bluuebunny/crossref_metadata_2025 huggingface dataset:
An analysis of the spatial distribution of ciliary units in a ciliate, Euplotes minuta
Authors: Frankel Joseph
Published: April 2021

Six to eleven longitudinal ciliary rows are arrayed over the dorsal surface of the ciliate Euplotes minuta. Forty-two to 129 ciliary units are distributed among these rows. The number of rows depends on genotype, clonal age, and vegetative ancestry, while the total number of units is controlled partly by the number of rows and also by the separate action of genetic and environmental factors. The pattern of distribution of units among different rows of non-dividing cells can be analysed on the basis of the percentage of the total unit complement of the cell that is found in each individual row. If the assumption is made that ciliary rows are uniformly spaced over a dorsal field whose width is independent of the number of rows, then it can be shown that units are distributed among rows according to a relatively invariant spatial pattern. The form of this pattern remains the same in the face of variation in the absolute number of rows and of units. Prior to cell division new units develop anterior and posterior to old units situated within the equatorial zone of each row. About one-half of the original units are included within this zone. The cell fission line develops within this zone such that the total number of units passed to the anterior and posterior division products are about equal. The pattern according to which units of different zones (proliferating and non-proliferating) are distributed among different rows has been mapped in cells that have completed the process of proliferation of units but have not yet completed cell division. The results of this mapping show that the pattern of distribution of units in the equatorial zone at the conclusion of proliferation is not the same as the overall pattern in non-dividing cells. Further analysis indicates that the geometry of proliferation can be most simply represented as a result of two superimposed processes, one of which is the recruitment of old units into the zone of proliferation, while the other is the intensity of proliferation, i.e. the number of new units formed adjacent to each old unit. Both recruitment and intensity have constant values in the central region of the dorsal field, while recruitment is higher and intensity lower near both margins. The recruitment and intensity distributions are mutually nearly reciprocal, with slight asymmetries that formally account for the more dramatic asymmetry of the pattern of non-dividing cells. A dualistic hypothesis is formulated for the control of the formation of new ciliary units within ciliary rows. The position of each new unit is largely controlled locally in relation to pre-existing units, while the decision of whether or not new units will develop at all, and how many will be formed, depends on superimposed positional systems operating within the context of the entire dorsal surface.
On the origin of haemopoietic stem cells in the avian embryo: an experimental approach
Authors: Dieterlen-Lievre Françoise
Published: April 2021

It is currently accepted that stem cells of the definitive blood cell lines originate from the yolk-sac blood islands. Experiments were devised to examine the validity of this theory in the avian embryo. These involved grafting two-day-old quail embryos on to chick yolk-sacs of comparable developmental stages, i.e. before or shortly after the establishment of vascularization. The conclusions of the experiments are based on the possibility of distinguishing chick cell nuclei from those of the quail.

In the developing haemopoietic organs (spleen and thymus) of quail embryos grafted on to the chick and subsequently incubated for 6 – 11 days, all cells, whether belonging to the granulopoietic, erythropoietic or lymphopoietic series, are of quail type. Thus these organs have not been colonized by chick stem cells.

On the other hand, coelomic graft experiments show that the development of these organs is indeed dependent on an extrinsic colonization by haemopoietic cells; quail spleen or thymus rudiment, developing in the coelom of a chick, is populated by chick cells. Thus no incompatibility which would prevent heterospecific colonization exists in this system.

It is concluded that haemopoietic stem cells of the definitive blood cell series originate from some source other than the yolk-sac, and that this source must be intra-embryonic.
Development of parthenogenetic and fertilized mouse embryos in the uterus and in extra-uterine sites
Authors: Iles S. A. , Mcburney M. W. , Bramwell S. R. , Deussen Z. A. , Graham C. F.
Published: April 2021

Mouse eggs were activated with hyaluronidase in vitro and subsequently transferred to the oviduct. In the female reproductive tract they formed morulae and blastocysts which died soon after implantation. Haploid blastocysts were transferred beneath the kidney capsule and here some formed disorganized egg-cylinder structures in a week. Morulae and blastocysts from haploid and diploid parthenogenones were also transferred beneath the testis capsule. Two to four months later the growths which had formed were sectioned. They contained neural tissue, pigment, keratinized epithelium, glandular epithelium, ciliated epithelium, cartilage, bone, muscle, adipose tissue, and haemopoietic tissue. The range of cell types was similar to that produced by fertilized control blastocysts except that the parthenogenones did not form identifiable yolk-sac carcinoma or embryonal carcinoma cells.

The growths from haploid and diploid parthenogenones in the testis were stained with Feulgen and their DNA content measured. Growths from diploid embryos contained the normal diploid amount of DNA while growths from haploid embryos contained less than this amount. Cell cultures were prepared from the growths. The cells which were investigated contained no Y chromosome, suggesting that they were derived from the embryonic cells rather than the cells of the male host. These cells contained a near diploid chromosome number, although some of them were originally derived from haploid embryos.
Morphogenèse de l’autopode chez l’embryon de poulet
Authors: Pautou Marie-Paule
Published: April 2021

Observations were made on chick embryo feet between 6 and days of incubation in order to (a) give a precise description of programmed cell death in the interdigital membranes; (b) correlate the evolution of interdigital necrosis with the differentiation of the cartilaginous phalangeal skeleton; (c) measure the relative growth rates of digits and interdigits.

The programme of interdigital cell death proceeds in three phases which comprise the appearance, the extension and the disappearance of necrotic areas. Fourteen distinct stages are described.

The evolution of programmed cell death can be strictly correlated to the chondrogenesis of successive phalanges, in the sense that each stage of necrosis (except two of them) differs from the preceding one by the differentiation of an additional phalanx.

Shaping of the foot results from differential growth rates and proceeds in three phases, the second of which is characterized, between days 8 and 10 of incubation, by the actual shortening (decrease of absolute length) of the interdigital membranes.

These observations are compared to those that were previously made on other avian and mammalian species and the morphogenetic role of programmed cell death is discussed in the light of that comparison.
The development of the notochord in the chick embryo, studied by scanning and transmission electron microscopy
Authors: Bancroft Mary , Bellairs Ruth
Published: April 2021

The notochord of the chick embryo between stages 5 and 23 inclusive has been studied by scanning electron microscopy, supplemented by transmission electron microscopy. Three main phases of development are described, and these have been designated: bilaminar; rod-like, unvacuolated; rod-like and vacuolated. The change in shape of the organ from bilaminar to rod-like is accompanied by changes in the shape, orientation and position of the cells, an increase in the complexity of the cell contacts, and the laying down of a basal lamina. The change from the unvacuolated to the vacuolated phase is accompanied by increasing complexity within the cytoplasm. Most of the vacuoles are intracellular and appear empty though some contain a granular material. The notochordal sheath appears to be secreted by the notochordal cells and fine fibrillar material has been seen in the intercellular spaces. By stage 23, most of the notochordal cells have become so highly vacuolated that the cytoplasm has become closely packed around the nucleus.
Foetal and placental ornithine decarboxylase activity in the rat - effect of maternal undernutrition
Authors: Williams John P. G. , Mcanulty Peter A.
Published: April 2021

The activity of the enzyme ornithine decarboxylase and the accumulation of nucleic acids were examined in the rat foetus and placenta during normal development and during maternal undernutrition.

Maternal undernutrition resulted in a reduced rate of increase in weight of both the foetus and placenta towards the end of gestation. In the placenta the failure to increase in weight was accompanied by a failure of DNA to increase. In the foetus the amount of DNA failed to increase over a short period and then made a compensatory response to return to a normal amount by the end of gestation. Undernutrition failed to affect RNA in either the foetus or placenta. These results differ from those obtained during maternal protein deficiency.

The activity of foetal and placental ornithine decarboxylase was normal during much of gestation in the undernourished group. However, at the same time as the compensatory increase in foetal DNA, there was a marked increase in enzyme activity in both tissues. It is suggested that a single compensatory stimulus is responsible for the changes in both ornithine decarboxylase and DNA.
Comparison of growthin vitroandin vivoof post-implantation rat embryos
Authors: New D. A. T. , Coppola P. T. , Cockroft D. L.
Published: April 2021

Rat embryos explanted at early head-fold stage and grown in vitro by improved culture methods were compared with littermates in vivo. Very similar rates of growth and differentiation were obtained over a period of 48 h, while the embryos developed to around the 25-somite stage.
Investigation of inner cell mass determination by aggregation of isolated rat inner cell masses with mouse morulae
Authors: Rossant J.
Published: April 2021

Inner cell masses (ICMs) dissected from -day rat blastocysts were aggregated with -day mouse morulae. Successful aggregates formed blastocysts in vitro and morphologically normal -day conceptuses in the mouse uterus. Immunofluorescent analysis of these conceptuses revealed that rat cells were only present in the embryonic ectoderm and endoderm and never in the trophectoderm derivatives, although rat trophoblast did develop in the mouse uterus in various control experiments. The single-cell resolution of this technique extends the results obtained from aggregating mouse ICMs with mouse morulae and provides strong evidence that ICM cells, although not overtly differentiated, are determined by the blastocyst stage.
Incorporation of tritiated cytochalasin B into ectodermal explants of the amphibian gastrula
Authors: Perry M. M. , Selman G. G. , Jacob J.
Published: April 2021

Ectodermal explants from gastrulae of Trituras alpestris were exposed to tritiated cytochalasin B (5 and 10 μg/ml) for . The flat explants failed to heal into compact spheres and the component cells gradually rounded up. Radioactivity in the fixed and sectioned material was analysed by light and electron microscopic autoradiography. Silver grains were found predominantly over the yolk platelets, but were also scattered over other cellular components. Areas containing pigment granules or the feltwork material, present in the apices of dissociating cells of the superficial layer, exhibited higher activity than areas containing mitochondria or cytoplasmic matrix. Lipid droplets and nuclei showed comparatively little activity. The results are discussed in relation to previous findings on the uptake of tritiated cytochalasin D by cell fractions.
Postimplantation development of blastomeres isolated from 4- and 8-cell mouse eggs
Authors: Rossant J.
Published: April 2021

Blastomeres isolated from 4- and 8-cell mouse eggs were inserted into empty zonae and transferred to the oviduct. The products of both types of blastomere were capable of inducing decidual formation. One implant produced by an isolated blastomere from a 4-cell egg contained a small, retarded embryo at days but most decidua from blastomeres of either 4- or 8-cell eggs contained only a few trophoblast giant cells. It is suggested that this lack of totipotency is due to insufficient cells being present at cavitation rather than restriction in developmental potential.
Polarity and gradients in lepidopteran wing epidermis: II. The differential adhesiveness model: gradient of a non-diffusible cell surface parameter
Authors: Nardi James B. , Kafatos Fotis C.
Published: April 2021

For explaining the Manduca wing gradient (Nardi & Kafatos, 1976) a model which postulates a proximo-distal gradient in cellular adhesiveness is considered. The model is based on Steinberg’s (1963) differential adhesiveness hypothesis. Rosette formation in certain transposed and/or reoriented grafts can be adequately explained by this model. Several predictions, formulated by using the concept of surface free energy as a thermodynamic measure of adhesiveness, have been tested and proven correct. (1) Transposed grafts tend to assume circular forms, which are configurations of minimum free energy. (2) Because of the pressure difference expected across the interface of two cell populations with different surface free energies, cell densities increase in both distally and proximally transposed grafts. As a corollary to this rule, final size of a graft is a function of its distance from the original position. (3) Histological sections of host-graft boundaries suggest minimal cell contact at the interface. In proximal grafts placed in distal regions, cell density is far lower near the host-graft interface, as compared to the high interior density; the peripheries of distal grafts do not show this effect. (4) Juxtaposition of three different wing regions in all possible arrangements yields the expected two-dimensional configurations. (5) Differences in adhesiveness can be demonstrated by allowing two different wing grafts to interact in an essentially neutral environment (i.e. at a leg or antenna site). As the distance between two given graft regions increases, the extent of their final contact decreases.

When applied to other insect systems, the model not only offers an alternative interpretation for results currently explained by diffusible substance models, but also accounts for certain features that were unexplained by other models.
Injected nuclei in frog oocytes: fate, enlargement, and chromatin dispersal
Authors: Gurdon J. B.
Published: April 2021

A method is described by which nuclei associated with some cytoplasm can be rapidly prepared from a suspension of cells. The method involves the use of lysolecithin and bovine serum albumin.

Oocytes of Xenopus laevis were injected with about 200 nuclei prepared from human HeLa cells by this method. Nuclei were deposited in oocyte cytoplasm, in the oocyte nucleus, or in the dispersed contents of a ruptured oocyte nucleus.

Injected HeLa nuclei enlarge up to several hundred times in volume in the course of a few days. Their enlargement is associated with chromatin dispersion, increased binding of an acidic dye, and with the reduction in size, and eventual disappearance, of nucleoli. The amount of HeLa nucleus enlargement is much greater when the oocyte nucleus is ruptured. The fate of injected nuclei was followed by the use of HeLa nuclei whose DNA had been previously labelled with [3 H]thymidine. Labelled DNA does not pass from injected HeLa nuclei into the oocyte nucleus. Injected nuclei appear not to fuse with each other or with the oocyte nucleus.

Nuclei prepared by the above method look morphologically healthy in oocytes cultured in vitro for up to one month after nuclear injection. Nuclei prepared by other methods, such as those involving the use of detergents, undergo deterioration within a few days after injection into oocytes.
Patterns of lactic dehydrogenase isozymes in mouse embryos over the implantation periodin vivoandin vitro
Authors: Monk Marilyn , Ansell John
Published: April 2021

Following blastocyst implantation, or outgrowth in vitro, the LDH isozyme pattern changes from that of the maternally inherited B subunit isozyme form (LDH-1) to a pattern dominated by A subunits (Auerbach & Brinster, 1967, 1968). In preimplantation embryos we have also observed additional isozyme bands, as yet unidentified. An analysis of the pattern of newly synthesized LDH isozymes and specific activity of LDH in different regions of early post implantation embryos suggests that there is a sequential activation of A and B subunits, and that activity first appears in ICM-(inner cell mass) derived tissues and then in trophoblast-derived tissues. In vitro, in the absence of ICM cells, the transition of LDH-isozyme pattern does not occur in outgrowing trophoblast giant cells. This suggests a possible inductive interaction between ICM and trophoblast.
Determination of anteroposterior polarity in the axolotl forelimb by an interaction between limb and flank rudiments
Authors: Slack J. M. W.
Published: April 2021

It is shown that the mesoderm in the prospective forelimb-bud of the axolotl embryo is thickened and divided into somatic and splanchnic layers, while that of the flank is thinner and undivided. The first sign of the limb-bud itself appears at stage 38. A whole, a half or a third of a limb rudiment can develop into a normal or reduplicated limb when transplanted to the flank. An anterior half of a limb rudiment fails to develop when transplanted to the head but will do so if accompanied by a small piece of flank tissue. Small pieces of tissue from a wide area of the flank will cause reduplication of the fore-limb if grafted to the anterior margin of the rudiment. It is shown that the whole of the reduplication is formed from host tissue and has the morphological character of the host. Reduplications have posterior structures arranged symmetrically on both sides of the midline. Both muscles and cartilages are duplicated. It is suggested that the same interaction between prospective flank and limb is responsible for the capacity for growth on the head, the induction of reduplications and the formation of the anteroposterior pattern of the limb in normal development. A simple rule is proposed which explains the occurrence of reduplications in classical work on the amphibian limb.
On the Embryology of the Isopod Irona1
Authors: Nair S. Gopalakrishnan
Published: April 2021

The structure of the egg is described. Segmentation of the egg is followed from the eight-celled stage up to the formation of the blastoderm. A migration of blastomeres from one pole of the egg towards the opposite has been observed and in the course of this migration a circle of 10-11 cells moves in front of the others. Gastrulation takes place by immigration. A V-shaped mesodermal headband is differentiated which gives rise to the rudiments of the naupliar appendages after gastrulation is completed. The entire post-naupliar region of the body is formed by the activity of ectodermal and mesodermal teloblasts. No caudal furrow is formed. The gut is ectodermal, formed by the union of the stomodoeum and a long proctodoeum. An ectodermal dorsal organ forms in early development and persists throughout embryonic life. The pre-antennulary mesodermal strands become attached to this organ. The origin, development, and derivatives of the pre-antennulary mesodermal somites are described. The origin of the liver is traced from the naupliar mesoderm. The probability that the liver plays an important part in yolk absorption is discussed. The development of the trunk mesoderm and an early grouping of cells into segmental and intersegmental regions are described. The formation of the heart, pericardium, and dorsal aorta is described.
The Selective Transport of Antibodies from the Yolk Sac to the Circulation of the Chick
Authors: Brierley Joan , Hemmings W. A.
Published: April 2021

The yolk titre of eggs laid by hens actively immune to Salmonella pullorum is directly related to the serum titre, the concentration quotient being approximately 1/8. Fowl sera immune to S. pullorum or Brucella abortus when injected into the yolk-sac early in incubation give rise to circulating titres in the chick at hatching. A technique of injection into the yolk-sac after hatching is described. Immune fowl serum so injected gives rise to circulating titres. Immune rabbit, cow, and horse sera so injected do not give rise to circulating titres. Immune pigeon serum gives rise to titres at lower concentration quotient than fowl. It is concluded that the yolk-sac splanchnopleur is selective. Fowl antibody fed by mouth after hatching does not give rise to circulating titres.
Closure of the Secondary Palate in Three Strains of Mice
Authors: Walker B. E. , Fraser F. C.
Published: April 2021

AT the time when Peter reviewed the subject of secondary mammalian palate embryology (Peter, 1924), it had been established that the secondary palate is derived from two shelves of tissue, which originate in the dorsolateral wall of the oral cavity and grow downward toward the lower jaw, passing lateral to the tongue. The shelves subsequently come to lie in the transverse plane dorsal to the tongue, where they fuse with the nasal septum and with each other, thus forming the roof of the mouth. The problem in this sequence is how the shelves manage to reach a position dorsal to the tongue after having had the tongue tightly wedged between them. Various mechanisms postulated to explain this change of position were reviewed by Lazzaro in 1940. The theories fell into three categories: (1) external forces such as muscular pressure by the tongue, (2) growth changes involving regression of the ventral portion and an outgrowth in the horizontal plane; and (3) a rapid rotation of the shelves due to some intrinsic force. Lazzaro considered the evidence to be in favour of rapid movement, and cited the cases of embryos with one shelf vertical and the other shelf horizontal as examples of a rapid transitional stage in shelf rotation. He considered his own work to indicate a swelling in the shelves due to a considerable increase of intercellular substance in the embryo’s connective tissue. The result was visualized as a type of erection which would cause the shelves to rise when the obstacle of the tongue was removed. Lazzaro considered it universally recognized that the release of the tongue took place before anything else, even if the mechanism of release was ‘slightly obscure’. The mechanisms suggested were: (1) a lowering of the mandible and tongue, (2) a forward displacement of the tongue, (3) a lifting of the roof of the oral cavity, (4) changes in form of the tongue due to muscular development, and (5) muscular movements of the tongue.
Amino Acids in Developing Tissues of Xenopus laevis
Authors: Deuchar E. M.
Published: April 2021

Free amino acids in embryos and larvae of Xenopus laevis have been studied chromatographically. Quantitative measurements have been made on eight amino acids, and their concentrations have been compared between different regions of the embryo and between different tissues of the larva. Extracts of whole embryos showed higher concentrations of free aspartic acid and glutamic acid in the morula than in the early gastrula; significantly more leucine in the late gastrula than in the early gastrula, and less glutamine in the neurula than in the early tailbud. A number of free amino acids were more highly concentrated in the dorsal lip than in other parts of the early gastrula. Differences were also apparent between dorsal and ventral halves of the neurula, early tailbud stage, and hatched larva. In the early tailbud stage there was more glutamine in the head than in other regions and a higher percentage of glycine in the trunk. The main features of the free amino-acid concentrations in larval brain, eyes, somites, heart, liver, and skin are described and compared. In some features the free amino-acid concentrations in embryonic tissues resemble those of the larval tissues that derive from them in development. The evidence for special functions of certain amino acids in morphogenesis and in the synthesis of specific proteins is discussed.
Changes in the properties of the developing trophoblast of preimplantation mouse embryos as revealed by aggregation studies
Authors: Burgoyne Paul S. , Ducibella Thomas
Published: April 2021

Mouse embryos (8-cell to early blastocyst) were denuded with pronase, and apposed in pairs which represented a wide range of stage combinations. These pairs either formed aggregates which differentiated into double-sized blastocysts, or they failed to aggregate. The 8-16-cell stages would not envelop late morulae/early blastocysts to form layered aggregates. This must mean that as the embryo differentiates into a blastocyst, the outer surface of the trophoblast loses its capacity for supporting cell spreading. The aggregation data also demonstrate that embryos almost completely lose their potential for aggregation at a very discrete stage in development -namely, between 8 and 9 h before blastocoel formation. It is argued that this is the stage at which the zonular tight junctional seal is completed, and that it is this physical barrier which prevents aggregation.

It has been argued previously that the zonular tight junctional seal allows the creation of the special microenvironment which is necessary for the determination of the inner cells as inner cell mass. The completion of this seal 8-9 h before it is required for the formation of a blastocoel would provide a suitable time period for this cell determination to occur.

The results obtained also relate to the technique of chimera production. Since the aim of this technique is to generate mice with mixed cell populations, it is important that the blastocyst formed following aggregation should have both cell lines present in the inner cell mass. This can best be assured by using relatively late morula stages (75 h post-HCG injection) since these will have already segregated their inner cells, but the incomplete seal will still allow aggregation to take place.
Cell growth and differentiation of murine extra-embryonic fetal and adult hematopoietic tissues in diffusion chamber cultures
Authors: Weinberg Sheila R. , Chovaniec Margaret E. , Stohlman Frederick
Published: April 2021

Studies were conducted with diffusion chambers (DC) filled with cell suspensions from different CFr murine hematopoietic tissues: adult peripheral blood; adult tibial marrow; day 17·5 of gestation fetal liver, spleen and thymus; day 14·5 of gestation fetal liver; day 10-5 of gestation yolk sac. After an initial decrease in DC cell numbers on day 2 of culture, growth of each cell group continued, but, at different rates. ATM had the highest growth ratio and FT-D17·52 had the lowest. The growth rates for APB and FL-D17·5 were similar. FS-D17·5 and FL-D14·5 cultures did not recover from the day 2 values (i.e. FL-D14-5 DC values on day 13–14 of culture were half that recorded on day 2). The YS-D10·5 DC cell numbers continued to increase throughout the 14 days of study. The profile of cellular elements from the DCs did not reflect the original cell suspensions. The predominant cell type recovered from peripheral blood cultured for 14 days was the macrophage. By day 10–14 of culture, the populations of cells harvested from the fetal tissue DC groups were similar to that of tibial marrow. Both proliferative and mature granulocytes, and macrophages were the predominant cell types. The yolk-sac pattern of cytodifferentiation recorded on day 7—14 was unlike that of the other groups. These DC cultures were comprised of mainly macrophages and plasma cells.
Nuclear transplantation from intestinal epithelial cells of early and lateXenopus laevistadpoles
Authors: Marshall J. A. , Dixon K. E.
Published: April 2021

The aim of these experiments was to test whether the developmental potential of nuclei from intestinal epithelial cells of Xenopus laevis tadpoles declined during the life of the functional larval gut. The results of transplantation of nuclei from three different stages of development were compared: stages 46-48, when feeding begins and while yolk is still present but before the formation of the typhlosole; stage 57, just prior to the onset of metamorphic reorganization; and stage 54, an intermediate stage. The results showed that there was no change in developmental potential of these nuclei during the life of the larval gut, thereby disproving the hypothesis that nuclear transplants from intestinal epithelial cells of early tadpoles of X. laevis will support extensive development because the cells are not fully functional. However, nuclei from the intestinal epithelial cells were less able to support development than blastula nuclei. It was concluded therefore, that the developmental potential of the gut nuclei is restricted relative to that of the blastula nuclei, but that these restrictions are reversed in a small proportion of cases.
The blastomere pattern in echinoderms: cleavages one to four
Authors: Prothero John W. , Tamarin Arnold
Published: April 2021

The results of a longitudinal study of the blastomere pattern in six embryos during the first four cleavages are reported. At each cleavage stage optical sections through an embryo, taken at vertical intervals of 5 or 10 μm, were recorded on 35 mm film: digitization of the blastomere contours and computer analysis allow calculation of the center, radius, surface area and volume of each blastomere.

The subjective impression of exquisite regularity seen in normal echinoderm blastulae acquires a quantitative dimension from the present study. For example, the individual angles formed by the various quartets of blastomeres depart from right angles by at most a few degrees. The egg volume was found to be conserved up to the fourth cleavage. At the 16-cell stage, unlike the earlier stages, the blastomere positions cannot be ascribed solely to the position and orientation of the respective cleavage planes. Finally, a few features of a formal model of these early cleavages are sketched.
Cell disposition and adhesiveness in the developing chick neural retina
Authors: Jones G. E.
Published: April 2021

The adhesive properties of neural retinal cells located in the ventral and dorsal hemispheres of chick embryonic eyes were investigated. Cell adhesion was monitored using the collision efficiency method; this technique provides a system in which it is possible to identify any preferential adhesions that may occur between cells. In this study no adhesive specificity was detected between cells of the dorsal and ventral retina. This evidence would not support theories which invoke preferential cell adhesion as an explanation of the ordered projection of the neural retina onto the optic tectum during development.
Fusion of dissociated fish embryonic cells
Authors: Mizukami Setsuro , Satoh Noriyuki
Published: April 2021

The induction of a frequent fusion in dissociated fish embryonic cells is reported. Fusion was induced during mechanical isolation of blastomeres in normal saline solution or Ca2+-free saline solution by quickly bringing about physical contact between cells within about 1·5 min of dissociation. Fused blastomeres were obtained in about 18% yield from early morula cells, in about 68% yield from early blastula cells and in about 5% yield from early gastrula cells.
Alkaline phosphatase activity in the preimplantation mouse embryo
Authors: Johnson Lincoln V. , Calarco Patricia G. , Siebert Margaret L.
Published: April 2021

Alkaline phosphatase (AP) activity has been assayed in frozen sections of preimplantation mouse embryos by an azo-dye cytochemical method. The results indicate that during preimplantation mouse development AP activity is first expressed between the 8- and 16-cell stages and develops in all cells by the late morula stage. During blastocyst formation AP activity is lost or greatly reduced in trophoblast cells while activity is maintained in the inner cell mass.
The development of functional innervation in the chick wing-bud following truncations and deletions of the proximal-distal axis
Authors: Stirling R. Victoria , Summerbell Dennis
Published: April 2021

Sections of the proximal-distal axis were removed so as to produce wings lacking entire skeletal levels. The innervation of the resulting limb from the appropriate spinal nerves was tested by electrophysiological recording, gross dissection and serial sections. The nerves form repeatable and ordered patterns in the modified limbs which can be readily related to the normal pattern. In general the segmental nerves only innervate their appropriate territory irrespective of its location; the route followed by the nerves is characteristic for the skeletal level they traverse. If a target is missing then so is the normal nerve branch to that region.
Aspects ultrastructuraux de 1’interaction uretère-mesenchyme, au cours de l’induction néphrogène, chez les amphibiens
Authors: Gipouloux J.-D. , Delbos M.
Published: April 2021

Ultrastructural features of ureter-mesenchyme interaction, during nephrogenic induction in Amphibia

Transmission electron microscopy was used to study the interface between the ureter and the mesonephric blastema. When the blastema is induced in a functional organ, numerous pseudopodial protrusions of the ureter and of the mesonephric cells lead to a close apposition between the two structures. The presence of squamous material, perhaps of a mucopoly-saccharidic nature, with a network of collagen fibres is always found on this interface. These particular processes seem to play a role as a morphological basis for the phenomenon of induction. The importance of the extracellular matrix is discussed. Neither the occurrence of zones of close contact, reported by several authors, in other species, nor the fusion of membranes has ever been observed, in Amphibia.
Uridine and guanosine incorporation by the mouse one-cell embryo
Authors: Young R. J. , Sweeney K. , Bedford J. M.
Published: April 2021

The activity of the embryonic genome prior to the first cleavage has been assessed by studying the uptake of [3H]uridine, its phosphorylation and incorporation into RNA by mouse one-cell embryos. One-cell embryos incorporated [3H]uridine linearly into cold trichloracetic acid (TCA) insoluble material at a low level 1-9 h post fertilization. The incorporation of [3H]guanosine was also low but followed a biphasic curve which had a steeper slope at 1-3 h than during the period 4-9 h post fertilization. Unfertilized mouse ova incorporated very little [3H]uridine or [3H]guanosine into TCA insoluble material, and much of this was RNase insensitive. Dimethyl sulfoxide (DMSO) enhanced the uptake of [3H]thymidine and its incorporation into pronuclear DNA by one-cell embryos, but had no effect on the incorporation of [3H]uridine by them, or of [3H]uridine and [3H]guanosine by unfertilized ova. The uptake and incorporation of [3H]guanosine by one-cell embryos were enhanced by DSMO, but only during the period 1-3 h post fertilization.

Sugar derivatives of UDP, and UMP, UDP, UTP, CMP, CDP and CTP have been identified in the soluble fraction obtained from mouse one-cell embryos incubated with [3H]uridine 1-3 h post fertilization. Very little of the [3H]uridine taken up by the embryos is present as [3H]UTP, or [3H]CTP; most is found as [3H]UMP or [3H]UDP or as the sugar derivatives. Alkaline or ribonuclease (A, T1 and T2)hydrolysis of the 3H-labeled ethanol insoluble material precipitated from the lysate of one-cell embryos incubated with [3H]uridine 1-3 h post fertilization liberated radioactive cytidine and uridine-3’-phosphates. This demon strates that [3H]uridine is incorporated into an internal position in RNA and suggests that RNA synthesis does occur in the one-cell embryo 1-3 h post fertilization. Since pronuclei of one-cell embryos incubated with [3H]uridine were not labeled it appears, however, that the RNA synthesized at the one-cell stage is not a product of the embryonic genome.
The diencephalic course of regenerating retinotectal fibres in Xenopus tadpoles
Authors: Gaze R. M. , Grant P.
Published: April 2021

The normal retinotectal path in the diencephalon of Xenopus tadpoles is widely distributed in the form of a wedge of fibres extending from the central grey to the outer margin of the diencephalon. Regenerating optic nerve fibres were shown, by silver-staining and proline autoradiography, to follow an abnormal path up the extreme lateral edge of the diencephalon. Study of tadpoles at various stages of development, and of optic nerves allowed to regenerate for various periods, indicates that all new incoming optic fibres pass up the lateral edge of the diencephalon. The inner/outer order of the fibres in the normal diencephalon thus reflects the radial distribution of the retinal cells of origin.
Morphogenesis by dissociated immature rat testicular cells in primary culture
Authors: Davis John C.
Published: April 2021

Dissociated cells from immature (15-day) rat testes maintained in primary culture were shown to undergo morphogenesis. Dissociated cells (1–4 ×106) were cultured in 2 ml medium NCTC-135 containing 10% rat serum at 32·5 °C under an air: CO2 atmosphere (95%:5%). During the initial culture period (1–3 days) the dissociated cells attached to the culture dish and formed a monolayer. After 4–5 days of culture, aggregates of cells formed at discrete foci within the monolayer; these structures averaged 50 μ m in diameter and numbered 3–4 × 103/dish. Within 5–6 days of culture some of these aggregates (2–3 × 102) released their contact with the substratum. Histological examination of released aggregates indicated a more regular, tissue-like organization with increasing time in culture. Aggregates at earlier time periods (4–5 days) exhibited concentric rings of cell while by day 6 some aggregates exhibited a vesicular appearance with a single layer of columnar epithelium surrounding a fluid-filled lumen. The type of structure formed varied with plating density; at densities less than 2 × 10G/dish the structures were spheroid while at greater densities tubes were formed. Time lapse observations indicated that spheres formed by movements of cells into an aggregating center while tubes formed by a rolling from the edge of the monolayer. The cells comprising the vesicle epithelium appeared to be predominantly one cell type as determined by light microscopy. These results therefore indicate that dissociated testicular cells have the ability to reform tissue-like associations in culture.
Cinemato graphical study of cell migration in the opened gastrula of Ambystoma mexicanum
Authors: Kubota H. Y. , Durston A. J.
Published: April 2021

The migration of inner marginal cells was studied in the Ambystoma gastrula, using scanning electron micrography and time-lapse cinemicrography.

Scanning electron micrographs of gastrulae which were fixed while intact revealed that the migrating cells have flattened lamellipodia at their anterior end and a rounded cell body, which can sometimes be seen to be attached to a neighbouring cell by a slender posterior process. Films of opened gastrulae showed actively moving cells, with the same features described above. Details of their movements are reported and discussed in relation to the mechanism of gastrulation.
Cell culture of individual Drosophila embryos: I. Development of wild-type cultures
Authors: Cross David P. , Sang James H.
Published: April 2021

A new procedure is described for the preparation of in vitro cell cultures from individual early gastrulae of Drosophila melanogaster. In these cultures several identifiable cell types differentiate within 24 h (nerve, muscle, fat-body, haemocyte and chitin-secreting): their initial appearance and continuing development over a period of weeks is described. It is proposed that this technique may be used to analyse abnormalities of cellular development in embryonic lethal mutants. Culture in vitro of cells from lethal embryos is seen to have two broad roles: (1) to test the developmental capacity of individual cell types in a situation where they are relatively free from possible deleterious interactions with other cell types and are liberated from the system of the dying embryo, and (2) through the preparation of mixed cultures from normal and mutant embryos, to determine the influence of the presence of wild-type cells on observed abnormalities of a particular cell type.
Catch-up growth in the rat skull after retardation during the suckling period
Authors: Williams J. P. G. , Hughes P. C. R.
Published: April 2021

In rats whose growth was restricted by rearing in large litters the skull was less affected than the spine and the brain case less than the face. No sex difference was apparent during undernutrition but on subsequent rehabilitation females had caught up to controls in four out of five skull measurements within 4 weeks and by the end of the experiment the skulls of the neonatally undernourished females were the same size and shape as the controls. In the case of males, however, the skull of the undernourished rats never attained the same width as the controls.
Time of commitment of inside cells isolated from preimplantation mouse embryos
Authors: Handyside A. H.
Published: April 2021

Groups of inside cells (ICs) and inner cell masses (ICMs) were isolated from individual mouse embryos between the late morula and day expanded blastocyst stages using a modified immunosurgical procedure, and their purity and developmental potential were assessed in vitro.

Several different techniques failed to detect the presence of viable contaminating outside cells on ICs isolated from any of the stages studied. The numbers of inside cells isolated from the earlier stages, counted in air-dried preparations, were considerably higher than previous estimates from serial sections; whereas the numbers isolated from expanded blastocysts were in reasonable agreement. Thus the proportion of inside cells recovered by immunosurgery decreases over this period of development. In view of the evidence that inside cells divide at a faster rate than outside cells at these stages, it is argued that there may be an outward movement of inside cells capable of forming trophectoderm, during expansion of the blastocyst.

ICs and ICMs in vitro were observed to develop in one of two distinct ways according to the stage at which they were isolated. ICs from late morulae and some early cavitating blastocysts formed blastocyst-like vesicles over a period of 24-36 h in culture. The presence of trophectoderm cells in these vesicles was confirmed by the persistence of giant cells after ectopic transfer. In contrast ICs from a minority of early cavitating blastocysts, and all ICMs from day expanded blastocysts did not form vesicles, but proliferated endodermlike cells. Thus at least some inside cells do not appear to lose the capacity to form trophectoderm and do not become committed to an ICM fate until after the initial formation of the blastocoel cavity.
Postembryonic development of the visual system of the locust, Schistocerca gregaria:I. Patterns of growth and developmental interactions in the retina and optic lobe
Authors: Anderson Hilary
Published: April 2021

The visual system of the locust, Schistocerca gregaria, has a highly ordered and predictable arrangement of neurons. The retina and the outermost layer, or lamina, of the optic lobe are each composed of repeating units, ommatidia and cartridges respectively. Each ommatidium has eight photoreceptor cells, which send axons directly to a group of five neurons in the lamina to form the cartridge. The importance, for the development of this precise pattern, of the mode of growth of the two arrays and of interactions between them was investigated.

The spatial and temporal sequences of cell proliferation, differentiation and death in the developing retina and optic lobe were examined quantitatively under normal and experimental conditions.

The retina grows from its anterior margin by addition of new ommatidia formed from recruited epidermal cells. The lamina also grows by addition of new neurons to its anterior margin, but these neurons are derived from a stem cell population. The parallel pattern of growth of the retina and lamina may be important for the formation of neuronal connexions between them.

The retina grows and differentiates even when deprived of the underlying lamina. In laminae deprived of the ingrowth of new axons from the retina, the production of new neurons is also autonomous, but these neurons do not differentiate, but degenerate. A limited amount of cell death occurs in the laminae of control insects. These two observations suggest that a plausible mechanism for coordinating the sizes of the two arrays during normal development might be production of lamina neurons in excess of requirements and death of those remaining non-innervated.
Intercalary regeneration around the circumference of the cockroach leg
Authors: French Vernon
Published: April 2021

Epidermal cells from different circumferential positions around the femur of Blabera craniifer can interact to form an intercalary regenerate. Removal of a longitudinal strip of integument (cuticle plus epidermis) from any position around the circumference leads to the cut edges healing, localized growth and intercalary regeneration of the missing section of the circumference, so that the resulting femur is approximately normal in size and pattern of cuticular structures. Grafting a longitudinal strip of femur integument into a different circumferential position on the host femur confronts epidermal cells from different positions along both the inner and outer longitudinal graft/host junctions. In numerous different situations this results in local growth and intercalary regeneration of that section of the circumference normally separating graft and host positions, by the shorter route around the circumference. Confrontation of opposite positions results in the intercalation of either of the intervening half circumferences. In one opposite confrontation, between mid-anterior and mid-posterior, there was also a third result where graft and host healed together, provoking no intercalary regeneration. Grafts made with reversed proximal/distal polarity show that a confrontation between different circumferential positions gives the same result, regardless of the proximal/distal levels involved, hence circumferential position is an independent aspect of position on the femur.

These results strongly suggest that epidermal position is not specified with respect to two transverse axes running through the epidermis and internal tissue of the leg, but that there is a continuous circular sequence of positional values running around the circumference, in the epidermis. This is analogous to but independent of the sequence previously shown by Bohn (1967) and Bullière (1971) to run proximal/distal along a leg segment. Hence epidermal position on the femur is specified in two dimensions and can be represented in terms of the French, Bryant & Bryant (1976) polar co-ordinate model. Interactions along the edges of the strip-grafts conform to the Shortest Intercalation Rule (French et al. 1976).

At the proximal and distal ends of strip-grafts intercalation restores normal sequences of positional values where possible. However, where the graft, together with the intercalary regenerates formed at the longitudinal graft/host junctions and the adjacent host tissue formed a complete sequence of circular values, then a supernumerary distal regenerate was formed, in agreement with the Complete Circle Rule of French et al. (1976).

The problem of generating a continuous circular sequence of positional values by one or more circumferential gradients, is briefly discussed.