bluuebunny/crossref_metadata_2025 huggingface dataset:
The Penetration of Phosphate into Whole and Dissected Amphibian Embryos
Authors: Thomason Doreen
Published: April 2021

Embryos of Siredon mexicanum and Xenopus laevis were shown, by the use of 32P, to take up small but measurable amounts of phosphate from the culture medium. The rate of uptake was higher in embryos than in unfertilized eggs, and was related to the stage of development. The rate was proportional to the concentration of phosphate in the medium. Spontaneously occurring microcéphalie embryos took up much more phosphate than normal embryos. Injured embryos and dissected fragments of embryos took up more phosphate than intact embryos. Dissected neurulae took up more phosphate than dissected blastulae, and half-gastrulae took up more than either. Vegetative fragments of blastulae took up more phosphate than animal fragments, particularly towards the end of the 6-hour period studied. Ventral fragments of gastrulae took up the same amount of phosphate as dorsal halves during the first 2 hours after cutting, but subsequently took up more. The phosphate uptake of dorsal fragments of neurulae was at first the same as that of ventral fragments, but from 4 to 6 hours after cutting was about twice as rapid. 10 – 4 M p-dinitrophenol had a slight inhibiting effect on uptake of phosphate by whole embryos, counterbalanced by adsorption of 32P on killed cells. The phosphate uptake of fragments was cut down by the inhibitor to about one-half to one-third the level of the controls.
The Embryology of Cortisone-induced Cleft Palate
Authors: Walker B. E. , Fraser F. C.
Published: April 2021

Cortisone treatment causes cleft palates by interfering with the development of the condition within the palatine shelves that forces them to change their alignment from the vertical to the horizontal plane. The consequent delay in shelf movement, the apparent inability of the shelves to grow wider without the stimulus of being fused, and the continued increase in head width, result in a palate in which the shelves are too far apart to touch and fuse when they finally become horizontal.

The strain difference between C57BL and A/Jax mice in their susceptibility to the teratogenic action of cortisone is due in part to the earlier closing of the palate in C57BL embryos, and in part to the lesser inhibition of shelf movement in C57BL embryos as compared to A/Jax embryos. These differences suggest that the C57BL maternal-embryo complex has a more efficient metabolic system for developing palate shelf movement than exists in the A/Jax strain.
The time of action of three mutations affecting Drosophila eye morphogenesis
Authors: Ransom Robert
Published: April 2021

Histology and clonal analysis are used to look at the time of action of the mutant Drosophila genes eyeless2, eyeless dominant and sine oculis. The findings suggest that eyeless dominant has its effect during the first two larval instars, whilst eyeless2 and sine oculis act during the third larval instar.
Differential mitosis and degeneration patterns in relation to the alterations in the shape of the embryonic ectoderm of early post-implantation mouse embryos
Authors: Poelmann R. E.
Published: April 2021

The shape of the embryonic ectoderm of early post-implantation mouse embryos changes greatly in the period of 6 ·2–7 ·3 days post coitum. The subcellular morphology of the embryonic ectoderm remains unchanged, except in the primitive-streak region. Cell kinetics differ between ectodermal regions. These differences may be related to the changes in the shape of the ectoderm. The increase in cell number in the lateral ectoderm (the prospective surface ectoderm) exceeds that in the frontal ectoderm (the future neurectoderm). This is not due to differences in the duration of the cell cycle. It can be explained, however, by the occurrence of different relative numbers of dividing and non-dividing cells. These numbers vary between the two regions. The percentage of non-dividing cells in the frontal ectoderm may reach 45, whereas in the lateral ectoderm this percentage is not higher than 15. Autoradiography in tritiated thymidine-treated embryos combined with the mitotic indices gave us all of the parameters necessary to present a model capable of clarifying the growth of the ectoderm during gastrulation, as well as the changes in the shape of the ectoderm.
Origin and cytochemistry of the animal dimple granules inDiscoglossus pictus(Anura) eggs
Authors: Andreuccetti Piero , Campanella Chiara
Published: April 2021

At the centre of the animal hemisphere of the 1000μm ovarian oocytes of Discoglossus pictus there is the germinative area, a slightly depressed disc, 700 μm wide. During the passage of the oocyte through the oviduct this area becomes invaginated to form the ‘animal dimple’, which is the only site where successful sperm entrance can occur. Granules (G) with a central electron-dense core and a peripheral portion containing sparse fibrous material are found in the peripheral cytoplasm of the animal dimple.

The origin and the cytochemistry of G’s have been investigated. G’s originate from Golgi complexes located in the peripheral cytoplasm of the germinative area only. Recently formed G’s migrate to the oocyte cortical region, where vesicles appear to participate in G’s maturation. The core of G’s can be digested by pronase, is negative to a test for acid phosphatase detection, and contains a few polysaccharide complexes. In view of their origin from Golgi complex, their location in the oocytes and their exocytosis upon activation, G’s seem to correspond to the typical cortical granules of Anurans. However, they appear to have a macromolecular content different from that of the cortical granules.
Formation of marrow cavity and ossification in mouse limb buds grownin vitro
Authors: Johnson D. R.
Published: April 2021

Explanted mouse limb buds aged 12, 13 or 14 days cultured for 9 days in vitro failed to develop a marrow cavity or show endochondral ossification.

Explants aged 15 days developed a marrow cavity and showed signs of endochondral ossification. The periosteum in these limbs was perforated and laminated and cells appeared to be passing between the laminae to populate the marrow cavity. This suggests that there is a periosteal contribution to the bone marrow even in the absence of a blood supply.
The initiation of pupariation in Drosophila : dependence on growth of the imaginal discs
Authors: Simpson P. , Berreur P. , Berreur-Bonnenfant J.
Published: April 2021

Regeneration was induced in the imaginal discs in situ following lesions caused by heatsensitive cell-lethal mutations. A clonal analysis of this event demonstrated that the subsequent delay in pupariation was correlated with the amount of extra growth that occurred during the regeneration. Pupariation of heat-treated gynandromorphs bearing the mutations was also retarded, and the duration of larval development increased with greater amounts of mutant tissue, it was therefore correlated with the extent of the lesions in the imaginal discs. Elimination of entire imaginal discs, or the presence of very small amounts of lethal tissue, did not result in prolonged larval life.
Development of the rat conceptusin vitroand associated changes in components of culture medium
Authors: Sanyal Mrinal K.
Published: April 2021

Rat conceptuses of pregnancy day 11 (embryonic age approximately 10.5 days) with embryos within the yolk and amniotic sacs and polar allantoic placental tissues were cultured by the ‘New system’ utilizing homologous serum in 60ml roller bottles with 20% O2, 5% CO2 and 75% N2 gas environment (five conceptuses/10 ml serum). Embryonic growth and development was assessed by external morphology and somite counts, and by measurement of DNA, RNA and protein contents. The embryonic growth was considerably retarded beyond 24 h when culture was extended to 48 h.

During continuous culture of conceptuses for 48 h, the partial pressure of O2 in the medium decreased gradually with simultaneous increase of and decline of pH values. Glucose level was depleted considerably and small quantities of urea, uric acid and creatinine accumulated in the medium. The concentrations of electrolytes (Na+, K+, Cl-) and total Ca and P, and lactic dehydrogenase activity in the medium increased during the latter part of the 48 h culture period.

The growth and differentiation of embryos were significantly improved by transferring conceptuses to fresh serum medium with 40% O2, 5% CO2 and 55 % N2 gas phase after 22–24 h culture and continuing the culture for an additional 24 h. Embryos grown in vitro for 48 h developed 39 somites and showed a tenfold increase in DNA content and a five- to seven-fold increase in RNA and protein contents, over initial values.
Morphogenetic properties of the skin in axolotl limb regeneration
Authors: Slack Jonathan M. W.
Published: April 2021

A study has been made of the morphogenetic properties of anterior and posterior skin from the lower forelimb of the axolotl. The basic experiment consisted of a graft of a half cuff of skin from a donor to a host limb followed by a 2-week healing period, amputation through the graft, and a study of the resulting regenerate. Limbs with double posterior skin formed double posterior regenerates and, in contrast, limbs with double anterior skin formed normal or slightly hypomorphic regenerates. Posterior skin from post-metamorphic animals had a similar but weaker effect to that from ordinary axolotls.

Immunological rejection of allografts could be completely avoided if the donor limb was transplanted to the flank of the host when both were at the stage of tail-bud embryos, and the skin graft was later carried out between the supernumerary limb and one of the host limbs. This technique was used to show that immunological rejection does not affect the formation of duplicates from the limbs with double posterior skin, and to facilitate the studies of the cellular provenance of the regenerate.

The cellular composition of duplicate regenerates was studied by using both triploid donors and triploid hosts. It was shown that the posterior side of the duplications consisted wholly of host tissue and the anterior side consisted of mixed donor and host tissue. Formation of the duplicated regenerate therefore seems to involve positional reprogramming of both donor and host tissues together with metaplasia of the donor tissue.

It was not possible to inhibit the duplication-inducing property of posterior skin by treatment with a variety of enzymes.

A model based on the serial threshold theory of regeneration is advanced to explain the results. This model successfully accounts for the observed non-equivalence of anterior and posterior skin, and also explains the different regeneration behaviour of anterior and posterior half limbs, the limited regeneration of double anterior limbs, and the pattern expansion and contraction shown by regenerates from double posterior limbs.
Somite formation in cultured embryos of the snapping turtle,Chelydra serpentina
Authors: Packard David S.
Published: April 2021

A simple, reliable method for the in vitro cultivation of snapping turtle embryos was dem-onstrated. This technique was used to study somite formation in expiants containing segmental plates. Segmental plates formed a full complement of somites whether the neural tube or the neural tube and notochord was present. Explanted snapping turtle segmental plates formed an average of 6·6 ± 1·2 somites. Removal of the node region or tail bud from cultured intact embryos led to a cessation of somite formation after an additional 6·1 ± 1·8 somites had formed. These results indicate the number of somites the snapping turtle segmental plate will form. Also, the number of somites formed by explanted segmental plates showed only slight variation over a wide range of segmental plate lengths. It was concluded that while snapping turtle segmental plates formed significantly fewer somites than chicken or Japanese quail segmental plates, they were similar to the avian explants in their ability to form a consistent number of somites regardless of the length of the segmental plate.
The Mode of Growth of the Tail in Urodele Larvae
Authors: Bijtel J. Hubertha
Published: April 2021

In the developing tail-bud of urodele larvae, the neural and the mesodermal components of the tail fold along their boundary and surround the caudal extremity of the notochord. The first growth of the tail-bud is brought about by an autonomous lengthening of the neural and the mesodermal tissues. The notochord does not have an active part in the process of the lengthening of the tail, but plays a passive role. It is a supporting organ, acting as a splint. In this way it determines the ultimate length of the tail. It is not the notochord, but the combination of the neural and the mesodermal tissues, which in the first place determines the direction in which the tail grows.
Expression of serologically detectable H-2 antigens on mid-gestation mouse embryonic tissues
Authors: Kirkwood Katrina J. , Billington W. D.
Published: April 2021

Mixed haemadsorption assays using antibody-coated indicator sheep erythrocytes and mouse alloantisera revealed that major histocompatibility complex (H-2) antigens were expressed on cells of 24–72 h cultures of mid-gestation mouse embryonic skin, gut, lung, limb-bud and heart but not of embryonic gonad or kidney. The precise time of detection of H-2 antigen expression and the proportions of cells expressing these determinants depended on inbred strain, specific haplotype, tissue of origin and antiserum batch employed. In all tissues the proportion of cells expressing H-2 increased progressively from day 11–12 postcoitum onwards. The findings are discussed with respect to hypotheses concerning the possible role of major histocompatibility antigens in cellular recognition and interactions during embryogenesis.
Induction of cleft lip in cultured rat embryos by localized administration of tunicamycin
Authors: Eto Kazuhiro , Figueroa Alvaro , Tamura Gakuzo , Pratt Robert M.
Published: April 2021

Whole-embryo culture techniques have advanced to the point where the study of normal and abnormal primary palate development in vitro is possible. The purpose of this study was to ascertain whether localized administration of tunicamycin (TM) an inhibitor of protein glycosylation, into the region of the developing primary palate would induce cleft lip in culture. Rat embryos were explanted on late day 11 of gestation and cultured with open yolk sacs for 40 h. TM was administered by implanting a sterile eyelash soaked in TM into the nasal placode region. The contralateral placode was used as the control by implanting an eyelash lacking TM. Under these conditions, TM-treated placodes were found to develop cleft lip in 14 out of 15 embryos compared to 0 for the controls. These experiments demonstrate that localized administration of TM results in cleft lip formation in whole embryo culture. The technique of localized administration of drugs and teratogens in whole embryo culture should prove useful for similar studies on embryonic development.
A general cell marker for clonal analysis of Drosophila development
Authors: Lawrence Peter A.
Published: April 2021

The mitochondrial enzyme, succinate dehydrogenase, can be localized by specific histochemical stains. A naturally occurring variant which gives heat-labile enzyme is used to map a gene responsible for succinate dehydrogenase. New alleles at the sdh locus are produced by mutagenesis and most of these are found to be homozygous lethal to flies. However, clones of cells which are homozygous for the new alleles can be produced by mitotic recombination, and are found to develop normally. If the chromosome arm bearing an sdh allele also carried brown, clones can be found in the eye. At the border of the clone the brown and sdh phenotype coincide showing that the sdh phenotype is expressed as a cell autonomous marker. Clones of sdh have been observed in the adult epidermis, the muscles, the gut, the heart and oenocytes where they display a clear phenotype. This new marker may be useful in studying the development of the internal organs of Drosophila.
Experimental evidence for autonomous action of the periodic albinism (ap) gene within developing retinal pigment cells and melanophores ofXenopus laevis
Authors: MacMillan Gillian J.
Published: April 2021

Genes which affect pigment elaboration may do so by autonomous action within the developing pigment cells or by way of tissue interactions leading to pigment cell differentiation. The site of action of the periodic albinism (ap) gene was investigated by substituting presumptive neural ectoderm of gastrulae of one genotype with uncommitted ectoderm of different genotype. Retinal pigment cells and melanophores arising from such grafts were found to differentiate according to their own genotype in spite of having spent their entire developmental history in tissues of different genotype. This finding demonstrates autonomous action of the ab gene within pigment cell derivatives and does not support recent proposals that the ap gene is involved in inductive interactions leading to melanogenesis. Experiments in which portions of presumptive dorsal mesoderm, implanted in gastrulae of different genotype, induced secondary pigment cells of host phenotype further support the proposal that the ap effect on pigment cells is not mediated by inductive interactions.
Reactivity of monoclonal antibodies against intermediate filament proteins during embryonic development
Authors: Kemler Rolf , Brûlet Philippe , Schnebelen Marie Thérèse , Gaillard Jean , Jacob François
Published: April 2021

Monoclonal antibodies (mAbs) against a preparation of intermediate filaments from trophoblastoma cells were studied for their reactivity pattern during embryonic development and on adult tissue cells. Up to day 12 of embryonic development, epithelial cells of the three germ layers reacted with these mAbs. Later during development and in adult tissues, positive reactions could be observed only with epithelial cells derived from mesoderm and endoderm. Because of their tissue distribution, the proteins reacting with these mAbs might belong to the keratin family of intermediate filaments or they might represent a new group of intermediate filaments.
Comparative analysis of amphibian somite morphogenesis: cell rearrangement patterns during rosette formation and myoblast fusion
Authors: Youn B. Woo , Malacinski George M.
Published: April 2021

Detailed SEM observations of the changes in cellular morphology, arrangements, and contacts that occur during the process of somite formation were made in two species of urodele amphibians, Ambystoma mexicanum and Pleurodeles waltlii, and one species of anuran amphibian, Rana sphenocephala. After fixation, embryos were fractured transversely, horizontally, and parasagittally, and the intrasomitic cellular arrangement pattern was examined with the SEM. It was found that Ambystoma and Pleurodeles embryos followed exactly the same development sequence in rosette formation and myoblast fusion. Rana somites did not, however, appear to form rosettes. Those myotomal cells underwent fusion immediately after a few segmentations occurred.

Patterns of cellular rearrangement were also described during urodele rosette formation at the time of somite segmentation and during myoblast fusion. Extensive changes in cell shape and orientation appeared to occur during those processes. When cells changed their orientation, they often exhibited a triangular configuration. Probable roles of these triangular-shaped cells in rosette formation and myoblast fusion are discussed.

During the initial period of myoblast or myotomal cell fusion, cells first send out specialized cell processes and then establish their cell–cell contacts. The establishment of such contacts eventually leads to tight membrane appositions and fusion. Since myoblast fusion appeared to occur between two cells which were tandemly arranged in a rosette, the origin of multinuclearity in the fused cells is discussed.

Finally, comparative analyses of the pattern of somite formation and subsequent muscle development were made between different species of amphibians. The possibility is discussed that patterns of somitogenesis may provide useful indicators for determining how different families of amphibians evolved.
Hypoblast induction of multiple area vasculosae, and stabilization of the area opaca vasculosa in young chick blastoderm
Authors: Zagris Nikolas
Published: April 2021

Multiple vascular areas are formed in unincubated and prestreak chick blastoderms under the influence of multiple transplanted hypoblasts. Though the transplanted hypoblasts merge into one continuous layer, they do not participate collectively in forming one streak and embryonic axis with one area vasculosa at its postero-lateral end, but each hypoblast seems to form an embryonic centre or fraction of a centre. It may be that the merged hypoblasts do not lose their individuality or that they have induced their prospective embryonic centre before merging. This is an indication that the hypoblast is able to initiate certain events to which the epiblast responds. Composite blastoderms with stage-2 host epiblasts and with two or more transplanted hypoblasts form the embryonic axis at its prospective plane and two area vasculosae, the area opaca vasculosa (a.o.v.) as in the control blastoderm, and an induced area vasculosa 180° anteriorly. However, composite blastoderms with stage-3 epiblasts and with two or more transplanted hypoblasts behave as the control blastoderms forming the embryonic axis and the a.o.v. at their prospective sites. This indicates that the typical a.o.v. in the chick blastoderm is stabilized to blood island formation at stage 3. The stage dependence which involves progressive restriction of the areas in which blood islands will develop, suggests the existence of a centre which creates organization by integrating short-lived fields. It seems that there are no particular cell groups of the unincubated blastoderm determined to form erythrocytes but that the organizing capacities of the area are necessary to induce the first early commitments of prospective erythroblasts along this course.
Lineage analysis of inner cell mass and trophectoderm using microsurgically reconstituted mouse blastocysts
Authors: Papaioannou Virginia E.
Published: April 2021

The fate of mouse blastocyst tissues was examined following reconstitution of blastocysts from isolated inner cell mass (ICM) and trophectoderm differing for electrophoretic variants at the glucose phosphate isomerase (GPI-1) locus. A modified microsurgical method was used and a more sensitive enzyme assay allowed finer dissection of developing chimaeric conceptuses. In seven of nine cases, the extraembryonic ectoderm or the later ectoderm of the chorion was entirely of the blastocyst trophectoderm enzyme type, providing the first direct evidence that this tissue can be wholly derived from the trophectoderm. The two exceptions could represent contamination of the ICM with trophectoderm or might indicate some developmental lability of ICM cells. In addition, the results confirm the cell lineages of other tissues of the 7· 5- to 9· 5-day pc embryo and, for the first time, directly demonstrate the ICM origin of the parietal endoderm.
Enhancement of Growth of Chick Host Spleens following Chorio-allantoic Membrane Grafts of Homologous Tissues1
Authors: Mun A. M. , Kosin I. L. , Sato I.
Published: April 2021

A striking enlargement of the host chick embryo spleen was obtained following chorio-allantoic grafts of adult chicken spleen tissue. When the adult chicken spleen tissue was killed by freezing and thawing before implantation on the chorio-allantoic membrane, no enlargement of the host chick embryo spleen was observed. However, a large number of the frozen grafts failed to ‘take’. X-irradiation of the donor spleen, at a level sufficient to block or inhibit mitosis, also removed the growth-stimulating abilty of the grafted tissue in spite of the fact that the grafts were well incorporated. This suggested that donor cells capable of undergoing mitosis were necessary for producing enlarged host spleens. Because of the possibility that antibody-forming mechanisms were destroyed at these levels of irradiation, the involvement of such mechanisms in this reaction was studied. In a comparison of the effect of spleen grafts between two inbred lines of White Leghorn chickens (S and R), a lesser stimulation was obtained when spleens from 5 line chickens were implanted on S line embryos than on R line embryos. Similarly, a lesser stimulation was obtained when R spleens were implanted on R embryos than on 5 embryos. Spleens from S line chickens also evoked a greater response than spleens from R line chickens. To test the role of antibodies in this reaction, spleens from adult chickens previously injected with chick embryo spleens were implanted on the chorioallantoic membrane. In all cases (7) the spleens from the injected chickens stimulated the host embryo spleen to a significantly lesser degree than spleens from non-injected chickens. Spleens from different animal species, including the turkey, pheasant, rat, and guinea-pig, were implanted on the chorio-allantoic membrane of the early chick embryo. The turkey and pheasant spleens stimulated the host chick embryo spleens to a significantly lesser degree than adult chicken spleen in spite of the greater genetic diversity and subsequently successful incorporation in the chorio-allantoic membrane. From the available evidence the authors suggest that the enlargement of the host chick embryo spleen following chorio-allantoic membrane grafts of homologous adult chicken tissue probably involves two separate steps: (1) a stimulation which may occur in the absence of intact cells; (2) an immune-type reaction which results in necrosis of areas in the host spleen, and stunting of growth of the hatched chicks.
An Immunological Approach to the Problem of Lens Regeneration
Authors: Langman J. , Prescott B. D.
Published: April 2021

Application of Boyd’s precipitin test showed the presence of lens antigens in extracts of pigment layer of the retina, ventral and dorsal parts of the iris, cornea, vitreous body, and in aqueous humour obtained from eyes in which the lens was removed 6-7 weeks prior to the test. Their presence was not detected in the neural layer of the retina, sclera, or in any other extra-ocular tissue (Table 1). Extracts prepared from lens-containing eyes showed exactly the same results. The number of lens antigens in these tissues was determined by the agar diffusion technique of Ouchterlony and was found to vary from 2 to 7, depending on the source of tissue used (Table 2, Plate, figs. 1-6). The antigens found in pigment layer of the retina, iris, cornea, vitreous body, and aqueous humour appeared to be identical to antigens found in the lens (Table 3, Plate, fig. 7). Since iris, pigment layer of the retina, and cornea have the property to regenerate a lens after removal of the original lens, the obtained data suggest that there is a relationship between the lens regeneration capacity and the presence of antigens identical to those of the lens.
The Submicroscopic Structure of the Drosophila Egg
Authors: Okada Eiko , Waddington C. H.
Published: April 2021

A study has been made with the electron microscope of the structure of the growing oocyte and associated nurse and follicle cells in Drosophila melanogaster. The fully grown oocyte has a cortical plasm which is thrown into deep folds, at the base of which are small delta granules. Immediately below this is a zone of periplasm which contains: well-developed mitochondria; some ergastoplasmic elements, probably mainly tubular, though sometimes taking the form of concentric oval sheets; many alpha granules which when well fixed are irregularly star-shaped and are probably lipoidal in composition; a number of stacks of annulate lamellae. Yolk granules, which may be built of a few tens of smaller particles, are found mainly at deeper levels, and so are the electron-light and probably fluid beta granules and the rather darker gamma granules. Epsilon granules, with a definite membrane and vacuolated interior, occur mainly in the posterior end of the egg and later in the pole cells. The vitelline membrane, which in earlier stages has a spongy structure, begins to appear between oocyte and follicle cells earlier than below the nurse cells. The appearance of small vesicles in the ooplasm beneath the developing membrane suggests that it is secreted mainly by the oocyte. There is very complex folding of the membranes between oocyte and follicle cells and still more between oocyte and nurse cells. Attention is drawn to: (i) the great enlargement in the area of the nurse-cell nuclear membranes, (ii) the striking differences in appearance between the nuclear membranes in the nurse cells and follicle cells, (iii) the formation of elaborately organized ergastoplasmic structures in the cytoplasm of the degenerating nurse cells, (iv) the large number and orderly arrangement of the elements in the stacks of annulate lamellae, which is held to suggest a process of in situ synthesis.
Mesectodermal capabilities of the trunk neural crest of birds
Authors: Nakamura Harukazu , Lievre Christiane S. Ayer-Le
Published: April 2021

Orthotopic transplantation experiments have shown that in birds, under normal conditions, mesectodermal capabilities seem restricted to the cephalic neural crest down to the level of the 5th somite.

In the present study the mesectodermal capabilities of trunk and lumbar neural crest were investigated at early stages of development by heterotopic, heterospecific transplantation of the neural primordium. The quail-chick nuclear marker system was used to identify the grafted cells.

Mesectodermal cells did not arise from the trunk neural crest when this was implanted orthotopically, even though the neural primordium was taken early in development at the level of unsegmented plate mesoderm just anterior to Hensen’s node.

Mesectodermal derivatives (connective tissues, dermis and muscle but no cartilage or bone) developed from the same trunk neural crest fragments when they were heterotopically grafted at the cephalic level and mixed with host cephalic neural crest cells. These host cephalic neural crest cells emigrated from the contralateral neural primordium when the graft was unilateral or from the fringe area of the operation in cases of bilateral transplantations.

As a control, unsegmented paraxial mesoderm was inserted alongside the cephalic neural tube; its cells did not migrate ventrally in the neural crest-derived area and they differentiated in the dorsal region of the host.

These results indicate that mesectodermal capabilities, though reduced, exist in the trunk neural crest at early stages of development but the differentiation of these mesectodermal derivatives is largely dependent upon environmental influences which may be found in early cephalic levels.
Differentiation potentiality of rat visceral yolk sac in organ culture
Authors: Lu Y. L. , Sobis H. , Hove L. Van , Vandeputte M.
Published: April 2021

Visceral yolk sacs removed at day 12 of pregnancy in the rat were kept in organ culture for as long as 28 days. During this in vitro culture, proliferation of the endoderm and the mesoderm as well as of poorly differentiated cells was observed. The latter displayed neither the characteristics of endodermal nor mesodermal cells and their presence was frequently associated with the development of giant trophoblast cells. The hypothesis is proposed that these trophoblast cells originate from these poorly differentiated cells that acquire in vivo and in vitro the potentiality to differentiate.
Experimental analyses of cytoplasmic rearrangements which follow fertilization and accompany symmetrization of inverted Xenopus eggs
Authors: Neff Anton W. , Wakahara Masami , Jurand Arthur , Malacinski George M.
Published: April 2021

Cytoplasmic rearrangements which follow fertilization were monitored in inverted eggs. A set of yolk compartments was resolved by cytological analyses of both normally oriented and inverted eggs. Those compartments were characterized by their yolk platelet compositions and movement during egg inversion. In addition to the major yolk masses which contain either small, intermediate or large platelets, minor cytoplasmic compartments which line the egg cortex were also identified.

During egg inversion the yolk compartments shift. Those yolk mass shifts occurred only after the inverted egg was activated (by sperm, electrical or cold shock). The direction of shift of the major yolk components, rather than the sperm entrance site (as in normal orientation eggs), determines the dorsal/ventral polarity of the inverted egg. Among different spawnings the rate of shift varied. Eggs that displayed the fastest rate of shift exhibited the highest frequency of developmental abnormalities during organogenesis.

Isopycnic density gradient analysis of yolk platelets and blastula blastomeres showed that isolated yolk platelets and mid-blastula blastomeres are not of uniform buoyant density. Three major yolk platelet density bands were resolved. Large, intermediate, and small yolk platelets were found in all bands. The high density band had the largest proportion of the large yolk platelets and the low density fraction showed the largest proportion of the small yolk platelets.

Interpretation of novel observations on cytoplasmic organization provided criticisms of some earlier models. A new ‘Density Compartment Model’ was developed and presented as a coherent way to view the organization of the egg cytoplasm and the development of bilateral symmetry.
Structural basis of the activation wave in the egg of Xenopus laevis
Authors: Takeichi Tetsuo , Kubota Hiroshi Y.
Published: April 2021

A series of changes in the surface of activated Xenopus eggs was observed. Within a few seconds of prick activation a light area appears near the pricking point and expands as a circular light zone (light wave). Some 60s later this is followed by a dark area expanding as a circular dark zone (dark wave). Both waves travel at a rate of about 9 μm/s at 21 °C. In the light zone, cortical granules are breaking down, microvilli are elongating, and the egg surface is expanded. On the other hand, the elongated microvilli are reshortening to become globular and the egg surface is contracted in the dark zone.
Cell relationships during aggregation between preimplantation embryos and teratocarcinoma-derived cells
Authors: Lehtonen E. , Wartiovaara J. , Reima I.
Published: April 2021

Cleavage-stage mouse embryos aggregate and form chimaeric blastocysts with embryonal carcinoma (EC) cells. We used scanning and transmission electron microscopy to study cell relationships during aggregate formation between 8-cell-stage embryos and F9 EC cells. Relations between heterotypic cells were similarly studied in aggregation experiments with embryos and teratocarcinoma-derived visceral (PSA5-E) and parietal (PYS-2) endoderm cells and in experiments with EC cells and endoderm cells.

The embryos and F9 cells always adhered to each other and rapidly formed compacted aggregates. Numerous microvilli and cell processes, originating from both embryo and EC cells, extended between the two cell types during adhesion and early phases of aggregation. The aggregation process involved spreading of the blastomeres on the EC cells. Frequent adherent junctions and close contacts, including possible focal gap or tight junctions were observed between the embryo and F9 cells after 3 h of culture. Apparent gap or tight junctions were infrequent during the early phases of aggregation but during further culture, extensive typical gap junctions were also seen between embryo and EC cells.

The embryos adhered only irregularly and loosely to PSA5-E and PYS-2 cells; this interaction never led to aggregate formation comparable to that seen in the experiments with embryos and EC cells. Close contacts but no gap or tight junctions could be observed between the embryo and endoderm cells. On the other hand, both PSA5-E and PYS-2 cells readily adhered to and aggregated with EC cells.

The present results suggest that microvilli and cell processes mediate membrane interactions during adhesion and early phases of aggregation between embryos and EC cells. During aggregation, blastomeres spread over the EC cells, and rapid formation of adherent junctions and close contacts, including possible focal gap or tight junctions is involved during the early phases of this process. After this initial phase, typical gap junctions are also seen between the embryo and EC cells. Interestingly, adhesive properties of embryo and EC cells differ: the former aggregate only with EC cells, whereas the latter do so also with teratocarcinoma-derived visceral and parietal endoderm cells. Mechanisms operating in the morphogenetic movement of cells in this experimental setup may be involved also in the development of the blastocyst in vivo.
The structure of supernumerary leg regenerates in the cricket
Authors: French Vernon
Published: April 2021

In many insects, grafting a larval leg onto the contralateral leg stump reverses one transverse axis and leads to the regeneration of supernumerary legs at each of the two points of maximum discrepancy on the graft/host junction. These operations were performed on the cricket Acheta domesticus, grafting between tibiae of pro- and metathoracic legs, and between tibia and tarsus, in order to deduce the mode of origin of the supernumeraries from their graft type, host type or composite structure.

Supernumerary legs formed after A/P axis reversal are always half- and-half in structure, being of host type on the host side and graft type on the graft side, while supernumeraries formed after M/L axis reversal are variable in structure. These results are generally consistent with the recent Polar Co- ordinate Model (whereby supernumeraries form because the pattern of intercalation between graft and host generates two complete circumferences at the junction), provided that intercalation is restricted by the borders between anterior and posterior leg compartments. However there are features of the structure of the M/L supernumeraries which the Polar Co- ordinate Model does not explain. Medial supernumeraries are often of pure graft type (and lateral ones of host type) or half- and-half with anterior graft type and posterior of host type (while lateral supernumeraries often have the converse structure).
Mapping of cortical histogenesis in the ferret
Authors: McSherry G. M.
Published: April 2021

The columnar organization of forebrain cortical neuron production allows the neuroepithelium to be analysed in terms of a simple growth model. The pattern of neuron release within each column is repeated with great regularity across the surface of the developing cerebral hemisphere, resulting in the accumulation of cortical neurons in radial stacks above the proliferative ventricular epithelium. The time course of recruitment of adjacent tissue into neuron production accounts for the observed rostrocaudal and laterodorsal gradients of cortical neuron release. The present study plots the history of this front of neuron production across the surface of the developing cerebral vesicle in the ferret and interprets the resulting maps of cortical development stages in terms of a unified growth model that links the radial and tangential aspects of neuron production. These observations are discussed in relation to other studies of gradients in developing nervous tissue and their implications for the study of experimentally induced abnormalities of brain development.
The role of endoderm in blood cell ontogeny in the newt Pleurodeles waltl
Authors: Deparis P. , Jaylet A.
Published: April 2021

In order to determine the origin of blood cells we performed embryonic grafts of different portions of mesoderm from various locations between diploid and tetraploid embryos at the tail-bud stage. The tetraploid animals were the hosts. The size differences between tetraploid and diploid cells made identification possible by direct microscopic examination of blood smears. In a previous report we showed the important role of truncal anterior mesoderm in the genesis of blood cells. We now establish that this effect is brought about by the inductive capacity of the hepatic endoderm or by the fact that the environmental conditions are more appropriate for blood stem cell development, whereas in the absence of the hepatic endoderm the blood stem cells fail to appear. Grafting of hepatic anlage containing endoderm and mesoderm gives rise to numerous graft-derived blood cells which last throughout the life span of the hosts. The same result is obtained by grafting truncal posterior ventral or lateral mesoderm onto hepatic endoderm. Heterotopic grafting of truncal anterior mesoderm isolated from its underlying hepatic endoderm leads to the formation of only a few blood cells which last only during larval life. This demonstrates that the whole lateral and ventral truncal mesoderm is able to differentiate into blood cells when associated with hepatic endoderm.
Cell cycle analysis of facial mesenchyme in the chick embryo : I. Labelled mitoses and continuous labelling studies
Authors: Minkoff Robert
Published: April 2021

Cell cycle parameters were analysed in mesenchyme of the maxillary process and the roof of the stomodeum in the chick embryo from stages 19 through 28. The generation times at stages 24 –26 were determined by pulse labelling of embryos with [3H]thymidine, followed by labelled mitosis counts and construction and analysis of percent-labelled mitosis curves employing computer-assisted curve-fitting techniques. The median generation time was approximately 10·6 h in the maxillary process, and 16 h in the roof of the stomodeum; corresponding values for mean generation times were approximately 12 ·0 and 18 ·2 h, respectively. Median values for transit times of G1, S, and G2 were 2·0, 5·4, and 2 ·5 h in the maxillary process and 5 ·2, 6 ·7, and 2 ·7 h in the roof of the stomodeum. The distribution of generation times of cells in the roof of the stomodeum, however, appeared to be more heterogeneous than those of cells in the maxillary process.

The percentage of cells which continue to cycle rapidly (i.e. the ‘growth fraction’) was determined by repeated-labelling experiments with [3H]thymidine in chick embryos from stages 19 through 28. Cumulative labelling of mesenchymal cells in both the maxillary process and roof of the stomodeum approached 100 % at stage 19 but dropped markedly from stage 19 to 25 declining to approximately 60 –70 % in the maxillary process, and to 30 % in the roof of the stomodeum. The decline in cell proliferation rates for these regions, determined in previous studies with labelling indices, appears to be a result of the removal of cells from rapidly cycling cell populations into subpopulations which are cycling more slowly and possibly into subpopulations which have become quiescent; the difference in growth rates between these regions could be attributed to the time of appearance and the size of these emerging slow cycling or quiescent subpopulations.
Cell cycle analysis of facial mesenchyme in the chick embryo
Authors: Minkoff R. , Martin R. E.
Published: April 2021

The spatial distribution and developmental fate of quiescent and/or slow cycling cell populations of the primary palate were studied employing label-dilution techniques. -day-old chick embryos were labelled sequentially for 12 h with [3H]thymidine and then chased with cold thymidine. The embryos were reincubated to continue development and were subsequently sacrificed at intervals from the end of labelling at 4 days to 14 days of incubation (10 days after labelling) and processed for autoradiography. Retention of label was used as the assay for identification of quiescent and/or slow-cycling cells. Grain density over the nuclei of labelled cells was determined in the maxillary process and the roof of the stomodeum. Cells with a label density at later time points comparable to that found in cells immediately after the labelling period were defined as label-retaining cells, i.e. those which had become quiescent or had significantly altered generation times. The location and developmental fate of these cell populations were confirmed using slides containing adjacent sections stained with Nuclear Fast Red, Alcian Blue, and Tartrazine. The results demonstrated an association between label-retaining cells and chondrogenic differentiation in the roof of the stomodeum. Subpopulations of label-retaining cells (quiescent and/or slow cycling) which we believe to be prechondroblasts appeared in the chondrogenic region of the roof of the stomodeum prior to, or coincident with, cartilage formation. The retention of label, as evidenced by comparison of nuclear grain counts at the end of the labelling period with subsequent time points, indicated that a cell cycle block may have occurred in the prechondroblastic cell population. The block lasted until these cells expressed the chondrogenic phenotype, after which they resumed cell division.
Characterization of a cell-surface differentiation antigen of mouse spermatogenesis: timing and localization of expression by immunohistochemistry using a monoclonal antibody
Authors: Bechtol Kathleen B.
Published: April 2021

The XT-1 antigen, bound by monoclonal antibody XT-I, is a differentiation antigen of germ cells in the mouse testis. As seen in immunoperoxidase-stained tissue sections from several juvenile ages and adult, the antigen becomes detectable on early (leptotene/zygotene) spermatocytes and increases in staining during spermatocyte development. During spermatid development the distribution of the determinant shifts from its relatively uniform surface distribution on spermatocytes to a more restricted localization on the base of the head, tail and cytoplasmic lobe of the elongating spermatid. The antigen is not detectable on juvenile or adult Sertoli cells. Detection of the antigen is dependent on the presence of germ cells of appropriate developmental stage. It is, thus, a marker for spermatocytes and later germ cells, for a cell-surface molecule related to spermatogenesis and for redistribution and/or modification of the molecule during spermatid elongation.
Fibre order in the normal Xenopus optic tract, near the chiasma
Authors: Fawcett J. W. , Taylor J. S. H. , Gaze R. M. , Grant P. , Hirst E.
Published: April 2021

In juvenile Xenopus retinotopic fibre order in the optic tract near the chiasma was investigated by labelling small groups of optic fibres from peripheral retina with HRP. This selective fibre labelling with HRP was combined with autoradiography following administration of tritiated thymidine to the eye, so that the HRP-labelled fibres could be located within the borders of the optic tract.

Fibres arising from the periphery of all four retinal quadrants were superficially located in the optic tract near the chiasma, with dorsal retinal fibres showing the greatest tendency to travel deep in the diencephalon. Retinal lesions closer to the optic nerve head labelled fibres which ran deeper in the optic tract. Near the chiasma, fibres from ventral retina tended to group rostrally while fibres from dorsal retina tended to group caudally. However, no obvious localization of fibres arising in temporal or nasal retina was seen in the lower optic tract.