bluuebunny/crossref_metadata_2025 huggingface dataset:
Teratogenic effects of calcium salts on chick embryos
Authors: Grabowski Casimer T.
Published: April 2021

This investigation began as an attempt to protect chick embryos from the teratogenic effects of hypoxia by means of exogenously applied calcium pantothenate. The attempt was not only a failure, but it appeared that the compound alone was highly teratogenic. Since it was disturbing to consider that a vitamin, in low dosage, was teratogenic, the phenomenon was studied further by injecting equivalent concentrations of other calcium salts into the embryo. It quickly became apparent that very small quantities of calcium chloride solution injected into either the subgerminal area of the yolk sac or the allantois also produced pronounced abnormalities.
Studies on pattern regulation in hydra
Authors: Webster Gerald , Wolpert Lewis
Published: April 2021

The regulation of hydra into hypostomal and non-hypostomal regions is considered as a model for the regulation of a linear pattern into two compartments. Regulation of such a system requires graded differences and a ‘principle of limited realization’. The hypostome is the dominant region in hydra and the time for its determination in isolated pieces depends upon the original position of the piece along the linear axis. The time increases in a disto-proximal direction from 4 h to more than 20 h. The determination of the hypostome is the first detectable event in distal regeneration and is probably the time-determining step in this process. Work on other hydroids is reinterpreted in these terms. The time for hypostome determination in proximal regions is significantly affected by the presence of more proximal regions, while in distal regions the time appears independent of the presence of more proximal regions.
Isolation and characterization of a low-molecular-weight substance activating head and bud formation in hydra
Authors: Schaller H. Chica
Published: April 2021

From crude extracts of hydra, a substance activating head formation was isolated and enriched at least 100000-fold. The molecular weight was determined to be approximately 900. Sensitivity against proteases suggests that it is a peptide. The substance acts at a concentration equivalent to the extract of 1 hydra per ml or at a concentration of less than 10 * 10M. In its highly purified form the substance activates head and bud formation.
Histone synthesis during development ofTriturusembryos
Authors: Imoh Hiroshi , Kawakami Izumi
Published: April 2021

Synthesis of histone fractions and one basic protein fraction, which moved fast on gel electrophoresis and had been reported to increase in nuclei accompanying a decrease in cytoplasm during development, were studied with radioactive carbon dioxide as a tracer. Acid-extractable proteins of nuclei or cytoplasm, isolated from labelled embryos, were fractionated by polyacrylamide disc electrophoresis and the histone fractions and the fastmoving basic protein were identified. Radioactivities in these fractions and DNA were determined.

Synthesis of the fast-moving basic protein was not detected throughout the period of development studied and this fraction was thought to move in from the cytoplasm to the nucleus during development. Syntheses of histone fractions were observed as early as the blastula stage. Rates of syntheses of four histone fractions (f3, f2b, f2a2 and f2al) per embryo increased thereafter, keeping pace with the increase in the rate of DNA synthesis with advancing development. The rate of the very lysine-rich f1 histone synthesis per embryo did not increase after the gastrula stage and the rate remained almost constant until the late tail-bud stage.

Compositions of newly synthesized histones, calculated from the radioactivities incorporated into histone fractions, were almost the same during development and among different regions of neurula or tail-bud-stage embryos, with the exception of the f1 fraction, which varied depending on the stage and region of the embryos.

The results are discussed in relation to the possible roles of the histone fractions in developing embryos.
Differentiation of the mammalian hepatic primordiumin vitro:I. Morphogenesis and the onset of haematopoiesis
Authors: Johnson G. R. , Jones R. O.
Published: April 2021

This study was made to determine the nature of tissue contributions to murine hepatic morphogenesis, the developmental potential in vitro of various hepatic regions prior to and during definitive liver development, and to accurately determine the time of onset of hepatic haematopoiesis in vitro. Embryos were precisely staged by somite counts as well as time of original mating, and tissues were removed from the hepatic area at stages between anterior intestinal portal (9 days gestation) and definitive foetal liver (11·75–12 days gestation), and maintained in vitro for up to 4 weeks.

Expiants of anterior intestinal portal origin gave rise only to sheets of epithelial cells, whereas tissues from embryos of 10 –11 days gestation, containing the hepatic sacculation of the ventral wall of the gut, gave rise to sheets of polygonal, frequently binucleate cells and granule containing cells, both suggestive of hepatic cytodifferentiation. Sinusoidal morphogenesis was also observed. Haematopoiesis was detected in vitro only in explants from 11·5-to 12-day embryos (28 to 30+ somites). The blood elements observed consisted of erythroblasts, granulocytes, megakaryocytes as well as macrophages and yolk sac derived erythroblasts. Duct systems, probably representative of the bile system, were also observed to develop.

Current theories regarding hepatic morphogenesis are considered in the light of these observations. The inductive and cell seeding concepts of the origin of haematopoietic cells are discussed in view of the observed precise timing of the onset of hepatic haematopoiesis. Due to the substantial gestation time-gap between the detection of possible circulating haematopoietic stem cells (9 days gestation) and the actual onset of hepatic haematopoiesis (11·5 days gestation), it is suggested that either a suitable microenvironment must first develop within the hepatic area for haematopoiesis to occur, or that haematopoietic tissue arises in situ in the hepatic Anlage.
Genetic and physiologic control of fissioning and sexuality in planarians
Authors: Grasso Mario , Benazzi Mario
Published: April 2021

Several fissiparous strains of the planarian Dugesia gonocephala s.l. have been subjected for many months to continuous feeding on crushed tissues of sexually mature specimens of the planarians Polycelis nigra or (in a few cases) Dugesia lugubris. In a very high percentage of cases (especially after feeding on Polycelis nigra crushed tissues) the fissioning phenomena have been stopped and a sexual state has been induced. The sexualized specimens developed hyperplasie ovaries, testicular follicles and a more or less complete copulatory apparatus; some of them went so far as to lay sterile cocoons. As for the nature of sexualizing substances contained in crushed tissues of sexual planarians, further researches are required; we suggest they are neurosecretions stimulating sexuality and so inhibiting fissioning phenomena.
Measurements of cell adhesion:II Quantitative study of the effect of divalent ions on cell adhesion
Authors: Hornby Janet E.
Published: April 2021

The forces of interaction found for 5-day chick limb-bud cells in media containing different divalent ions (magnesium, calcium, strontium or barium) show that the cells are most adhesive in the presence of magnesium ions, then calcium and strontium, then barium. When magnesium and calcium ions are present together at similar concentrations the calcium ions modify the action of the magnesium ions. The importance of magnesium ions in cell adhesion is discussed.
Dermo-epidermal interactions between birds and mammals: differentiation of cutaneous appendages
Authors: Dhouailly Danielle
Published: April 2021

The capacity of skin constituents to participate in feather and hair morphogenesis has been analysed in chick and mouse embryos. Reconstituted homo- and heterospecific skin explants, consisting of epidermis and dermis from both species, were cultured for 8 days on the chorioallantoic membrane of the chick. Recombinants of dorsal 11·5- and 12·5-day mouse epidermis and dorsal 7-day or tarsometatarsal 12-day chick dermis gave rise to stage 2 abnormally elongated hair prepapillae. Associations of plantar 14·5-day mouse epidermis with dorsal 7-day chick dermis formed stage 3 hair papillae. The reverse combinations of dorsal 5- and 6-day chick epidermis and dorsal 11-5- to 14-5-day mouse dermis gave rise to arrested feather buds (with 11·5- and 12·5-day dermis) and to short and aberrant feather filaments (with 12·5-, 13·5- and 14·5-day dermis). These short filaments were characterized by the differentiation of easily recognizable but chaotically arranged barb-ridges. The same type of feather differentiation was obtained in recombinants of normally glabrous epidermis from the comb, midventral apterium, or tarsometatarsum from 10-day chick embryos and 13·5- and 14·5-day dorsal mouse dermis. Control homospecific recombinations formed typical well organized feather filaments or stage 4–5 hair cone follicles. Heterospecific associations of feather- or hair-forming epidermis with dermis from glabrous regions did not differentiate any kind of cutaneous appendages. When distribution of feather filaments was compared in recombinants of chick epidermis with either dorsal pelage hair dermis or upper-lip vibrissal dermis, it was found that the feather pattern conformed with the regional origin of the mouse dermis. It was concluded that, during feather and hair development, the dermis transmits two kinds of morphogenetic messages: one that is apparently non-specific and can therefore be understood and expressed by a foreign epidermis from another zoological class, leading to the formation of feather or hair buds, in conformity with the origin of the epidermis; the other message contains specific cues necessary for specific morphological organization of feather and hair.
Morphogenetic properties of the parts of the colony ofClytia johnstoni
Authors: Hale L. J.
Published: April 2021

The morphogenetic potencies of the various parts of Clytia johnstoni have been ascertained by isolation and by grafting. The various parts of the colony behave on isolation in the following ways: Immediate development of a stolon (which in turn may grow hydranths, as in a normal colony). Shown by (i) all parts of the stolon except sometimes the growing tip, (ii) stalk primordia of length 0·5–1·4 mm, (iii) stalks of open hydranths (polarized, the stolon grows out of the cut basal end). Immediate differentiation of a polyp. Shown by (i) stalk primordia longer than 1·7 mm and some between 1·4 and 1·7 mm, (ii) bulbs greater than 0·28 mm diameter (i.e. had reached contractile stage), (iii) bulb primordia of all sizes having a ‘stalk’ longer than 0·35 mm; only the larger bulbs became polyps if the ‘stalk’ was shorter than 0·35 mm. Immediate incipient differentiation (of a polyp ?) was shown by some stalk primordia of length 1·4–1·7 mm long. Partial hydranth differentiation (stomach and buccal region, no tentacles) was shown by an occasional isolated bulb. Delayed stolon development. The time delay is variable but not random, with a marked tendency to start after 3–5 days and a less marked tendency after 9 days isolation. Shown by (i) all isolates which differentiated a polyp immediately on isolation, (ii) most bulb primordia less than 0·23 mm diameter and ‘stalks’ shorter than 0·35 mm, (iii) a few bulbs 0·23–0·27 mm in diameter. No development at any time. Shown by (i) Stalk primordia less than 0·5 mm long, (ii) bulbs of less than 0·23 mm diameter, (iii) some stolon tips, (iv) most isolated polyps (after regression). There is some evidence that a contractile growth region in an isolate gives it the power of immediate differentiation, in a stalk primordium to produce a stolon and in a bulb to a polyp. The time at which a stalk primordium passes to a bulb primordium appears to correspond to the time when, on isolation, it switches from being stolon producing to being hydranth producing. The peaks of regenerative activity (noted in 2(d) above) are the same as the most likely life-spans of hydranths but it is not known if there is any relation between the two sets of observations. The tips of growing stolons and hydranth stalk primordia have specific but weak inductive powers.
Size regulation in chimaeric mouse embryos
Authors: Buehr Mia , McLaren Anne
Published: April 2021

The size of the inner cell mass and egg cylinder was estimated in mouse embryos derived from the aggregation of two 8-cell stages and in control ‘single’ embryos. The comparison suggests that growth regulation in the ‘double’ embryos takes place fairly rapidly, after the formation of the egg cylinder but before the appearance of the pro-amniotic cavity.
Analyse morphologique des chimères obtenues par greffes embryonnaires chez les Amphibiens Urodèles
Authors: Charlemagne Jacques , Houillon Charles
Published: April 2021

Allogenic and heterospecific chimaeras have been made between four species of Amphibian Urodeles: Pleurodeles waltlii Michah., Triturus alpestris Laur. Trituras helveticas Raz. and Ambystoma mexicanum Shaw. These chimaeras are complementary (groups A, B, C) or not (groups D and E) and possess different morphologic types.

Allogenic chimaeras develop normally, are able to breed and easy to achieve. Their principal interest, especially for E group, is that each one possesses two pairs of gonads.

A number of certain types of heterogenic chimaeras have been obtained and have reached metamorphosis: 158 chimaeras between Pleurodeles waltlii and Triturus alpestris and 134 chimaeras between Pleurodeles waltlii and Triturus helveticas. Some live several years and raise interesting problems: immune reactions, growth regulation and sexual differentiation.
The development of Bithynia tentaculata (Prosobranchia, Gastropoda) after removal of the polar lobe
Authors: Gather James N. , Verdonk Nico H.
Published: April 2021

The polar lobe of the egg of Bithynia, with a volume of less than 1 % of that of the egg, was surgically removed. Lobeless embryos form no mesentoblast cell nor mesoderm bands. They fail to establish bilateral symmetry and to form eyes, foot, operculum, shell, etc. They always differentiate larval head cells, ganglia, larval liver and mesenchyme and sometimes columnar epithelium, stomodeal entrance cells. endodermal tubes and muscles.

These results are discussed in relation to the structure of the lobe, the analysis of development of Bithynia and to similar experiments in other species.
Interaction between the proximo-distal and antero-posterior co-ordinates of positional value during the specification of positional information in the early development of the chick limb-bud
Authors: Summerbell Dennis
Published: April 2021

The experiments examine the extent of reduplication of skeletal parts across the anteroposterior axis, following the transplantation of a zone of polarizing activity (ZPA) to the anterior margin of the limb-bud at successively later stages. Previous studies have suggested that the function of the apical ectodermal ridge (AER) is to maintain cells in a special region at the distal tip (the progress zone) labile, with respect to their positional value along the proximo-distal axis. Similarly, the results of these experiments demonstrate that cells in the progress zone are able to change their antero-posterior positional value under the influence of the grafted ZPA, while cells at more proximal levels remain unaffected. In turn, the ZPA may effect the activity of the AER and hence the progress zone.
Comparative remarks on the development of the tail cord among higher vertebrates
Authors: Hughes A. F. , Freeman R. B.
Published: April 2021

The development of the caudal region of the neural tube is compared in tailed mammals with that of the chick and human. In rat, mouse, opossum and pig, the lumen of the cord extends caudally in an even manner, whereas in the chick and in man the addition of small cavities to the lumen results in a phase of irregular growth. In mammals with unreduced tails, the site of closure of the posterior neuropore is at the tip of the tail, whereas in pig, man and in the chick closure occurs before the formation of the tail-bud. The teratological implications of these findings are discussed.
Irradiated cells and blastema formation in the adult newt, Notophthalmus viridescens
Authors: Desha David L.
Published: April 2021

This investigation primarily consisted of labeling cells in forelimbs of the newt; irradiating the labeled limb; and then inducing regeneration with a non-irradiated skin graft.

The labeled cells were obtained by injecting tritiated thymidine intraperitoneally into newts with regenerating right forelimbs. The cells in the regenerate which were undergoing DNA synthesis were labeled, and those which differentiated and ceased to divide remained labeled for long periods. The labeled regenerates were irradiated with 2000 R, and subsequently the irradiated limbs were re-amputated. Some limbs were supplied with a hind-limb skin autograft; others received no graft. The limbs without the grafts did not regenerate, whereas several of those with grafts did.

Histological studies of the blastemas of the new regenerates indicated that labeled, irradiated cells were released from the internal tissues near the amputation surface and were incorporated into the blastema. These cells presumably formed a portion of the differentiated tissues of the new regenerate. Studies were performed to verify that the labeled cells in the blastemas were derived from irradiated tissues and were not derived from extraneous sources.

This investigation substantiates reports that irradiation with 2000 R inhibits limb regeneration, and that at least some irradiated cells can contribute to a blastema formed on an irradiated limb.s
Etudes expérimentales sur le rôle des somites au cours des premiers stades du développement du membre antérieur chez l’embryon du Chélonien Emys orbicularis L.
Authors: Vasse J.
Published: April 2021

Experimental study on the role of the somites during the early stages of development of the front limbs of the embryo of the chelonian Emys orbicularis L

Ablation of postotic somites 6—13 on one side in embryos of Emys orbicularis L. at the developmental stage when 20–23 somite pairs were present, led to arrest of forelimb-bud development in the somatopleure adjacent to the ablated somites on the operated side. Limb development in the somatopleure adjacent to intact somites on the operated side was unaffected, attaining the same stage as on the non-operated side. Ablation at later stages (25–33 somite pairs) did not prevent development of the limb adjacent to the ablated somites. When a part of the prospective somatopleure was injured, the remaining part formed a small limb-bud. When an obstacle was placed between the somatopleural mesoderm and the adjacent somite, development of the somatopleure stopped at this level.

These results corroborate those obtained from previous studies in various reptilian embryos concerning the role of the ventral somite extensions as activators of proliferation in the somatopleural mesoderm. Injury to the ventral extension alone led to serious dis-turbances in the somatopleural mesoderm adjacent to this somite.
The relation between larval and adult abnormalities in the abdominal segmentation of Calliphora erythrocephala (Diptera)
Authors: Pearson M. J.
Published: April 2021

Early embryonic stages of Calliphora erythrocephala were X-irradiated to produce abdominal abnormalities of segmental pattern. Abnormal patterns were examined in the puparial stage: 75 (Series AA) larvae with dorsal or lateral abnormality were classified and the larval abnormality compared with the pattern of abdominal segmentation in the emerging adult fly; another 75 (Series aa) larvae were examined in dorsal, lateral and ventral aspect with respect to segmental abnormality and again in relation to abnormality in the adult.

It was observed (i) that the pattern of abdominal intersegmental membranes is not necessarily maintained through metamorphosis and may regulate to normal; (ii) that tergal abnormalities in the adult result from a failure of correct bilateral fusion of corresponding contralateral hemitergites; (iii) that reduction or displacement of scleral structures in an adult abdominal segment is correlated with deficiency or displacement of epidermal muscle insertions, and hence presumably with the histoblast anlagen which are normally associated with them. In the case of dorsal abnormalities, hemitergite differentiation is normal.

Larval abdominal abnormality patterns point to the mode of bilateral morphogenesis of the germbands in embryogenesis. The relation of adult to larval abnormalities suggests some similar independence of contralateral hemisegments at metamorphosis.

The possible developmental origin of abdominal abnormalities produced by X-irradiation of embryos is discussed, and the conclusions of the analysis of the relation between larval and adult abnormalities in Calliphora are set against the propositions of previous students of such abnormalities in Drosophila.
Gastrulation in the mouse : Growth and regionalization of the epiblast
Authors: Snow M. H. L.
Published: April 2021

Histological determination of cell numbers in the mouse embryo between and days post coitum show that growth during this period, in which gastrulation occurs, is not uniform. Prior to primitive streak formation mean cell generation time is about 9 h. Co-incidental with the appearance of the primitive streak the embryo enters a period of rapid growth, lasting about 24 h, during which the mean cell generation time must be about 5 h in order to account for the increase in cell numbers. A more detailed study, in which variations in mitotic activity in different regions of the embryo have been analysed, has identified a small region, the so-called ‘proliferative zone’, constituting about 10 % of the whole epiblast, in which cell generation time may average as little as 2·3 h over a 24 h period. The cell generation time for other epiblast regions is estimated at about 6·5 h.

It is calculated that the proliferative zone, in the 24 h period commencing with primitive streak formation, could generate about half the cells in the -day embryo. The topographical consequences of such a rapidly expanding region in the embryo are discussed in the light of other, circumstantial evidence, and it is postulated that the cells generated in the PZ may constitute the ectoderm of later stage embryos.
Localization and synthesis of alphafoetoprotein in post-implantation mouse embryos
Authors: Dziadek M. , Adamson E.
Published: April 2021

The localization and synthesis of alphafoetoprotein (AFP) during mouse embryogenesis were studied by immunoperoxidase and by immunoprecipitation after radioactive labelling, using an antiserum prepared against AFP. AFP is first detectable in embryos on the 7th day of gestation (7th day embryos). In 7th and 8th day embryos AFP is confined to visceral (proximal) endoderm cells around the embryonic region of the egg cylinder. Visceral extra-embryonic and parietal (distal) endoderm cells do not contain AFP. By the 9th day of gestation AFP is also present in the extra-embryonic ectoderm, mesoderm and embryonic ectoderm cells around the three cavities of the embryo. These tissues do not synthesize AFP when cultured in isolation, but can adsorb AFP when it is added to the medium. On the 12th day of gestation AFP synthesis is confined to the endoderm layer of the visceral yolk sac. It is concluded that the ability to synthesize AFP is a property which is restricted to the visceral endoderm during early post-implantation development. The presence of AFP in other tissues of the embryo appears to be due to adsorption.
Différenciation in vitro de blastodermes de Truite (Salmo irideus) dépourvus de couche enveloppante
Authors: Devillers Ch. , Colas J. , Richard L.
Published: April 2021

L’étude structurale et fonctionnelle du blastoderme de Poisson conduit à y distinguer deux ensembles: la couche enveloppante et les blastomeres profonds. Si du seul point de vue quantitatif (volume total des cellules) la couche enveloppante est beaucoup moins importante que la masse blastomérienne, du point de vue qualitatif elle représente un élément essentiel dans le développement du blastoderme depuis le stade indivis jusqu’à la fermeture du blastopore. C’est en elle que résident les propriétés d’imperméabilité, de coordination des mouvements cellulaires, de contractilité et d’expansibilité d’ensemble du blastodisque qui entrent en jeu à divers stades de la prémorphogenèse et de la morphogenèse. Vis-à-vis de ce revêtement ‘actif’ le groupe blastomérien profond fait plutôt figure de masse inerte, ou tout au moins incohérente, incapable ‘d’initiative’ et dont les possibilités morphogénétiques, en particulier les mouvements lors de la gastrulation, ont besoin d’être coordonnées, dirigées par la couche enveloppante. Mais c’est de cet ensemble que dérive la quasi-totalité du matériel cellulaire qui édifiera l’embryon; la couche enveloppante ne constituera que l’assise la plus superficielle de l’épiderme, après avoir fourni au matériel de la zone marginale un appoint cellulaire, presque négligeable en quantité.
In vitro studies on the morphogenesis and differentiation of the mesoderm subjacent to the apical ectodermal ridge of the embryonic chick limb-bud
Authors: Kosher Robert A. , Savage Mary P. , Chan Sai-Chung
Published: April 2021

It has been suggested that one of the major functions of the apical ectodermal ridge (AER) of the embryonic chick limb-bud is to maintain mesenchymal cells directly subjacent to it (i.e. cells extending 0·4–0·5 mm from the AER) in a labile, undifferentiated condition. We have attempted to directly test this hypothesis by subjecting the undifferentiated subridge mesoderm of stage-25 embryonic chick wing-buds to organ culture in the presence and absence of the AER and the ectoderm that normally surrounds the mesoderm dorsally and ventrally. During the period of culture, control explants comprised of the subridge mesoderm capped by the AER and surrounded by the dorsal/ventral ectoderm undergo progressive morphogenesis characterized by polarized proximal to distal outgrowth and changes in the contour of the developing explant, and ultimately form a structure grossly resembling a normal distal wing-bud tip. tin contrast, explants from which the AER and dorsal/ventral ectoderm have been removed (minus ectoderm explants) or from which just the AER has been removed (minus AER explants) form compact, rounded masses exhibiting no signs of morphogenesis. During the polarized proximal to distal outgrowth control explants undergo during the first 3 days of culture, as cells of the explant become located greater than 0·4–0·5 mm from the AER, they concomitantly undergo a sequence of changes indicative of their differentiation into cartilage. However, those cells which remain 0·4–0·5 mm from the AER during this period retain the characteristics of non-specialized mesenchymal cells. In marked contrast to control explants, virtually all of the cells of minus ectoderm explants initiate chondrogenic differentiation during the first day of culture. Cells comprising the central core of minus AER explants also initiate chondrogenic differentiation during the first day of culture, but in contrast to minus ectoderm explants, non-chondrogenic tissue types form along the periphery of the explants subjacent to the dorsal/ventral ectoderm. These results indicate that the AER maintains cells directly subjacent to it in a labile, undifferentiated condition, and that when mesenchymal cells are freed from the AER’s influence either artificially or as a result of normal polarized outgrowth, they are freed to commence cyto-differentiation. The results further suggest that the dorsal/ventral ectoderm may have an influence on the differentiation of the mesenchymal cells directly subjacent to it, once the cells have been removed from the influence of the AER.
The activity of cholinesterases during the development of Xenopus laevis
Authors: Gindi Teresa , Knowland John
Published: April 2021

The activity of cholinesterases during the early development of Xenopus laevis has been examined, and the activity of acetylcholinesterase in particular has been distinguished from other cholinesterases. In contrast to some earlier findings, the activity of acetylcholinesterase is low at early stages and gradually increases during development. Possible reasons for the differences between the earlier results and those reported here are discussed.
Investigation of the fate of 4·5 daypost-coitummouse inner cell mass cells by blastocyst injection
Authors: Gardner R. L. , Rossant J.
Published: April 2021

Two distinct patterns of chimaerism were found in conceptuses produced by injecting dissociated 4-5-day inner cell mass cells into genetically dissimilar blastocysts. Pattern 1 : donor cells were found in the endoderm layer of the visceral yolk sac, but not in the adjacent mesoderm layer of this organ or in the foetus itself. Pattern 2: donor cells were found in the mesoderm layer of the visceral yolk sac and/or foetus, but never in the yolk-sac endoderm as well. Primitive endoderm cells of donor inner cell masses are responsible for the first pattern and primitive ectoderm cells for the second. These results, together with those of previous studies, suggest that the entire foetus, including its endodermal components, is formed from the primitive ectoderm, and that primitive endoderm forms only extra-embryonic endoderm of the conceptus.
Marginal zone cells – the primitive streak-inducing component of the primary hypoblast in the chick
Authors: Azar Yehudit , Eyal-Giladi Hefzibah
Published: April 2021

(1) Removal of both the area opaca and the marginal zone of the area pellucida from a blastoderm stripped of its hypoblast (type-IV operation) prevents the regeneration of a normally functioning primary hypoblast. (2) Stage-XTH E.G & K blastoderms (prior to the appearance of PS) after a type-IV operation do not form a primitive streak. (3) In older type-IV operated blastoderms in which the primitive streak has already begun to appear, the regeneration of a non-functional hypoblast did not support the normal maturation of the primitive streak, and in many cases the already existing rudimentary streak was absorbed. (4) Type-IV operated blastoderms from stage 3+ H & H and on developed normally. (5) It is concluded that the cellular contribution of the marginal zone to the primary hypoblast is instrumental in the latter’s capacity to induce a PS.
Twirler: A Mutant Affecting the Inner Ear of the House Mouse
Authors: Lyon Mary F.
Published: April 2021

The mutant twirler, symbol Tw, of the house mouse, Mus musculus, was first recognized by the ‘waltzing’ behaviour which the heterozygotes show. It was later found to affect the morphology of the inner ear and, when homozygous, to cause death of new-born animals through harelip and cleft palate.
Experiments in vitro on the Role of Movement in the Development of Joints
Authors: Lelkes G.
Published: April 2021

It has been pointed out by Fell & Canti (1934) as a result of their experiments in vitro concerning the early formation of the avian limb skeleton and kneejoint, that the appearance of the articular rudiment is independent of the blood- and nerve-supply as well as of mechanical influences. These authors believe that the formation of articular surfaces occurs in consequence of the differential growth of the scleroblastema (the ‘Anlage’ of the limb skeleton, skeletal rudiment) the essential factor in joint formation being the association of undifferentiated tissue with the rapidly growing chondrification centres. They emphasize, however, that only the earlier stages of joint formation can be obtained in vitro; the conditions of cultivation are not adequate for the further development of the joints. The articular rudiment disappears by secondary fusion of the cartilages of the limb skeleton. Fell & Canti mention the possibility that though mechanical movement is not necessary for the appearance of the joint, it may be an important and possibly an essential factor in its subsequent development.
The Mechanism of Hardening of the Salmonid Egg Membrane after Fertilization or Spontaneous Activation
Authors: Zotin A. I.
Published: April 2021

The embryonic development of fishes proceeds under the protection of rigid egg membranes which preserve the embryo from mechanical injury. Salmonid fishes bury their eggs in sandy and stony ground so that they are particularly liable to mechanical damage. This is apparently the reason why the membrane of the salmonid embryo is extremely strong, resisting a load of 3–4 kg. per ovum (Gray, 1932; Hayes, 1942,1949; Hayes & Armstrong, 1942; Zotin, 1953a). This mechanical property of the membrane does not appear immediately after fertilization or activation but is preceded by a whole set of processes which are elicited in the membrane by external factors and by the fertilized or activated egg itself. Thus, according to Manery, Fisher, & Moore (1947), hardening of the egg membranes in the speckled trout sets in 2 hours after the release of the egg into water. Ca ions have been shown to be of great significance for membrane-hardening in Salvelinus fontinalis (Manery, Fisher, & Moore, 1947; Warren, Fisher, & Manery, 1947; cf. also Hoar, 1957) and Oncorhynchus keta (Kusa, 1949 a, b). In distilled water, membrane-hardening is slower than in ordinary water and is completely blocked when Ca ions are bound by 0·01 N sodium citrate or 0·02 N sodium oxalate.
Retinal pigment epithelium: pattern of proliferative activity and its regulation by intraocular pressure in postnatal rats
Authors: Stroeva O. G. , Panova I. G.
Published: April 2021

The postnatal proliferative activity of retinal pigment epithelium (RPE) cells and its dependence on intraocular pressure were studied using pHJthymidine and [14C]thymidine autoradiography in normal and experimentally induced microphthalmic pigmented rats. The regulation of RPE growth by intraocular pressure was shown to involve the control of the number of binucleated cells by means of stimulation of cell entry into the S phase of the cell cycle. Binucleated cells in the rat RPE are formed by acy to kinetic mitoses between days 2 and 9. The significance of the postnatal proliferation and formation of binucleated cells in the RPE is discussed in terms of the specificity of the G2 phase for melanotropic hormone action on RPE differentiation.
A study of the properties, morphogenetic potencies and prospective fate of outer and inner layers of ectodermal and chordamesodermal regions during gastrulation, in various Anuran amphibians
Authors: Dettlaff T. A.
Published: April 2021

In both the ectodermal and the chordamesodermal regions of Anuran embryos, the outer layer of cells possesses epithelial properties and has the same restricted morphogenetic potencies. It is thus interchangeable between the regions, capable of epiboly and, when underlain by notochord material, of the formation of bottle-shaped cells as at the blastoporal groove, and invagination. When taken from the chordamesoderm region, this outer layer has no inducing effect on the ectoderm of the early gastrula. In normal development the outer layer of the neural plate takes an active part in forming the neural tube cavity. It gives rise to the neuroepithelial roof of the diencephalon and medulla oblongata and, when underlain by neuroblasts that develop from the inner cell layers, to ependymal cells of the brain wall. The outer layer of the notochord material is included in the epithelial layer underlying the roof of the gastrocoel -the hypochordal plate. The inner layers of these regions consist of loosely arranged cells and normally have no epithelial properties although, when taken from the ectoderm region, they may acquire such properties upon long-term contact with the environment. However they have wide morphogenetic potencies; the differences in these potencies between cells taken from the various presumptive regions being less than the differences between outer and inner cell layers in each region. Maps are provided which show the arrangement of presumptive rudiments in the ectoderm and chordamesoderm on sagittal sections through Bombina bombina embryos in early and late gastrulation.
Genetic analysis of developmental mechanisms in hydra. VIII. Head-activation and head-inhibition potentials of a slow-budding strain (L4)
Authors: Takano Jun , Sugiyama Tsutomu
Published: April 2021

Morphogenetic potentials involved in head formation were examined in a hydra strain (L4) which has a very low budding rate and a large polyp size, and the results were compared to those of the normal strain (105).

Hydra tissue has two types of antagonistic morphogenetic potentials which are thought to play important roles in head structure formation: the head-activation potential and the headinhibition potential. Lateral tissue transplantation (Webster & Wolpert, 1966) was used to compare the levels of the two potentials in L4 and the normal strain. It was found that the intact polyp of L4 has a nearly normal or slightly lower head-activation potential but a significantly higher head-inhibition potential than the normal strain. During the course of regeneration after head amputation, the levels of the two potentials in L4 changed in significantly different patterns from those in the normal strain. These abnormalities of the two potentials may be responsible for the developmental and morphological abnormalities in L4. The significance of these observations is discussed in light of the current hydra pattern formation models (Wolpert, Hornchurch & Clarke, 1974; Meinhardt & Gierer, 1974).
The effects of inhibition of protein glycosylation on the aggregation ofDictyostelium discoideum
Authors: Mcdonald Charles John , Sampson Jeffrey
Published: April 2021

At concentrations greater than 10 μg ml-1 tunicamycin inhibited the incorporation of [3H]mannose into glycoproteins during the early phase of development in Dictyostelium discoideum, however, total protein synthesis was unaffected. Tunicamycin also interfered with the normal process of aggregation. In its presence small aggregates were observed at the time of normal aggregation, but amoebae failed to aggregate completely and subsequent development was inhibited. Inhibition of normal aggregation by tunicamycin was found to be reversible. The appearance of cell-associated and secreted cyclic AMP phosphodiesterase and cell-surface contact sites A was prevented by tunicamycin but cell surface cyclic AMP receptor activity developed normally in its presence. Tunicamycin also prevented amoebae from acquiring the ability to chemotact toward cyclic AMP. Addition of exogenous cyclic AMP phosphodiesterase restored the ability of amoebae to chemotact toward cyclic AMP in the presence of tunicamycin. Our data suggest that the primary block in aggregation caused by tunicamycin results from the inhibition of expression of active cyclic AMP phosphodiesterase.
An increase in cell—cell adhesion in the chick segmental plate results in a meristic pattern
Authors: Cheney Clarissa M. , Lash James W.
Published: April 2021

Cell-cell adhesion in the anterior portion of the segmental plate plays an important role in the initiation of somitogenesis. Dissociated somites show a marked tendency to reassociate into somite-size clumps within a few hours after dissociation. Segmental plate cells show very little tendency to reassociate, even after 24 h in culture. The cells from the anterior portion of the segmental plate do show a tendency to reassociate. This supports the hypothesis that cell-cell adhesion between the cells in the anterior portion of the segmental plate plays a major role in the initiation of somitogenesis.
A Description of the Technique for Nuclear Transplantation inXenopus laevis
Authors: Elsdale T. R. , Gurdon J. B. , Fischberg M.
Published: April 2021

Technical details are given of a method of transplanting embryonic nuclei in X. laevis. This technique is based on Briggs & King’s method for R. pipiens. Owing to certain differences between the eggs of Rana and Xenopus, their technique has been modified for Xenopus. The main modification for Xenopus concerns the use of ultra-violet irradiation instead of enucleation by a needle. Differences between transplantation techniques for Rana and Xenopus are unlikely to account for the differences in experimental results obtained with these species.
Rat embryonic ectoderm as renal isograft
Authors: Švajger Anton , Levak-Švajger Božica , Škreb Nikola
Published: April 2021

Experimental results obtained many years ago revealed that during gastrulation (with the primitive streak and the mesoderm formation as distinct features) the early rodent embryo undergoes essential changes in its response to extrinsic teratogens (Russell & Russell, 1954; Wilson, 1954; Škreb, 1961; Škreb & Bijelic, 1962; Škreb & Frank, 1963). It has also been shown that the ultrastructural, histochemical and biosynthetic features of the embryo are subject to substantial changes during this period (Solter, Damjanov & Škreb, 1970, 1973; Dziadek & Adamson, 1978; Bode & Dziadek, 1979; Wartiovaara, Leivo & Vaheri, 1979; Jackson et al. 1981; Franke et al. 1982a, b). This suggests a restriction of developmental capacities (i.e. the loss of the capacity of regulation) in groups of embryonic cells at this developmental stage.
The discontinuous visual projections on the Xenopus optic tectum following regeneration after unilateral nerve section
Authors: Willshaw D. J. , Gaze R. M.
Published: April 2021

The establishment of retinotectal projections following transection of one optic nerve in developing Xenopus has been investigated. Between 3 weeks and 11 months after the operation, the nerve fibre tracer horseradish peroxidase (HRP) was applied to either the operated or the unoperated nerve, and the brains were prepared for examination as whole mounts.

In most cases fibres from the operated nerve innervated both tecta, with the result that one tectum was doubly innervated and one tectum singly innervated. Two months after transection of the optic nerve in tadpole life, between stages 50 and 54, this nerve usually made a uniform projection on the contralateral tectum and a striped projection on the ipsilateral, doubly innervated, tectum. The projection made by the unoperated nerve on this tectum was a similar pattern of stripes, which ran generally rostrocaudally. Two months after transection of the optic nerve of newly metamorphosed animals, the projection formed by the operated nerve on the doubly innervated tectum was usually a pattern of spots or spots mixed together with stripes in no particular orientation superimposed on a roughly uniform background. In a small number of cases the projections made by the same nerve on the two tecta were approximately complementary; that is, the presence of label on one tectum corresponded with its absence on the other tectum.

The results are examined in the context of the development of the retina and of the tectum. It is suggested that the consistently oriented stripes which result from nerve transection at a stage at which only a small proportion of the retinal fibres had reached the tectum are formed by the interaction of two equally matched sets of developing fibres, stripe orientation being determined by the mode of growth of the optic tectum. The formation of patterns of spots or spots mixed together with stripes following nerve transection after the end of the main phase of tectal histogenesis, and when 50 % of the optic fibres had already reached the tectum, is attributed to an unequal competition between the two sets of fibres.
A physiological measure of shifting connections in the Rana pipiens retinotectal system
Authors: Fraser Scott E. , Hunt R. Kevin
Published: April 2021

The retinotectal connections of developing Rana tadpoles and froglets have been studied using light-pipe techniques to directly assay the pattern of the projection from the retina to the tectum. The projection site of the retina surrounding the optic nerve head was determined at two different stages of development (late larval and metamorphic frog) on the same animal. Small electrolytic marker lesions were used to mark the tectal sites to which the optic nerve head projected at these two times. Comparison of the positions of the two lesions gives a direct measure of the shift in the projection during the interlesion time interval of one week. The results indicate a shift in the projection of 275 μm week−1 in late larval life. Previous work in Xenopus using the light-pipe techniques indicated a qualitatively similar shift during equivalent stages of development, but significantly smaller in magnitude. In the present study, topographic postsynaptic units could be recorded at all stages investigated, indicating functional synapses between the optic nerve fibres and the tectum. Thus, these studies offer evidence of a significant shift in the functional connection pattern of the amphibian retinotectal map during development, in agreement with the recent anatomical data from other laboratories on the Rana and goldfish visual system.
Protein requirements for germinal vesicle breakdown in ovine oocytes
Authors: Moor R. M. , Crosby I. M.
Published: April 2021

The regulation of the cell cycle during the transition from prophase to metaphase I was studied by analysing protein changes and introducing protein blocks during the transition phase. The results show that the progression to metaphase in ovine oocytes is totally dependent on new protein synthesis. By delaying the addition of the inhibitor, cycloheximide, for progressively longer periods after the resumption of meiosis it was established that the required synthesis occurs in the 1–2 h immediately preceding germinal vesicle breakdown (GVBD). The action of cycloheximide was fully reversible: removal of the drug resulted in GVBD between 3 and 4h later.

The synthesis and modification of proteins during these first few hours of maturation were studied by short-term radiolabelling of oocytes with [35S]methionine and [32P]phosphate followed by rapid assessment of their precise nuclear configuration. Changes in phosphorylation of two polypeptides were detected 4–5 h after the beginning of culture, but these changes were not dependent upon protein synthesis. The earliest change in synthesis was the appearance of a new polypeptide 6–8 h after explantation, immediately before GVBD. This polypeptide (Mr 47×103, pI 5·8) was not significantly phosphorylated and was relatively stable. Oocytes released from cycloheximide treatment began to synthesize this molecule 3–4 h later, again coinciding with GVBD. Synthesis of the polypeptide was suppressed by inhibition of transcription with α-amanitin.
Reconstruction of bipinnaria larvae from dissociated embryonic cells of the starfish, Asterina pectinifera
Authors: Dan-Sohkawa M. , Yamanaka H. , Watanabe K.
Published: April 2021

Cells dissociated from swimming embryos of the starfish are able to reconstruct bipinnaria larvae. This process consists of reaggregation (stage 1), formation of the external epithelium (stage 2), development of the internal cavities which will eventually grow either into the blastocoel or the intestinal lumen (stage 3), gastrulation or fusion of the internal and the external epithelia (stage 4), formation of the mouth (stage 5) and the established bipinnaria (stage 6).

The optimal population of cells to support the process of reconstruction is estimated to fall between 500 and 1000, values corresponding to one eighth and one fourth the total number of cells of a normal embryo, respectively.

Morphogenetic events of reconstruction are discussed in relation to the normal course of starfish development and to the reconstruction process of the sea urchin.