bluuebunny/crossref_metadata_2025 huggingface dataset:
The presence of F9 antigen on the surface of mouse embryonic cells until day 8 of embryogenesis
Authors: Buc-Caron M. H. , Condamine H. , Jacob F.
Published: April 2021

The fate of F9, a surface antigen common to embryonal carcinoma cells and cleavage embryos, as well as to male germ line cells has been studied in post-implantation mouse embryos. The antigen is readily detected on the surface of 7-day and 8-day, but not on 9-day embryonic cells, using anti-F9 serum absorption experiments and indirect immunofluorescence staining. In addition, it is shown that an anti-F9 serum absorbed with 8-day (but not with 9-day) embryonic cells does not react with cleavage embryos (morulae). It is concluded that the antigenic determinants, which are recognized on the surface of morulae by the anti-F9 serum, persist until day 8 of embryogenesis, but are not detected on day 9, either due to their absence, masking or quantitative reduction.
Colchicine induces multiple axis formation and stalk cell differentiation inDictyostelium discoideum
Authors: O’day Danton H. , Durston Antony J.
Published: April 2021

Colchicine is shown to have several effects on the development of the pseudoplasmodia of the cellular slime mould Dictyostelium discoideum At concentrations of 0·01 M and above culmination was prevented, while differentiation of cells into stalk cells occurred at the rear of cell masses. Essentially all cells transformed into stalk cells when slugs were left on colchicine agar for a long time. At concentrations of 0·01 M normal slug architecture was maintained while above 0·025 M pseudoplasmodia reorganized into multiple mounds. Each of these mounds developed an apparently normal discrete tip which was devoid of prespore cells as shown by immunofluorescent staining. The same effects were observed in growing cultures and in regulating slugs treated with colchicine. The data are consistent with the ideas that microtubules are involved in the maintenance of slug architecture and in the differentiation of stalk cells. The modes by which these intracellular structures may operate in these functions are discussed.
Facial development in the mouse; a comparison between normal and mutant (amputated) mouse embryos
Authors: Flint O. P. , Ede D. A.
Published: April 2021

This work extends previous investigations into cell interactions involved in specific morphogenetic events during the development of normal and mutant (amputated) mouse embryos. In the mutant mesenchyme, cells tend to clump together and form far more extensive areas of cell contact than are found in normal mesenchyme. This is confirmed for mutant facial mesenchyme. Facial outgrowth in the mutant is retarded. The first stages of this abnormality can be seen in the naso-frontal region at 10·5 days after conception. Neither the quantity of cells contributing to naso-frontal outgrowth nor cell proliferation in the naso-frontal region differ from normal in the mutant, and these factors can be eliminated as causes of the anomaly. Instead, cell clumping and increased areas of contact in the mutant arrest the normal expansion of the naso-frontal mesenchyme which presumably occurs as a result of increased secretion of intercellular matrix material between 9·5 and 10·5 days of development. The importance of this early expansion phase for facial development has not previously been recognized.
Patterns of cellular proliferation during thyroid organogenesis
Authors: Smuts Marybeth S. , Hilfer S. Robert , Searls Robert L.
Published: April 2021

The changes in rate and location of cellular proliferation were analyzed to determine if localized areas of cell division were influencing shape changes in the chick thyroid. Pulse labeling with tritiated thymidine indicates that the gland’s labeling index declines throughout its development. Initially, the thyroid placode has a lower labeling index than the neighboring pharyngeal epithelium. An evaluation of the positions of pulse-labeled cells reveals that the evaginating thyroid grows by annexing cells from the pharyngeal epithelium. The older evaginated regions of the gland exhibit the lowest labeling indices. The newly acquired regions still maintain higher labeling indices.
A study of digit fusion in the mouse embryo
Authors: Maconnachie Elaine
Published: April 2021

During the embryonic development of the mouse limb separation of the digits is followed by their union. This is a true, though temporary, epithelial fusion, a fused layer of epidermal cells remaining intact until separation takes place after birth. The periderm cells in the line of fusion are displaced to the dorsal or ventral surface of the foot. On the dorsal surface-these displaced cells form a prominent interdigital ridge of elongated, intertwined cells which remains until the periderm is shed. During the fusion of the eyelids, and also of the pinnae to the scalp, a similar ridge of periderm cells is formed.
The influence of local environment on the organization of mesenchyme cells
Authors: Fisher Marilyn , Solursh Michael
Published: April 2021

Limb, somite, and neural crest mesenchyme from quail embryos were implanted orthotopically and heterotopically into chick hosts to ascertain the relative importance of the local environment on mesenchyme migration. It was found that mesenchyme behavior is strongly influenced by the environment. Normally non-migratory, limb mesenchyme is capable of spreading like sclerotome when placed in the somite region. A somite placed in the limb acquires an appearance typical of limb mesenchyme. Neural crest placed in the limb migrates only along the co-implanted neural tube or axons growing out from it. The orthotopic transplantations showed that quail mesenchyme behaves normally in chick embryos. Furthermore, it was observed in the orthotopic transplants that there was no intermingling of quail and chick cells even at the edge of the graft. This result indicates that cells within mesenchyme are normally not locomotory; rather, the mesenchyme ‘migrates’ by spreading and expansion of the tissue as a unit in response to local influences.
Experimentelle Beiträge zu einer Analyse der spezifischen Induktionsleistung heterogener Induktoren
Authors: Engländer von Hans , Johnen Anna Gisela
Published: April 2021

With the use of the ‘Einsteck’ method the specific inducing abilities of several tissues of the guinea-pig were tested. Competent ectoderm of early gas-trulae of Triturus vulgaris and T. helveticus served as reacting material. After treatment with alcohol for a short period kidney (renal cortex) and parotid gland showed a deuterencephalic-spinocaudal, liver and heart-muscle an archencephalic inductive effect. Increasing the duration of alcohol treatment (up to 20 days) changed the inducing abilities of kidney and parotid from deuterencephalic-spinocaudal to archencephalic-deuterencephalic. The same effect appeared after prolonged semi-starvation (3–4 weeks) of the donor animals. The archencephalic inductive effect of the liver and heart-muscle was not changed either by prolonged alcohol treatment of the implants or by starvation of the donor animals (only liver was tested). No dependence of inducing ability on age of donor animals was found. These results permit the conclusion that there are two different modes of reaction in the competent ectoderm produced by the underlying action system. It seems that each inducing system contains the archencephalic component which can be dominated by deuterencephalic-spinocaudal inducing factors. If the latter should disappear through any change of the inducing material, e.g. a denaturation caused by alcohol treatment, archencephalic differentiation tenden-cies appear in every case. The fact that induced structures of the deuterencephalic-spinocaudal com-plex decreased in number either as a consequence of alcohol treatment of the implants or through starvation of the donor animals indicates the importance of a degradation or decrease of proteins in the inductive material. The experiments do not support the assumption that the ribonucleic acids are of decisive impor-tance in the realization of the archencephalic complex.
The Action of Testosterone and Oestradiol on the Sebaceous Glands and Epidermis of the Rat
Authors: Ebling F. J.
Published: April 2021

A method is described for estimating the mean volume and mean number of sebaceous glands per unit area from sections of skin. The enlargement of the sebaceous glands which resulted from the implantation of testosterone in spayed rats aged 25 weeks was shown to be due to increases in both cell proliferation and cell volume; at the same time cell loss appeared to have been accelerated. The effect of oestradiol, which reduced the volume of the sebaceous glands, appeared to be due mainly to an acceleration of cell breakdown rather than to an inhibition of cell proliferation; cell size was not affected. When both hormones were administered simultaneously the identity of their individual effects appeared to be maintained, although the size of the resulting glands was not significantly different from normal. Oestradiol reduced the thickness of the epidermis (stratum germinativum plus stratum granulosum) in spayed rats without altering the incidence of mitoses, but testosterone had no significant effect.
Development of the Intestinal Tract during the Larval Period of Drosophila
Authors: Shatoury H. H. El , Waddington C. H.
Published: April 2021

A few hours before the end of the second larval instar the first pair of lymph glands hypertrophies, then releases cells into the haemocoele. This is quickly followed by the growth of the primordia of the more posterior pairs of lymph glands. The cellular contents of the first pair of glands then disintegrates nearly completely and the glands are regenerated from small primordia lying at their posterior end. A similar but less well-marked process takes place at the end of the first larval instar. At the time of the hypertrophy of the first pair of lymph glands in the second larval instar (and to a lesser extent also in the first instar) the main epithelium of the mid-gut hypertrophies, giving off a large number of lumps of cytoplasm, mostly without nuclei, into the lumen of the gut which becomes temporarily filled up with them. When the more posterior lymph glands develop this hypertrophy ceases, the cytoplasmic masses cytolyse and are largely resorbed by the mid-gut epithelium. Rather similar processes of hypertrophy occur in the imaginal rudiment at the anterior end of each salivary gland and in the imaginal rudiment of the hind-gut which lies just caudal to the entrance of the Malpighian tubules. Lying beneath the main epithelium of the mid-gut in the newly hatched larva are scattered small cells referred to as basement cells. It seems likely that these are derived from the lymph glands during the end of the embryonic period. Towards the end of the second larval instar the basement cells are joined by further lymph-gland cells. During the third larval instar these multiply, forming small imaginal primordia each consisting of a nest of deeply basophilic cells, the more peripheral cells throwing out long processes which extend round and enclose the others. Towards the end of the third larval instar, when the lymph gland hexagons become melanized and degenerate, the basement cells also suffer degeneration though not melanization. At the time of puparium formation the central cells of the imaginal primordia proliferate to form the wall of the imaginal mid-gut. The peripheral cells of the imaginal primordia are thrown off into the gut-lumen where they form a continuous layer around the degenerating main larval epithelium.
Some Histochemical Observations on the Endometrium and the Yolk-sac Placenta of Erinaceus europea
Authors: Morris B.
Published: April 2021

An account is given of the distribution of RNA, fats, iron, glycogen, and alkaline phosphatase in the endometria of non-pregnant animals and in the foetal tissues and decidua of the yolk-sac placentae of pregnant forms. The RNA content of the cytoplasm of the uterine and glandular epithelia of the oestrous uterus of Erinaceus is low, and little lipoidal material is present. Iron and glycogen are entirely absent. The uterine secretions must play only a minor role in the nourishment of the early blastocyst. The histochemical reactions of the tissues which comprise the avascular yolk-sac and the vascular yolk-sac placentae are described. The yolk-sac placenta is concerned in the nourishment of the embryo in early stages of pregnancy —up to about the 7-mm. stage, for it is involved in the uptake of substances, particularly fats and sugars from the maternal blood. Subsequently, the yolk-sac placenta retrogresses. Whereas in early stages the trophoblast of the yolk-sac wall is rich in alkaline phosphatase in late stages very little of the enzyme is present in this tissue. In Erinaceus the yolk-sac fluid of late stages of pregnancy cannot be regarded as an important source of absorbable substances, and it is improbable that the yolk-sac splanchnopleur, the histochemical reactions of which are described, is as important as a placental structure in this species as it is in the rodents. The histochemical and tinctorial reactions of Reichert’s membrane are described, and these reactions are compared with those that have been described for the membrane of Reichert formed in the rat. Since the membrane is unstained by Weigert’s resorcin fuchsin elastic tissue is not one of its components. Most of its observed properties suggest that it is formed of collagenous fibres. In the hedgehog its formation is more or less coincident with the onset of the retrogression of the yolk-sac placenta.
Studies on the Development of the Foregut in the Chick Embryo
Authors: Bellairs Ruth
Published: April 2021

It is generally believed that the foregut in the chick embryo is induced by the mesoderm (Waddington & Schmidt, 1933; Waddington, 1952). In particular the splanchnic mesoderm is thought to be important (Rudnick & Rawles, 1937; Rudnick, 1952). In normal development the splanchnic mesoderm becomes fused with the presumptive foregut floor whilst the gut is developing and both become considerably thickened. During this period of induction there is a rise in the mitotic rate in this region of the endoderm (Bellairs, 1955). Similarly, Balinsky (1955) reported that the mitotic rate is raised in tissues when they are stimulated to form a limb. He also found that there is a high rate of division in the regions capable of inducing limb development.
The Effect on Embryogenesis of a Sex-linked Female-Sterility Factor inDrosophila melanogaster
Authors: Counce S. J. , Ede D. A.
Published: April 2021

Eggs from females homozygous for a sex-linked mutant factor, fsnasA, will not support the development of a viable embryo. Approximately half of the eggs produced by fsnasA females are abnormal, containing little or no yolk. Twenty per cent, of the embryos die during the first 2 hours of development. The remaining embryos develop into monster larvae which are not capable of hatching from the eggs. The major effect of the factor is on the synchrony of cleavage and blastoderm mitoses. Moreover, the regular pattern in which disturbances occur suggests stratification of the egg cytoplasm. Gastrulation and all subsequent developmental processes are abnormal. Germ-band formation and the development of mesodermal elements are strongly affected. The posterior mid-gut invaginates from the ventral surface of the embryo, and the proctodaeum and Malpighian tubules never form. The possible effects of the factor on the processes of chromosome duplication during cleavage are discussed in connexion with Painter’s theory. The developmental effects of fsnasA are compared with those of a sex-linked recessive lethal factor X2. The basic similarities of the two are probably the result of abnormal rates of mitotic division during blastoderm stages. Differences between the two suggest there may be a posterior to anterior gradient in regional differentiation of the embryo. Gonad formation in fsnasA embryos from pole cells which migrate through the blastoderm wall during the early stages of gastrulation supports Poulson’s theory of gonad formation. The broader implications of studies on female-sterility genes in Drosophila are briefly discussed.
A cellular mechanism for the palatal shelf reorientation from a vertical to a horizontal plane in hamster: light and electron microscopic study
Authors: Shah Ravindra M.
Published: April 2021

Cellular and subcellular events during reorientation of the palatal shelf in hamster fetuses are described. An alteration in the morphology of the epithelial and the mesenchymal cells is observed during shelf realignment from a vertical to a horizontal plane. The mesenchymal cells elongate and subsequently appear to protrude in the medially bulging palatal shelf. Microtubules, microfilaments and close contacts are associated with elongation of the mesenchymal cells. The cells of the thickened epithelium may play a mechanical role in providing direction to the mesenchymal cells during palatal shelf reorientation. The altered morphology of the mesenchymal cells may be associated with the intrinsic shelf force implicit in Walker and Fraser′s theory of palatal shelf reorientation.
Molecular differentiation of inside cells and inner cell masses isolated from the preimplantation mouse embryo
Authors: Johnson M. H.
Published: April 2021

Clusters of inside cells (ICs) were isolated immunosurgically from morulae and early cavitating blastocysts, and cultured for varying periods in vitro. The ICs responded to their changed position by transformation to a blastocyst-like vesicle and also showed a correlated synthesis of trophectodermal-marker polypeptides. Both changes were inhibited by α-amanitin, indicating that transcriptional events are involved in this response to changed position. Inner cell masses (ICMs), isolated immunosurgically from expanded blastocysts, did not undergo a morphological transformation to a blastocyst-like structure and did not show a corresponding and complete change in synthesis of trophectodermal-marker polypeptides. Elements of the change in polypeptide activity were, however, present, suggesting an ineffective response to position by the ICMs.
The target tissue of limb-bud polarizing activity in the induction of supernumerary structures
Authors: MacCabe Jeffrey A. , Parker Brenda W.
Published: April 2021

When polarizing mesoderm from the posterior border of the 4-day chick limb bud is placed adjacent to anterior limb mesoderm and ectodermal ridge, the anterior ridge thickens and mesodermal outgrowth ensues, resulting in supernumerary limb structures. This apposition of anterior and posterior limb tissues can be accomplished by cutting off the apical one third of the limb bud and reimplanting it on the stump with its anteroposterior axis reversed. The preaxial response to polarizing activity can be obtained after only 12-18 h in the reoriented position. Reversed apical mesoderm develops supernumerary digits when combined with untreated ectoderm. The reciprocal combination, reversed ectoderm and untreated mesoderm, fails to develop supernumerary structures. We have interpreted this as evidence that, in inducing supernumerary limb structures, polarizing activity acts only on the mesoderm.
Reversible inhibition of chondrogenic expression by certain hyaluronidase preparations
Authors: Pennypacker John P. , Goetinck Paul F.
Published: April 2021

Embryonic chick chondrocytes were cultured in the presence or absence of different preparations of testicular hyaluronidase. This treatment inhibited the accumulation of cartilage matrix as indicated by phase-contrast microscopy, by Alcian green staining, and by accumulation of 35S-labeled material. In addition, most preparations of testicular hyaluronidase caused a conversion of the cells to a fibroblastic phenotype characterized by a faster growth rate and the synthesis of type-I collagen. This effect was found to be concentrationdependent and was not observed at the minimum concentration of hyaluronidase required to inhibit matrix accumulation. Since two more highly purified hyaluronidase preparations prevented matrix accumulation but did not cause the fibroblastic transformation, it is likely that the conversion to a fibroblastic phenotype is caused by a contaminant in the other hyaluronidase preparations.
Metabolic co-operation between embryonic and embryonal carcinoma cells of the mouse
Authors: Gaunt Stephen J. , Papaioannou Virginia E.
Published: April 2021

Mouse embryonal carcinoma (EC) cells form permeable junctions at their homotypic cell-to-cell contacts which permit intercellular exchange of metabolites (metabolic co-operation). Hooper & Slack (1977) showed how this exchange could be detected by autoradiography as the transfer of [3H]nucleotides between PCI3 (a pluripotential EC line) and PCI 3-TG8 (a variant of PC13 which is deficient in hypoxanthine guanine phosphoribosyltransferase). We now show that cells taken from several different tissues of early mouse embryos, that is, from the morula, the inner cell mass of the blastocyst, and the endoderm, mesoderm and embryonic ectoderm of the 8th day egg cylinder, are able to serve as donors of [3H] nucleotides to PC13TG8. In contrast, trophectodermal cells of cultured blastocysts, and the trophectodermal derivatives in the 8th day egg cylinder, that is, extra-embryonic ectoderm and ectoplacental cone cells, showed little or no metabolic co-operation with PC13TG8. With reference to some common properties of EC and embryonic cells, we suggest how our findings may provide insight into cell-to-cell interactions in the early mouse embryo.
Immunofluorescence studies for myosin, α-actinin and tropomyosin in developing hearts of normal and cardiac lethal mutant Mexican axolotls, Ambystoma mexicanum
Authors: Lemanski Larry F. , Fuldner Rebecca A. , Paulson Daniel J.
Published: April 2021

Recessive mutant gene c in axolotl embryos results in an absence of normal heart function. Immunofluorescence studies were done to determine the distributions of myosin, tropomyosin and a-actinin in the hearts of normal and mutant siblings. Anti-myosin specifically stains the A bands of myofibrils in normal hearts and reveals a progressive increase in myofibril organization with development. Mutant hearts display less staining for myosin than normal and localization is mainly in amorphous collections. Anti-α-actinin stains the Z lines of myofibrils in normal myocytes. Mutant cells also have significant staining for α-actinin but show no striations. Antitropomyosin intensely stains the I bands of myofibrils in normal cells; however, there is very little staining for tropomyosin in mutant hearts. Thus, mutant myocardial cells have reduced but significant amounts of actin (Lemanski, Mooseker, Peachey & Iyengar, 1976) and myosin, even though non-filamentous, and substantial amounts of a-actinin. The cells appear to contain little tropomyosin.
Stable programming for map orientation in fused eye fragments in Xenopus
Authors: Straznicky C. , Gaze R. M.
Published: April 2021

Compound eyes were formed in Xenopus embryos at stages 32/33 by fusion in the right orbit of (1) two right naso-ventral halves, (2) two right ventral halves, (3) two right temporoventral halves, (4) one right and one left naso-ventral half and (5) one right and one left temporo-ventral half. The contralateral visuotectal projections from the operated eyes later showed abnormalities reflecting the anatomical arrangement of the fused fragments. The experiments thus revealed considerable stability of the developmental programme leading to the later development of map orientation, in the face of operative disturbance of the types used.
Stable programming for map orientation in disarranged embryonic eyes in Xenopus
Authors: Gaze R. M. , Straznicky C.
Published: April 2021

In Xenopus embryos of stage 32/33 either the temporal or nasal half of the right eye anlage was replaced by a corresponding left half, giving a right eye in which the grafted half was inverted dorsoventrally. In other embryos either the dorsal or ventral half of the right eye anlage was replaced by a corresponding left half, giving an eye in which the grafted half was reversed nasotemporally. These four types of operation were intended to produce eyes that were disarranged internally but which each had a complete range of positional values. The visuotectal projections from such eyes, recorded later in life, in most cases showed axial reversal of half of the map, reflecting the nature of the operation. The results thus demonstrate that the developmental programme in each of the fused retinal fragments is stable in relation to the eventual orientation of the map from that fragment.

Operations to produce eyes with an inverted temporal half, if performed in operating solution of low ionic strength, may result in mirror reduplication and the formation of double nasal maps. It is suggested that this phenomenon may underlie previous reports of reprogramming of one eye fragment by another.
Sulfated proteoglycan accumulation during development of the embryonic chick limb bud studied by electron microscopic autoradiography
Authors: Cioffi Moira , Searls Robert L. , Hilfer S. Robert
Published: April 2021

Cartilage cells are characterized by a high concentration of extracellular sulfated proteoglycan. Electron microscopic autoradiography was used to compare the incorporation of sulfate into proteoglycan by limb-bud chondrogenic and myogenic cells. From stage 19 to stage 21 there was no significant difference between the cartilage- and muscle-forming regions in the number of silver grains over either the extracellular space or the intracellular space. From stage 22 to 25 the number of extracellular silver grains was significantly greater in the chondrogenic region than in the myogenic region, but the number of intracellular silver grains was the same. Since most of the silver grains were intracellular, no significant difference in the total number of grains was found between the two tissues. Stage-26 and -27 embryos showed a significantly greater number of silver grains over both the cells and the extracellular space in the cartilage region than in the muscle region. Thus, the first step of cartilage differentiation involves a decrease in the extracellular deposition of sulfated proteoglycan in the myogenic region rather than an increase in deposition in the chondrogenic region between stage 22 and 25. After stage 25 there is an increase in sulfated proteoglycan synthesis in the chondrogenic region relative to the myogenic region.
Genetic and experimental studies on a pigment mutation, Pale (P
a), in the frog, Bombina orientalis
Authors: Ellinger Mark S.
Published: April 2021

A mutant gene, Pale, (Pa) has been discovered in the discoglossid frog, Bombina orientalis. Breeding experiments indicate that the gene is recessive to the wild-type allele (P). Embryos, tadpoles and adults homozygous for the Pale gene are lighter in coloration than wild-type animals. Eggs produced by Pale females appear normally pigmented. Neural-retina defects were apparent in Pale tadpoles. Parabiosis experiments revealed that the Pale and wild-type phenotypes were unaffected by circulating factors from the opposite phenotype. Neuralcrest-grafting experiments revealed that Pale melanophores retain the Pale phenotype when placed in a wild-type cellular environment. Likewise, wild-type chromatophores are unaffected by residence in Pale tissues. Melanophores of Pale tadpoles display reduced numbers of mature melanosomes. This is the primary morphological basis of the Pale phenotype. However, other chromatophore classes (xanthophores, iridophores) were also less intensely pigmented, demonstrating that a single gene may affect the pigmentation of all chromatophore classes in B. orientalis.
Presence of cap structures in the messenger RNA of mouse eggs
Authors: Schultz G. A. , Clough J. R. , Johnson M. H.
Published: April 2021

The presence of 5′-terminal 7-methylguanosine cap structures in the messenger RNA molecules in mouse eggs was assessed by (1) translational inhibition in a message-dependent reticulocyte cell-free system with the cap analogue 7-methylguanosine-5′-triphosphate, and (2) enzymatic removal of cap structures with tobacco acid phosphatase followed by endlabelling with γ-32P-ATP and polynucleotide kinase. The results suggest that the majority of mRNA molecules contain cap structures. There was no detectable difference in degree of capping in unfertilized versus fertilized egg mRNA.
Compositional and structural heterogenicity of the cardiac jelly of the chick embryo tubular heart: a TEM, SEM and histochemical study
Authors: Hurle J. M. , Icardo J. M. , Ojeda J. L.
Published: April 2021

The hearts of chick embryos of stages 9 –13 were subjected to SEM, TEM and histochemical studies to ascertain possible regional differences in the structure and composition of the cardiac jelly. Two distinct regions, the cardiac jelly filling the space located between the myocardium and the endocardium (MECJ) and the cardiac jelly filling the dorsal mesocardium (EECJ), were distinguished by their structural and histochemical properties. MECJ is formed by amorphous and fibrillar material arranged between the endocardial and myocardial layer. The amount of its components increases when cetylpyridinium chloride is introduced into the fixative, and it appears intensely stained by ruthenium red and alcian blue at low concentrations of MgCl2. The amount and arrangement of its components increase during the beginning of the looping process of the heart tube. The EECJ is very rich in ruthenium-red-positive basal-lamina-like material and the addition of cetylpyridinium chloride to the fixative does not modify its appearance. It also appears poorly stained by alcian blue at low concentrations of MgCl2 and its arrangement undergoes modifications closely associated with the events of endocardial fusion. The possible significance of these results in the early morphogenesis of the heart is discussed.
Analysis of glycosaminoglycans during chondrogenesis of normal and brachypod mouse limb mesenchyme
Authors: Shambaugh Janet , Elmer William A.
Published: April 2021

Studies have been carried out to characterize radioactive incorporation rates and steadystate levels of hyaluronic acid (HA) and chondroitin sulfate (CS) as well as hyaluronidase activity in the hind limbs of normal and brachypod mouse embryos between 11 –14 days of gestation. The results of the analysis show that changes in the synthetic and degradative rates of HA and CS occur at about the 12·5-day stage in normal hind limbs. These changes include an increased rate of CS synthesis, a decreased rate of HA synthesis, and a correspondingly sharp, transitory rise in hyaluronidase activity. Similar changes also occur in brachypod hind limbs but appear to be delayed in onset by approximately one-half day. In addition, the mutant hind limb exhibits a slower loss of HA at a time when turnover would be expected to be on the increase. These changes are concomitant with cell surface alterations and abnormal mesenchymal condensation formation which have been previously shown to occur in this mutant.
Regeneration of reversed aneurogenic arms of the axolotl
Authors: Wallace H.
Published: April 2021

Aneurogenic arms of young axolotls were implanted into the flank as heterotopic autografts with reversed proximo-distal orientation. The formerly proximal ends of such arms regressed to a variable extent, and then either regenerated or could do so following a second amputation. The regenerate always contained a complete sequence of skeletal elements between the adjacent stump skeleton and terminal digits, being a mirror image of the implanted arms with identical transverse axes but an opposed proximo-distal axis. Many reversed arms also regenerated fingers from the implanted hand. Identical results were obtained from reversed arms of control larvae, confirming previous studies on reversed well-innervated arms. Nerves are not required for the establishment of a new proximo-distal axis, therefore, and probably have no influence on the determination of any limb axis. Morphogenesis of the regenerate is clearly related to the position along the proximo-distal axis where the blastema originates. Although this axis is reasonably envisaged in terms of a gradient, its polarity is ignored during regeneration.
Behavioural properties of chick somitic mesoderm and lateral plate when explanted in vitro
Authors: Bellairs Ruth , Sanders E. J. , Portch P. A.
Published: April 2021

Tissue culture, time-lapse cinematographic and electron microscopic techniques have been used to study the properties of chick mesoderm at several stages of differentiation. Lateral plate, unsegmented mesoderm (segmental plate), and newly formed somites were dissected from stage-12 embryos, whilst dermo-myotomes and sclerotomes were dissected from stage-18 embryos. Each type of mesoderm was found to exhibit a characteristic pattern of behaviour.

The explants from the unsegmented mesoderm, from the newly formed somites and from the older embryos could be placed in a developmental sequence; with increasing differentiation they settled and spread on the substrate more readily, whether explanted as pieces of tissue or as individual cells, and it was concluded that this implied an increased adhesion to the substrate. Similarly, with increasing differentiation, the cells segmented at a faster rate. No significant differences could be discerned in the internal structure of the different types of cells, although differences in the general shape were apparent.

The lateral plate mesoderm cells, which bear some resemblances to the unsegmented mesoderm cells in the embryo, also show some morphological resemblances to them in vitro. However, the lateral plate cells had a much greater success in attaching to glass or plastic substrates. They were also found to have the highest speed of locomotion of all the tissues studied, whereas the unsegmented had the lowest. It is concluded therefore, that although cells may look similar to one another morphologically, their behaviour may differ greatly, probably because they are already partially determined.
Changing patterns of proteoglycan synthesis during chondrogenic differentiation
Authors: Ovadia Michael , Parker Charles H. , Lash James W.
Published: April 2021

The pattern of proteoglycan synthesis was examined in the cartilages of the anterior and the posterior limbs, the vertebra and the sterna of the developing chick embryo, during chondrogenic differentiation. At stage 18, the limb primordia synthesize small monomeric proteoglycans. In all nine cartilages examined, there was a shift during differentiation from small to larger intermediate forms followed by a transition toward the aggregate forms. As development proceeds, the proportion of aggregates increases and the small proteoglycans almost disappear. Chondrogenic differentiation is thus marked by a increase in the size of the proteoglycan molecules, and an increase in the proportion of the large proteoglycan aggregates.
Studies on the possible role of cyclic AMP in limb morphogenesis and differentiation
Authors: Kosher Robert A. , Savage Mary P.
Published: April 2021

Recent studies indicate 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, and that when mesenchymal cells are freed from the AER’s influence either artificially or as a result of normal polarized proximal to distal limb outgrowth, they are freed to commence cyto-differentiation. In a preliminary attempt to investigate at a molecular level the mechanism by which the AER exerts its ‘negative’ effect on the cytodifferentiation of subjacent mesenchymal cells, we have examined the effect of a variety of agents that elevate cyclic AM P levels on the morphogenesis and differentiation of the unspecialized subridge mesoderm in an organ culture system. In vitro in the presence of the AER, undifferentiated subridge mesoderm explants undergo remarkably normal morphogenesis characterized primarily by progressive polarized proximal to distal outgrowth and changes in the contour of the developing explant. In the presence of cyclic AMP derivatives, explants fail to undergo the polarized outgrowth and contour changes characteristic of control explants. In fact, in the presence of di butyryl-cyclic AMP and theophylline, AER-directed morphogenesis essentially ceases during the first day of culture. The cessation of AER-directed morphogenesis in the presence of cyclic AMP derivatives is accompanied by the histochemically and biochemically detectable precocious chondrogenic differentiation of the subridge mesenchymal cells. In control explants, cartilage differentiation only occurs in those proximal cells of the explant which gradually become located greater than 0·4 –0·5 mm from the AER. In contrast, in the presence of cyclic AMP derivatives, cartilage differentiation by cells within 0·4 –0·5 mm of the AER is detectable from the first day of culture, and by the third day cartilage formation has occurred throughout the entire explant. Overall, these results indicate that elevating the cyclic AMP content of the subridge mesenchymal cells enables the cells to overcome negative influences on cytodifferentiation and the positive influences on morphogenesis being imposed upon them by the AER. On the basis of this observation and previous studies, a testable model on the role of cyclic AMP in limb morphogenesis and differentiation is proposed.
Regulation and potency in the forelimb rudiment of the axolotl embryo
Authors: Slack J. M. W.
Published: April 2021

Anterior, posterior, dorsal and ventral halves of the pre-bud forelimb rudiment of tail-bud axolotl embryos can all give rise to normal limbs after the complementary half has been removed.

A histological study of the regulation of the posterior half rudiment showed no requirement for mesodermal healing across the gap, and no proliferative zone. The development of the limb bud on the operated side lags behind that of the control bud for several weeks of larval life.

When half limb rudiments and double half limb rudiments were grafted to the head they did not develop unless both the posterior and the dorsal margin were present. Double posterior and double dorsal halves could develop into duplications on this site, single halves formed normal or hypomorphic limbs.

When half limb rudiments were grafted to the flank the anterior halves developed into normal limbs and the posterior halves into duplicate limbs.

The results are interpreted to indicate that at the pre-bud stage the limb rudiment is a homogeneous group of cells with no internal regional subdivisions. Its regulative behaviour is thus similar to that of early embryos and different from the regeneration behaviour shown by adult organs.
Qualitative changes in DNA indicating differential DNA replication during early embryogenesis of the newt Triturus vulgaris
Authors: Lohmann Klaus , Schubert Lore
Published: April 2021

During gastrulation of the newt Triturus vulgaris considerable changes in the melting behaviour and in the CsCl density gradient pattern of DNA occur. The melting curves of DNAs from mid to late gastrulae (stages 11 b–12c) deviate from the regular shape. Whereas the Tm values are identical in the stages 11 a (early gastrula) and 15 (early neurula), and correspond to the standard DNA (stage 36 = tailbud), a significant rise of Tm (0· 8–1·2 °C) has been recorded in the stages 12 a/b (yolk plug). The differences in melting behaviour become visible by the deviation of the curves above Tm. These deviations from the normal sigmoidal shape are caused by the fact that a portion of DNA melts at higher temperatures than usual. Therefore the thermal denaturation of DNA is completed at approximately 3–4 °C later than in standard DNA. Both the derivative curves and the plots on normal probability paper demonstrate a heterogeneity of DNA in the stages 11 b–12c which indicates the presence of an additional GC-rich satellite fraction. These findings are confirmed by CsCl density gradient studies. Thus, in the stages 12a/b a slight shoulder on the heavy side of the gradients occurs, being absent in the other stages. From these facts we have to conclude that there is a. stage-dependent multiplication and elimination of GC-rich sequences.
Changes in lectin-mediated agglutinability during primary embryonic induction in the amphibian embryo
Authors: Barbieri Francisco D. , Sánchez Sara S. , Pino Enrique J. Del
Published: April 2021

The present study was undertaken to investigate structural alterations at the surface of presumptive neural cells after primary embryonic induction. For this purpose, plant lectin-mediated agglutinability of dissociated cells from the epiblast of Bufo arenarum gastrulae was tested. Two fragments of epiblast were excised from the same mid-gastrula: one from the dorsal side of the egg, making contact with the invaginating chordamesoblast and assumed to be composed of determined cells and the other from the ventral region of the egg, facing the blastocoele cavity and assumed to be composed of undetermined cells. Cells of the pooled fragments were dissociated in calcium-free Holtfreter’s solution with potassium oxalate and incubated in the presence of different concentrations of phytohemagglutinin and concanavalin A. Epiblast cells overlying the archenteron roof are less agglutinated with both lectins than undetermined cells. On the other hand, when egg fragments were removed from the dorsal and ventral regions of early gastrulae before the archenteron was formed, no significant difference in lectin-mediated agglutinability was observed, even after having been cultured in vitro in absence of inducing tissue. These results suggest that the target of the inducing signal generated in the mesoblast is likely to be located on the surface of epiblast cells. Additional experiments showed that cells pretreated with colchicine, cytochalasin B or colchicine and cytochalasin B simultaneously exhibit no significant variation in agglutinability, suggesting that the cytoskeleton was not be involved in the cell surface alteration here described.

Treatment of whole embryos or sandwich explants with concanavalin A or phytohemagglutinin has no effect on neural tube formation, suggesting that the carbohydrate-containing binding sites for these lectins are not involved in primary embryonic induction. Changes in cell agglutinability described in this paper are to be interpreted thus as a secondary expression of structural alterations in the cell surface concomitant with neural determination.
Somitogenesis in amphibian embryos: III. Effects of ambient temperature and of developmental stage upon pattern abnormalities that follow short temperature shocks
Authors: Cooke Jonathan , Elsdale Tom
Published: April 2021

Temperature shocks of a few minutes duration at 37 °C to tail-bud embryos of Rana induce zones of abnormal segmentation along the somite files subsequently produced. The immediate result of a temperature shock is a temporary arrest of development as a whole, following which the schedule of somite determination and formation is resumed at the normal rate. It is during the period immediately following this that the zone of abnormal somite pattern is determined. Thus the length of the abnormal zone reflects the total time taken by the morphogenetic system to recover from the disturbance, and might depend upon variables affecting both the duration of the initial arrest and the duration of the recovery period itself.

Observations are presented demonstrating how the lengths of abnormal zones, caused by a temperature shock of any particular severity, are affected by three variables : (1) the ambient temperature to which the embryos were adapted before shock, (2) the ambient temperature of post-shock development, (3) the stage in somitogenesis, i.e. the number of somites already formed at the time of shock.

The data (in this and previous papers of the series) support models postulating that the spatial periodicity in cell behaviour, that is somite morphogenesis, reflects a normal interaction between two hidden aspects of development, one a wavefront of cellular activation passing down the body axis, and the other having the character of a temporal periodicity throughout the tissue. Temperature shock, as well as halting the wavefront (i.e. stopping development) temporarily, leads to a subsequent period during which there is only gradual recovery of normal co-ordination between the periodicity within cells of the tissue and the wavefront progress. It is the relative rate of this recovery, alone, that is responsible for variation in the length of the abnormal zone.
Developmental fate of a distinct class of chick myoblasts after transplantation of cloned cells into quail embryos
Authors: Womble Mark D. , Bonner Philip H.
Published: April 2021

A technique appropriate to investigation of the developmental fates of distinct embryonic cell types is described and the fate of a particular type of chick myoblast (CMR-I) examined. CMR-I myoblast clones are morphologically different from other chick myoblast clone types and can readily be identified in living cultures.

After two weeks of culture CMR-I myoblast clones were collected, aggregated, and transplanted into the prospective dorsal thigh region of young quail embryos. After four days of growth, cells of the transplant-containing quail legs were grown as clones. Chick clones were located by Feulgen staining and identified as muscle or non-muscle and, if muscle, as CMR-I or not; 91 % of the chick clones recovered from transplants were muscle clones, and of these 97% were CMR-I. It was concluded that CMR-I myoblasts do not undergo a change in differentiated state identifiable by clonal analysis.

Other transplant-containing quail legs were fixed, sectioned, and Feulgen stained. The locations of chick nuclei were determined. The only region in which chick nuclei appeared at significantly greater frequency than in control tissue was the dorsal thigh muscle, the region into which the cloned chick cells were placed originally. Dorsal thigh multinucleated myotubes exhibited the highest percentage of chick nuclei of all tissues examined. It was concluded that the fate of CMR-I myoblasts is fusion to form myotubes.