysis. It seems likely that lysosomal enzymes are directly involved in sarcoplasmic degeneration. The relationship between lysosomes and myofibrillar degradation is difficult to establish. The subject is discussed in the light of relevant information (mainly mammalian) on muscle dystrophies. Anuran tail muscle is highly degraded before its probable phagocytosis by mesenchymal macrophages.
The developmental capacity of nuclei transplanted from keratinized skin cells of adult frogs
Authors: Gurdon J. B. , Laskey R. A. , Reeves O. R.
Published: April 2021

Nuclei from keratinized skin cells of adult Xenopus foot-webs have been transplanted to enucleated eggs of the same species. The cells used to provide donor nuclei were obtained as a monolayer outgrowth from cultured foot-web expiants. When explants were cultured without plasma for 3 days, over 99-9 % of the outgrowth cells contained keratin as revealed by the binding of monospecific fluorescent antibody prepared against purified Xenopus keratin. Nuclei were transplanted from cells which had been cultured for 3days. None of the first transfer embryos developed as far as tadpoles. Eleven clones of embryos were prepared from the nuclei of partial first-transfer blastulae by use of serial nuclear transplantation. Eight of these clones contained swimming tadpoles with functional muscle and nerve cells, and six clones contained tadpoles with beating hearts, well differentiated eyes, and other organs. To prove that the nuclei of nuclear-transplant tadpoles were derived from the transplanted skin cell nuclei and not from a failure of ultraviolet light to inactivate the recipient egg nucleus, 1-nu skin cell nuclei were transplanted to eggs laid by 2-nu frogs. Several advanced tadpoles from six clones were analysed for nucleolar and chromosome number and found to be 1-nu diploids. The six clones of advanced tadpoles which were proved to carry the donor nuclear marker represent six first-transfer nuclei in a total sample of 129 skin cell nuclei originally transplanted. The probability that all six nuclei were derived from the 01 % of the donor cell population not proved to contain keratin is less than one in 1010. We conclude that cell specialization does not involve any loss, irreversible inactivation or permanent change in chromosomal genes required for development.
An experimental investigation into the possible neural crest origin of pancreatic APUD (islet) cells
Authors: Andrew Ann
Published: April 2021

It has recently been contended that pancreatic APUD cells are neural crest derivatives. In an experimental investigation, isotopic grafts of neural tube containing neural crest cells were transplanted from chick and quail embryos labelled with tritiated thymidine, and from unlabelled quail embryos, to host chick embryos at the same stage of development. Transplantations were performed at various levels between somites 5 and 24 in embryos at 6- to 24-somite stages. In operated embryos at days of incubation, the pancreatic APUD cells were not labelled; nor did their nuclei show quail features. Migration of cells from the graft was evidenced by the presence of quail nuclei and/or radioactive label in autoradiographs, in spinal and sympathetic ganglia in the operated region.

It is concluded that the pancreatic APUD cells of the -day-old chick embryo are not derived from the trunk neural crest up to the level of somite 24. It is unlikely that more caudal levels contribute, because APUD cells are already concentrated in the dorsal pancreatic bud region at the 24-somite stage, by which time no migration of crest cells has occurred caudal to somite 24. This conclusion probably concerns A, B and D pancreatic endocrine cells.
High tyrosinase activity in albino Xenopus laevis oocytes
Authors: Wyllie A. H. , Robertis E. M. De
Published: April 2021

Tyrosinase was measured in oocytes of the recently described albino mutant (apap) of Xenopus laevis. Although these oocytes show no pigmentation and the eggs are known to contain no melanosomes, tyrosinase -which is probably the only enzyme necessary for melanin synthesis from tyrosine -was increased more than twofold relative to the wild type. Tyrosinase recovered from albino and wild type oocytes showed the same K31 with respect to tyrosine, and this was not altered by previous gonadotrophin stimulation in vivo. The tyrosinase assay, based on [14]tyrosine incorporation into acid-insoluble products, was of greater sensitivity than previously described methods of the same type, through removal of low molecular weight material from the oocyte homogenate prior to incubation, and the use of tyrosine of high specific activity.
An Autoradiographic Study on the Uptake of Radiosulphate in the Rat Embryo1
Authors: Friberg U. , Ringertz N. R.
Published: April 2021

The uptake of radiosulphate in rat embryos 7–22 days old was investigated with autoradiography and compared with the occurrence of metachromasia after toluidine blue staining and a positive PAS reaction. The youngest embryos retained rather small amounts of radiosulphate, which was evenly distributed. In the older embryos the amount of retained radiosulphate was considerably higher and regionally well differentiated. Marked changes in the autoradiographic pattern of certain organs occurred with growth. The uptake of radiosulphate was as a rule paralleled by metachromasia with toluidine blue. No direct relationship was found between fixation of radiosulphate and PAS reactivity of the tissues. Radiosulphate was found to be incorporated into cells and tissues containing inorganic sulphate (mineral part of bony tissues) and sulpho-mucopoly-saccharides (mesenchyme, mast-cells, &c.).
Development of Embryonic Mouse Gonads Transferred to the Spleen: Effects of Transplantation Combined with Genotypic Autonomy
Authors: Russell Elizabeth S. , Murray Louise M. , Small Eleanor M. , Silvers Willys K.
Published: April 2021

Certain aspects of the pleiotropic relationship between the embryonic anaemia and germ-cell defect produced by deleterious alleles of the W-series in the mouse were tested by transfer of gonads from new-borns and 12–16-day embryos into a neutral site with rich blood-supply, the spleen of adult castrates. Splenic residence cut down the recovery of ovarian tissue from transplants at early stages, and slightly inhibited the amount of spermatogenesis at all stages. In spite of such environmental limitations, it was clear that at all stages transplants of both ovaries and testes contained fewer germ-cells at the 14-day post-natal stage if the donor were of defective sterile genotype than if it were of normal fertile type. This supports the hypothesis that genotypic autonomy of germ-cell level is established by the 12th day of embryonic life, and further development is independent of the W-genotype of surrounding tissue. The implications of these findings for understanding of pleiotropic relations are discussed.
Cell division, cell elongation and distribution of α-, β- and γ-crystallins in the rat lens
Authors: Mcavoy J. W.
Published: April 2021

The vertebrate lens comprises cells from only one cell lineage and these exist in two distinct forms. Fibre cells make up the bulk of the lens and a monolayer of epithelial cells covers the anterior surface of the fibres. A quantitative analysis of cell division and cell specialization (elongation) in the lenses of 1-day-old and 6-to 7-week-old rats showed that the rat lens can be separated into two compartments; a proliferation compartment in the epithelium of the anterior lens and an elongation compartment in the posterior lens. In 6-to 7-week-old rats the proliferation compartment is divided into three sub-compartments which appear to be related to the anatomy of the anterior eye. Lens epithelial cells lying in the vicinity of the ciliary body have an average cell cycle time of 7·2 days, epithelial cells which lie below the iris have an average cell cycle time of 32·3 days, and cells in the central epi-thelium divide most slowly. The epithelium is bathed for the most part by the aqueous humour and the posterior part of the lens is surrounded by the vitreous humour. From this analysis as well as evidence from other laboratories it is suggested that a proliferation factor(s) may be present in the aqueous and that an elongation factor(s) which comes from the retina may be present in the vitreous.

There are three major groups of lens specific proteins, α-, β-and γ-crystallins. These proteins were separated by gel chromatography and antibodies raised against them in rabbits. Alpha-, β-and γ-crystallins were localized in sections of the 1-day-old rat lens by the indirect immunofluorescence method. Epithelial cells in the proliferation compartment contained only α-crystallin but all three groups of crystallins were detected in cells of the elongation compartment. β-Crystallin was detected first in elongating cells that had stopped dividing and γ-crystallin was detected later in the elongation process. Thus, synthesis of α-and γ-crystallins may normally depend on the elongation factor(s) from the retina. Also, since there is a close relationship between cessation of cell division and detection of β-crystallin, another factor governing the synthesis of β-crystallin may be whether the cells have ceased dividing. In this way the expression of crystallin genes may be co-ordinated as the lens grows and cells make the transition from proliferation to elongation compartments.
Chromosome analysis of early postimplantation presumptive haploid parthenogenetic mouse embryos
Authors: Kaufman Matthew H.
Published: April 2021

The chromosome constitution of early postimplantation presumptive haploid parthenogenetic mouse embryos was examined. All the embryos isolated were at the egg-cylinder stage and seven contained dividing cells. In two of the apparently healthy embryos only haploid mitoses were seen, whereas in five others an approximately equal proportion of haploid and diploid mitoses was observed. Out of 52 cells in which unequivocal counts could be made, only one contained more than the euploid number of chromosomes (mouse, n = 20). Possible reasons for the poorer development of haploid compared to diploid parthenogenetic embryos are discussed.
In vitro development of inner cell masses isolated immunosurgically from mouse blastocysts: I. Inner cell masses from 3·5-day p.c. blastocysts incubated for 24 h before immunosurgery
Authors: Hogan Brigid , Tilly Rita
Published: April 2021

This paper describes the in vitro development of inner cell masses isolated immunosurgically from mouse blastocysts which had been collected on 3 ·5 days p.c. and then incubated for 24 h. The inner cell masses continue to grow in culture and develop through a series of stages with increasing complexity of internal organization. By day 1 all of the cultured ICMs have an outer layer of endoderm, and by day 3 some of them have two distinct kinds of inside cells; a columnar epithelial layer and a thin hemisphere of elongated cells. Later, mesodermal cells appear to delaminate from a limited region of the columnar layer, close to where it forms a junction with the thinner cells. By day 5, about 25 % of the cultured ICMs have a striking resemblance to normal 7 ·5-day p.c. C3H embryos, with embryonic ectoderm, extra-embryonic ectoderm and chorion, embryonic and extra-embryonic mesoderm, and visceral endoderm. When mechanically disrupted and grown as attached clumps of cells in a tissue dish, these embryo-like structures give rise to trophoblast-like giant cells. These results suggest that the inner cell mass of 4 ·5-day p.c. blastocysts contains cells which can give rise to trophoblast dérivâtes in culture.
Cell division and cell allocation in early mouse development
Authors: Kelly S. J. , Mulnard J. G. , Graham C. F.
Published: April 2021

Cell division was observed in intact and dissociated mouse embryos between the 2-cell stage and the blastocyst in embryos developing in culture. Division to the 4-cell stage was usually asynchronous. The first cell to divide to the 4-cell stage produced descendants which tended to divide ahead of those cells produced by its slow partner at all subsequent stages of development up to the blastocyte stage. The descendants of the first cell to divide to the 4-cell stage did not subsequently have short cell cycles. The first cell or last cell to divide from the 4-cell stage was labelled with tritiated thymidine. The embryo was reassembled, and it was found that the first pair of cells to reach the 8-cell stage contributed disproportionately more descendants to the ICM when compared with the last cell to divide to the 8-cell stage.
Effect of oxygen concentration on morphogenesis of cranial neural folds and neural crest in cultured rat embryos
Authors: Morriss Gilltan M. , New D. A. T.
Published: April 2021

Rat embryos, days old, cultured with a 5 % or 10% O2 gas phase underwent normal or near-normal cranial neurulation; however, culture at 20% or 40% O2 resulted in abnormal morphogenesis of the cranial neural folds from the 9-somite stage onwards, and the brain tube frequently failed to close. Normal morphogenesis was characterized by a narrowing V-shaped profile, development of a slightly concave neuroepithelial surface, and formation of a sharp mediad curvature of the most lateral region prior to midline apposition and fusion. These morphogenetic events were related to cellular changes within the neuroepithelium, namely cell death, onset of neural crest cell migration, and loss of apical microfilament bundles from the most lateral cells. In 20% and 40% O2-cultured embryos, failure of curvature of the neuroepithelium was associated with failure or retardation of the related cellular changes; it may therefore have been due to the maintenance of an excessive rigidity which opposed the forces involved in bringing about the final stage of brain-tube formation.

Mitochondria in normal (low O2 and in vivo) embryos were of the anaerobic type, having few cristae; in high O2-cultured embryos they were of the characteristic aerobic type, indicating an adaptation to the abnormal environment.
Fine structure of the lumbosacral neural folds in the mouse embryo
Authors: Wilson Doris B. , Finta Laurel A.
Published: April 2021

The neural folds in the lumbosacral region of the normal 8-day and 9-day mouse embryo were studied by means of transmission electron microscopy with and without lanthanum treatment. The cells showed an abundance of ribosomes, microtubules arranged parallel to the long axes of the cells, and microfilaments extending across the apices. At the luminal border junctional complexes were common, and an occasional midbody was seen stretching between adjacent cells nearing the end of telophase. In the 8-day embryos, gap junctional vesicles (annular nexuses) bounded by layered membranes and containing cytoplasm with ribosome-like material were commonly observed; at 9 days the vesicles were relatively rare. The lanthanum-treated material demonstrated that the tracer was able to pass through the subluminal junctional complexes and throughout the intercellular spaces. However, the space between the membranes of the gap junctional vesicles lacked lanthanum and thus apparently did not communicate with the intercellular space.