bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of the somitic mesoderm in the development of the thorax in bird embryos
Authors: Chevallier Alain
Published: April 2021

The regional embryonic origin of trunk and limb musculature was determined through heterospecific homotopic or heterotopic transplantations of quail somitic or somitic-somatopleural mesoderm into chick hosts, and through localized X-irradiation of the somitic mesoderm. Experiments were performed on 2-day embryos.

Results show that the myoblastic component of all truncal and appendicular muscles is of somitic origin. Intra- and perimuscular connective tissue as well as tendons are of somatopleural origin. X-ray destruction of the somitic mesoderm at and beyond the wing level resulted in the complete or almost complete absence of musculature in the wing and corresponding truncal region.

The mapping of the cephalocaudal origin of the various muscles was found to be as follows:

In the heterotopic transplantations, the grafted somitic mesoderm gave rise to site-specific morphogenesis, irrespective of the cephalocaudal level of its origin. This result demonstrates that, at 2 days of incubation, the myogenic somitic cells are not regionalized.
Sorting out behaviour of disaggregated cells in the absence of morphogenesis inDictyostelium discoideum
Authors: Tasaka M. , Takeuchi I.
Published: April 2021

Cells disaggregated from slugs of Dictyostelium discoideum were cultured in Bonner’s salt solution in roller tubes. Cells rapidly stuck together to form an amorphous loose agglutinate which was later transformed into a spheroidal tight agglutinate surrounded by slime sheath material. Prespore cells in the loose agglutinate underwent partial dedifferentiation by starting to decompose their specific antigen until formation of the tight agglutinate, in which the antigen was resynthesized. During the process, there was some decrease in the proportion of prespore cells.

Changes in the distribution of prespore and prestalk cells in the agglutinates were examined by using immunocytochemical staining. They were randomly distributed in the early agglutinates, but became well separated in 4 h agglutinates in such a way that prestalk cells were completely enveloped by prespore cells. Prestalk cells later came outside to be partially enveloped and finally occupied a hemisphere side by side with prespore cells. During the process, cells in one or two outer layers differentiated into prestalk or stalk cells. Similar changes in the distribution pattern were observed, when labelled prestalk cells were cultured with unlabelled prespore cells and their distribution in co-agglutinates was followed by autoradiography. It was concluded from these results that the majorities of prestalk and prespore cells isolated from slugs are sorted out in agglutinates without changing their original cell types, and that the sorting-out occurs in the complete absence of polar structures and movement of the cell mass. The distribution patterns in agglutinates of prestalk and prespore cells were discussed with reference to intercellular adhesion among/between them.
Nitrogen Excretion in Developing Chick Embryos
Authors: Fisher James R. , Eakin Robert E.
Published: April 2021

An analysis, more extensive than hitherto, has been made of nitrogen excretion in developing chicks. It was found that the concentration of ammonia in the allantoic fluid was constant from the 5th to the 11th day and equalled the concentration in the extra-allantoic fluids, e.g. yolk. The increase into total ammonia content of the allantois during development is apparently due to the increase in volume of the organ and not to excretion by the embryo. The concentration of urea in the allantoic fluid increases during development and injected urea concentrates in that organ. The total amount and concentration of uric acid in allantoic fluid increases during development. The ratio of urea nitrogen to uric-acid nitrogen is relatively constant from the 6th to the 11th day of development indicating that no major shift from urea excretion to uric-acid excretion occurs. No urease activity was observed even in the blastodiscs of unincubated eggs. The distribution of arginase activity in 7-day-old chicks did not resemble that of ureotelic organisms. Activity of heads, bodies, and livers were essentially the same. From these results it was concluded that ammonia is not an excretion product and that the developing chick does not pass through either a typical ammonotelic or ureotelic stage of excretion.
The Pulmonary Return as an Agent in the Final Development of the Atrium in Rana Temporaria
Authors: Simons J. R.
Published: April 2021

The lungs of tadpoles of R. temporaria were removed at an early stage (12 mm.) in order to ascertain the effect on the development of the atrium and the interauricular septum of the heart. Serial sections of the hearts of experimental and control tadpoles at three comparable stages of development between the operation and metamorphosis were prepared. The operation causes a reduction in the absolute volume of the atrium. When it is first formed, the left auricle in the normal tadpole averages 25 per cent, of the total atrial volume but, as growth proceeds, it comes to average about one-third of the total atrial volume by the time metamorphosis occurs. In the experimental tadpoles the left auricle, when first formed, averaged about one-fifth of the total atrial volume and maintained a similar proportion throughout development to metamorphosis. The presence of the pulmonary return is thus necessary for the normal enlargement of the proportional volume of the left auricle. The obliteration of the pulmonary return did not affect the origin and normal development of the interauricular septum.
The effect of cell killing by X-irradiation on pattern formation in the chick limb
Authors: Wolpert L. , Tickle C. , Sampford M. , Lewis J. H.
Published: April 2021

It has been suggested that positional information along the proximo-distal axis of the limb-bud is specified by time spent in the progress zone. Mesenchyme cells have been killed by X-irradiation, reducing the rate cells leave the zone. The time spent there by some cells is thus increased. When limbs, stage 18/19, stage 21, or tips of stage 24, are treated with increasing doses of X-irradiation, from 1000 rads to 2500 rads proximal structures are progressively lost, whereas distal ones - the digits - are relatively unaffected. There was no evidence for intercalation of missing parts. These effects are due to killing or damage of mesenchyme cells: the ectoderm is not affected at these doses. The results are consistent with a quantitative analysis based on the progress zone model, in which viable cells repopulate the progress zone and gradually restore it to normal as non-dividing cells are diluted out. It is suggested that any treatment causing damage to the mesenchyme at early stages will give similar results.

The mesenchyme cells appear to be surprisingly resistant to radiation damage. The form of the limb-bud is not altered by damaging the mesenchyme. Differences in the development of structures at similar proximo-distal levels, following irradiation, is considered in terms of the requirement of a threshold number of cells.
The zone of polarizing activity: evidence for a role in normal chick limb morphogenesis
Authors: Summerbell Dennis
Published: April 2021

When an impermeable barrier is placed so as to divide the early chick limb-bud into anterior and posterior parts then development continues only on one side of the barrier. The detailed results are inconsistent with mosaic development. They can readily be explained by supposing that pattern is specified by the concentration of a diffusible morphogen controlled by the zone of polarizing activity. A simulation of appropriate concentration profiles is presented and its relevance to similar experiments published elsewhere is discussed. It seems probable that the zone of polarizing activity is active during normal development.
Inhibition of tooth germ differentiationin vitroby diazo-oxo-norleucine (DON)
Authors: Hurmerinta Kirsti , Thesleff Irma , Saxén Lauri
Published: April 2021

Molar tooth germs from mouse embryos were studied in a Trowell-type organ culture. After 5 days of culture the odontoblasts had secreted predentine and the ameloblasts had differentiated. When cultured in the presence of 10 – 50 μ M diazo-oxo-norleucine (DON), which is a glutamine analogue, the differentiation of odontoblasts was inhibited, but the teeth looked otherwise healthy. When DON was added after 2 days of culture in control medium (at this time the odontoblasts in the cuspal area were already differentiated), it did not inhibit predentine secretion, ameloblast differentiation, nor enamel secretion. However, this was seen only in the cuspal area and the boundary to the undifferentiated, more cervical cells was distinct.

The results support the concept that the mechanism of the differentiation of odontoblasts is different from that of the ameloblasts. We have shown earlier that a close association between the basement membrane and the mesenchymal cells is required for odontoblast differentiation. Because DON interferes with glycosaminoglycan and glycoprotein synthesis we suggest that DON inhibits odontoblast differentiation by affecting the mesenchymal cell surface and/or the basement membrane.
Interaction between inner cell mass and trophectoderm of the mouse blastocyst : II. The fate of the polar trophectoderm
Authors: Copp A. J.
Published: April 2021

Selective labelling of polar trophectoderm cells in early mouse blastocysts has allowed the fate of polar cells to be followed during in vitro and in vivo blastocyst development. Results show that there is cell movement from polar to mural regions as blastocysts grow. This indicates that trophectoderm cells directly opposite the inner cell mass are the oldest mural cells. However, after implantation polar cells invaginate into the blastocoelic cavity and contribute to the extra-embryonic ectoderm. It is suggested that the morphogenetic changes occurring in the mouse embryo at implantation result from the maintenance of a balance between (a) regional differences in rates of cellular proliferation, and (b) mechanical constraints on the direction in which growth can occur.
Factors regulating the degree and extent of experimental chimaerism in the mouse
Authors: Mystkowska Ewa T. , Ożdżeński Wacław , Niemierkos Anna
Published: April 2021

The degree of chimaerism of the coat, bone marrow and cornea in mouse chimaeras obtained by aggregation of an albino inbred embryo of A strain with an AxCBA-T6T6 hybrid was investigated. Out of 21 individuals born, 18 were chimaeras. Statistically significant correlation has been demonstrated between chimaerism of the coat, bone marrow and the cornea. The contribution of the two components appears to be affected by two factors: first, variable participation of the two components in the embryonic ectoderm of the chimaeric egg cylinder, and second, the rate of proliferation of the two cell lines.

A photometric method is described which permits the quantitative evaluation of coat chimaerism. The method is sensitive and reliable.
Rôle de la sérotonine et des catecholamines dans la régénération de la planaire Polycelis tenuis
Authors: Franquinet R.
Published: April 2021

During traumatic regeneration of Planaria Polycelis tenuis, determination of serotonin, noradrenaline and dopamine levels revealed important variations of serotonin and catecholamines from the time of excision. The use of specific inhibitors of these hormones delayed regeneration whereas simultaneous addition of an hormone and its antagonist restores a standard time of regeneration. Serotonin acts through adenylate cyclase system. Results allow us to assume that dopamine acts through the same mechanism. The action of noradrenaline is so far not elucidated although propranolol (β antagonist) delays or inhibits completely regeneration.
Regulation and limb regeneration: the effect of partial irradiation
Authors: Maden M.
Published: April 2021

The regulative ability of the regeneration blastema has been studied by the technique of partial irradiation. Longitudinal halves of fore- and hindlimbs were irradiated and the product of regeneration from the unirradiated halves characterized. Such half irradiated limbs could regulate only to a very limited extent. In the upper arms the anterior halves merely produced a few autopodial elements whereas complete limbs regenerated from the posterior halves. This striking regenerative inequality was less marked in the lower arm where the two halves each produced regenerates of two to three digits. In the hindlimb dorsal halves produced more than ventral halves and thus it was concluded that the posterior-dorsal quadrant has some special regenerative property. These results highlight the inadequacy of current models of limb regeneration and are discussed with reference to the arrangement of positional values in the limb and the question of the totipotency of blastemal cells.
The Early Development of the Interorbital Septum and the Fate of the Anterior Orbital Cartilages in Birds
Authors: D’A. Bellairs A.
Published: April 2021

The development of the interorbital septum and anterior orbital cartilages in birds has been studied with special reference to the chick embryo. In the chick the trabeculae are at first separated by a bar of intertrabecular mesenchyme which projects downwards between them to form a prominent keel. Later this mesenchyme fuses with the trabeculae and anterior orbital cartilages (preoptic roots) to form the interorbital septum. In some other Sauropsida (i.e. certain turtles and birds) the intertrabecular bar of mesenchyme is also well developed and has a keel. Although this bar is always partly blended with the trabeculae and orbital cartilages, its appearance is sufficiently distinctive to justify the use of the term intertrabecula for it. In other Sauropsida (i.e. lizards, the sparrow) the trabeculae seem to develop closer together and the intertrabecular mesenchyme is less clearly differentiated. The ventral keel is not well developed, and the use of the term intertrabecula is not indicated. The differences between this and the previous group (chick, turtles, &c.) are, however, probably of degree rather than kind. During embryonic life the olfactory nerves in the chick are temporarily enclosed in cartilaginous tunnels formed mainly by the fusion of the anterior orbital cartilages with the roof of the nasal capsule. The subsequent regression of the orbital cartilages is responsible for the exposure of the nerves in the orbits. The different relationships of the olfactory nerves in certain other birds are shown to depend on relatively slight variations of the structure of the orbitonasal region of the chondrocranium. The formation of the interorbital septum, the growth and regression of the anterior orbital cartilages and the disposition of the olfactory nerves are virtually unaffected by the experimental ablation or partial ablation of one eye at a stage before the onset of skull development. Conditions similar to those in the operated specimens were found in three chick embryos which showed naturally occurring, unilateral microphthalmia.
The Dependence of the Embryonic Inductive Action of HeLa Cells on Their Growth Media
Authors: Saxén Lauri , Toivonen Sulo
Published: April 2021

HeLa cells which had been cultured in various growth media were used as implantation material in induction experiments, the object of which was to find out to what extent the inductive capacity of the cells is dependent on the media.

HeLa cells grown in untreated (‘active’) pooled human serum proved to be strong deuterencephalic-spinocaudal inductors. The inductive capacity was the same in cells grown in different pooled sera. Heating of cells grown in active serum for 30 minutes at 56° C. did not influence their inductive capacity. By contrast, heating for 30 minutes at 65° C. completely destroyed the deuterencephalic and spinocaudal inductive effects, but subsequently the cells still induced archencephalic structures. Continuous cultivation in serum heated at 56° C. almost completely destroyed the spinocaudal inductive effect of the cells. Simultaneously, the archencephalic effect was strengthened. Cultivation under the same conditions for a short time (3 days) caused a similar, though slighter, change. When some of the cells continuously grown in heat-inactivated serum were returned for 3 days to active serum, their inductive capacity was found to be almost the same as that of cells continuously grown in active serum. Cultivation in serum heated for 30 minutes at 65°C. markedly weakened the spinocaudal inductive capacity of the cells, although the latter still grew normally. Even after cultivation for 14 days this weakening was clearly observable, and at the same time there was an increase in the number of archen-cephalic structures. After 28 days’ cultivation the cells exhibited the same inductive effect as cells continuously grown in serum inactivated at 56°C. Cultivation in serum-free Parker’s 199 solution rapidly weakened the spinocaudal inductive capacity of the cells, but the latter were not capable of growing continuously in this solution. The conclusion is drawn that, in accordance with the gradient theory previously advanced by the authors, the change in inductive capacity may be explained as a weakening of the mesodermalizing (M) principle in the cells, whilst the neuralizing (N) principle remains the same. A result of this change in the N/M balance would be that the spinocaudal action is weakened and the archencephalic effect is strengthened. At the same time the results show that the mesodermalizing action of the cells is dependent on external factors, whilst the neuralizing principle seems to be more stable. The results are compared with previous investigations on the changes in the inductive capacity of tissues caused by starvation, rapid growth, and malignancy.
Metabolism of [14C]glucose by postimplantation mouse embryos in vitro
Authors: Clough J. R. , Whittingham D. G.
Published: April 2021

Carbon dioxide and lactate production from [14C]glucose were measured for post-implantation mouse embryos aged 6 to days post coitum in static cultures with a defined medium. The rate of metabolism increased rapidly and paralleled the increase in protein content indicating a fairly uniform rate of metabolism throughout the period. At all stages studied more than 90 % of the glucose utilized was converted to lactate. Over a quarter of carbon dioxide produced was derived from the C-l position resulting in high C-l: C-6 ratios, indicating that the Pentose Phosphate Shunt is a major oxidative pathway.

The influence of various culture condition on CO2 production showed that high concentrations of glucose did not affect glucose utilization whilst high lactate concentrations had a significant inhibitory effect. Pyruvate had no discernible effect.
Pattern regulation in isolated halves and blastomeres of early Xenopus laevis
Authors: Kageura H. , Yamana K.
Published: April 2021

Xenopus embryos at the 2-cell stage were cut into right and left halves, those at the 4-cell stage into dorsal and ventral halves or individual blastomeres, and those at the 8-cell stage into lateral, animal and vegetal halves. Defect embryos, that is, 8-cell embryos from which a particular pair of blastomeres had been removed, were also prepared. These halves, blastomeres and defect embryos were cultured in 50 % Leibovitz (L-15) medium supplemented with 10 % foetal calf serum and then in 10 % Steinberg solution. Their development was determined from their macroscopic appearance when controls reached stage 26 (early tailbud stage) or later.

The only halves that could develop into normal larvae or frogs were lateral ones of 2- and 8-cell embryos. An interesting finding was that these halves of 2-cell embryos developed into only half-embryos when cultured in the above Leibovitz medium beyond the beginning of gastrulation. On the other hand, most or all the dorsal and ventral halves at the 4-cell stage and the animal and vegetal quartets at the 8-cell stage did not form normally proportioned embryos. Defect embryos lacking any two blastomeres of the animal half gave rise to nearly normal embryos, whereas those lacking two dorsal or two ventral blastomeres of the vegetal half did not.

From the present results and those of studies now in progress, it is concluded that development of blastomeres and halves from these early embryos, except lateral halves from 2- and 8-cell embryos, is not regulative as expected earlier, and that a certain combination of blastomeres is essential for complete pattern regulation.
Establishment of embryonic axes in larvae of the starfish, Asterina pectinifera
Authors: Kominami Tetsuya
Published: April 2021

In order to clarify the relationships between the first cleavage plane and the embryonic axes, early cleavage pattern of the fertilized eggs of the starfish, Asterina pectinifera was reexamined. It was ascertained that the polar bodies were formed at the site to which the germinal vesicle had closely located before the initiation of the meiotic division, and that the first cleavage plane passed near this site of polar body formation. While some of the early embryos of this starfish were observed to show various cleavage patterns during early cleavage stage, more than 70 % of the embryos developed according to, so to say, the ‘typical’ cleavage pattern.

Next, horseradish peroxidase (HRP) was injected into one of the blastomeres of the 2-cell- or 8-cell-stage embryos. The embryos were allowed to develop up to either the early gastrula or the early bipinnaria stage and stained to detect the descendants of the blastomere injected with HRP. In early gastrulae still retaining radial symmetry, the activity of HRP injected at the 2-cell stage was found only in one side of the embryo partitioned by one of the symmetrical planes. When one of the four blastomeres lying nearer to the polar bodies at the 8-cell stage was marked with HRP, its descendants constituted one quarter of the anterior part of the gastrula, and descendants of a blastomere opposite the polar bodies were found in the posterior region of the embryo. It was concluded that the animal-vegetal (AV) axis was preexisting in the fertilized egg and that the first cleavage plane contained this primary axis.

In early bipinnariae with their dorsoventral (DV) axes already established, the region of activity of the HRP injected at the 2-cell stage was still demarcated by a plane which passed through the AV axis, but the plane of the boundary had no fixed relation to the DV axis. The results indicate that the first cleavage plane does not necessarily correspond to the median plane of the starfish larva, unlike the case in sea-urchin eggs (Horstadius & Wolsky, 1936). In other words, the DV axis of the starfish embryo is not predetermined in the fertilized egg, and might be established in the course of development through cell-to-cell interactions, while the AV axis is established mainly according to the pre-existing egg polarity.
Quantitative regulation of acetylcholinesterase development in the muscle lineage cells of cleavage-arrested ascidian embryos
Authors: Whittaker J. R.
Published: April 2021

Some embryos of Ciona intestinalis which were permanently cleavage-arrested with cytochalasin B at the 1-cell, 4-cell, or 8-cell stages produced, after 12 or 16 h of development time (18 °C), a level of muscle acetylcholinesterase activity equal to that found in normal early and later larval stage embryos of the same age. Enzyme activity was measured quantitatively in single whole embryos by a colorimetric procedure using microdensitometry. Quantitative regulation of a differentiation end product indicated that the usual transcriptional and translational control mechanisms for that histospecific protein continued to operate normally in the cleavage-arrested embryos. Acetylcholinesterase expression was apparently regulated independently of the usual cell cytoplasmic volume in the muscle lineage cells and possibly also independently of the normal nuclear number in the lineage. There is an egg cytoplasmic determinant that is segregated into the muscle lineage cells during cleavage and which appears to specify the pathway of larval muscle development. Quantitative control of muscle acetylcholinesterase is possibly one of the consequences of how the agent releases genetic expression in the presumptive muscle cells. Quantitative regulation was not, however, a general functional activity of cleavage-arrested embryos. Mitochondrial cytochrome oxidase, an enzyme whose development is believed to be unaffected by cytoplasmic determinants, was not regulated quantitatively in cleavage-arrested embryos. Cytochrome oxidase activity of cleavage-arrested embryos, measured in single whole embryos by a colorimetric microdensitometry assay, increased only slightly during 16 h of development time whereas the activity in normal control embryos doubled during that time.
Development of the lateral line system in Xenopus laevis : II Cell multiplication and organ formation in the supraorbital system
Authors: Winklbauer Rudolf , Hausen Peter
Published: April 2021

Cell multiplication was studied during development of the supraorbital lateral line system in Xenopus laevis. The increase in cell number is biphasic. The first phase extends from the beginning of primordial elongation to the end of primary organ formation. Cell number increases linearly during this interval. Throughout this phase, a constant number of cells is in S phase of the cell cycle at a given time, despite a more than 10-fold increase in total cell number. After their formation, the number of the primary organs remains essentially constant. The individual primary organs are not clones of cells. Different organs grow at different rates, and become more and more heterogeneous in size. The second phase which is correlated with accessory organ formation is characterized by an elevated growth rate. This phase was not studied in detail. If developing larvae are starved, growth is normal up to completion of the first growth phase but is arrested at this point. The frequency distribution of the sizes of such growth-arrested organs approximates a binominal distribution. From its characteristics, a detailed model of cell proliferation and organ formation can be deduced: cell multiplication occurs through asymmetrically dividing stem cells, which become allocated to the forming organs at random and go through a fixed number of cell divisions.
The transition from oocyte-coded to embryo-coded glucose phosphate isomerase in the early mouse embryo
Authors: West John D. , Green J. F.
Published: April 2021

The proportions of glucose phosphate isomerase (GPI-1) allozymes produced by early (Gpi-1sa/Gpi-1sb ♀ × Gpi-1sc/Gpi-1sc ♂)F1 mouse embryos were analysed by quantitative cellulose acetate electrophoresis. Technical controls showed that this system is extremely sensitive, quantitatively reproducible and quite accurate. Genetic controls established that the Gpi-1sa/Gpi-1sb mothers were homozygous for the Gpi-1tb temporal allele, that produces relatively high GPI-1 activity in the oocyte. The oocyte-coded enzyme lasted until about days post coitum (p.c.) or shortly thereafter. The maternally derived, embryonic Gpi-1s allele was expressed no earlier than the paternally derived allele. This was first expressed between and days p.c. In this cross, most of the transition from oocyte-coded to embryo-coded GPI-1 occurred between and days p.c.
Inhibition of proteolysis in rat yolk sac as a cause of teratogenesis. Effects of leupeptin in vitro and in vivo
Authors: Freeman Stuart J. , Lloyd John B.
Published: April 2021

Conceptuses from 9·5-day pregnant rats were cultured for 48 h in heat-inactivated homologous serum to which leupeptin, a specific inhibitor of the lysosomal cysteifie-proteinases, was added for the final or the penultimate 6h.

The presence of leupeptin (25 μg/ml or above) increased the protein content of yolk sacs at harvesting to approximately twice the control value. The protein content of the embryo at harvesting was lower than that of controls.

When 125I-labelled polyvinylpyrrolidone was added to the culture serum for the final 6 h of culture, radioactivity was found in the yolk sac at harvesting, but not in the embryo. The presence of leupeptin did not affect the rate of uptake of the radiolabelled macromolecule by the yolk sac, nor facilitate its entry into the embryo.

When formaldehyde-denatured 125I-labelled bovine serum albumin was added to the culture medium for the final 6 h of culture, little radioactivity was found in the yolk sac at harvesting, and barely any was found in the embryo. Trichloroacetic acid-soluble radioactivity was found in the culture serum. The presence of leupeptin sharply increased the levels of radioactivity in the yolk sac (but not the embryo) and sharply decreased the acid-soluble radioactivity of the culture medium.

When rat serum whose proteins were labelled with [3H]leucine was used as culture medium, radioactivity was found in both yolk sac and embryo at harvesting. The presence of leupeptin increased the amount found in the yolk sac and decreased that found in the embryo.

These results are interpreted as follows. Leupeptin enters the lysosomes of the yolk sac, inhibiting their cysteine proteinases. The digestion of proteins pinocytosed by the yolk sac is consequently inhibited, resulting in the accumulation of protein by the yolk sac and a decreased flow of amino acids to the embryo.

Leupeptin (50 mg/kg), injected into pregnant rats at either 8·5 days or 9·5 days of gestation, induced congenital malformation in the offspring. It is proposed that leupeptin exerts its teratogenic action by inhibiting proteolysis in the lysosomes of the yolk sac, and so depriving the developing embryo of its supply of amino acids at a critical stage of development.
Effect of exogenous sex steroids upon the number of germ cells and the growth of foetal ovaries grafted under the kidney capsule of adult ovariectomized hamsters
Authors: Arrau J. , Roblero L. , Cury M. , González R.
Published: April 2021

The effect of estradiol E, progesterone P and testosterone propionate T upon growth and germ cell population of foetal ovaries transplanted under the kidney capsule of adult ovariectomized hamsters was examined. Foetal ovaries were obtained 15 dayspostcoitum and the host received daily subcutaneous injections of E (1 μg/day), P (5 mg/day), T (500 μ g/day) or E + P in 0·1 ml oil for 25 days beginning 5 days before grafting. One day after the last injection, the size of the ovary, the germ cell population and plasma steroid levels were assessed. The results of hormone assays indicate that daily steroid administration was able to maintain continuously elevated plasma levels of the corresponding hormone. Interconversions or steroid secretion by the graft, if any, were not reflected in the peripheral circulation. The growth of the graft was stimulated by T and inhibited by P, in comparison with E and oil-treated controls. All germ cells were at the stage of primary oocyte forming part of a primordial or growing follicle. Their absolute number was significantly increased by T and E and significantly decreased by P and E + P. The number of oocytes per mm3 of ovary was increased 80 %, 48 % and 40 % with E, T and E + P, respectively.

It is concluded that, in the hamster, exogenous sex steroids given to the host can exert specific effects upon the growth and oocyte population of a grafted foetal ovary. Whether or not the action of steroids upon the graft is a direct one and whether they influenced oogonial mitosis, the evolution of the meiotic prophase or atresia of primary oocytes remains to be determined.
The distribution of muscle fibre types in chick embryo wings transplanted to the pelvic region is normal
Authors: Laing N. G. , Lamb A. H.
Published: April 2021

Chick embryo wing buds were transplanted to the pelvic region in place of, or in addition to, the hindlimb bud prior to innervation. The wrist muscle ulnimetacarpalis dorsalis (umd) was innervated by middle-dorsal or middle-ventral motoneurons in the lumbar lateral motor column (LMC) in a rostrocaudal position which varied with the rostrocaudal position of the wing. Despite the heterotopic innervation the subsequent development of the distributions of fast and slow muscle fibres, as judged by ATPase staining, was normal in all muscles examined. The pattern of innervation in the umd, as judged by acetylcholinesterase staining also developed normally. It is probable that muscle fibre type is intrinsically, not neurogenically, determined.
Mechanical aspects of mesenchymal morphogenesis
Authors: Oster G. F. , Murray J. D. , Harris A. K.
Published: April 2021

Many embryonic cells generate substantial contractile forces as they spread and crawl. These forces mechanically deform each cell’s local environment, and the resulting distortions can alter subsequent cell movements by convection and the mechanisms of contact guidance and haptotaxis. Here we develop a model for the cumulative effects of these cell-generated forces and show how they can lead to the formation of regular large-scale patterns in Cell populations. This model leads to several predictions concerning the effects of cellular and matrix properties on the resulting patterns. We apply the model to two widely studied morphogenetic processes: (a) patterns of skin-organ primordia, especially feather germ formation, and (b) the condensation of cartilagenous skeletal rudiments in the developing vertebrate limb.
Special Problems of Experimenting in ovo on the Early Chick Embryo, and a Solution
Authors: Silver P. H. S.
Published: April 2021

A method has been described for experimenting on the early chick embryo. By its use it is possible to make an opening in the vitelline membrane large enough for the easy performance of any major operative procedure. The air space over the blastoderm is not topped up. The egg is incubated on a horizontal ttirntable, rotating around a vertical axis, at about 8 cycles per minute through an angle of about 90°, until the embryo has reached the end of the 3rd day of development. Successful results, using embryos of 4–12 somites, have been achieved in 74 per cent, of 120 major experimental procedures. The rationale of the method has been explained.
The histogenetic capacity of tissues in the caudal end of the embryonic axis of the mouse
Authors: Tam P. P. L.
Published: April 2021

The caudal end of the embryonic axis consists of the primitive streak and the tail bud. Small fragments of this caudal tissue were transplanted from mouse embryos of various developmental stages to the kidney capsule in order to test their histogenetic capacity. The variety of mature tissues obtained from these small fragments was similar to that obtained by grafting a larger caudal portion of the embryo. Initially, the grafted tissue broke up into loose masses of embryonic mesenchyme and this was later re-organized into more compact tissues and into cysts that were lined with various types of epithelia. After 14 days in the ectopic site, grafted tissues coming from embryos of the primitive-streak, the early-somite and the forelimb-bud stages differentiated into structures that has presumably originated from the three embryonic germ layers. Many of these structures were related to the caudal region of the adult body, such as the mid- and hindgut segments and urogenital derivatives. The histogenetic capacity for endodermal tissues and urogenital organs was lost when the grafted tissue consisted entirely of the tail bud of the hindlimb-bud-stage embryos. The behaviour of the caudal tissues suggested that (1) the primordia for the various parts of embryonic body were derived from a small progenitor population in the primitive streak and the tail bud, and (2) the histogenetic capacity of this population changed during development.
Corneal epithelial-specific cell surface antigen recognized by a monoclonal antibody
Authors: Langer Marian G. , Sundarraj C. V. , Sundarraj Nirmala
Published: April 2021

Monoclonal antibodies, specific against cell surface differentiation antigens of human corneal epithelial cells, were developed using epithelial cells resected from human corneas as the immunogens. One of these antibodies reacted specifically with corneal epithelial cells and not with epithelial cells of other tissues when tested by an indirect immunoperoxidase technique. Nonidet P-40 extracts of different subcellular fractions of human corneal epithelial cells were tested for their reactivity against this antibody using an enzyme-linked immunosorbent assay. The results indicated that the antigen recognized by this antibody is associated with the plasma membrane. This was further verified by immuno-electron-microscopic analysis using ferritin-conjugated anti-mouse IgG antibody. This antigen was not detectable in the corneal epithelial cells in primary cultures nor in the epithelial cells from early stages of developing cornea (12 to 18 weeks in utero) but was present in the epithelial cells in the corneas of an 8-month-old infant. Therefore, this surface-associated antigen identified in the present study is a developmentally regulated marker of human corneal epithelium.
The nature of developmental restrictions in Xenopus laevis embryos
Authors: Heasman Janet , Snape Alison , Smith J. C. , Wylie C. C.
Published: April 2021

Fate maps of the late blastula stage of the Xenopus laevis embryo indicate that the cells of the vegetal pole area are destined to become part of the endoderm germ layer (Keller, 1975; Heasman, Wylie, Hausen & Smith, 1984). By labelling single cells from this region and transplanting them into the blastocoel cavity of host embryos, we have shown that the determinative process that restricts blastomeres to this their normal fate occurs between the early blastula and early gastrula stages (Heasman et al. 1984). To progress towards an understanding of this process, we need to establish some fundamental points. In particular, the following issues are discussed here. (1) Is cell interaction required for determination to proceed? (2) What is the cellular nature of determination?

We have used the labelling and transplantation technique described previously (Heasman, Snape, Smith & Wylie, 1985; Heasman, Snape, Smith, Holwill & Wylie, 1985) to study these questions in relation to the mechanism of determination of vegetal pole cells in Xenopus laevis.
Regeneration in the anterior—posterior axis of the insect thoracic segment
Authors: French Vernon , Rowlands Tamara F.
Published: April 2021

After removal of a transverse strip of ventral thorax from the beetle, Tenebrio molitor, interaction occurred between epidermis posterior to the mesothoracic leg and that anterior to the metathoracic leg. Depending on the size and position of the excision, this interaction resulted in either the regeneration of the extirpated tissue or its replacement by an A/P reversed pattern of sclerites and supernumerary leg. By either route, local pattern continuity was restored between the normal meso- and metathoracic legs. Similarly, when a leg plus adjacent tissue was extirpated, continuity was restored by leg regeneration or by formation of an A/P reversed duplication of sclerites.

The results of these strip excisions can be understood in terms of two current models of the ventral thorax (the Boundary Model and the Polar Coordinate Model), each of which postulates a distinct compartment or region intervening between the epidermis surrounding the bases of successive legs. However, the models do not explain the large differences in the frequency of formation of the duplication/deletion pattern after excisions of different widths. The results are also compatible with a different model, involving an A-P sequence of positional values similar to that proposed for the abdominal segment. Regeneration would restore continuity within the sequence by the shortest route, forming either the midsegment (including the leg) or the intersegmental region.

The meso- and metathorax differ in the structure of the ventral sclerites and in the segmentation of the tarsus of the leg. The structures regenerated after the various excisions show that the segment border is not crossed during regeneration and indicate that an A/P compartment border running through the leg is usually also respected. There is no sign, however, of a third line of lineage restriction that would indicate a subdivision of the segment into three compartments (as proposed in the Boundary Model).
Stimulatory effects of insulin-like growth factors on DNA synthesis in the human embryonic cornea
Authors: Hyldahl Louise , Engström Wilhelm , Schofield Paul N.
Published: April 2021

10- to 12-week-old human embryonic eye globes were microdissected so that a passage was opened between the outer environment and the anterior chamber which rendered free access of tissue culture medium to the endothelial cell monolayer. The dissected eye globes were maintained in organ culture for 24 h in the continuous presence of tritiated thymidine. Cross sections were cut through the whole eye globes and subjected to autoradiographic analysis in order to estimate the mitogenic response of human embryonic corneal endothelial cells to externally supplied growth factors and hormones.

It was found that the corneal endothelial cells could be stimulated to initiate DNA synthesis by exposure to insulin-like growth factor I (IGF-I). The thymidine-labelling index doubled after IGF-I supplementation.

Northern blot analysis revealed the abundant presence of IGF-II transcripts in the posterior eye. In contrast, the anterior portion of the eye, including the cornea, contains barely detectable levels of IGF-II transcripts. IGF-I transcripts were detected in both parts of the eye at much lower concentrations than those for IGF-II. No insulin transcripts were found. These results demonstrate that mRNA for both IGF-I and IGF-II is present in the late first trimester eye. The observed stimulatory effects of IGF-I in organ culture suggest that local production of IGF-I and IGF-II may stimulate cell proliferation in vivo.
The development of XO gynogenetic mouse embryos
Authors: Mann Jeff R. , Lovell-Badge Robin H.
Published: April 2021

Diploid gynogenetic embryos, which have two sets of maternal and no paternal chromosomes, die at or soon after implantation. Since normal female embryos preferentially inactivate the paternally derived X chromosome in certain extraembryonic membranes, the inviability of diploid gynogenetic embryos might be due to difficulties in achieving an equivalent inactivation of one of their two maternally derived X chromosomes. In order to investigate this possibility, we constructed XO gynogenetic embryos by nuclear transplantation at the 1-cell stage. These XO gynogenones showed the same mortality around the time of implantation as did their XX gynogenetic counterparts. This shows that the lack of a paternally derived autosome set is sufficient to cause gynogenetic inviability at this stage. Autosomal imprinting and its possible relation to X-chromosome imprinting is discussed.
Cell proliferation is not required for the initiation of early cleft formation in mouse embryonic submandibular epithelium in vitro
Authors: Nakanishi Yasuo , Morita Toshiteru , Nogawa Hiroyuki
Published: April 2021

An X-ray irradiation method was employed to analyse the role of cell proliferation in vitro in the cleft formation of mouse embryonic submandibular epithelium at early stages. When the mid 12-day gland was exposed to 200 rad of X-rays, the growth was severely retarded. In contrast, late 12-day and early 13-day glands grew apparently in a normal fashion, as did the control gland, for up to 40 h. In either case, they formed shallow clefts within 10 h of culture. With 1000 rad irradiation, the mid 12-day gland did not grow at all, but formed clefts within 20 h of culture followed by a rapid degeneration. Under, the same conditions, the growth of the late 12-day gland, which was at the stage just before branching, was retarded until 10 h of culture, followed by a slight increase in epithelial size, but cleft formation was also observed within 6-10 h, as in the control gland. When exposed to a dose of 1000 rad of X-rays, the early 13-day and the late 12-day glands exhibited similar radiosensitivity; the initial narrow clefts in the epithelium deepened and new clefts began to form within 6-10 h of culture. [3H]thymidine incorporation studies revealed that a dose of 1000 rad reduced DNA synthesis of mid and late 12-day glands by 72 and 65 %, respectively. Histological examination of X-irradiated late 12-day gland showed that mitotic figures were rarely seen in the epithelium at 6 h of culture. Aphidicolin, a specific inhibitor of DNA synthesis, could not halt the cleft formation of the late 12-day gland. In this experiment 89 % of DNA synthesis was inhibited. Treatment of an X-ray irradiated late 12-day gland with aphidicolin blocked 92 % of the DNA synthesis, but did not prevent cleft formation taking place. These results indicate that neither cell division nor DNA synthesis, is required for the initiation process of the cleft formation of the mouse embryonic submandibular epithelium at early morphogenetic stages in vitro.
A monoclonal antibody detects a difference in the cellular composition of developing and regenerating limbs of newts
Authors: Fekete Donna M. , Brockes Jeremy P.
Published: April 2021

We have previously described a monoclonal antibody (called 22/18) that reacts with the early blastemal cells of the regenerating limb of the newt (Notophthal-mus viridescens). In embryos of two newt species the antibody reacts with the epidermis, glial cells in the neural tube, the lens and cells in a restricted region of the aorta. In the developing limb bud less than 1 % of the mesenchymal cells were reactive with 22/18, although most cells stained brightly with an antibody to another cytoskeletal component. When limbs were amputated prior to the arrival of nerves (axons and Schwann cells) at the amputation plane there was no extra reactivity with 22/18 as compared to the contra-lateral unamputated control, even though the amputated buds regenerated satisfactorily. Limbs amputated after nerves are present at the plane of amputation respond by forming a 22/ 18-positive blastema. The appearance of the 22/18 response is a function of the stage of limb development as shown by amputation of forelimb and hindlimb buds at a larval stage where development of the forelimb is greatly advanced relative to the hindlimb. The distribution of the 22/18-positive cells in larval blastemas showed them to be closely associated with axons as detected by double staining with an antiserum to a neurofilament subunit. The clear antigenic difference between development and regeneration may be related to the relationship between embryonic regulation and epimorphic regeneration, and also to the acquisition of nerve-dependent proliferation of blastemal cells.