bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitative morphological analysis of early mouseembryogenesisin vitro:I. Perfusion culture system, tissue preparation, sampling
Authors: Deter Russell L.
Published: April 2021

To 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

To 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

The 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

The 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

Approximately 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

After 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

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

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

Aggregation 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

Digit 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

Mouse 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

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

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

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

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

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.
Changes in responsiveness of preimplantation mouse embryos to serum
Authors: Fishel Simon B. , Surani M. Azim H.
Published: April 2021

Changes in uptake of radioactive uridine and its incorporation into RNA were determined in preimplantation mouse embryos, from the 2-cell to the blastocyst stage, as a measure of their responsiveness to extracellular conditions. Two media were tested, one contained serum and the other contained bovine serum albumen as a control. An increase in the acid-soluble pool occurred at the 8-cell stage and a marked increase in RNA synthesis occurred at the early blastocyst stage when the embryos were incubated with serum.
Gastrulation in the mouse: assessment of cell populations in the epiblast of tw18/tw18 embryos
Authors: Snow M. H. L. , Bennett D.
Published: April 2021

The appearance of the primitive streak at the onset of gastrulation in the mouse heralds a 24 h period of extremely rapid growth (Snow, 1976). During that time, from 6·5 to 7·5 days post coitum, at least in the random bred Q strain of mice, the epiblast, an apparently uniform population of about 600 cells, generates the ectoderm and mesoderm of the pre-somite embryo which total about 15000 cells. The definitive endoderm, which in the foetus replaces the primary endoderm (Gardner & Papaioannou, 1975), has not yet been identified at this stage.
Transfilter induction of kidney tubules as a function of the extent and duration of intercellular contacts
Authors: Saxén Lauri , Lehtonen Eero
Published: April 2021

The kinetics of kidney tubule induction were examined in transfilter experiments by varying the time of transfilter apposition, the porosity and pore size of the filters, and the culture conditions. Transfilter contact between the interacting cells is established within an hour when cytoplasmic processes emerge through the interposed filter; then a further 16–24 h are needed for completion of induction. This lag is a function of thickness and pore size of the filter, and is not reduced by precultivation of the inductor on the filter. Material that accumulates on the far side of the filter during such cultivation displays no morphogenetic activity.

The intensity of the mesenchymal response was roughly quantified and shown to be a function of pore size, pore density and duration of transfilter contact.
Investigation of the potency of cells from the postimplantation mouse embryo by blastocyst injection: a preliminary report
Authors: Rossant J. , Gardner R. L. , Alexandre H. L.
Published: April 2021

Chimaeric conceptuses have been produced by injection of and day extra-embryonic ectoderm and day embryonic and extra-embryonic endoderm into day mouse blastocysts. Extra-embryonic ectoderm cells contributed only to the ectoplacental cone and/or trophoblast giant cell fractions, reflecting the probable trophectoderm origin of these cells. Proximal (visceral) endoderm cells overlying both the embryonic and extra-embryonic ectoderm contributed cells only to the endoderm of the visceral yolk sac, indicating that the definitive embryonic endoderm has not formed by days p.c.
Features of cell lineage in preimplantation mouse development
Authors: Graham C. F. , Deussen Z. A.
Published: April 2021

The cell lineage of the mouse was studied from the 2-cell stage to the blastocyst. Lineage to the 8-cell stage was followed under the microscope. Each cell from the 2-cell stage divided to form two daughter cells which remained attached. Subsequently, these two daughters each produced two descendants; one of these descendants regularly lay deep in the structure of the embryo while the other was peripheral. Lineage to the blastocyst was followed by injecting oil drops into cells at the 8-cell stage, and then following the segregation of these drops into the inner cell mass and trophectoderm. Between the 8-cell stage and the blastocyst, the deep cells contributed more frequently to the inner cell mass than did the peripheral cells.
Fluctuations of adenylate cyclase activity during anterior regeneration in Owenia fusiformis (Polychaete Annelid)
Authors: Coulon Josiane , Marilley Monique
Published: April 2021

Biochemical assays of adenylate cyclase activity were performed during the early phases of regeneration in Owenia fusiformis (Polychaete Annelid).

The results indicate the existence of a strong stimulation in an early phase following trauma. This stimulation is then followed by periodic fluctuations exhibiting a diurnal rhythm correlated with the cell cycle. Adenylate cyclase activity is also shown to be neuro-transmitter-dependent.

In this paper it is proposed that neurotransmitters might participate in the regulation of cyclic AMP formation, by means of adenylate cyclase acting on target blastema cells, undergoing the cell cycle.
A mutant ofTetrahymena thermophilawith a partial mirror-image duplication of cell surface pattern
Authors: Frankel Joseph , Jenkins Leslie M.
Published: April 2021

The CU-127 clone of Tetrahymena thermophila, which manifests an unusually high number of ciliary rows plus a second set of abnormal oral structures and of contractile vacuole pores with partial mirror-image reversal of asymmetry (Jerka-Dziadosz & Frankel, 1979), has been subjected to breeding analysis. The progeny ratios obtained in various crosses indicate that the abnormalities of cell-surface asymmetry are brought to expression as a result of the action of a recessive allele at a single gene locus, here named janus. When previously normal cells were made homozygous for the jan allele, the cortical pattern characteristic of the CU-127 clone came rapidly to expression, often without associated change in number of ciliary meridians. Conversely, when cells previously expressing jan re-acquired the wild-type (jan+) allele, they returned to the normal pattern of a single normal oral structure and a single nor-mally located set of contractile vacuole pores while still retaining the high ciliary meridian number characteristic of the original CU-127 clone. The capacity for manifestation of the unique asymmetry pattern depends solely on homozygous expression of the janus allele, whereas the stable number of ciliary meridians in janus clones and the degree of expression of secondary OAs is modulated by other factors, probably at least in part genic. These results, taken together with those of the preceding paper, indicate that the janus allele promotes the propagation and/or expression of a condition of reversed asymmetry in a precisely located cell region, and further indicates that the propagation and expression of this condition are largely independent of the number and asymmetry of ciliary meridians.
The Behaviour of Basophil Cytoplasmic Substances during Neural Induction in the Chick
Authors: Lavarack J. O.
Published: April 2021

Basophil cytoplasmic substance of the cells concerned in neural induction in the chick was investigated by methyl green-pyronin staining and the action of ribonuclease. Comparison of a number of stages indicated that changes in both distribution and concentration occur. Most of the basophil substance was in the dorsal zone of the cytoplasm in presumptive neural and presumptive mesodermal epiblast. In the subsequent differentiation of neural epithelium and chorda-mesoderm its concentration throughout the cytoplasm of both cell-groups increased considerably. The highest concentrations observed developed in a sharply localized zone at the ventral poles of the cells of the neural groove in its early stages and in some somite cells. The time relationships of concentration changes in adjacent cells did not indicate whether concentration of the substance at the base of the neural epithelium depends on transfer from other cells.
The Effects on Foetal Development of Freezing Pregnant Hamsters(Mesocricetus auratus)
Authors: Smith A. U.
Published: April 2021

Golden hamsters at different stages of pregnancy were cooled until breathing and heart-beats stopped and until they froze with deep body temperatures below 0° C. They were subsequently resuscitated. Animals frozen for 30 min. at days or at days had normal numbers of well-developed foetuses when killed at days of gestation. Others frozen for 30 min. at these times gave birth to litters and reared young. Freezing for 45 min. at days of gestation was also harmless as judged by the number and appearance of foetuses at days. By contrast, freezing for 45 min. at days of gestation arrested development or caused malformation of most of the foetuses. The abnormalities included hydrocephalus, anencephaly, herniation of the brain, absence of one or both eyes, hare-lip, cleft palate, and deformities of the feet. There was a critical period of pregnancy between and days when uterine haemorrhage and foetal resorption resulted whether the hamsters were allowed to re-warm from body temperatures of 15 – 17° C. or whether they had been chilled below zero and frozen for 30 – 45 min.
Further Studies in Tissue Homotransplantation in Cattle
Authors: Billingham R. E. , Lampkin G. H.
Published: April 2021

The present contribution presents a sequel to our previous investigations into problems which arose when attempts were made to use skin grafting to differentiate between monozygotic and dizygotic twins in cattle. In each of three trials grafts from a dam elicited similar reactions when transplanted to each of her one-egg twin offspring. On the basis of this finding the asymmetry of response which the majority of two-egg twins show towards grafts from their dam may be taken as evidence of their dizygotic origin.It has been shown that mutual graft exchange between unlike-sexed twins can be used as a reliable method for distinguishing reproductively normal females from freemartins. The complete success of this method provides strong evidence that homograft tolerance and the freemartin condition have a common anatomical origin.Grafts from a dam to her tetrazygotic offspring lived for upwards of 70 days, whereas grafts from a dam to her offspring of single birth rarely live for as long as 14 days. It is argued that this great prolongation in the life of their grafts is the outcome of the quadruplets having previously exchanged cells in foetal life through anastomoses of their circulations. Each must be incapable of reacting against a very wide spectrum of antigens since it will accept grafts from all its brothers and sisters.Evidence is presented which suggests that cells from her foetus not infrequently gain access to a dam and sensitize her to subsequent grafts of her offspring’s skin. A first pregnancy may be sufficient to elicit this sensitization. On the other hand, if maternal cells gain access to the foetus, this must occur very rarely for in none of seventeen calves tested with grafts of their dam’s skin was there the slightest evidence that they were tolerant.New-born calves react as vigorously as adult cattle against homografts, even when they have not received colostrum. Since new-born calves possess no serum globulins, including antibodies, this provides strong evidence that immune globulins play no essential part in the homograft reaction.
A Comparative Study of the Desoxyribonuclease Activity in Adult and Embryonic Tissue
Authors: Blumenthal Gertrude
Published: April 2021

Determinations have been made of the desoxyribonuclease (DNase) activity of various embryonic stages and adult tissues of a sea-urchin, a frog, and the domestic fowl. Special attention has been paid to the pH optimum and the magnesium requirement of the enzymes. Of the three species investigated only the sea-urchin exhibited DNase activity during early embryonic development. This activity was essentially the same as that of crystalline bovine pancreatic DNase, although it is doubtful that the two enzymes are identical. The possible correlation of this enzyme with the amount of preformed desoxyribonucleotides in the egg is discussed. At later stages of development, all three species contain an enzyme which is similar to DNase II of mammalian origin. The possibility that the difference in enzyme activity between embryonic and mature tissue is due to the presence of inhibitors has been ruled out. The data obtained in this study and that of other workers suggests that the adult DNase may play a role in the processes of cell destruction and cell turnover in adult metazoans.
Neuroglial Development and Myelination in the Spinal Cord of the Chick Embryo
Authors: Bensted J. P. M. , Dobbing J. , Morgan R. S. , Reid R. T. W. , Wright G. Payling
Published: April 2021

The widespread occurrence of the demyelinating diseases of the central nervous system makes the study of the events that accompany normal myelin formation one of major significance in neuropathology. In the latter part of the last century the earlier stages in the development of the nervous system in embryos were studied in detail by many investigators, but since then, in spite of its evident importance, this aspect of embryogenesis has attracted little attention from embryologists and neurohistologists. In view of the advances now being made in the chemistry of the nervous system, the time seems opportune to return to the problem of myelinogenesis with the hope of bringing together some of the many important relevant observations in neural morphology and biochemistry.
The utilization of an inhibitor of spermidine and spermine synthesis as a tool for the study of the determination of cavitation in the preimplantation mouse embryo
Authors: Alexandre H.
Published: April 2021

The inhibition of spermidine and spermine synthesis by methylglyoxal-Bis(guanylhydrazone) (MeGAG) at concentrations of 5, 10 and 20μM, induces a reversible metabolic quiescence of mouse embryos, cultured in vitro from the 2-cell stage, at an average of 10·2, 8·5 and 6·9 cell stages respectively. In contrast, the inhibition of putrescine synthesis by a-methylornithine (α-MeOrn) at concentrations up to 10 mM fails to inhibit blastocyst formation, as shown previously.

Complete reversibility of this induced arrest of development is observed for treatments up to 31 h with MeGAG at 10μM. In agreement with the biological clock theory of Smith & MacLaren’s hypothesis, the delay in cavitation is proportional to the length of treatment.

However, the average cell numbers of the ‘delayed nascent blastocysts’ of all treated embryos (21·8–24·2) are consistently lower than that of control embryos (33·6) irrespective of the duration of treatment. It seems therefore that under some experimental conditions, DNA and chromosome replication on the one hand and cytoplasmic maturation on the other may be desynchronized. This suggests a role for a cytoplasmic factor in the induction of cavitation.
Evidence for differential cellular adhesion as the mechanism of sorting-out of various cellular slime mold species
Authors: Sternfeld John
Published: April 2021

Various authors have shown previously that if the amoebae of two species of slime molds are mixed they have the ability to sort themselves out. In the work reported here, the sortingout of cells of several slime mold species was examined in clumps of cells in suspension.

Cells of four species, Dictyostelium discoideum (Dd), D. mucoroides (Dm), D. purpureum (Dp), and Polysphondylium violaceum (Pv), were mixed in pairs in suspension and clumps of cells formed. Dd and Pv cells sorted out completely and formed separate clumps, each of single species. Both Dd and Dm, when mixed separately with Dp, formed clumps containing both species. Sorting-out took place in these clumps such that the cells of Dd and Dm partially enveloped the Dp cells. Finally, in the Dd–Dm mixtures, the Dm cells always sorted out such that they surrounded the Dd cells. When mixed in a 1:2 ratio (Dd:Dm) the Dm cells formed a complete shell around a sphere of Dd cells.

Sorting-out of cells in clumps in suspension can occur by either of two possible mechanisms: response of cells to a chemotactic gradient or differences in cell surface strengths of adhesion (Steinberg, 1964). Mixing of two species in a clump of cells and observing the process of sorting-out permits one to distinguish between these two mechanisms (Steinberg, 1964). By such an analysis it was found that the sorting-out observed in mixtures of Dd and Dm is consistent with the mechanism of differential cellular adhesion. The major reasons for this are (1) when the adhesive properties of the cells are known to change the Dd cells began to move inside the clumps, (2) the Dd cells coalesced into islands rather than streaming inward independently, and (3) the Dd cells and cell masses did not lie at the center of the clumps but rather lay randomly within the clumps. The partial envelopment observed in the Dd–Dp and Dm–Dp mixtures and the separate clumps formed by the Dd–Pv mixtures are also consistent with differential cellular adhesion. They represent cases in which the interspecific strengths of adhesion are low (Dd–Dp and Dm–Dp) and near zero (Dd–Pv).
Changes in collagen ultrastructure, macroscopic properties and chemical composition of chick embryo cartilage induced by administration of aβ-D-xyloside
Authors: Hjelle J. T. , Gibson K. D.
Published: April 2021

Nine-day chick embryos were injected with a β-xyloside and their sternal cartilage was examined 3 days and a week later. Sterna from 16-day embryos showed a reduction in size as compared to controls, with little or no change in the fraction of extracellular space, and a significant decrease in tensile strength. At the ultrastructural level, collagen fibrils in control sterna were dispersed evenly in the interstitial space, with few contacts between adjacent fibrils. In sterna from treated embryos, almost all collagen fibrils were aggregated into clumps and arrays throughout the interstitial space, with fibril-free areas in between. No abnormalities could be detected in the morphology of individual fibrils or in the ultrastructure of the chondrocytes. The changes in spatial distribution of collagen were fully evident 3 days after drug administration.

The hydroxyproline/DNA ratio was the same in control and treated sterna, and no change was observed in the type of collagen. The uronic acid/DNA ratio was reduced by 14% 3 days after drug administration and by 40% after a week. The degree of sulfation of chondroitin sulfate was reduced from 80% in control sterna to 40% in treated sterna; almost all of this chondroitin sulfate was attached to peptide and the sedimentation pattern of the proteo-glycan resembled that of normal cartilage proteoglycan.

The function of chondroitin sulfate in embryonic cartilage is discussed in terms of our results and others. It is suggested that a major physiological role of the proteoglycan is to control the spatial distribution of collagen fibrils as they assemble to form a cross-linked gel.
Phosphatase activity and ion levels associated with normal and abnormal skeletogenesis in the fetal rat
Authors: Brummett Elaine S. , Johnson E. Marshall
Published: April 2021

Limbs from rat fetuses exposed to the alkylating agent chlorambucil on day 14 of gestation undergo abnormal skeletogenesis (Brummett & Johnson, 1979). The abnormal developmental sequences are manifest as marked disruption of chondrogenesis and ossification. The present study examines some of the biochemical factors normally related to initial mineralization and their possible alteration during teratogenesis.

The specific activities of the acid, alkaline and pyro-phosphatases were determined for normal and abnormal (drug-treated) fetal rat limbs during days 15–17 of gestation, the period of cartilage-model calcification. This was done to determine if altered enzymatic activity leading either to depressed localized phosphate levels or hydroxyapatite crystal growth inhibition would account for the decreased calcification. The level of alkaline phosphatase increased dramatically (sixfold in 3 days), in association with normal cartilage formation. In the abnormal limbs, this rise was only half as great. Pyrophosphatase and acid phosphatase activity in both normal and abnormal limbs did not change over the 3-day period.

The normal concentrations of ions critical to calcification, i.e. phosphate, calcium and magnesium, were determined for maternal serum, amniotic fluid, whole fetuses and fetal limbs. Mean phosphate and calcium levels increased slightly in the limbs with increasing gestational age. The ion levels in drug-treated fetuses were within normal limits except in amniotic fluid where phosphate was increased significantly on day 17. Also the protein concentration in the fluid was elevated on day 16 and 17.
Replacement of posterior by anterior structures in theDrosophilawing caused by the mutationapterous-blot
Authors: Whittle J. Robert S.
Published: April 2021

The recessive mutation apterous-blot in Drosophila melanogaster causes replacement of posterior wing structures by anterior ones, with variable penetrance and expressivity. Extreme transformations resemble mirror-image duplicate anterior wings as in the mutant engrailed. Anterior structures in the posterior wing only appear on the dorsal surface. Duplications solely of posterior structures are also seen.

Clonal analysis shows that extra cell proliferation occurs in the posterior area but is complete by 108 h after egg deposition. Lineage analysis is consistent with a clonal perpetuation of the transformation. Genetic mosaics to test the cell-autonomy of apterous-blot show that it is not autonomously expressed in clones.

The results of lineage analysis, the phenotypes of combinations of apterous-blot with other apterous alleles including a deletion for the locus and with various other homoeotic mutations, are together used to distinguish three alternative modes of action of this mutation. It is concluded that apterous-blot is unlikely to be a selector gene mutation but instead may cause the transformation by an event like transdetermination following a local failure in cell function in the wing disc.
Crinkly-tail, a mild skeletal mutant in the mouse
Authors: Johnson D. R. , Wallace Margaret E.
Published: April 2021

Crinkly-tail, cy, is a new recessive mutant with imperfect penetrance, in chromosome 4 of the mouse. The only abnormality is in the shape of the vertebrae for one, more rarely two, lengths of the region C9 to C14. This is expressed briefly in the 11-day-old embryo as a duplicated tail gut. None of the mechanisms operating in most of the 20 known tail mutants in the mouse operates in crinkly-tail. The defect is probably due to misallocation of the tissue derived from the primitive streak.
The orientation of the visuotectal map in Xenopus: developmental aspects
Authors: Gaze R. M. , Feldman Joan D. , Cooke J. , Chung S-H
Published: April 2021

Rotations and translocations of the eye anlage were performed in Xenopus embryos of stages ranging from 21/22 to 30. Some of the operations involved grafting wild-type eye anlagen into albino host orbits. Operations were performed under a variety of operating media and conditions. In later larval life, or after metamorphosis, the visuotectal maps from the operated eyes were recorded electrophysiologically. Results fell into two classes. In the majority, the orientation of the visuotopic map corresponded to the orientation of the eye at the time of recording. In the minority the visuotopic maps were ′compound′, consisting of two parts each with its own independent orientation. The organization of the compound maps was such that one component was oriented in correspondence with the orientation of the eye, while the other component was normally oriented. Histological analysis and observations on genetically marked grafts indicated that the component parts of the compound eye were of dual cellular origin. The component giving the rotated (or translocated) map belonged to the originally operated eye tissue; whereas the component giving the normally oriented map was derived from newly grown eye tissue coming from the optic stalk. In no case was a normally oriented map obtained from a rotated or trans-located eye. The results are discussed in relation to mechanisms proposed to account for the determination of map-related retinal specificity.