bluuebunny/crossref_metadata_2025 huggingface dataset:
‘Transdifferentiation’ of chicken neural retina into lens and pigment epithelium in culture: controlling influences
Authors: Pritchard D. J. , Clayton R. M. , Pomerai D. I. De
Published: April 2021

The in vitro transdifferentiation of chicken embryo neural retina into pigment epithelium and lens cells was investigated under a variety of experimental conditions. Our findings suggest that some aspects of the phenomena are a function of medium composition and volume, whereas others depend upon conditions which develop during culture growth. Before melanin is visible, potential pigment cells are recognized as foci within epithelial sheets which remain in contact with the dish. The final area occupied by colonies of potential pigment cells is directly proportional to bicarbonate concentration. Low total medium volume also favours formation of potential pigment cells. In contrast the extent of cells other than potential pigment cells is not related to bicarbonate and is favoured when the volume of medium is large. Accumulation of melanin within the potential pigment cell colonies is suppressed when cells are crowded together. Lentoid bodies are formed from cells which are distinct from potential pigment cells and arise in crowded situations, in association with multilayering. Another type of structure superficially resembling a lentoid is derived from cell aggregates formed during the initial establishment of cultures. The survival of these ‘aggregate bodies’ is inversely related to bicarbonate concentration. Crystallin content is unrelated to lentoid numbers. The results provide the basis for a new hypothesis concerning cytodifferentiation in this system.
Interaction between inner cell mass and trophectoderm of the mouse blastocyst:I. A study of cellular proliferation
Authors: Copp A. J.
Published: April 2021

Increase in cell number has been compared with mitotic activity in the polar and mural trophectoderm and in the inner cell mass (ICM) of mouse blastocysts. The results indicate that whereas ICM cells divide at a rate which is compatible with the rate of increase of ICM cell number, polar trophectoderm cells divide faster and mural trophectoderm cells slower than can account for their own rates of cell number increase. It is suggested that the ICM induces a high rate of proliferation in the polar trophectoderm and that there is a resulting cell shift from polar to mural regions during blastocyst development. Mural trophectoderm cells close to the ICM divide faster than those farther away, indicating that cells may retain a ‘memory’ of ICM contact for some time after leaving the ICM. There is considerable cell death in the blastocyst, but this is restricted to a short period of time coincident with the appearance of primitive endoderm.
Participation of the cell surfaces in determining the developmental courses in the cellular slime mould Dictyostelium purpureum
Authors: Saito M. , Yanagisawa K.
Published: April 2021

Dictyostelium purpureum S5 and S6, mating type strains, form fruiting-bodies in a mono-clonal culture, but produce macrocysts in a mix culture. The effects of Concanavalin A (Con A) on both fruiting-body formation and macrocyst formation, and changes of Con A-mediated cell agglutinability during development were studied. It was found that Con A inhibits macrocyst formation but not fruiting-body formation, and that macrocyst-forming cells are much more susceptible to Con A agglutination than are fruiting-body-forming cells during the aggregation stages. When fruiting-body-forming cells are treated with either trypsin or α-chymotrypsin, their Con A agglutinability is enhanced to the same extent as that of macrocyst-forming cells. It was also found that when S6 cells are treated with pro-teases they sometimes produce normal macrocysts even in a monoclonal culture.

The results obtained in these experiments showed that the surface properties of fruiting-body-forming cells and macrocyst-forming cells are different, and that the cell surface might play an important role in determining the two developmental courses.
Cell adhesion and chondrogenesis in brachypod mouse limb mesenchyme: fragment fusion studies
Authors: Duke Jackie , Elmer William A.
Published: April 2021

This study is a continuing investigation of the effect of the brachypod mouse mutation on cell interactions and chondrogenesis during early limb development. In this report, cell adhesiveness was assessed in fused fragments of brachypod and normal limb-bud mesenchyme. Examination of the interface of fused distal postaxial limb fragments show brachypod limb mesenchyme to be more adhesive than normal limb mesenchyme. Chondrogenesis within brachypod fragments is delayed and less extensive than in normal fragments. In addition, chondrogenesis within normal fragments is not affected by the juxtaposition of the brachypod fragment, and vice versa.
Regional differences in the morphology and motility of mesodermal cells from the early wing-bud of normal and talpid3 mutant chick embryos
Authors: Bell D. A. , Ede D. A.
Published: April 2021

A method of culturing has been employed to compare the properties of cells migrating from small mesodermal explants taken from different regions of normal and mutant limb-buds at different stages of development. An analysis by time-lapse cinematography of the morphology and mobility of cells migrating from explants defines a distal region within the limb-bud where these properties are distinct from those of cells from more proximal regions. In the normal wing-bud distal cells subjacent to the apical ectodermal ridge possess a characteristic multipolar morphology and translocate slowly in vitro. Cells from more proximal regions tend to be bipolar and translocate more rapidly. Distal and proximal cells also probably differ in their adhesive strengths. In the mutant, talpid3, distal and proximal cells do not differ in the above properties and cells from all regions of the limb-bud are multipolar, translocate slowly and are more adhesive than normal cells. A study of light micrographs and scanning electron micrographs suggests that these regional differences are found in the limb-bud in vivo and are not merely an effect produced by the in vitro culturing system.
Lens regeneration from cornea of larvalXenopus laevisin the presence of the lens
Authors: Reeve Julie G. , Wild Arthur E.
Published: April 2021

In Xenopus laevis tadpoles, wounding of the outer cornea failed to initiate lens regeneration. If both the outer and inner corneas were wounded or if the lens was dislocated, lens regeneration was initiated but failed to continue beyond stage III. However, lensectomy followed by re-implantation of the lens resulted in the regeneration of a fully differentiated lens in several cases, despite the presence of the re-implanted lens. Although some of the regenerates in these eyes were also arrested at stage III, those which attained full lens differentiation, i.e. stage V, developed normally and synthesized crystallins from the onset of stage IV as indicated by a positive immunofluorescence reaction.

Histological examination of the dislocated and re-implanted lenses showed the majority of them to be normal in appearance.

Cornea transplanted to the posterior chamber of the eye also regenerated a lens in the presence of the re-implanted lens. All these regenerates underwent lens fibre differentiation to give stage-V regenerates.

These findings show that lens regeneration from the cornea can occur in the presence of lens. Results are discussed on the basis that contrary to earlier suggestions, an inhibitory lens factor does not exist in vivo, but rather that a factor for the initiation and maintenance of regeneration emanates from the eye cup and upon wounding of the inner cornea is able to reach the inner cell layer of the outer cornea and initiate lens regeneration.
Cell contacts and sorting outin vivo:the behaviour of some embryonic tissues implanted into the developing chick wing
Authors: Tickle C. , Goodman M. , Wolpert L.
Published: April 2021

The interaction of cells from embryonic liver, neural retina and mesonephros with cells from limb-bud mesenchyme has been investigated in vivo by grafting these tissues into the developing chick wing-bud. The implanted cells were in all cases from quail tissue which can be recognized histologically. As embryonic liver and neural tube are tissues that sort externally to limb-bud mesenchyme in mixed aggregates, it would be expected, from a dif-ferential adhesiveness hypothesis, that heterotypic adhesions along the borders of graft and host would be favoured over cell-cell adhesions in the graft. No morphological signs of this were evident: rather the grafted cells maximized like-like contacts. The cells of the grafts, including those from control mesenchyme, did not invade into the wing. The results were the same irrespective of whether the graft was a fragment of tissue or a pellet of reaggre-gated cells. This supports the idea that cells within tissues are not actively moving around and also provides controls for assaying the invasiveness of other cell types, such as malig-nant cells into the wing.
The mechanical role of the cranial base in palatal shelf movement: an experimental re-examination
Authors: Brinkley L. L. , Vickerman M. M.
Published: April 2021

Straightening of a cranial base flexure observed in the midsagittal presphenoid region of mice has been postulated to play a major role in palate closure by providing the internal shelf force for palatal shelf movement. The straightening is thought to take place during the 8 h immediately preceding closure. This mechanical model assumes that straightening of the cranial base flexure is transmitted laterally to the alar regions of the sphenoid and then downward to the palatal shelves. According to this hypothesis, if the flexure did not straighten or the force generated by this form change was not transmitted to the palatal shelves, movement to the horizontal plane should not take place. Physical disruption of the area of the flexure should remove the potential for form change through force transmission. Swiss-Webster mouse fetuses which were 18 or 24 h prior to palate closure were obtained and the heads removed. Tongue and brain were then removed from each head. In the experimental specimens a midsagittal lesion, averaging 407 μm in length and 84 μm in width, extending from the nasal septum through the craniopharyngeal area was made. This lesion ablated the flexure region of the cranial base far in advance of the time straightening is thought to take place. Heads of litter-mates with intact cranial bases served as controls. Specimens with intact and ablated flexures were suspended in a submerged, circulating culture system which was continuously gassed. After 18 h of culture, palatal shelf elevation had occurred in fetuses of both ages whether or not their cranial bases were intact. Palatal shelf elevation in vitro does not require an intact cranial base.
Adenylation and ADP-ribosylation in the mouse 1-cell embryo
Authors: Young R. J. , Sweeney K.
Published: April 2021

The incorporation of [3H]adenosine into cold trichloroacetic acid (TCA) insoluble material by the mouse 1-cell embryo has been studied. Incorporation of label was high immediately after fertilization, then decreased over the next 7 h with the sharpest decline occurring 3-5 h after fertilization. A small maximum was observed at the time of pronuclear DNA synthesis. Actinomycin D at a concentration which inhibited the cleavage of 1-cell embryos by 50 % had little effect on this incorporation, which in the period 1-6 h post-fertilization was shown by autoradiography to be confined to the ooplasm of the newly fertilized ovum. [3H]Adeno-sine and poly ([3H]A) were released from embryo RNA labelled 1-3 h after fertilization with [3H]adenosine by digestion with a mixture of ribonucleases A and Tx. The poly ([3H]A) segments were hydrolysed by alkali to 3’-[3H]AMP and [3H]adenosine ([3H]AMP/[3H]adeno-sine = 5/1), and by snake venom phosphodiesterase to 5’-[3H]AMP but very little [3H]adeno-sine. These results suggest that adenylation of RNA occurs soon after fertilization, that this is a cytoplasmic event, and that most of the newly synthesized poly ([3H]A) segments are joined to pre-existing poly (A) tracts. The unusual polynucleotide, poly (ADP-ribose), identi-fied by its resistance to alkali and the release of 2’-(5”-phosphoribosyl)-5’[3H]AMP on incu-bation with snake venom phosphodiesterase, was also found in the ribonuclease digest.
Duplicated axolotl regenerates
Authors: Wallace H. , Watson A.
Published: April 2021

Three series of palette stage regenerates were prepared by amputating both arms of juvenile axolotls in the mid-forearm, above the elbow, or close to the shoulder. Within each series, excised regenerates were replaced in their original orientation (as a control) or rotated at 90° intervals about the proximodistal axis, or were transplanted to the contralateral arm with identical rotations. Control grafts occasionally caused the formation of a single extra digit. All experimental rotations provoked duplicate or triplicate structures, ranging from accessory digits to extra forearms. Shoulder level grafts were subject to a pronounced correctional derotation and yielded a variable proportion of duplications. Forearm and elbow-level rotations invariably yielded duplications, which therefore result from an axial discrepancy rather than complete axial opposition between graft and host. These results are incompatible with the clockface model of positional information and demand a modification of other current models. The recorded frequency and orientation of duplications suggest that a limb contains at least two polarized transverse axes which cannot be respecified during regeneration. A substantial discrepancy on either axis reduces the normal regulative interaction between graft and host, allowing either of them to regenerate independently.
Post-embryonic determination of the ecdysial line in the cockroach: evidence for pattern regulation in the medio-lateral axis
Authors: Shelton P. M. J.
Published: April 2021

By removing or transplanting sections of the ecdysial line in the cockroach Grompha-dorhinaportentosa, pattern regulation in medio-lateral axis of an insect has been demonstrated. The line can reform after sections have been removed and when epidermal grafts from either side of the midline are grafted with confronting medial edges. The results are explicable in terms of known mechanisms for pattern regulation in insects.
Formation and consequences of cell patterns in preimplantation mouse development
Authors: Graham C. F. , Lehtonen E.
Published: April 2021

The behaviour of groups of cells was studied in culture during preimplantation mouse development. The following observations were made with intact embryos minus the zona pellucida and with embryos whose cells had been dissociated and recombined. The form of the 4-cell embryo was related to the behaviour of the first cell to divide to this stage. The form of the 8-cell embryo depended on contact between the groups of four cells each derived from a single cell at the 2-cell stage. The form of the 16-cell embryo depended on cell movement during and after division from the 8-to the 16-cell stage. These results suggest that the morpho-genetic movements of these early embryonic cells are principally governed by continuous cell interactions after fertilization. The cell surfaces of the embryos were examined with scanning electron microscopy in an attempt to discriminate between the mechanisms which could account for these movements.
The Keratin Defect and Hair-cycle of a New Mutant (Matted) in the House-mouse
Authors: Jarrett A. , Spearman R. I.
Published: April 2021

The gene matted (symbol ma) reported by Searle & Spearman (1957) causes the body-hair of affected mice to be brittle and inflexible; this results in longitudinal splitting and breaking due to friction against the cage and other objects. In the present paper the keratin abnormality of the hair is studied. The defect in matted hairs is compared with that of Naked (N/ +) mice (Grüneberg, 1952), and the hair-cycle in matted mice is described.
The Composition and Origin of the Allantoic Fluid in the Rabbit
Authors: Dickerson J. W. T. , McCance R. A.
Published: April 2021

The allantoic fluid of the rabbit at the 20th day of gestation has been found: (a) to be opalescent; (b) to be hypotonic relative to the maternal serum; (c) to contain higher concentrations of urea and potassium than the maternal serum; and (J) to contain lower concentrations of sodium and chloride. The facts known about this fluid indicate that it may be very largely a product of the foetal mesonephros.
Embryonic Responses to Structurally Related Inhibitors
Authors: Liedke Kathe B. , Engelman Morris , Graff Samuel
Published: April 2021

Seventeen of 27 structurally related compounds which could act as purine or pyrimidine antagonists inhibited embryonic development to different degrees. Several benzotriazoles were found to exert similar effects on embryos, the intensity varying with substituents. Older, more differentiated, stages are more susceptible to the benzotriazoles than are early cleavage stages. Exposure to the benzotriazoles at the blastula stage results in hypomorphic cyclopian development without necrosis. There is always a marked delay in the rate of development. Swelling and loss of cells is found, particularly in neurula and tail-bud stages, and usually is followed by death. These findings suggest that the surface coat is interfered with. All active benzothiadiazoles, benzimidazoles, and quinoxalines have the same effect on the embryo; the intensity of the response varying with substitution. Younger, and particularly cleavage, stages are more susceptible, and resistance increases with age of embryo. Exposed blastula stages are frequently arrested as dwarfed tail-buds showing extensive necrosis, particularly of the nervous system. Rarely is there arrest in neurula stages, or if it occurs, these are abortive neurula-exogastrulae with large yolk-plug, no swelling, and larger-sized cells than is normal for this stage. There is always a selective cellular response: early differentiating and very rapidly dividing cells are most sensitive and become necrotic first, while other cells are enlarged and remain arrested. The type of response is determined by the compound, the degree or intensity of response by the substituted groups. It is greatest if only a single nitro group is substituted in the benzothiadiazoles, benzimidazoles, and benzotriazoles, but not in the quinoxalines in which other substitutions seem to have the same degree of effectiveness. On the other hand, some substituents, amino or diphenyl groups for example, decrease the effectiveness of the quinoxalines and benzimidazoles. No direct correspondence between structure and biological function has been discerned.
Effects of X-rays on nerve-dependent (limb) and nerve-independent (jaw) regeneration in the adult newt, Notophthalmus viridescens
Authors: Wertz Richard L. , Donaldson Donald J.
Published: April 2021

The newt limb requires nerves for successful regeneration, but the jaw appears to be nerve independent. Among the current hypotheses for the regeneration-inhibitory action of X-rays is one proposing inactivation of nerves as the main cause. We decided to test this hypothesis by comparing the irradiation levels necessary for inhibition of limb and jaw regeneration.

Jaws and left front limbs were exposed locally to doses of ionizing X-irradiation ranging from 250 to 2000 R at least 6 weeks prior to amputation of the jaw and both front limbs. After 90 days post-amputation all surviving animals were examined grossly for signs of regeneration. In addition, some of the controls and most of those receiving 250, 500 and 1000 R were processed for histological examination.

All unirradiated limbs and jaws supported regeneration. Those exposed to 250 R also regenerated, but a third of the jaws were hypomorphic. At 500 R and above, neither jaws nor limbs regenerated. Since both systems were affected by similar doses of X-rays, it appears that nerves are not the primary X-ray target in adult newts.
The dynamics of Drosophila melanogaster spermatogenesis in in vitro cultures
Authors: Cross David P. , R David L. Shellenbarge
Published: April 2021

A photographic description of meiosis and spermatogenesis in single sperm cysts of Drosophila melanogaster cultured in vitro is presented. In addition to the utility of this description for the study of spermatogenesis in whole live testes, the culture procedure provides a means for studying the dynamic development of individual sperm cysts from flies carrying male-sterile mutations, as illustrated with X/O males. Several deviations of spermatogenesis in vitro from that in vivo suggest that sperm morphogenesis is not rigidly coordinated.
Responses of the early chick embryo to external cAMP sources
Authors: Gingle Alan R. , Robertson Anthony
Published: April 2021

Early chick embryos were stimulated with local sources of cAMP. Three major effects were observed: bending of the embryonic axis, attraction of cells on the ventral surface of the embryo, and disruption of the blastodisc. Each had a characteristic concentration dependence. These results are compared with those from studies of cells disaggregated from similar embryos.
Cell differentiation in isolated inner cell masses of mouse blastocystsin vitro:onset of specific gene expression
Authors: Dziadek Marie
Published: April 2021

Inner cell masses (ICMs) were isolated by immunosurgery from giant blastocysts formed by the aggregation of three morulae. A layer of endoderm cells formed on the outer surface of these primary ICMs in vitro. When this layer was removed by immunosurgery, a secondary endoderm layer formed. Alphafetoprotein (AFP) was used as a biochemical marker to characterize visceral endoderm formation in these cultured ICMs. The immunoperoxidase reaction on sections of ICMs cultured for intervals up to 120 h in vitro showed that some primary endoderm cells contained AFP, but these were always in the minority. The secondary endoderm layer, on the other hand, was composed of predominantly AFP-positive cells. It is concluded that the primary endoderm contains mainly parietal endoderm cells, while the secondary layer contains visceral endoderm cells. A model is proposed for the consecutive differentiation of parietal and visceral endoderm cell types from the ICM of mouse blasto-cysts.
Fate maps and cell differentiation in the amphibian embryo – an experimental study
Authors: Landström Ulf , Løvtrup Søren
Published: April 2021

The aim of this paper is to test two different fate maps for the amphibian blastula with respect to their predictions concerning the process of cell differentiation. The first of these fate maps is the one proposed by Vogt, according to which all three germ layers can be projected on to the surface of the embryo. The second is a revision which claims that only endoderm and ectoderm are located in the surface, while the mesoderm is represented by free cells in the interior of the embryo.

The testing has been performed by observing the differentiation of small explants of cells taken from various regions of the embryo.

It was found that the spontaneous cell differentiation comprises three patterns: undifferentiated cells (free interior cells and circumpolar endodermal cells), fibroblast-like cells (the remaining endodermal cells) and epidermis (ectodermal cells).

Further differentiation occurs only through induction, exerted either by the fibroblast-like endodermal cells or by heparan sulphate. When induced, the equatorial ectodermal cells give rise to swollen, hyaline cells (chordocytes), while the remaining ectodermal cells form a sequence of cell differentiation patterns, mesenchyme cells, nerve cells, melanophores and xanthophores.

The free interior cells differentiate into striated muscle cells and elongated collagen-producing fibroblasts.

Our results thus confirm the revised fate map, and they also give an insight into the mechanisms of the initial cell differentiations in the amphibian embryo.
Development of the tibiotarsus in the chick embryo: biosynthetic activities of histologically distinct regions
Authors: Stocum David L. , Davis Richard M. , Leger Marilyn , Conrad H. Edward
Published: April 2021

The dynamics of the histological changes which occur in the distal half of the tibial portion of the embryonic chick tibiotarsus from day 8 to day 18 of incubation are correlated with the capacities of histologically distinct zones to incorporate isotopic precursors into mucopolysaccharides and collagen. At the distal end of the tibia, which abuts the suture line formed by the fusion of the two tarsals with the tibia, there persists throughout embryonic development a narrow band of small, round or oval, rapidly dividing chondrocytes which synthesize chondroitin SO4 and collagen at low rates. Just proximal to this zone is a broader zone of flattened, disc-shaped chondrocytes which divide more slowly and are extremely active in chondroitin SO4 and collagen synthesis. Proximal to the zone of flattened chondrocytes is a zone of non-dividing, hypertrophied chondrocytes which are large and round and increase continually in size going from the distal to the proximal end of the zone. The biosynthetic activities of the cells in this zone fall sharply with their distance from the zone of flattened chondrocytes. Finally, there is a fourth zone, the marrow cavity, formed by a proximal to distal disintegration of the hypertrophied chondrocytes, starting at mid-diaphysis. The marrow cavity is surrounded by a shell of periosteal and intra-membranous bone which extends to the distal end of the zone of hypertrophied chondrocytes. Our data suggest that as the tibiotarsus grows in length the small, round rapidly dividing cells of the tibia differentiate first to flattened chondrocytes which synthesize matrix at a high rate and ultimately to low activity, hypertrophying chondrocytes. This sequence proceeds in a linear fashion.
Cell contact and positional communication in hydra
Authors: Wakeford R. J.
Published: April 2021

Positional communication and the functional coupling of muscular reflexes were examined in grafted hydra. A head and distal gastric region inhibited head regeneration by a host sub-hypostome within 4 –5 h of grafting. Functionally coupled pathways which indicated the presence of gap junctions also formed between graft and host during this time. It is suggested that gap junctions provide a channel for positional communication.
Development of retinal synaptic arrays in the inner plexiform layer of dark-reared mice
Authors: Fisher Leslie J.
Published: April 2021

In the central area of the retina of mouse the rate of synaptogenesis in the inner plexiform layer (IPL) drops precipitously at about the time the eyes open. To determine if the visual input at eye opening provides a signal for the neurons to stop adding synapses, mice were raised in darkness during the period of maximal synaptogenesis and through eye opening. Retinal synaptic arrays of dark-reared and normally reared animals were compared qualitatively. The rate of synaptogenesis after eye opening in dark-reared mice indicated that the onset of visual stimulation was not the cue to stop synaptogenesis. However, the synaptic arrays of the IPL of dark-reared mice consistently had more conventional synapses than those of normally reared mice. It is concluded that the number of conventional synapses in the central retina was increased by dark-rearing.
Elevation of lesioned palatal shelvesin vitro
Authors: Brinkley L. L. , Vickerman M. M.
Published: April 2021

Fetuses were obtained from CD-1 mice at a time estimated to be 12 h prior to in vivo secondary palate closure. One of the palatal shelves of each partially dissected fetal head was lesioned in one of five ways, the other left intact to serve as a control. Single transverse cuts extending the width of the shelf were made at one of three positions along the longitudinal axis of the shelf : one-third, one-half or two-thirds the shelf length estimated from the rostral edge. Some specimens were cut in two places, dividing the shelf into three equal segments. Another group received a lesion which separated the caudal third of the shelf from its maxillary connections. All specimens were cultured for 18 h. At the end of the culture period the heads were fixed, examined and the degree of elevation of each shelf piece assessed.

Intact, control shelves of all preparations were elevated in the rostral two-thirds of the shelf, while the caudal third was partially elevated. Results seen in lesioned shelves depended upon both the size of the segment and the region of the shelf contained in the segment. The rostral two-thirds of the shelf, the presumptive hard palate, whether intact or in segments elevated without physical connections to neighboring shelf tissue. Thus, it is unlikely that this elevation requires a wave of contraction be transmitted from the caudal soft palate region. In contrast, the presumptive soft palate requires continuity with the rostral portions of the shelf both to maintain structural stability and to elevate.
The effect of prolonged decompaction on the development of the preimplantation mouse embryo
Authors: Johnson M. H. , Chakraborty J. , Handyside A. H. , Willison K. , Stern P.
Published: April 2021

A rabbit antiserum to a mouse embryonal carcinoma cell line blocks compaction of cleaving mouse embryos. Cell division is not affected up to the 32-cell stage but intracellular junctions fail to develop. Removal of the antibody at this stage permits compaction to occur and a normal blastocyst develops. Prolonged decompaction beyond the 32-cell embryo results in an increasing proportion of malformed blastocysts in which trophectodermal cells predominate and functional inner cell mass (ICM) cells are reduced or absent. The relationship of compaction to the generation of ICM and trophectoderm lineages in the intact embryo is discussed.
Quantitative staging of embryonic development of the grasshopper,Schistocerca nitens
Authors: Bentley David , Keshishian Haig , Shankland Martin , Toroian-Raymond Alma
Published: April 2021

During development of the grasshopper embryo, it is feasible to examine the structure, pharmacology, and physiology of uniquely identified cells. These experiments require a fast, accurate staging system suitable for live embryos. We present a system comprising (1) subdivision of embryogenesis into equal periods, (2) expression of stage in percent of complete embryogenesis time, (3) characterization of stages by light micrographs (and descriptive text), and (4) illustration of stages at the egg, embryo, and limb levels of resolution. Advantages of a percent-system include communicability, flexibility in temporal resolution, accurate assignment of elapsed time in developmental processes, and uniform coverage of the period of embryogenesis. The stages described are at 5 % intervals with an estimated error of ±1 %.
Translocation of neural crest cells within a hydrated collagen lattice
Authors: Davis Edward M.
Published: April 2021

Chick neural tubes were cultured either on planar substrata of collagen-coated Falcon plastic in growth medium with serum or within a hydrated collagen lattice (HCL) in growth medium either with or without serum. Using time-lapse cinemicrography, neural crest cells were observed emigrating from neural tubes over the collagen substrata. Once separated from the neural tube, they seldom reunite with it. Though the average rate at which the neural crest cells translocate was the same in the different culture conditions, approximately 1·0 μm/min, distinct differences in morphology and mode of translocation were observed. Neural crest cells on collagen-coated culture dishes have a flattened fibroblastic morphology and mode of translocation; in an HC1 with serum, they have a bipolar shape and translocate by advancing a long, narrow leading protrusion and by periodically retracting the attenuated trailing portion of the cell; and in a serum-free HCL, they have a unipolar shape and translocate by advancing a long, narrow, branched leading protrusion and by periodically transferring the cytoplasm of the large, rounded trailing cell body forward, past a bulbous structure, and into the leading protrusion.
Drosophila nuclei replicate in Xenopus eggs
Authors: Smith Christina , Brill David , Bownes Mary , Ford Christopher
Published: April 2021

Nuclei isolated from a permanent cell line derived from Drosophila melanogaster embryos have been injected, along with a radioactive DNA precursor [3H]TTP, into Xenopus laevis eggs. In culture, less than 7 % of the cells were in S phase. After a 90 min incubation, following injection into eggs, 99% of the nuclei were shown by autoradiography to have synthesized DNA. In a similar experiment, a density label BrdUTP was injected into eggs along with the nuclei. Subsequent analysis on caesium chloride gradients showed that this DNA synthesis was semi-conservative replication. Therefore we conclude that signals present in Xenopus egg cytoplasm can initiate and sustain true semi-conservative DNA replication in nuclei from an invertebrate organism.
The effect of 6-aminonicotinamide on limb development
Authors: Mclachlan John C.
Published: April 2021

The morphological effect of the nicotinamide analogue 6-aminonicotinamide on the development of the embryonic chick limb was studied, with special reference to muscle, cartilage, feather germ formation, and ossification. No evidence was found to support theories of control of differentiation by nicotinamide-like substances, although the effect of nicotinamide analogues has often been quoted as evidence for such theories.

However, the effect of 6-AN in shortening the limb provides an opportunity to study the interaction of various tissues in normal growth and development, and the results are used to shed further light on the processes involved in muscle splitting, and feather germ formation.
On the role of germ cells in planarian regeneration:II. Cytophotometric analysis of the nuclear Feulgen-DNA content in cells of regenerated somatic tissues
Authors: Gremigni V. , Miceli C. , Picano E.
Published: April 2021

Previous findings by our group have shown how primordial male germ cells take part in regenerative blastema formation in planarians by migrating to the wound.

The role of these cells in rebuilding transected tissues has been investigated in a population of Dugesia lugubris s.l. which is particularly suited for our purpose. In fact, these planarians provide a clear karyological marker to distinguish diploid male germ cells (2n = 8) from tryploid embryonic or somatic cells (3n = 12). In this study we employed the cytophotometric analysis of the nuclear Feulgen-DNA content in order to distinguish non-replicating male germ cells from reserve and somatic cells. The Feulgen-DNA content in cells from the gonad-free caudal area was measured after complete regeneration. Most non-replicating cells (94–95 %) were found to have a DNA amount typical of cells previously estimated as triploid. Some (5–6%) nuclei containing a DNA amount typical of cells previously estimated as diploid male gonia were also found. These findings seem to support the view that primordial male germ cells also participate in rebuilding somatic tissues according to the field influence they encounter during regeneration. The possibility that metaplasia (or cell transdifferentiation) may occur in planarians is finally discussed.
Expression of the maternally derived X chromosome in the mural trophoblast of the mouse
Authors: Frels William I. , Chapman Verne M.
Published: April 2021

Only the maternally derived allelic form of the X-chromosome-linked enzyme phosphoglycerate kinase (PGK-1) is observed in the mural trophoblast of heterozygous female progeny in F1 and backcross matings. We have demonstrated that this expression of the maternally derived PGK-1 is not a result of maternal tissue contamination nor of selection of cells expressing the maternal X chromosome (Xm). Our results suggest that the expression of Xm in mural trophoblast is a consequence of nonrandom X-chromosome inactivation in trophectoderm cells.
Intercalary regeneration in the amphibian limb and the rule of distal transformation
Authors: Maden M.
Published: April 2021

The applicability to the amphibian limb of the rule of distal transformation, which states that tissue from any level can only become more distal, has been tested during intercalary regeneration following various types of shift-level transplantation. Following the grafting of distal blastemas to proximal levels, such that part of the presumptive pattern is missing, complete limbs nevertheless formed (Series 1). That the intercalated tissue arose entirely from the stump was shown by exchanging blastemas between black and white animals. When the proximal stump was irradiated and its contribution eliminated, intercalary deletions were produced (Series II). This was not due to the inability of irradiated and normal tissue to communicate since irradiated distal blastemas grafted onto proximal stumps still stimulated intercalary regeneration (Series III). When proximal blastemas were grafted to distal levels intercalary regenerates were obtained in about 20% of the cases (Series IV) and under these circumstances the grafted blastema was the sole source of intercalated tissue. The precise structure of these intercalated elements was impossible to ascertain, but it is suggested that they might be of reversed polarity as found in insects. These results are discussed in relation to similar experiments on the insect limb.
In vitro imaginal disc development and moulting hormone
Authors: Guillermet Christiane , Mandaron Paul
Published: April 2021

imaginal leg and wing discs obtained from late-third-instar Drosophila larvae were cultured in vitro in various concentrations of ecdysterone ranging from 10−10 to 10−5 M in order to test the effect of hormone concentration on evagination and cell differentiation.

At the optimal concentration of 8 × 10−8 M discs evaginated normally, secreted the pupal cuticle, underwent apolysis, differentiated imaginal structures and secreted the imaginal cuticle.

At suboptimal concentrations (10−8 M and less), evagination was incomplete in a variable proportion of appendages. Morphogenetic movements were limited to the earlier ones; so that appendages did not emerge from the peripodial sac. Subsequent development, whenever it occurred, took place inside the peripodial sac. This particular type of ‘endoevagination’ was only obtained with sub-optimal hormone concentration.

At supra-optimal concentrations (10−6 M and more), evagination was always complete but further differentiation was inhibited.

These results show that endoevagination is strictly related to insufficient supply of hormone and that morphogenesis and cell differentiation in imaginal discs are two independent phenomena, which respond to different levels of hormone stimulation.
Regeneration of an abnormal ipsilateral visuotectal projection inXenopusis delayed by the presence of optic fibres from the other eye
Authors: Straznicky Charles , Tay David , Glastonbury John
Published: April 2021

Optic fibre regeneration was studied by [3H]proline autoradiography and by mapping electrophysiologically the direct visuotectal projections to the contralateral and ipsilateral tecta 12 –16 weeks after sectioning the right optic nerve in Xenopus two to four weeks after metamorphosis. The experiments were carried out in three groups : (A) optic nerve section in newly metamorphosed animals with embryonic left-eye enucleation; (B) optic nerve section with simultaneous left-eye enucleation; and (C) optic nerve section with delayed left-eye enucleation 5 –31 days prior to sacrifice.

In all but three animals regenerated optic fibres were demonstrated morphologically both in the contralateral and ipsilateral tecta. The contralateral visuotectal projection was fully restored within the 12 –16 weeks in all animals. In animals with embryonic enucleation or in those where the enucleation was carried out simultaneously with optic nerve section, a direct ipsilateral visuotectal projection was established at the same time as the restoration of the contralateral projection. In contrast, no direct ipsilateral visuotectal projection was detectable in the presence of optic fibres from the other eye in the doubly innervated tecta. However, 14 –31 days after the removal of the incumbent optic fibres by left-eye enucleation a direct visuotectal projection from the right eye to the ipsilateral tectum was established, and its polarity corresponded to the normal contralateral retinotectal projection.

The apparent disparity between morphological and electrophysiological findings in the doubly innervated tectum suggests that superimposed optic fibres are unable to form normal synaptic relations with tectal neurons during early regeneration, delaying the establishment of the induced direct ipsilateral visuotectal projection.
Experiments on developing limb buds of the axolotl Ambystoma mexicanum
Authors: Maden M. , Goodwin B. C.
Published: April 2021

Various experiments were performed on the limb buds of axolotls to compare the behaviour of amphibian limbs with that previously reported for chick limbs. Following removal of the tip or whole limb bud, extensive powers of regulation were observed since complete limbs always formed. Similarly after distal to proximal grafts intercalary regulation occurred to produce perfect limbs and after proximal to distal grafts serial repetitions resulted. Transplantation and rotation of limb buds to reverse either the dorso-ventral, antero-posterior or both axes resulted in the induction of supernumerary limbs in a large proportion of cases. Such regulatory behaviour of axolotl limb buds is in contrast to the mosaic nature of chick limbs and as a result, theories such as the progress-zone theory which have been formulated on the basis of data from chick limbs are not relevant to general principles of vertebrate limb development. Possible reasons for the diverse behaviour between the two systems are discussed.
Changes in fucosyl-glycopeptides during early post-implantation embryogenesis in the mouse
Authors: Muramatsu Takashi , Condamine Hubert , Gachelin Gabriel , Jacob François
Published: April 2021

Six-day to 12-day mouse embryos were dissected and radiolabelled by culture in the presence of [3H]fucose. The radiolabelled embryos were extensively digested with Pronase. The resulting glycopeptides were analysed by Sephadex G-50 column chromatography. Glycopeptides from 6-day-old embryos were separated into two main peaks: one eluted near the excluded volume, the other in a well-retarded position. This elution profile was similar to that observed with glycopeptides prepared from embryonal carcinoma cells. The relative amount of the high-molecular-weight glycopeptides decreased during embryonic development and particularly around day 9. Glycopeptide elution profiles from 10-day embryos, or isolated organs of 12-day embryos, were indistinguishable from those obtained from differentiated teratocarcinoma-derived or adult cells. At least 30% of the large molecular weight glycopeptides appear to be located at the cell surface.
Changes in the patterns of collagens and fibronectin during limb-bud chondrogenesis
Authors: Dessau W. , Mark H. Von Der , Mark K. Von Der , Fischer S.
Published: April 2021

The distribution and sequence of appearance of fibronectin and of type-I and type-II collagen in the developing cartilage models of embryonic chick hind-limb buds was studied by immunofluorescence, using specific antibodies directed against these proteins. Fibronectin and type-I collagen are evenly distributed throughout the intercellular space of the mesenchyme prior to condensation of core mesenchyme of the limb anlage and formation of the cartilage blastema. With the onset of the condensation process fibronectin and type-I collagen appear to increase in the cartilage blastema compared to the surrounding loose mesenchyme, reaching a maximal density at the time of cartilage differentiation. The latter process is marked by the appearance of type-II collagen in the cartilage blastema. As cartilage differentiation progresses, type-I collagen is gradually replaced by type-II collagen; fibronectin disappears and is completely absent from mature cartilage.

The transient appearance of type-I collagen and fibronectin suggests a temporal role in cell-matrix or cell-cell interactions in chondrogenesis, since it had been shown that (a) type-I collagen substrates stimulate cell proliferation and cartilage differentiation in limb-bud mesenchyme cell cultures; (b) fibronectin mediates attachment of cells to collagen substrates; and (c) fibronectin is directly involved in cellular interactions in chondrocyte cultures.
Is there a ventral neural ridge in chick embryos? Implications for the origin of adenohypophyseal and other APUD cells
Authors: Levy N. B. , Andrew Ann , Rawdon B. B. , Kramer Beverley
Published: April 2021

Two- to ten-somite chick embryos were studied in order to ascertain whether, as has been proposed, there exists a ‘ventral neural ridge’ which gives rise to the hypophyseal (Rathke’s) pouch. Serial sections and stereo-microscopy were used.

The neural ridges arch around the rostral end of the embryo onto the ventral surface of the head, but no evidence was found for their extension to form a ‘ventral neural ridge’ reaching the stomodaeum: in fact a considerable expanse of non-thickened surface ectoderm was seen to separate the ventral portions of the neural ridges from the stomodaeum. The thickening of neural ectoderm which does appear on the ventral surface of the head results from apposition and fusion of the opposite neural ridges flanking the neural plate and thus the tip of the anterior neuropore – the classically accepted mode of closure of the neuropore.

These findings are in accord with the generally accepted concept of the origin of the hypophyseal pouch rather than with its derivation from a ‘ventral neural ridge’.

No sign of neural crest formation was encountered ventrally; this observation excludes the possibility that endocrine cells of the APUD series could originate from neural crest in this region.
The ontogeny of erythropoiesis in the mouse detected by the erythroid colony-forming technique: II. Transition in erythropoietin sensitivity during development
Authors: Rich Ivan N. , Kubanek Bernhard
Published: April 2021

The erythroid colony-forming technique has been used to study the erythropoietin (Ep) sensitivity of CFU-E during ontogenesis. Evidence is provided which indicates that an age-related decreasing Ep sensitivity of CFU-E occurs as the animal develops. In addition, an intermediate Ep-sensitive CFU-E population represented by the 2-day-old neonate is present during the transition from foetus to adult. The Ep sensitivity of the foetal, neonatal and adult CFU-E populations is shown to be an intrinsic property of these populations.
Differentiation of glomerular filter and tubular reabsorption apparatus during foetal development of the rat kidney
Authors: Schaeverbeke Jean , Cheignon Madeleine
Published: April 2021

Differentiation of the glomerulus and the proximal tubule was studied in the rat foetus, especially with regard to the development of the protein filtration-reabsorption apparatus. Filtration starts several days before full differentiation of the glomerulus, when the glomerular basement membrane consists of a thin lamina alongside the podocyte membrane. Endocytosis is functional from this time, but fusion between endocytic vesicles and lysosome-like bodies occurs 2 days later. Foetal urine electrophoresis shows the presence of many proteins, including high molecular weight ones, this proteinuria seeming chiefly due to the immaturity of the glomerular barrier.