bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quantitative morphological analysis of early mouseembryogenesisin vitro:I. Perfusion culture system, tissue preparation, sampling
Authors: Deter Russell L. 
Published: April 2021

ABSTRACTTo facilitate a quantitative morphological analysis of early mouse development under controlled conditions, a perfusion culture system capable of supporting embryogenesis to blastocyst stage has been developed. The use of a mesh system allows identification of individual embryos by position, and control of their orientation during culture and preparation for light and electron microscopy. Quantitative evaluation of tissue-processing procedures has permitted selection of conditions which reduce changes in linear dimensions to –1·6 ± 1·8% in two-cell embryos. Through the definition of a coordinate system based on mesh structure and the development of a special sectioning procedure, sections can be localized within the intact embryo and three-dimensional coordinates given to any element of embryo volume.
Mesodermal expansion after arrest of the edge in the area vasculosa of the chick
Authors: Augustine J. M. 
Published: April 2021

ABSTRACTTo investigate whether mesodermal expansion in the area vasculosa is caused by tension produced by outward migration of cells either in the somatic mesoderm or at the mesodermal edge on an ectodermal substratum, stage 18–20 embryos were transferred to a culture dish. There mesodermal expansion proximal to an arrested edge could be compared with that proximal to a moving edge by measuring the amount of vascular elongation occurring in each. A proximo-distal gradient in vascular elongation rate was detected both in normal embryos in ovo and in explants. This gradient was reversed following arrest of the edge, and the rate of vascular elongation proximal to the arrested edge decreased to 60–70 % of that proximal to a moving edge. Nearly all of the mesoderm producing this expansion was located in the proximal two-thirds of the area vasculosa, where vascular elongation rate on the stopped side of the explant was not significantly different from that on the moving side. Similar results were obtained in the absence of the ectoderm, and when liquid culture medium was used instead of semisolid medium. It is concluded that tensile force derived from mesodermal migration plays no role in expansion of the proximal two-thirds of the area vasculosa mesoderm.
Analysis of endoderm formation in the avian blastoderm by the use of quail-chick chimaeras: The problem of the neurectodermal origin of the cells of the APUD series
Authors: Fontaine J. , Le Douarin N. M. 
Published: April 2021

ABSTRACTThe formation of the endoderm has been investigated in chimaeric embryos resulting from the combination of the lower and upper germ layers taken from chick and quail embryos at stages 2–6 of Vakaët (1962). The ability to recognize quail from chick cells made it possible to follow the fate of each germ layer during development. It appeared that the primitive hypoblast participates in the formation of the anterolateral extra-embryonic endoderm while the embryonic endoderm is formed later by migration of cells of the ectomesoblast through Hensen’s node and the primitive streak.Further interspecific combinations were carried out between ectoderm and endoderm + mesoderm from quail and chick embryos at stages 5–7 of Hamburger and Hamilton. The explants were grafted into chick embryos for several days and the intestinal structures which developed were observed. No contribution of cells from the neurectoderm to the endoderm was found. In contrast, cells coming from the neural crest colonized the intestinal structures and gave rise to the enteric ganglia. It was concluded from these observations that the enterochromaffin and endocrine cells of the gut epithelium do not originate from the neurectoderm.
Ultrastructural analysis of the apical ectodermal ridge during vertebrate limb morphogenesis
Authors: Fallon John F. , Kelley Robert O. 
Published: April 2021

ABSTRACTThe fine structure of the apical ectodermal ridge of five phylogenetically divergent orders of mammals and two orders of birds was examined using transmission and freeze fracture electron microscopy. Numerous large gap junctions were found in all apical ectodermal ridges studied. This was in contrast to the dorsal and ventral limb ectoderms where gap junctions were always very small and sparsely distributed. Thus, gap junctions distinguish the inductively active apical epithelium from the adjacent dorsal and ventral ectoderms.The distribution of gap junctions in the ridge was different between birds and mammals but characteristic within the two classes. Birds, with a pseudostratified columnar apical ridge, had the heaviest concentration of gap junctions at the base of each ridge cell close to the point where contact was made with the basal lamina. Whereas mammals, with a stratified cuboidal to squamous apical ridge, had a more uniform distribution of gap junctions throughout the apical epithelium. The difference in distribution for each class may reflect structural requirements for coupling of cells in the entire ridge. We propose that all cells of the apical ridges of birds and mammals are electrotonically and/or metabolically coupled and that this may be a requirement for the integrated function of the ridge during limb morphogenesis.
Events in the germ cell lineage after entry of the primordial germ cells into the genital ridges in normal and u.v.-irradiatedXenopus laevis
Authors: Züst Brigitta , Dixon K. E. 
Published: April 2021

ABSTRACTApproximately 20–25 primordial germ cells leave the endoderm between stages 38–41 and localize in the dorsal root of the mesentery by stage 43/44. At this time all the cells contain large quantities of yolk which is gradually resorbed. The cells begin dividing between stages 48–52. The number and size of the germ cells were measured in tadpoles between stages 48–54 of development. The results indicate that in females the germ cells divide more often than in males. In both sexes the mitoses are grossly unequal, leading to the formation of a new generation of germ cells which are considerably smaller (one-tenth to one-fifth) than the size of the primordial germ cells at stage 48. The germ cells in male tadpoles at stage 54 are larger than in female tadpoles at the same stage. In tadpoles which developed from eggs irradiated in the vegetal hemisphere with u.v. light at the 2- to 4-cell-stage, primordial germ cells migrate into the genital ridges much later (stage 46–48) than in unirradiated embryos. They also differ morphologically from germ cells in control animals at this stage in that they are approximately one-tenth the size, lacking yolk in the cytoplasm and have a more highly lobed nucleus. Comparison of the results in unirradiated and irradiated animals suggests that the germ cell lineage is composed of a series of ordered, predictable events, and serious disruption of one of the events deranges later events.
Effects of cyclophosphamide treatment before implantation on the development of rat embryos after implantation
Authors: Spielmann Horst , Eibs Hans-Georg , Merker Hans-Joachim 
Published: April 2021

ABSTRACTAfter treatment of pregnant rats 24 h before implantation with a single injection of cyclo-phosphamide (20 –80 mg/kg), a dose-dependent increase in resorption was observed at term but no malformed fetuses could be found. The lowest cyclophosphamide dose that caused 100 % resorption was 60 mg/kg. Somite number and wet weight indicated retardation of about 24 h during organogenesis. Determination of the time of implantation revealed that the developmental retardation in treated embryos was not due to delayed implantation. At implantation, 24 h after cyclophosphamide treatment, a significant and dose-dependent decrease of the cell number of blastocysts was found. Embryo transplantation experiments showed that early cyclophosphamide treatment interfered with the subsequent development of both the embryo and the mother. The decidual reaction seemed to be more affected by the treatment than the embryos. Most teratologists hold that mouse embryos after treatment in the preimplantation period either die before implantation or survive to term without being malformed. The present study, however, proves that the reaction of drugs at this early stage of pregnancy is more complex than is generally assumed.
Cell death in the posterior necrotic zone (PNZ) of the chick wing-bud: a stereoscan and ultrastructural survey of autolysis and cell fragmentation
Authors: Hurle J. , Hinchliffe J. R. 
Published: April 2021

ABSTRACT
The participation of lysosomes and cell profile changes were studied during mesenchymal cell death in the PNZ of forelimbs of the day chick embryo.
Lysosome participation was studied cytochemically using as substrate either β-glycerophosphate or p-nitrophenylphosphate. Acid phosphatase (AP) is localized within the Golgi cisternae of the prospective dying cells, and small AP-positive autophagic vacuoles appear when degeneration commences. As degeneration by enzymic digestion proceeds, these vacuoles increase in size and appear to become autolytic since part of the AP activity seems to leak’ out of the autophagic vacuoles. Next, the cells fragment and the fragments are then enclosed in heterophagic vacuoles of macrophages where digestion is completed.
The SEM showed that these intracellular changes in degenerating cells are accompanied by changes in the cell surface structure. First, the degenerating cells lose the stellate appearance of healthy mesenchymal cells and become rounded and pitted, then constrictions appear and finally the cytoplasm breaks up into many small pieces. This final fragmentation may be an active process rather than a mere consequence of vacuolation.
Experimental studies of the shape and structure of isolated cardiac jelly
Authors: Nakamura Atsuyo , Manasek Francis J. 
Published: April 2021

ABSTRACT
The properties of the early chick embryonic heart cardiac jelly were studied. The cells of the heart were removed by sequential treatments with calcium magnesium-free medium; the same medium containing 5 mM EDTA; and aqueous 0·1 % deoxycholate. The transparent, naked cardiac jelly retained the original shape and size of the untreated original heart when immersed in physiological ionic strength medium. Its size and shape responded to changes in the ionic strength of the surrounding media. Alcian blue, cetylpyridinium chloride and testicular hyaluronidase abolished the ability of the jelly to respond to ionic strength changes. Electron microscope examination of the negatively stained spread cardiac jelly revealed an extensive network of collagenous fibrils and fine filaments with some amorphous adhering material. Treatment with testicular hyaluronidase removed much of the amorphous material and improved the details of the filaments. These results suggest that glycosaminoglycans play an important part in the hydration of the cardiac jelly and that the stability of the cardiac jelly shape is mainly due to the filamentous network and their possible interactions with macromolecules of the cardiac jelly matrix. It is suggested that the factors that control the deposition of the connective tissue macromolecules and the assembly of the filamentous network are significant factors which influence the morphogenesis of the early embryonic heart.
Variability of chimaeras and mosaics
Authors: Falconer D. S. , Avery P. J. 
Published: April 2021

ABSTRACTAggregation chimaeras and X-inactivation mosaics in mice are alike in general appearance, but chimaeras are very much more variable in the proportions of the cell types (p) seen for example in coat pigmentation. The distribution of p in chimaeras is not binomial, but is uniform, or flat, between the two extremes. The greater variability of chimaeras arises from two sampling events that occur when cellular heterogeneity is already present in chimaeras but before it arises in mosaics. These are the differentiation of the inner cell mass from the trophectoderm and of the primary ectoderm from the primary endoderm. The second of these generates the flat distribution of chimaeras as a consequence of the two cell types being unmixed at that time. The two sampling events generate single-colour individuals in roughly the proportions observed. Consideration of the second sampling event provides evidence that the primordial germ cells must originate in the primary ectoderm and not in the yolk-sac.Estimation of numbers of progenitor cells on the supposition of binomial sampling is not valid unless the clone-size is known or the cells in the sample are not contiguous. Data on coat pigmentation are consistent with the assumptions that X-inactivation is random in about 21 cells, that the sampling of melanoblasts is binomial (because they are not contiguous), and that the melanocytes of the head and body are descended from about 34 progenitor cells.
Digit regeneration in the amphibian –Triturus cristatus
Authors: Smith A. R. 
Published: April 2021

ABSTRACTDigit regeneration has been examined in Triturus cristatus. Because of their size, blastemas that form after digit amputation are relatively a lot more suitable for quantitative studies that involve for example the counting of cells in histological sections. They are also very useful for the study of some basic histological aspects of regeneration particularly cartilage formation. This has been looked at in regenerating digits, as there are only a maximum of three bones to regenerate and these lie in sequence, one after the other. It was seen that the cartilage is laid down as a solid rod by about 17 days post-amputation, and that by about 20 days, it starts to be split up into its three elements.An X-ray study of the growth of digit regeneration together with autoradiography experiments were also carried out as a comparison to studies already undertaken on larger more proximal blastemas. It was shown that in fact the behaviour of digit blastemas is very similar to those of a more proximal origin. This fact, together with the advantages of its size, make the digit a very strong candidate for the further study of regeneration.
Participation of cultured teratocarcinoma cells in mouse embryogenesis
Authors: Papaioannou V. E. , Gardner R. L. , Mcburney M. W. , Babinet C. , Evans M. J. 
Published: April 2021

ABSTRACTMouse blastocysts were microsurgically injected with embryonal carcinoma cells from in vitro teratocarcinoma cell lines C17, C86, SIKR-OSB, and PCC3/A/1. The embryos were allowed to develop to term and the resulting offspring were analysed for chimaerism using coat colour markers and isozyme differences of the enzyme glucose phosphate isomerase. When injected into blastocysts, cell line C86 produced tumours in six of 74 animals born. The tumours were detected at birth and were poorly differentiated neuroectodermal teratocarcinomas. Cell line C17 gave 13 chimaeras in 77 mice born, five of which showed chimaerism only in normal tissues, mainly melanocytes of the coat and eye. The other eight chimaeras developed tumours. Seven of these developed in adult animals and were mainly fibro-sarcomas. Cell line SIKR-OSB resulted in one normal chimaera in 44 mice born. Of 86 animals born following injection of cell line PCC3/A/1, there was one chimaera with a small tumour and three normal chimaeras. The levels of chimaerism were generally very low. The mice were test bred but with no evidence of germ line chimaerism. The karyotypes of all the cell lines were abnormal. How this and other factors such as cell cycle times might affect the incorporation of embryonal cells into the developing embryo is discussed.
Ultrastructural observations on the chorionic epithelium, parathyroid glands and bones from chick embryos developed in shell-less culture
Authors: Narbaitz Roberto , Jande Sohan S. 
Published: April 2021

ABSTRACT
Three-day-old chick embryos were cultured in Petri dishes until they reached developmental stages 37 or 39 (Hamburger & Hamilton, 1951). The electron microscopical study of the chorio-allantoic membranes showed that, even in the absence of the shell and the corresponding calcium supply, ‘capillary-covering’ and ‘villus-cavity’ cells differentiated well. The parathyroid glands from the cultured embryos showed ultrastructural signs indicative of active synthesis and secretion of the parathyroid hormone. This correlates well with the significant hypocalcemia (5·4 mg/100 ml) observed in these embryos.
In all cultured embryos mineralization of bones was greatly reduced as shown by alizarin bulk staining and confirmed by histological and electron microscopical analysis. The ultrastructural characteristics of osteoblasts and osteocytes, as well as of the bone matrix, appeared normal. The defect in mineralization appeared thus to be due to a deficiency in the availability of calcium and not to a delay in bone differentiation. This implies that the yolk sac appears to lack calcium regulatory capacity since it cannot compensate for the absence of shell by increasing its own contribution in order to assure an adequate mineralization of the embryonic bones.
Cell culture of individual Drosophila embryos: II. Culture of X-linked embryonic lethals
Authors: Cross David P. , Sang James H. 
Published: April 2021

ABSTRACT
Results are reported from the culturing in vitro of cells from individual early gastrulae of the following four groups of X-linked embryonic lethal mutants of Drosophila melanogaster. (1) Notch lethals. Five Notch mutants were studied which have been reported to give similar abnormalities in whole embryos: the nervous system displays a three-fold hypertrophy as part of a shift in the pattern of differentiation within ectodermal derivatives, and mesodermal derivatives do not differentiate. An hypertrophy of nerve was found in cell cultures prepared from embryos of all five mutants. In addition, four of the five alleles consistently gave abnormalities of muscle differentiation: when compared to controls, Notch cultures had a reduced frequency of myotubes, and displayed unusual clusters of myocytes which had either failed to fuse or had fused incompletely. Results from mixed cultures prepared from two embryos were consistent with the autonomous expression of nerve and muscle abnormalities by Notch-8 cells in the presence of wild-type cells. It is argued that the Notch locus has a direct role in the differentiation of both nerve and muscle. (2) white deficiencies. Cells carrying either of two deficiencies gave a clear-cut pattern of abnormalities: initial cellular differentiations were normal, but nerve, muscle and fat-body cells progressively deteriorated during the culture period. Mixed cultures showed that wild-type cells could not ‘rescue’ mutant muscle and fat-body cells; however, the status of the autonomy of mutant nerve abnormalities in these cultures was unclear. Both white deficiencies remove cytological band 3C1, and this permits a comparison of results with those from cultures of cells from Notch-S embryos (also deficient for 3C1). Abnormalities displayed in cultures of the two types of mutant show no overlap. Therefore no consistent cellular abnormality can be attributed to absence of band 3C1. (3) lethal(l)myospheroid. In contrast to earlier observations on in vitro cell cultures (Donady & Seecof, 1972) muscle was seen to differentiate, though its morphology was extremely abnormal. Observations indicated that all cell types within the cultures had poor properties of adhesion to a glass substrate. It is argued that the observed abnormalities are not consistent with a mutant lesion which is restricted to the basement membrane (contraWright, 1960), and that all cell types carry a basic defect which may reside in the cell membrane. (4) shibirets alleles. Cultures of two temperature-sensitive lethal shibire alleles (shils1, shits3) were normal at the permissive temperature of 22 °C. At the restrictive temperature (29° C) early cell differentiation was normal but subsequent development was blocked. This blockage could be partially reversed by shifting cultures to the permissive temperature after as much as 10 days exposure to the high temperature. It is suggested that shits cells are mutant in a process which is basic to several cell types.
Changes of the external and internal pigment pattern upon fertilization in the egg of Xenopus laevis
Authors: Paleček J. , Ubbels Geertje A. , Rzehak K. 
Published: April 2021

ABSTRACT
External and internal pigment shifts in Xenopus laevis eggs were studied between fertilization and first cleavage.
Externally visible, constant features are: (1) the ‘activation contraction’, a pigment shift towards the animal side taking place between 5 and 15 min post fertilization (p.f.) and (2) the concentration of the pigment around the sperm entrance point leading to the formation of the grey crescent at the opposite side of the egg. Hence, in Xenopus the grey crescent is not formed by rotation of the pigmented cortical layer with respect to the internal egg mass.
Histological examination reveals that during the activation contraction the pigment is mainly concentrated in the cortical cytoplasm. Except in the region around the sperm entrance point, from 15 min p.f. onwards, the pigment progressively disperses through the sub-cortical layer and part of it even moves more deeply into the egg. After fusion of the pronuclei (45-60 min p.f.) the pigment in the subcortical layer forms aggregates.
During the pigment shift the yolk-free cytoplasm is displaced dorsally and is ultimately found opposite the sperm entrance point. Thin fibrillar structures in the yolk-free cytoplasm progressively orient themselves parallel to the dorso-ventral plane, and from 40 min p.f. onwards towards the pronuclei.
These observations are discussed in connexion with cinematographic observations by Hara, Tydeman & Hengst (1977).
Scanning electron microscopic observations of the development of the somites and their innervation in anuran larvae
Authors: Kordylewski Leszek 
Published: April 2021

ABSTRACT
The development of the paraxial mesoderm in tadpoles of Xenopus, Bufo and Rana was observed with a scanning electron microscope. In addition to examination of the differentiation of the surface and the interior of the somites, some attention was also paid to the transformation of the material of the neural crests and to the innervation of the developing myotome.
Somite abnormalities caused by short heat shocks to pre-neurula stages of Xenopus laevis
Authors: Cooke Jonathan 
Published: April 2021

ABSTRACT
This paper describes the small disturbances, in the regular pattern of the somites and the fissures between them, that are seen following short (around 300 s) heat shocks at 37·5 °C delivered to pre-neurula stages of Xenopus laevis. Affected groups of cells still finally differentiate as somite muscle, but the normally precise spatio-temporal sequence in which they move beforehand to give rise to the actual pattern of somite blocks, is disrupted. Examination of the position and sizes of patches of disrupted morphogenesis, in relation to the precise embryonic stage at shock, leads to certain conclusions about the nature of the disturbance induced by a brief period at high temperature, in cells due to form somites. The pattern of results is compared with that produced by similar temperature shocks given to tail-bud (later) staged embryos. The discussion includes a brief consideration of how the various results of heat shocks, given at different embryonic stages, might be understood in terms of one particular model (Cooke & Zeeman, 1976) for the spatio-temporal control of the developing somite pattern.