bluuebunny/crossref_metadata_2025 huggingface dataset:
Viability and growth of mouse embryos after in vitro culture and fusion
Authors: Bowman Patricia , McLaren Anne
Published: April 2021

About 80 % of 8-cell mouse eggs developed to the blastocyst stage in culture, whether the zona pellucida was left intact, or removed with pronase (pre-incubated and dialysed) and the eggs then cultured singly or as fused pairs. When pronase was used without prior incubation and dialysis, the success rate was reduced to 50 %.

After transfer to uterine foster-mothers, 20–30 % of apparently normal blastocysts cultured with or without the zona, singly or fused, developed into live foetuses, compared with over 50 % of control blastocysts taken directly from the uterus. Some of the excess mortality of cultured embryos took place before implantation and some soon after.

The foetuses derived from cultured blastocysts averaged 0·1g lighter than those derived from control uterine blastocysts similarly transferred. No differences in the weights of the placentae were observed. Foetal and placental weights were unaffected by whether the eggs had been cultured singly or fused, implying that growth regulation of fused embryos is complete by the 17th day of gestation.

The longer the eggs were maintained in culture, the lower was their viability after transfer, and the lighter were the foetuses derived from them.
Tissue degeneration: an electron microscopic study of the pronephros of Rana temporaria
Authors: Fox H.
Published: April 2021

The structure of the non-degenerate and degenerating pronephros, of larval Rana temporaria, at different stages of the metamorphic cycle, was examined by electron microscopy.

Extra-renal cellular components in the circulation were likewise investigated, and particular consideration was given to their relationships with the pronephric tubules whose regression would seem to be bound up with them.

The activity of lysosomes in pronephric tubule degeneration suggests that they are an important component of the degeneration process, which probably embraces autolysis and phagocytosis.
Tissue interactions in embryonic mouse tooth germs: II. The inductive role of the dental papilla
Authors: Kollar Edward J. , Baird Grace R.
Published: April 2021

The response of embryonic mouse dental epithelium and mesoderm to tissues of ectopic origin was examined. Isolated molar or incisor mesoderm was confronted with epithelium isolated from the plantar surface of the embryonic mouse foot plate or from the snout.

Harmoniously structured teeth were formed from the foot epithelium and incisor or molar mesoderm. These data are interpreted as an unequivocal demonstration of the inductive role of the dental mesenchyme.

Teeth were absent in confrontations of dental mesenchyme and snout epithelium. The presence of hair follicles in these explants is described and discussed with reference to other integumental epithelio-mesenchymal interactions.

Dental epithelium forms keratinizing surface-like epithelium and invading bands of epithelium in association with foot mesoderm; definitive structures are not formed.

On the other hand, when incisor or molar epithelium is associated with snout mesoderm, hair follicles are seen in addition to keratinizing surface-like epithelial configurations.

The roles of the epithelial and mesenchymal tissues and the nature of epithelio-mesenchymal interactions in the developing mouse integument are discussed.
Experiments on chromosome elimination in the gall midge, Mayetiola destructor
Authors: Bantock C. R.
Published: April 2021

Cleavage in Cecidomyidae (Diptera) is characterized by the elimination of chromosomes from presumptive somatic nuclei. The full chromosome complement is kept by the germ-line nuclei.

The course of cleavage in Mayetiola destructor (Say) is described. After the fourth division two nuclei lie in the posterior polar-plasm and become associated with polar granules, and fourteen nuclei lie in the rest of the cytoplasm. All the nuclei possess about forty chromosomes. During the fifth division the posterior nuclei do not divide and the polar-plasm becomes constricted to form primordial germ cells (pole cells). The remaining fourteen nuclei divide and lose about thirtγ-two chromosomes so that twenty-eight nuclei are formed containing only eight chromosomes. These are the presumptive somatic nuclei. During subsequent divisions the pole cell nuclei retain the full chromosome number; these divisions occur less frequently than those of the somatic nuclei.

Experiments were performed on early embryonic stages to elucidate the properties of the posterior end during the time that chromosome elimination was taking place from the presumptive somatic nuclei. Ultraviolet irradiation, constriction, and centrifugation techniques were used.

The polar granules are concerned with the non-division of the germ-cell nuclei during the fifth division, since if the granules are dispersed by centrifugation, or if nuclei are prevented by constriction from coming into contact with them before the fifth division, all the nuclei divide with chromosome elimination at this division. With each technique it is possible to obtain embryos possessing germ cells with only eight chromosomes in their nuclei.

Individuals possessing germ-line nuclei with only eight chromosomes were allowed to develop to maturity. Abnormalities were confined to the germ cells only and were the same regardless of which technique had been used to produce the deficient germ line. An ovary containing germ-cell nuclei with only eight chromosomes is unable to form both oocytes and nurse cells. A testis containing germ-cell nuclei with only eight chromosomes is unable to form spermatocytes but cells which come to resemble gametes are formed. Experimental males and females are both sterile.

The results are discussed in relation to other experimental work on Cecidomyidae and the following main conclusions are reached: (a) the polar granules are responsible for preventing an irreversible loss of chromosomes from the germ-cell nuclei by preventing the mitosis of these nuclei during the fifth division; (b) the chromosomes normally retained in the germ line are required for gametogenesis, particularly for oogenesis.

The significance of chromosome elimination is discussed.
Study of the development of the internal organs of the double malformations of Chironomus dorsalis by fixed and sectioned materials
Authors: Yajima Hideo
Published: April 2021

The development of the internal structures was investigated by fixed sections of the ‘double cephalon’ and ‘double abdomen’ of Chironomus dorsalis.

The cell proliferation that gives rise to ‘germ Anlage’ or embryonic rudiment begins, in the double cephalon, along the entire convex (ventral) side of the egg and, in the double abdomen, at both ends of the flat (dorsal) side. As a result, a single fused Anlage of the double cephalon appears along the entire convex side of the egg and two germ Anlagen of the double abdomen appear at both ends of the flat side.

During the formation of the germ band, both the posteriormost part of the double cephalon which lies at the middle of the convex side of the egg and the anteriormost part of the double abdomen which is located at the middle of the convex side, fail to differentiate and later degenerate.

In each of the duplicated heads of double cephalon, cephalic segments anterior to the first maxillary segment are formed, but the thoracic and abdominal segments are entirely missing. In each half of the double abdomen, eight abdominal segments posterior to the second abdominal segment are produced and the cephalic and thoracic segments are omitted altogether.

The two pairs of mid-gut rudiment from both halves of the double cephalon are temporarily united but they break apart by the end of the blastokinesis. When the two pairs of mid-gut rudiment from both halves of the double abdomen meet, they remain fused with each other, being surrounded by the visceral mesodermal cells in the normal way, and develop into the mid-gut epithelium.

In the double malformations, the pole cells are contained in only one member of the duplicated structures. The pole cells of the double cephalon develop into the tetra-nucleate state (Hasper’s second step), but they fail to fuse to form the gonad. In the double abdomen, the gonad develops in the one abdomen containing the pole cells and no replacement occurs in the sister abdomen without the pole cells.

The embryonic envelopes of the double cephalon do no’ retract into the interior of the embryo, while they do in the normal way in the double abdomen.

The double cephalon can never hatch but the double abdomen can emerge.
The origin and movement of nephrogenic cells in the chick embryo as determined by radioautographic mapping
Authors: Rosenquist Glenn C.
Published: April 2021

The origin of the presumptive nephrogenic cells in the epiblast of the chick embryo was traced by radioautographic analysis of the movements of tritiated thymidine-labelled grafts excised from medium-streak to 5-somite stage embryos and transplanted to epiblast, streak, and the endoderm-mesoderm layer of similarly staged recipient embryos.

The nephrogenic cells originate near the area pellucida margin of the medium-streak-stage embryo, migrate toward the streak, and are invaginated about one-third to one-half the distance from the anterior to the posterior end of the streak, between the definitive-streak and I - to 4-somite stages. Their route into mesoderm is along a relatively narrow pathway between the cells migrating to the paraxial or presomite mesoderm on one side, and those destined for the proximal limbs of the lateral plate on the other.

The cells which will form the anterior part of the intermediate mesoderm are the most medially placed cells in epiblast, reach the streak at an earlier stage of development, and are the first nephrogenic cells to migrate into mesoderm. After about the 17- to 19-somite stage, cells from this group which have formed the pronephric cord or duct begin to move posteriorly in relation to the rest of the intermediate mesoderm, toward the future cloaca.

The last nephrogenic cells to leave epiblast and enter the streak and mesoderm are those destined for the posterior end of the intermediate mesoderm. This group of cells surrounds the posteriorly migrating pronephric (Wolffian) duct and differentiates into mesonephros.
Morphogenesis and functional differentiation of the rat parotid glandin vivoandin vitro
Authors: Lawson Kirstie A.
Published: April 2021

In comparison with the submandibular and the sublingual glands, the parotid develops slowly in the rat. The foetal rudiment appears a day later than that of the submandibular gland and the formation of adenomeres is slower, leading to a more diffusely branched structure. Cytodifferentiation, in the form of traces of mucopolysaccharide in the tubules and terminal buds, begins at, or just before, birth. There is a transitory increase in mucopolysaccharide production for a few days after birth until the presumptive acinar cells become pyramidal in shape with basal nucleus and granular cytoplasm. Amylase activity of the gland begins to rise between the second and third day after birth and reaches the adult level at weaning. That of the submandibular gland remains at the foetal level.

Parotid rudiments were cultivated on a film of agar over a medium of fowl plasma and chick embryo extract. The oxygen in the gas phase of air and 5 % CO2 was increased to 50 % after the first 9 days in vitro. Under these conditions the mass of the rudiments increased tenfold during 18 days cultivation and the initially unbranched rudiment formed adenomeres in which the cytodifferentiation followed the same course as in vivo. The rise in amylase activity of the explants was only slightly delayed compared with that in vivo, suggesting that systemic or environmental factors are not obligatory in the early postnatal development of the rat parotid.
Cell population kinetics of erythroid tissue in the liver of foetal mice
Authors: Tarbutt R. G. , Cole R. J.
Published: April 2021

Measurements have been made of the relative and total numbers of the various types of erythroid cells in the livers of random-bred Swiss foetal mice. It has been shown that the results can be interpreted in terms of two waves of erythropoiesis passing through the liver, one coinciding approximately with the erythropoietin sensitive phase of hepatic erythropoiesis, the other with the insensitive phase.

The mitotic index and thymidine labelling index of early erythroid cells do not change during the period studied, but the labelling index of the late cell types decreases from 30% at 13 days to 15 % at 18 days. This decrease has been interpreted as an increase in the proportion of non-dividing polychromatic erythroblasts.

The cell cycle time of early and late erythroid cells in foetal livers has been determined at 13 and 16 days of age. The cycle time of the early cells is about h at both stages of development, but that of late (polychromatic) erythroblasts decreases from 8 h at 13 days to 5–6 h at 16 days.

It has been shown that the results presented are consistent with the change in the rate of increase of hepatogenic red cells which is observed at about the 15th day of foetal life.
Thymus dysgenesis in nude (nu nu) mice
Authors: Pantelouris E. M. , Hair Janet
Published: April 2021

The thymic rudiment in mice homozygous for the recessive mutation nude (nu) has been compared to the normal at two stages: the 14-to 15-day foetus and the 1-to 2-day-old young. In the former, the normal thymus already comprises two adjacent lobes but in the nude it is represented by a pair of thin strands of tissue, each with a narrow central lumen. In further development these strands become thicker and vesiculated. They progress no further and are found in the 1-to 2-day young as small vestiges that are never populated with lymphoid cells.

The thyroid, parathyroids and mandible of homozygous nude mice are normal, indicating that the complex of structures derived from the third branchial arch is not affected as a whole.
In vitro analysis of the hormonal basis for the sexual dimorphism in the embryonic development of the mouse mammary gland
Authors: Kratochwil Klaus
Published: April 2021

Factors underlying the sexual dimorphism in the embryonic development of mouse mammary glands were analysed in vitro and the following results were obtained: Mammary gland rudiments of 13-day male embryos, explanted immediately before the onset of their regression, were perfectly capable of developing into female-type glands in vitro. Even some of the glands of 14-day male embryos, where the regression process had already begun, recovered after explantation and underwent female-type morphogenesis.Combined explantation of 13-day testes with mammary rudiments of female embryos of 12–14 days gestation resulted in male-type regression of the glands.The addition of testosterone to the culture medium caused a similar regression of explanted (female) mammary-gland rudrudiments. The minimal effective concentration of the hormone was 10−9M, or 0·00029 μg/ml.Cultured mammary rudiments of 15-day female embryos were no longer responsive to the presence of testis explants. They failed to undergo regression and continued their development in vitro.

From these results the following conclusions were drawn: (a) The sexual dimorphism in the embryonic development of mouse mammary glands is caused by their suppression in males and not by their stimulation in female embryos.(b) The androgenic hormones in male foetuses are solely responsible for the regression of the mammary rudiments. They exert their effect directly on the gland without the need for involvement of other endocrine organs.(c) The genetic sex of the gland itself has no influence on its developmental capacities as: (i) glands of male embryos are able to develop in the absence of androgens, and (ii) glands of female embryos undergo typical male-type regression in vitro when exposed to the presence of foetal testes or of testosterone.
Ontogeny of hemoglobin in the house sparrow
Authors: Bush Francis M. , Townsend J. Ives
Published: April 2021

A ‘switchover’ from synthesis of predominantly embryonic hemoglobin to synthesis of predominantly adult hemoglobin occurs during differentiation of the house sparrow. This ‘switchover’ is demonstrated by a change in electrophoretic pattern generally comparable with that of the chicken, slightly different from those of the duck and man, and, perhaps, dissimilar to that of the red-wing blackbird.

Differences in electrophoretic mobility show that 10-day embryos possess one hemoglobin not present in early hatchlings and two hemoglobins not present in adults. Major adult hemoglobin is synthesized by the tenth embryonic day; and minor adult hemoglobin, between the tenth embryonic day and the seventh day after hatching.

The major increase in concentration of hemoglobin occurs between 2 and 11 days after hatching, a time when the two predominant embryonic and two predominant adult hemoglobins are being synthesized. The percentage of packed cells (hematocrit) also increases significantly within this period.

Similarities of peptide maps for the house sparrow and other species, such as the owl, indicate the presence of α-and β-polypeptide chains in adult house sparrow hemoglobin. The shift to hemoglobins with faster anodic mobilities and the presence of a higher concentration of hemoglobin in adults than in early hatchlings suggest that this synthesis is predominantly in the β-chains.
Growth and differentiation of rat egg-cylinders under the kidney capsule
Authors: Škreb N. , Švajger A. , Levak-Švajger B.
Published: April 2021

Two groups of embryonic shields were transferred under the kidney capsule, on days and 9 of normal pregnancy. The first group was without mesoderm and the second one with well-formed mesoderm. Random-bred and inbred Fischer rats were used.

Killed and fixed 15 and 30 days after the operation, the grafts looked like teratomata with well-differentiated tissues. Differentiation was the same in embryos explanted at and 9 days, and from the two strains of rat.

In order to study the growth potential, transfers within and between each strain of rat were carried out. A difference in weight was found 15 days after the operation among some series. This was not observed 30 days after the transfer. Although the grafts in random-bred rats were larger than in the inbred Fischer strain, factors other than the immunological influence were invoked for the explanation of the initial difference in growth.

Long-term grafts were studied only in the inbred strain. Two, 4 and 6 months after the operation all well-differentiated tissues were still present. The amount of growth was very variable within each series, but no graft was found totally resorbed.

Only in the largest graft, 6 months after the operation, large masses of cells were found which seemed to be undifferentiated.
Feather morphogenesis and feather pattern in normal andtalpid3mutant chick embryos
Authors: Ede D. A. , Hinchliffe J. R. , Mees H. C.
Published: April 2021

A comparative study of feather morphogenesis and the development of feather pattern in normal and talpid3 embryos has been carried out.

The development of talpid3 CAM grafts shows that the effect of the gene is autonomous in the skin.

The most striking effect of the gene upon feather morphogenesis is the failure of normal feather germ condensations to appear within the dermis. This is reflected in the abnormal distribution of alkaline phosphatase through the dermis.

Dermal cells within and between condensations are not orientated in the mutant as they are in normal embryos, probably owing to the same defect in cell behaviour which causes condensation failure in talpid3 precartilage mesenchyme.

The role of dermal cell orientation and movement in generating the overall feather pattern is examined in both normal and talpid3 embryos.
The origin and movement of the limb-bud epithelium and mesenchyme in the chick embryo as determined by radioautographic mapping
Authors: Rosenquist Glenn C.
Published: April 2021

The origin of the limb-bud cells was determined by tracing the movements of [3H]thymidine-labelled grafts excised from late medium-streak to 5-somite stage chick embryos and transplanted to the epiblast, streak, and endoderm-mesoderm of similarly staged recipient embryos.

Although exact definition of the prelimb areas was not possible because of the small number of grafts placed at each developmental stage, the study showed in general that at the late medium-streak stage the future limb-bud epithelium is in the epiblast (dorsal) layer near the lateral margin of the area pellucida. It moves medially toward the embryonic axis, just lateral to the premesoderm cells which will be invaginated at the primitive streak. With regression of the streak, the limb-bud epithelium moves relatively anteriorly into a position dorsal to the limb-bud mesoderm, beginning at least as early as the early head-fold stage.

At the definitive-streak stage, the future limb-bud mesoderm is in the epiblast layer about halfway from the streak to the lateral margin of the area pellucida, at a level about halfway between the anterior and posterior ends of the streak. From this position the prelimb mesoderm migrates medially to the streak, and is invaginated into the mesoderm layer at a position about halfway between the anterior and posterior ends of the streak; after the head-process stage, it migrates anteriorly and laterally into the somatic layer of the lateral plate, ventral to the limb-bud epithelium. Mesoderm which will form the anterior limb-bud migrates anterior to mesoderm which will form the posterior limb-bud; mesoderm which will form the ventral portion of each limb-bud migrates posterolateral to mesoderm which will form the dorsal portion of each limb-bud.
Organization of the chick blastoderm edge
Authors: Downie J. Roger , Pegrum Susan M.
Published: April 2021

A band of cells forming the edge of the chick blastoderm, and attached to the vitelline membrane, causes the expansion of the blastoderm in the first few days of incubation by active migration across the vitelline membrane.

The structure and organization of these cells was examined by light microscopy (both on whole mounts and sections) and transmission electron microscopy. The account presented differs markedly from previous descriptions of these cells.

The band of cells at the blastoderm edge is an association, between 90 and 130 μm wide, of flattened, non-dividing cells forming a multilayer; some of these cells, and no other cells of the blastoderm, are attached to the vitelline membrane.

Each attached cell has a thin flattened lamella, centrifugally oriented and underlapping the next cell distally, except (1) the most distal cell, whose lamella is thick and long, though tapering, and is not overlain by other cells; and (2) the most proximal attached cell which has a short centripetally oriented lamella, as well as a centrifugal underlapping one.

The cells of the edge band not attached to the vitelline membrane also have flattened lamellae attached to the cells below; these lamellae are, however, unoriented.

The cells of the edge band all have plentiful cortical filaments and cytoplasmic microtubules. Specialized plaques are involved in the attachment of edge band cells to the vitelline membrane.

The form of this edge structure is compared with the outgrowth edge of a chick yolk sac epiblast explant cultured on vitelline membrane. It seems likely that the way the blastoderm edge cells are organized may explain their prodigious migratory activity.
Effect of erythropoietin on haemoglobin synthesis and haem synthesizing enzymes of mouse foetal liver cells in culture
Authors: Freshney R. I. , Paul John , Conkie David
Published: April 2021

The activities of aminolaevulinate synthetase, aminolaevulinate dehydratase and haem synthetase have been examined in short-term cultures of embryonic mouse liver.

Although synthesis of haemoglobin was induced by erythropoietin in these cultures no increase in activity was detected in any of the three enzymes over 24 h in culture. In each case, however, enzyme activity was higher when erythropoietin was present than in its absence.

The significance of these findings is discussed in relation to control of haemoglobin synthesis and it is concluded that enzyme activity is not rate limiting during induction of haemoglobin synthesis in vitro.
Dependence of tectal neuron differentiation on optic innervation in teleost fish
Authors: Schmatolla Ernest
Published: April 2021

The dependence of optic tectal development, especially differentiation of the stratum griseum periventriculare, on optic innervation is analysed in teleost fish in a comparative anatomical and experimental embryological study.

Tectal development of the blind cave fish, Astyanax hubbsi, lacking optic nerves hence having non-innervated tecta, is compared to its river relative, the normal-eyed A. mexicanus. In the embryonic tectum of cave fish there is less white and grey matter, with smaller sized nuclei in the subventricular zone; in the cave adult the tectum is hypoplastic with poorly differentiated neurons in the stratum griseum periventriculare.

Extirpation of eye Anlage in river fish embryos produced changes in the tectum comparable to the differences between embryonic tecta of cave and river fish.

One-eyed catfish, Ictalurus nebulosus, with a relatively fibre-poor optic nerve from an underdeveloped retina on the eyed side, showed better differentiated cells in the periventricular layer of the innervated side than in the non-innervated side. Periventricular neurons in the tecta of normal catfish were still better differentiated, demonstrating that differentiation of these cells is ‘dosage-dependent’ upon the amount of optic innervation.

Embryo zebrafish, Brachydanio rerio, subjected to extirpation of eye Anlage before optic nerve outgrowth, showed the dependence of differentiation of tectal subventricular cells on optic nerve ingrowth as early as the third day of development.

Zebrafish raised in the dark compared to those raised in light showed no discernible tectal differences under light microscopy.

Lack of differentiation of the neurons in the stratum griseum periventriculare in cave fish, and in eye-extirpated fish, has not been previously emphasized. Differentiation of these neurons appears largely dependent upon interaction with ingrowing optic axons, independent of visual function.
The occurrence of nuclear migration under thiol treatment effective in inhibiting neurulation
Authors: Messier Paul-Emil
Published: April 2021

Early chick embryos were explanted on culture media containing mercaptoethanol and dithiothreitol in concentrations reaching 10−1 M and 10−2 M respectively. Nuclear migration was found to occur normally even under such thiol concentration, which is more than required to inhibit neurulation. Electron miscroscopy revealed that microtubules were not affected in their number and morphology. However, nuclear migration was blocked with 2.5X10−5M colchicine; such treated embryos showed a loss of their microtubules. It is concluded that the two thiols do not act primarily on microtubules when they cause inhibition of neurulation.
Lens differentiation in vitro in the absence of optic vesicle in the epiblast of chick blastoderm under the influence of skin dermis
Authors: Mizuno Takeo
Published: April 2021

Dissociation and recombination experiments in vitro were found useful for analysing inductive tissue interactions involved in lens differentiation in the chick. When the presumptive cephalic region (epiblast plus hypoblast) of the embryo at pre-definitive streak to one-somite stage is cultivated in vitro combined with the dermis isolated either from the dorsal skin of 6·5-day embryo or from the 13·5-day tarsometatarsal skin, a lens with fibres or lentoid is produced in the epiblast. In no case is there an optic vesicle present in the explant. When the presumptive cephalic region (epiblast plus hypoblast) is cultivated without dermis, the lens is no longer formed. If the epiblast alone, dissociated from the hypoblast of the presumptive cephalic region, is recombined with the dermis of the 6·5-day dorsal skin, lenses or lentoids fail to develop. Cultivation of the epiblast alone cannot cause differentiation of the lens or lentoid. The dermis can be replaced by other mesenchymes or embryonic organs : gizzard mesen-chyme, mesonephros, sclerotome, liver and neural retina, though they are less effective than the dermis in producing lenses or lentoids in the epiblast. It may therefore be concluded that the lens is induced in vitro by the actions of at least two factors: the epiblast first becomes competent under the specific influence of the hypo-blast of the cephalic region. The lens will then differentiate from the competent epiblast by the non-specific action of various tissues such as the skin dermis, mesonephros, or sclerotome. The primary stage of lens induction (action of the hypoblast on the epiblast) seems not yet completed by streak stage.
Electron microscopic studies on developing cartilage II. Demonstration and distribution of glycogen in chick and mouse epiphyseal cartilage
Authors: Goel Suresh C. , Jurand A.
Published: April 2021

A procedure for the study of glycogen in the same cell, under both light and electron microscopes is described. The synthesis and accumulation of glycogen is a feature of chondrogenesis in the mouse epiphyseal cartilage and the amount of glycogen increases with the progress of differentiation. In contrast, no glycogen was detected in differentiating epiphyseal cartilage of the chick at any stage; except for a small amount of glycogen in the chick cartilage cells of the diaphysis. Because of this difference it is suggested that presence of glycogen is not essential for cartilage differentiation.
Properties of the primary organization field in the embryo ofXenopus laevis:III. Retention of polarity in cell groups excised from the region of the early organizer
Authors: Cooke J.
Published: April 2021

An experiment is described whose results strengthen the classical conclusion, due to Spemann and co-workers, that amphibian gastrulation movements are co-ordinated and controlled by properties intrinsic to the invaginating mesodermal zone, rather than by interaction between this and any field of cell-guiding information, symmetrically disposed about the presumptive head ectodermal region in the animal hemisphere of the blastula/ gastrula. The possibility remains, however, that the field of information coming to reside in the marginal mesodermal zone, is itself originally set up utilizing the animal pole as an origin, as well as the presumptive organizer site.

Experiments are then described where whole organizer apices, and also subapical squares of dorsal mesoderm from stage-10 donors, are implanted with presumptive polarity reversed 180° relative to that of the host. It is found that reasonably extensive migration, on the part of the graft and the influenced host tissue, is required for the individuation of recognizable axial structure, and that such migration is often prevented in reversed implants due to a retention of autonomous polarity in host and graft.

Reasons are suggested for the apparently greater autonomy, in this respect, of apical organizer plugs, but evidence is given that autonomy is nevertheless expressed even by squares of dorsal presumptive mesoderm of side ca. 0·1 mm. The significance of this observation, for theory concerning the nature of the cellular properties involved in the maintenance of embryonic fields, is discussed.
Inhibitors in amphibian morphogenesis: Enzymic degradation of an inhibitor for the vegetalizing factor
Authors: Born J. , Tiedemann H. , Tiedemann H.
Published: April 2021

A naturally occurring inhibitor for the vegetalizing inducing factor has been incubated with different enzymes. Pancreatic ribonuclease, ribonuclease-T1, deoxyribunuclease, neur-aminidase as well trypsin and papain diminish the inhibitor only very slightly or not at all. Pronase, a proteolytic enzyme from Streptomyces griseus inactivates the inhibitor completely.
Experimental studies on the organization of the preimplantation mouse embryo:I.Fusion of asynchronously cleaving eggs
Authors: Stern M. Susan , Wilson I. B.
Published: April 2021

The interaction between mouse eggs conjoined in pairs of different ages and stages of development has been examined:

Forty-two per cent of chimaeras formed from 8-cell eggs paired with late morulae or early blastocysts produced morphologically normal, but large, blastocysts. Fusion of pairs of vitally labelled and unlabelled eggs has shown that presumptive trophoblast derived from as late as the early blastocyst stage can become incorporated into the inner cell mass of chimaeras.

These observations suggest that the preimplantation chimaeric embryo can regulate for chronological differences in its constituent cells and that the trophoblast up to the early blastcyst stage may still be developmentally labile.
The role of water-regulating mechanisms in the development of the haploid syndrome in Xenopus laevis
Authors: Hamilton Louie , Tuft P. H.
Published: April 2021

The uptake of water by haploid and diploid sibling embryos of Xenopus laevis has been investigated by measuring the density changes which occur during the development of intact embryos from the blastula to the late tail-bud stage, and of explants from which most of the presumptive endoderm has been removed.

The results show that up to the mid-gastrula stage there is no difference between the haploid and diploid embryos; but from then on, whereas the diploid volume increases steadily, the haploid gastrulae undergo a series of cyclical volume changes due to loss of fluid through the blastopore. It is concluded that this is the result of an excessive inflow of water through the haploid ectoderm, because it was found that the volume of haploid ectodermal explants increased much more rapidly than the volume of similar diploid explants. Excess flow through the haploid ectoderm also accounts for other characteristics of the haploid syndrome-microcephaly and lordosis.

It is suggested that it is the doubling of the cell number in haploid embryos with the consequent 25% increase in aggregate cell membrane area which accounts for the difference between the uptake of water by the two types of embryos. It is also suggested that changes in the rate of water flow through the ectoderm and endoderm which are thought to account for the accumulation of water in the blastocoel and archenteron in the normal diploid embryo arise in a similar way.
Effect of growth conditions on development of the cellular slime mould,Dictyostelium discoideum
Authors: Garrod D. R. , Ashworth J. M.
Published: April 2021

The effect of growth in the presence and absence of 86 mM glucose on fruiting-body number and size, fruiting-body proportions and morphogenesis in the slime mould Dictyostelium discoideum, strain Ax-2, has been investigated. Cells grown in the absence of glucose (N.S. cells) formed 2·1 times more fruiting bodies than glucose-grown cells allowed to differentiate under the same conditions and at the same cell density. Glucose fruiting bodies were 2·6 times larger than N.S. fruiting bodies.

During aggregation, N.S. aggregation streams generally broke up into numerous secondary aggregation centres. Glucose streams generally did not break up but moved into the initial aggregation centre. Each secondary centre formed one small grex, whereas initial centres fragmented into several grexes which were larger than those formed from secondary centres. The preponderance of secondary centres in N.S. aggregation and of initial centres in glucose aggregation accounts for the difference in size and number of fruiting bodies. We speculate about the mechanism giving rise to the morphogenetic difference.

The spore: stalk ratio was 3·95:1 in glucose fruiting bodies and 2·70:1 in N.S. fruiting bodies. This difference is not related to the difference in fruiting-body size because proportions are size invariant for both fruiting-body types. Some difference in the physiological mechanism which determines proportions is suspected.
Observations on the ultrastructure of chick-embryo cardiac myoblasts re-aggregated in long-term cultures
Authors: Zacchei Anna Maria , Caravita Silvia
Published: April 2021

Myoblasts obtained by trypsin dissociation of 6-day chick-embryo hearts re-aggregated in rolling tubes and formed a pulsating mass within 1 h.

Newly formed intercalated discs (adhesion plaques) were the most frequent type of inter-cellular contact in the earlier stages of culture.

Desmosomes were also present.

Focal tight junctions were rare and difficult to identify.

In advanced aggregates more extended regions of very close plasma membranes apposition could be observed; lanthanum infiltration did not reveal obliteration of the intercellular gap.

The most striking feature, even after 12 days of culture, is the disorder of the contractile units within the sarcoplasm and the irregularity of the cell outlines. The ineffectiveness of the factors responsible for the orientated disposition of myofibrils in culture conditions has been emphasized.

The smooth endoplasmic reticulum never attains a regular arrangement in relationship with the myofibrillar banding. Subsarcolemmal cysterns containing a finely granular matrix (peripheral couplings) have been found after the first 24 h of culture; it has been observed that they reach their mature form only in the last stages of culture.

The T-system is lacking. Numerous pits, often complicated by beading, are present in the peripheral sarcoplasm.

All these features may affect the physiological response that can be recorded from these cells.
The effect of methotrexate on DNA synthesis and its reversal by folinic acid
Authors: Berry C. L. , Germain Jocelyn , Looker T.
Published: April 2021

In suckling mouse liver methotrexate is a powerful inhibitor of DNA synthesis, as assessed by the incorporation of tritiated deoxyuridine. Folinic acid is an effective antagonist.
Insulin and glucagon release from the isolated pancreas of foetal and newborn mice
Authors: Lernmark Åke , Wenngren Britt Inger
Published: April 2021

The simultaneous release of insulin and glucagon was studied with isolated pancreas preparations from foetal and newborn mice. Glucose, alone or in combination with arginine, did not affect immunoreactive insulin (IRI) of glucagon-like immunoreactivity (GLI) release from the pancreases of 18-day-old foetal mice. However, on the first postnatal day, glucose stimulated the release of IRI and, in the presence of arginine, depressed that of GLI. It is concluded that the systems for recognition of glucose in mouse pancreatic α2-cells as well as those in the β-cells do not mature until after birth.
In vitrostudies inTubularia:a morphological role for digestive cells
Authors: Glickman Marc H. , Lesh-Laurie Georgia E.
Published: April 2021

A chemically defined in vitro system for Tubularia has been developed. At 24 h after explantation of coenosarc, digestive cells attached to the substrate and migrated from the explant. The digestive cells migrated by a gliding motion with a fan-like membrane acting as a leading edge. Within 48 h a digestive cell monolayer was formed and invasion of this area by epithelio-muscular, gland and interstitial cells occurred. Autoradiographic study of 48-72 h cultures treated with [3H]thymidine showed nuclear incorporation of the label in digestive, epithelio-muscular, interstitial, cnidoblast and gland cells.

When explants were grown on collagen-coated coverslips, accelerated attachment and migration of digestive cells was observed. Explants were also grown on Millipore filters. No digestive cell attachment occurred but epithelio-muscular, gland and interstitial cell attachments to the filter were observed. From these experiments, a morphological role for the digestive cells as a substrate for other cells of the coenosarc is postulated.

Hydranth extract was supplemented to the culture medium. Studies with this material were performed with coenosarc from ‘late summer’ animals in which only 10-15% of the explants normally entered culture. However, with the addition of the extract, 100% of the explants went into culture. Interstitial cell populations increased 2-3 times in extract-treated explants.
Morphogenesis in the cellular slime mouldDictyostelium discoideum;the formation and regulation of aggregate tips and the specification of developmental axes
Authors: Farnsworth P.
Published: April 2021

A general discussion of ‘organizing regions’ and the specification of biological patterns is followed by introducing the idea that the tip of the slime mould cell mass is such an ‘organizer’. This view is supported by a discussion of the developmental ubiquity of the tip and its effects.

A staging system is described which assigns numbers to sequential morphological changes during development.

A set of experiments investigating the role of the tip are described, using techniques of cell labelling, grafting and bisection of cell masses with barriers, and the manufacture and use of cylindrical barriers of permeable cellulose.

The results of such experiments show:

That the tip of the cell mass is made of the same group of cells from stage 10 (late aggregate) to stage 20+ (culmination). That a stage 10 aggregate will regenerate a new tip in an average time of 32 min. That if a stage 10 aggregate is bisected by an impermeable barrier two tips, indicating two new developmental axes, develop in an average time of 34 min. That if a stage 10 aggregate is bisected for 40 min, the barrier removed and one of the tips removed, the remaining tip inhibits the re-formation of the second tip, and the polarity of the aggregate is again reorganized with respect to the remaining tip. That if experiments (3), (4) and (5) are repeated with a stage 9 aggregate, which is an hour younger, all the regulation times are increased by about 60 min. Similarly a stage 8 aggregate takes over 120 min longer to show the effect. That if part or all of a cell mass from any stage is placed inside a cellulose tube, all the enclosed cells differentiate into stalk cells.

These results are then discussed in relation to pattern formation and the role of the tip in polarization and the specification of new developmental axes in cell masses.

A model for culmination in the slime mould is proposed which takes account of the above results. The essence of this model is that at no time are stalk and spore cells ‘determined’ in the classical sense, and that, by a non-signalling positional information system, the size invariance of the ratio of stalk to spore cells seen in the fruiting body is a result of the mechanical process of culmination.
The pattern of growth ofClytia johnstoni
Authors: Hale L. J.
Published: April 2021

A quantitative study of the growth of Clytia johnstoni is described. The distance between hydranths is most commonly between 3 and 4 mm. The average internode lengths and their variability frequently differs not only between colonies but also between stolons of a single colony. The differences are therefore unlikely to be genetic ones. Occasionally much longer internodes occur (up to 8 mm). Hydranths and their stalks differ widely in size but not in morphology. The differences can be caused by the amount of food given. Very vigorous and very poorly growing colonies tend to have slightly longer internodes than the more common colonies of average vigour. Most colonies produce both additional (secondary) hydranths and stolon branches. Hydranth branches grow spaced from existing hydranths; in normal colonies the spacing appears to originate from the hydranth away from the growing tip in an internode. Ln vigorous growth the hydranth towards the growing stolon tip is the place of reference. Stolon branches occur mostly near to hydranths, either primary or secondary, more especially near to the hydranth farther from the growing tip of the main stolon. There appears to be a limit to the number of branches to an internode. In vigorous growth an optimum of two and a maximum of three is found, either secondary hydranths, or stolons, or both. Stolons vary in their rate of growth. A stolon slowly increases its rate of growth as it gets longer. In a colony of little vigour, the rate is low and variable and may cease and restart; the coenosarc sometimes breaks, dividing the colony. Hydranths take 1–2 days to grow, sometimes 3 days in colonies of little vigour. They remain open for a limited period: normally about 5–7 days; sometimes longer -up to 9 or 10 days; and significantly shorter, 1–3 days, in a colony of little vigour. At the end of their period of existence, hydranths regress. They normally start to regenerate a new hydranth within 1–2 days but some do not do so for longer or very long periods. The whole cycle of hydranth growth, maturity and regression falls into either a 6-to 7-day cycle or a 10-to 11-day cycle. Evidence is presented to support the suggestion that there is a situation of competitive interaction between growth of the various parts of the colony. A priority series for the various parts of the colony is constructed.
Evidence of morphogenetically significant diffusion gradients inHydra viridislengthened by grafting
Authors: Shostak Stanley
Published: April 2021

Morphogenetic inhibitory gradients were produced in Hydra viridis having 2–5 gastric regions or 2–5 peduncles grafted in tandem. The frequency of head regeneration at graft borders changed as a function of distance from the terminal head, and the frequency of foot regeneration changed as a function of distance from the terminal foot. The object of the study was to characterize and compare these morphogenetic inhibitory gradients in light of Crick’s (1970) model of diffusion gradients.

Heads regenerate more easily on gastric regions and feet on peduncles. This is shown in several ways: (1) on gastric regions more heads and fewer isolated tentacles and ‘spikes’ (isolated hypostomes) form, while the opposite is true on peduncles; (2) more heads are regenerated at graft borders between gastric regions than at those between peduncles at comparable distances from the terminal head, while more feet are regenerated at graft borders between peduncles than at those between gastric regions at comparable distances from the terminal foot; (3) the Y intercepts for gradients of the frequencies of head and of foot regeneration as functions of distance (which are the theoretical frequencies of regeneration at the ends of the animal) are higher for head regeneration on gastric regions than on peduncles, and for foot regeneration on peduncles than on gastric regions. This is explained in terms of relative differences in either competence to regenerate or sensitivity to inhibitors.

The slopes of the frequencies of head and of foot regeneration as functions of distance from the respective ends change inversely with the numbers of gastric regions and peduncles grafted. This is explained in terms of changes in the distance between the sources of diffusible inhibitors and the sinks which use them up. The results are taken to support Crick’s model in which a linear gradient of a diffusible substance is produced between its source and sink.
The development of tubular heart in RNA-treated post-nodal pieces of chick blastoderm
Authors: Niu M. C. , Deshpande A. K.
Published: April 2021

Post-nodal pieces of the stage-4 chick blastoderms were transected 0·6 mm posterior to Hensen’s node and cultured in vitro with and without chicken-heart RNA. After 24 h the expiants were fed daily with fresh egg-extract medium for 4 days. On the 4th day pulsating heart was found in the RNA-treated but not in the untreated series. Histological examination revealed that cell differentiation other than of erythrocytes and epithelial tissue seldom occurred in the control and, in contrast, pulsating heart and cardiac myoblasts were present in most of the RNA-treated expiants that had differentiated.
Interactions between Ovary and Lateral Oviduct in Drosophila melanogaster
Authors: Pantelouris E. M.
Published: April 2021

Experimental evidence is produced to show that during metamorphosis in Drosophila melanogaster:

The growth-of the lateral oviducts depends on an influence of the ovaries. The growth of the ovaries does not depend on a reciprocal influence. The growth of the vasa deferentia is independent of any influence from the testis.