bluuebunny/crossref_metadata_2025 huggingface dataset:
Essential role of the polyamines in early chick embryo development
Authors: Löwkvist B. , Heby O. , Emanuelsson H.
Published: April 2021

The polyamines putrescine, spermidine and spermine were analyzed in chick embryos during the first 2 days of development. A rapid increase in the activity of ornithine de-carboxylase (ODC), the initial and rate-limiting enzyme in polyamine synthesis, was observed immediately after onset of incubation. Peak activities were found at 15 and 23 h of incubation. The first peak coincides with gastrulation and the second peak with early neurulation in the embryo. All three polyamines varied in a similar manner as did ODC, with putrescine and spermidine at about the same level and spermine at a lower level. The ODC activity was blocked by α-difluoromethylornithine, an enzyme-activated irreversible inhibitor. The inhibitor was administered to embryos in ovo at 5 h of incubation, i.e. prior to the first major increase in ODC activity. This block prevented the accumulation of the polyamines and inhibited development at gastrulation, suggesting a decisive role for polyamines in this developmental event.
Distribution of antibody- and lectin-binding sites on dissociated blastomeres from mouse morulae: evidence for polarization at compaction
Authors: Handyside Alan H.
Published: April 2021

The distribution of binding sites for rabbit anti-species antiserum, Concanavalin A (Con A) and peanut agglutinin (PNA) on dissociated blastomeres from 2- to 16-cell mouse embryos has been investigated using direct and indirect fluorescence techniques. With each ligand, paraformaldehyde-fixed blastomeres from 2- to 8-cell precompact embryos were uniformly surface labelled; the majority (77 %) of late compact 8-cell blastomeres showed quantitative polarization of surface lebelling; and 16-cell blastomeres were either polarized (53·3%) or uniformly surface labelled. Binding of fluorescein-conjugated PNA increased at the 16-cell stage. Labelling patterns on unfixed blastomeres were similar to those on fixed blastomeres except that surface label was patched and became internalized, most rapidly from the less heavily labelled areas of 8- and 16-cell blastomeres.

Quantitative polarization of binding sites at postcompaction stages was detected after (i) fixation, (ii) pretreatment and labelling in the presence of azide, cytochalasin D and/or colcemid, or (iii) labelling with monovalent Fabx antibody fragments. It is probably due, therefore, to the presence of microvilli at the heavily labelled pole, which increase surface area and are known to become localized to the outer surface of the compact morula (Ducibella, Ukena, Karnovsky & Anderson, 1977).

The possibility that the cleavage of polarized blastomeres into dissimilar daughter blastomeres could provide a mechanism for the spatial differentiation of the inner cell mass and trophectoderm of the blastocyst is briefly discussed.
Analysis of elongating morphogenesis of quail anterior submaxillary gland: absence of localized cell proliferation
Authors: Nogawa Hiroyuki
Published: April 2021

Quail anterior submaxillary glands elongated extensively without branching (more than sevenfold) from 8 to 10 incubation days. Investigation of mitotic activity of the rudiments in vivo showed no localized cell proliferation throughout the rudiments, and recombination experiments in vitro to examine regional differences in mitogenic activity of the surrounding mesenchyme also showed that no mesenchymal region specifically stimulates the epithelial cell proliferation.

Histological observation of the rudiments showed that epithelial cells did not lengthen in a parallel direction to the long axis of the rudiment, and that mesenchymal cells encircled the epithelial cord perpendicularly to its axis. The basement membrane was obscure in the distal end of the rudiments, while it was easily detected in the other part of the rudiments.

These results suggest that the elongating morphogenesis of the anterior submaxillary rudiments is not achieved by localized cell proliferation but by almost uniformly distributed cell proliferation, and mesenchymal cells surrounding the rudiment or the basement membrane may be involved in the controlling mechanisms of the elongating morphogenesis.
Some effects of glucagon on chick embryo development
Authors: Anderson William A. , Gibson M. A.
Published: April 2021

Glucagon concentrations ranging from 1·16 to 300-0μg/0·1 ml diluent were injected into the yolk of chick embryos on incubation days 8,10, and 12. Studies of survival rates, embryo weights, blood sugars, liver and tibiotarsus glycogen histochemistry, and pancreatic alpha and beta tissue histogenesis were undertaken during the 9- to 16-day incubation period. Glucagon dosages of 37·5 and 150·0μg/0·1 ml diluent gave the best survival rates. Glucagon caused an increase in embryo weight, increased liver glycogen storage, a chondrocyte glycogen storage pattern which correlated with blood sugar levels, an increase in pancreatic beta tissue and a decrease in pancreatic alpha tissue. Studies of blood sugars following glucagon treatment showed that most concentrations caused an initial (first 16h) hyperglycemia. Following this, two general patterns were exhibited: (1) the lower glucagon concentrations caused hypoglycemia after about 24 h, and (2) the higher concentrations caused a more prolonged hyperglycemia when administered on incubation day 10 but caused hypoglycemia when administered on days 8 and 12. Interpretation of these results is based on the contribution of three factors to the expression and duration of the glucagon effect: (1) concentration of glucagon administered, (2) insulin secretion, and (3) levels of glycogen storage at the incubation stage of administration.
An autoradiographic analysis of the potency of embryonic ectoderm in the 8th day postimplantation mouse embryo
Authors: Beddington R. S. P.
Published: April 2021

The potency of 8th day mouse embryonic ectoderm cells has been studied by injecting them into synchronous embryos which were subsequently cultured for 36 h. The development of injected embryos in vitro was comparable to that of embryos maintained in vivo. Tritiated thymidine was used to label the donor cells so that chimaerism could be analysed histologically. The results demonstrate the pluripotency of embryonic ectoderm in situ in the late primitive-streak-stage embryo. In addition, the patterns of donor cell colonization vary according to the site of origin and injection of the donor tissue.
Embryonic development of the hirudinid leech Hirudo medicinalis: structure, development and segmentation of the germinal plate
Authors: Fernández Juan , Stent Gunther S.
Published: April 2021

The germinal plate of 5- to 12-day-old embryos of the leech Hirudo medicinalis consists of an anterior and a posterior sector that differ both structurally and developmentally. The posterior sector includes the five pairs of teloblasts and five paired longitudinal bandlets of stem cells and their descendant blast cells. The mesoteloblast pair and their descendant cells of the m bandlet divide spirally and give rise to bilaterally paired cell clusters. The four ectoteloblast pairs and their descendant cells of the n, o, p and q bandlet pairs divide unidirectionally and give rise to paired one-cell-thick and four-cell-wide ectodermal arches. The developmentally more advanced anterior sector of the germinal plate consists of differentiating ectodermal and mesodermal cells engaged in organogenesis. The mesodermal cell clusters develop into somites, whereas the expanding ectodermal arches develop into nerve cord ganglia and epidermis. Rostrocaudal expansion of somite tissue results in the formation of obliquely oriented intersegmental septa, causing the ganglia to take on an intersegmental distribution. The first sign that formation of body segments has been completed is the appearance of a bilateral gap in the mesodermal bandlet of the posterior sector of the germinal plate. This gap seems to trigger degeneration of the posterior sector of the germinal plate.
Regional biosynthetic markers in the early amphibian embryo
Authors: Slack Jonathan M. W.
Published: April 2021

A search has been made for regional differences in macromolecular synthesis in the axolotl embryo at a stage when the principal regions have become determined but terminal differentiation has not yet begun.

The epidermis of the neurula makes a number of abundant proteins which are not made elsewhere. Some of these are identified by immunoprecipitation as cytokeratins (relative molecular masses (Mr) 62,59,54,51 and 46×103). At the same stage a network of tonofilaments becomes visible by electron microscopy and is also confined to the epidermis.

There is no significant incorporation of 3H-sugars into glycoproteins before neurulation. During neurulation specific species begin to be made by the notochord (Mr 265 and 185 ×103), the mesoderm (315×103) and the epidermis (170×103). The latter species is water soluble, has a native Mr of 470×103, is somewhat resistant to trypsin and has a high sugar content. Since these characteristics do not relate to any known glycoprotein it has been given a new name: epimucin.

Several neutral glycolipids and gangliosides are present in the early embryo, the most abundant of which is identified as galactocerebroside. Synthesis occurs from fertilization onwards, however even by the neurula stage the qualitative pattern is the same in all parts except for the epidermis which shows two substantial enhancements and one reduction compared to other regions.

The differences reported probably relate to physiological functions rather than to the mechanism of determination itself, so their chief importance is as markers of early embryo regions in experiments on induction.
Dynamics of the control of body pattern in the development of Xenopus laevis : II. Timing and pattern in the development of single blastomeres (presumptive lateral halves) isolated at the 2-cell stage
Authors: Cooke Jonathan , Webber John A.
Published: April 2021

Xenopus embryos have been selected in which the first cleavage plane is tending strongly to correspond with that of bilateral symmetry for the future larval pattern. The two blastomeres produced by this cleavage have been separated and allowed to develop as reciprocal pairs of presumptive lateral-half isolates. The early development and the time course of the gastrulation movements, and the qualitative and quantitative aspects of larval mesodermal patterns, have been studied in relation to synchronously fertilized controls. The result is restoration of bilateral symmetry for developmental potential, and production of a pair of small gastrulae and larvae with qualitatively complete body plans but 50 % of control cell numbers each (see Kageura & Yamana, 1983). Most commonly, however, the resulting small patterns deviate from the normal range in their proportions in at least one of two ways. The notochord territory is rarely, if ever, under-represented (i.e. notochords contain at least 50% control cell numbers) but it is frequently over-represented, in some cases approximating that of control whole embryos. Reciprocal pairs of isolates thus tend, on average, to produce more notochordal tissue than they would have if developing normally. Secondly, the balance of cell population sizes assigned to somites up and down the axis is altered so that relatively anterior members of the series are less scaled down than those in trunk and tail regions. The mesodermal plan developed by a lateralhalf isolate is thus characteristically intermediate between that of a small, harmonious larva (the proportional presumptive fates of the materials, apart from loss of bilaterality), and that of the mosaically developing presumptive dorsoanterior cell pair from the 4-cell stage, discussed in the previous paper. A minority of the lateral isolates does develop a harmonious and thus well-regulated body plan, however, and the normality or otherwise of the schedules of gastrulation timing in isolates seems a good predictor of their morphogenetic performance in this respect. The results are discussed as informing us about the dynamics of the interactions, prior to gastrular stages, that underlie the normal mesoderm development.
Dynamics of the control of body pattern in the development of Xenopus laevis : III. Timing and pattern after u.v. irradiation of the egg and after excision of presumptive head endo—mesoderm
Authors: Cooke Jonathan
Published: April 2021

A series of Xenopus egg batches has been exposed to doses of u.v. (2537A) light on the vegetal hemisphere at precleavage stages, calculated to result in a range of minimal axial deficiency syndromes in the developing larvae. At the time of onset of gastrulation in synchronously fertilized but non-irradiated batch members, each experimental group was regularly scanned so that small subsamples of embryos could be set aside as showing particular, progressive degrees of delay in onset of the visible gastrulation movements. Such sampling was found to have preselected embryos showing generally progressive degrees of pattern impairment at larval stages, and this observation was extended by histological examination of the anterior axial anatomy. Such examination was also made of the least abnormal-looking members of a series of larvae resulting from excision of the presumptive head endo-mesoderm, traditionally called ‘the organizer’, from stage-10 gastrulae (Cooke, 1975). The results support the notion that production of the most anterior endo-mesodermal pattern parts (and of their inductive capacities in giving rise to the brain pattern) occurs only in material whose timing, in the onset of gastrulation activity, is close to the normal onset time after fertilization. Either an early failure of the egg to generate a location with the ‘position value’ corresponding with this extreme of the pattern, or the much later excision of the region from a physiologically normal gastrula, results in a system of pattern formation permanently truncated at its apical (head and dorsal) end. There is no evidence for any dynamic, in the system ascribing position value, that will cause regulative restoration of this cellular state (the most extreme ‘activation’ for development) in response to its absence after precleavage stages. An earlier statement (Cooke, 1975) that this could occur was based upon inadequate analysis of larvae with an often misleading external anatomy.

The present results are discussed as supporting the overall view of the early Xenopus patterning system that has been developed in the previous two papers of the series.
Differentiation of liver peroxisomes in the foetal and newborn rat. Cytochemistry of catalase and D-aminoacid oxidase
Authors: Stefanini S. , Farrace M. G. , Cerù Argento M. P.
Published: April 2021

Organules containing cytochemically detectable amounts of catalase and D-aminoacid oxidase activities are observed between the 14th and 21st day of development in the parenchymal cells of the foetal rat liver and in the liver of newborn rats.

As early as 14 to 15 days, a limited number of small microperoxisomes, scattered in the cytoplasm of very few hepatocytes, can be found. These are roundish shaped, have a granulous matrix and contain very low, hardly detectable levels of the above mentioned enzymes.

In later development both the size and the enzymatic content of the organules gradually increase, approaching adult levels at the end of foetal development. Starting from the 18th to 19th day of intrauterine life nucleoids can be seen in many peroxisomes.

The morphological and biochemical maturation from microperoxisomes to peroxisomes is accompanied by a gradual increase in the number of stainable organules, both per individual cell and per tissue area.
Regeneration of endoderm from primitive ectoderm in the mouse embryo: fact or artifact?
Authors: Gardner R. L.
Published: April 2021

The capacity of immunosurgically (IS) treated inner cell masses (ICMs) versus microsurgically (MS) isolated primitive ectoderms from blastocysts recovered on the 5th day of gestation to regenerate an external layer of endoderm cells in vitro was investigated. While the majority of IS-treated ICMs regenerated such a layer, MS-isolated ectoderms seldom did so. Examination of the two types of tissue fragments revealed that IS-treated ICMs almost invariably retained viable endoderm cells whereas MS-isolated ectoderms did so only exceptionally. The endoderm was found to be more than one cell layer thick in ICMs from 5th day blastocysts, suggesting that some endoderm cells survive IS because they are protected from exposure to antiserum. Typing of the endoderm layer that regenerated following IS treatment of recombinant ICMs composed of genetically dissimilar endoderm and ectoderm provided direct evidence that it originated from residual endoderm cells rather than the underlying ectoderm. Finally, blastocyst injection experiments confirmed that IS-treated ICMs behave like a mixture of ectoderm and endoderm tissue in vivo, and provided no support for the view that cells of the original and regenerated endoderm differ in developmental potential. These findings challenge earlier conclusions concerning cell lineage and determination in the primitive ectoderm that were based on development in vitro of IS-treated ICMs from giant blastocysts.
Calcium and neurulation in mammalian embryos
Authors: Smedley Martin J. , Stanisstreet Martin
Published: April 2021

The role of calcium in neurulation in rat embryos has been studied. Rat embryos at 10-4 days of gestation, when the cephalic neural folds have elevated but not fused, have been cultured in various media, and the effects of these media on the morphology of the cephalic neural folds have been observed by scanning and transmission electron microscopy. Embryos cultured in serum containing EDTA or EGTA, or in saline without divalent cations exhibit opening, then folding back (‘collapse’) of the cephalic neural folds. The neural cells lose their elongated shape and become rounded. Older embryos in which the cephalic neural folds have already fused do not show collapse of the neural tube. Culture of 10·4-day rat embryos with elevated but unfused cephalic neural folds in calcium- and magnesium-free saline to which either calcium or magnesium has been restored shows that calcium is the divalent cation which is essential for the maintenance of the elevated neural folds. In the presence of calcium, lanthanum, which competes for calcium, sites, causes opening but not collapse of the elevated cephalic neural folds. Embryos treated with trypsin show dissociation of the lateral (non-neural) ectoderm but the neural folds remain elevated. If embryos in which the cephalic neural folds have been caused to collapse are further cultured in serum the folds re-elevate, although normal neural tube morphology is not completely regained. The possible implications of these observations to the understanding of the cellular mechanisms of normal neurulation, and of neural tube malformations are discussed.
Maturation and polarization of the endocytotic system in outside blastomeres during mouse preimplantation development
Authors: Fleming Tom P. , Pickering Susan J.
Published: April 2021

The maturation and distribution of the endocytotic apparatus in outside cells of cleavage-stage mouse embryos have been studied to determine the nature and sequence of changes associated with the differentiation of the polarized trophectoderm epithelium of the blastocyst. Various quantitative and qualitative techniques used at the light and electron microscopic levels have revealed an incremental pattern of endocytotic maturation and polarization. Oocytes, eggs and blastomeres within embryos up to the early 8-cell stage contain clusters of prelysosomal endocytotic vesicles (endosomes) distributed randomly in the cortical cytoplasm. During the 8-cell stage and continuing into the early 16-cell stage, endosomes become progressively localized in the apical cytoplasm beneath the microvillous pole. Endosome polarization is initiated prior to overt polarization of the surface membrane. Concomitant with endosome polarization, pinocytotic activity at the cell surface, revealed by horseradish peroxidase labelling, becomes segregated preferentially to the apical rather than the basolateral membrane. The final maturation phase occurs at the late 16-cell stage when secondary lysosomes, characterized by trimetaphosphatase reactivity, form and polarize in the basal cytoplasm.
Participation of two different mesenchymes in the developing mouse mammary gland: synthesis of basement membrane components by fat pad precursor cells
Authors: Kimata Koji , Sakakura Teruyo , Inaguma Yutaka , Kato Masato , Nishizuka Yasuaki
Published: April 2021

Two different types of mesenchyme, fat pad precursor cells (FP) and fibroblastic cells (MM) are involved in the morphogenesis of mammary gland epithelium of mouse embryo. Especially, an interaction between FP and the epithelium is necessary for its characteristic shaping of ductal branching structure. To assess the relative participations of the mesenchymes, we have analysed the extracellular matrix products by immunofluorescent staining method using antibodies to laminin, proteoheparan sulphate, and fibronectin. The staining patterns suggested that, after the 16th day of gestation when fatty substances first appeared in FP and the epithelial rudiments started to elongate and branch rapidly, FP initiated synthesis of laminin and proteoheparan sulphate, while MM synthesized fibronectin at all times. Attention was also paid to differences in the epithelial basement membranes (BM) concomitant with ones in the mesenchyme. BM were always stained with antibodies to laminin and proteoheparan sulphate. However, topographical differences in thickness were observed: the one facing FP, often seen at the tip region of the end bud, was thin, while the other surrounded by MM, often at the flank region of the duct, was thick. Specific elaboration of BM-like extracellular matrix products by FP may attribute to observed differences in BM thickness which are related to the characteristic shaping of the mammary gland.
Mesoderm induction in Xenopus laevis: a quantitative study using a cell lineage label and tissue-specific antibodies
Authors: Dale L. , Smith J. C. , Slack J. M. W.
Published: April 2021

We have compared the development of the animal pole (AP) region of early Xenopus embryos in normal development, in isolation, and in combination with explants of tissue from the vegetal pole (VP) region. For the grafts and the combinations the animal pole tissue was lineage labelled with FLDx in order to ascertain the provenance of the structures formed.

The normal fate of the AP region was determined by orthotopic grafts at stages (early blastula), 8 (mid blastula) and 10 (early gastrula). At later stages most of the labelled cells were found in ectodermal tissues such as epidermis, head mesenchyme and neural tube (the last from stages and 8 only). However, in stage- and stage-8 grafts some of the labelled cells were also found in the myotomes and lateral mesoderm.

In isolated explants the AP region of all three stages differentiated only as epidermis assessed both histologically and by immunofluorescence using an antibody to epidermal keratin.

The fate of labelled cells in AP-VP combinations was quite different and confirms the reality of mesoderm induction. In combinations made at stages and 8 the proportion of AP-derived mesoderm is substantially greater than the proportion of labelled mesoderm in the equivalent fate mapping experiments. This shows that the formation of mesoderm in such combinations is the result of an instructive rather than a permissive interaction.

The formation of mesodermal tissues in stage- combinations was confirmed by using a panel of antibodies which react with particular tissues in normal tailbud-stage embryos: anti-keratan sulphate for the notochord, anti-myosin for the muscle and anti-keratin for epidermis and notochord.

Combinations made at stage 10 gave no positive cases and reciprocal heterochronic combinations between stages and 10 showed that this is the result of a loss of competence by the stage-10 AP tissue. Whereas stage- AP tissue combined with stage-10 VP tissue gave many positive cases, the reciprocal experiment gave only a few.

We have also tested the regional specificity of the induction. Stage- vegetal pole explants were divided into dorsal and ventral regions and then combined, separately, with stage- animal poles. The dorsovegetal tissue induces ‘dorsal-type’ mesoderm (notochord and large muscle masses) while ventrovegetal tissue induces ‘ventral-type’ mesoderm (blood, mesothelium and a little muscle).

We conclude that mesoderm formation in combinations is an instructive event and propose a double gradient model to explain the complex character of the response.
Cell movement in intact and regenerating planarians. Quantitation using chromosomal, nuclear and cytoplasmic markers
Authors: Saló Emili , Baguñà Jaume
Published: April 2021

One of the tenets of Wolff and Dubois’ ‘neoblast theory’ of planarian regeneration (Wolff & Dubois, 1948) is that blastema is mainly formed by the accumulation of undifferentiated parenchymal cells (neoblasts) that can migrate, if needed, over long distances to the wound. That neoblasts migrate was claimed by these authors after partial X-irradiation, and total X-irradiation and grafting using planarian strains of different pigmentation. From this they suggested that migration of neoblasts is stimulated by the wound and directed towards it.

To study the nature and extent of such ‘migration’ in intact and regenerating organisms, and in order to avoid the flaws of using pigmentation as a marker, we made grafts between sexual and asexual races of Dugesia(S)mediterranea that differ in a chromosomal marker, and between diploid and tetraploid biotypes of Dugesia(S)polychroa that differ in nuclear size. Also, fluorescent latex beads were used as cytoplasmic markers to follow ‘migration’ of differentiated cells. The hosts were irradiated or non-irradiated intact and regenerating organisms.

The results show that: 1) movement of graft cells into host tissues occurs in intact organisms at a rate of ≃40μm/day, and that this increases up to ≃75μm/day in irradiated hosts; 2) movement of cells occurs evenly in all directions; 3) regeneration does not speed up rate of movement nor drives cells preferentially to the wound; 4) spreading of cells is mainly due to the movement of undifferentiated cells (neoblasts) ; and 5) higher rates of movement are correlated with higher mitotic indexes. From this, it is concluded that the so-called ‘migration’ of neoblasts is not a true cell migration but the result of the slow, even and progressive spreading of these cells mainly caused by random movements linked to cell proliferation. The implications of these results for blastema formation and the origin of blastema cells are discussed.
Radiodestructions partielles chez l’embryon de Poulet aux stades jeunes et localisation des ébauches digestives
Authors: Douarin par Nicole Le
Published: April 2021

La localisation des territoires présomptifs du tractus digestif de l’embryon de Poulet a été établie aux stades initiaux du développement. En particulier, les travaux de Hunt (1932), Dalton (1935), Rawles (1936) et Rudnick & Rawles (1937) ont montré qu’aux stades de la ligne primitive et du prolongement céphalique, ces territoires s’échelonnent le long de la ligne primitive. Au niveau de la première moitié de cette ligne se situe le territoire de l’intestin antérieur et de ses annexes. Le reste du tube digestif se trouve en arrière de cette zone.
Visual deprivation and the maturation of the retinotectal projection in Xenopus laevis
Authors: Keating M. J. , Grant S. , Dawes E. A. , Nanchahal K.
Published: April 2021

There has been a resurgence of interest, recently, in the possible role of neural activity in the ordering of synaptic connections in the lower vertebrate retinotectal system. Blockade of all neural activity, by chronic administration of tetrodotoxin (TTX), during the regeneration of the optic nerve in goldfish has been found to prevent the re-emergence of a fully ordered retinotectal projection. We sought to determine the effects of visual deprivation, a less radical perturbation of neural activity than that produced by TTX, on the initial development of the retinotectal projection. The contralateral visuotectal projection was studied in Xenopus laevis which had been reared in darkness from before the onset of visual function. The projection mapped electrophysiologically at metamorphic climax, or in postmetamorphic juveniles, showed a normal retinotopic topography. The topographic precision of the projection, as revealed by the multiunit receptive field sizes, was the same in light- and dark-reared animals. The laminar distribution, in the superficial neuropil of the optic tectum, of terminals from different classes of retinal ganglion cells was also normal. It is concluded that the specific retinotectal connections underlying these features of the projection are generated by intrinsic developmental processes which do not require visual experience. Among these intrinsic processes might be ‘spontaneous’ neural activity.
Manipulation of gap junctional communication during compaction of the mouse early embryo
Authors: Goodall Harry
Published: April 2021

Three treatments that prevent cell flattening during compaction of the mouse preimplantation embryo were assessed for their effects on the onset of gap junctional communication. Medium low in calcium (LCM) and an antiserum to an embryonal carcinoma cell line (anti-EC; Johnson et al. 1979) both prevented the establishment of coupling between blastomeres of the 8-cell embryo as assessed by transmission of carboxyfluorescein or by ionic coupling. Since neither of these agents prevents the contact-mediated induction of cell polarity that occurs at this stage, it is concluded that the induction of this process is not signalled via gap junctions. A monoclonal antibody (ECCD-1; Yoshida-Noro, Suzuki & Takeichi, 1984), that recognizes more specific components of the calcium-dependent cell adhesion system, failed to prevent the onset of junctional coupling. This suggests that the onset of junctional coupling is not dependent upon extensive cell apposition and that the requirement for extracellular Ca2+ resides at a level other than that of cell adhesion. Moreover, neither LCM nor anti-EC could reverse cell coupling once it had become established despite their complete reversal of cell flattening.
Changes in composition of the porcine zona pellucida during development of the oocyte to the 2-to 4-cell embryo
Authors: Brown C. R. , Cheng W. K. T.
Published: April 2021

Our objective was to identify any changes that occur in the composition of the porcine zona pellucida during development of the 2-to 4-cell embryo from the oocyte. Oocytes, unfertilized eggs and single and 2-to 4-cell embryos have been recovered surgically and their zonae pellucidae 125I-labelled and analysed individually by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The zonae from ovulated eggs possessed two major glycoproteins Mr 250000 and 90000 which were absent from follicular oocytes but present in the fluid from the oestrus, but not luteal, oviduct. The glycoproteins remained on the zona pellucida of 2-to 4-cell embryos whose analysis showed the presence of additional polypeptides of Mr 150000, 57000, 50000 and 25000. It is concluded (i) that shortly after ovulation, and in spite of the presence around the egg of cumulus oophorus and corona radiata cells, significant amounts of oviducal glycoproteins are able to bind firmly to the zona pellucida, and (ii) that after contact with spermatozoa there is evidence of a limited hydrolysis of the structure by the sperm protease acrosin.
Ocular migration and the metamorphic and postmetamorphic maturation of the retinotectal system in Xenopus laevis \ an autoradiographic and morphometric study
Authors: Grant S. , Keating M. J.
Published: April 2021

The growth of the retina and tectum during larval life in Xenopus has previously been studied extensively. These two structures continue to grow in metamorphosing and postmetamorphic animals. During these later stages there are marked changes in eye position. We have used histogenetic and morphometric techniques to monitor retinal and tectal growth in Xenopus aged from stage 58 of larval life to ten years postmetamorphosis. The relative eye migration was quantified with optical techniques. An attempt has been made to relate modes of retinal growth to problems associated with changing interocular geometry.

The predominant mode of growth during this period is hypertrophic, that is, it is due largely to an increase in size and complexity of existing elements, rather than the histogenetic creation of new elements. In the retina, however, tritiated thymidine autoradiography reveals that histogenesis does persist until at least six months after metamorphosis. The rate of histogenesis is much decreased compared with that of larval stages but, like that of larval stages, it takes place at the ciliary margin. It is asymmetrically distributed in the retina, most histogenesis occurring at the ventral retinal pole and very little at the dorsal retinal pole. Some histogenesis occurs at the nasal and temporal retinal poles. Thymidine autoradiography and cell counts indicated that little significant histogenesis occurs in the tectum after metamorphic climax.

Two possible biological reasons for the asymmetry of retinal histogenesis have been examined. The first was the suggestion that the asymmetry was related to the emergence, during this period, of a binocular visual field secondary to the relative migration of the two eyes. It is shown that the asymmetric pattern of histogenesis is not closely related to those retinal areas that come to view binocular visual space. It was found, however, that the asymmetry of retinal growth from metamorphic climax was that required to stabilize retinal visual field positions with respect to body position. It is suggested that this minimizes the requirements for visuomotor readjustments that would otherwise be necessary to compensate for a situation in which eye position, relative to the body, is changing.
Abnormal accumulation of sulphated materials in lens tissue of mice with the aphakia mutation
Authors: Webster Earl H. , Zwaan Johan , Cooper Philip
Published: April 2021

Sulphated materials were tested for in the eyes of late gestational and postnatal normal mice and mice with the aphakia mutation using Spicer’s high iron diamine staining method. Qualitative identification of these materials was attempted with bovine testicular hyaluronidase and nitrous acid digestion methods. The grossly abnormal morphology of the aphakia lens made it necessary to confirm identification of lens-derived tissue by testing for lens crystallins using standard immunohistological methods. As seen in normal mouse lens maturation, accumulated inter- and intracellular sulphated materials were observed in aphakia lens tissue from just before birth through juvenile maturation. Large cyst-like structures consisting of lens-derived tissue were commonly seen in the eyes of young postnatal mutant mice. Sulphated materials formed basal lamina-like structures on many of these lens-derived units, but a well-defined lens capsule never formed. Abnormal fibrillar structures rich in sulphated materials were seen in the intraocular cavity in many older mutant specimens, most of which were largely resistant to both digestion methods. These results indicate that the potential to elaborate sulphated materials qualitatively similar to those seen in normal mouse lens maturation is present in the aphakia mutant, although the mode of accumulation is grossly disturbed.
Parthenogenesis and cytoskeletal organization in ageing mouse eggs
Authors: Webb Michelle , Howlett Sarah K. , Maro Bernard
Published: April 2021

The cytoskeletal organization of the mouse egg changes during ageing in vivo and in vitro. The earliest change observed is the disappearance of the microfilament-rich area overlying the meiotic spindle. This is followed by the migration of the spindle towards the centre of the egg. Finally the spindle breaks down and the chromosomes are no longer organized on a metaphase plate. This spindle disruption may result from changes in the microtubule nucleating material found at the spindle poles and from an increase in the critical concentration for tubulin polymerization. It is possible to correlate the changes in the cytoskeletal organization of the egg occurring during ageing with the different types of parthenogenetic embryos obtained after ethanol activation. These observations strengthen the hypothesis that the actin-rich cortical area that overlies the meiotic spindle forms a domain to which the meiotic cleavage furrow is restricted and provides some insights into the mechanisms by which different types of parthenogenetic embryos are generated.
Protein synthesis and messenger RNA levels along the animal–vegetal axis during early Xenopus development
Authors: Smith Rosamund C.
Published: April 2021

The patterns of proteins synthesized in animal and vegetal regions of Xenopus oocytes, eggs and embryos were examined by 2D gel electrophoresis. In oocytes and eggs, the only proteins synthesized asymmetrically along the animal–vegetal axis were a small number of proteins synthesized predominantly in the vegetal hemisphere. At the cleavage stage there were a total of four proteins synthesized unevenly in animal and vegetal regions: three synthesized predominantly in the vegetal hemisphere and one synthesized predominantly in the animal hemisphere. By the gastrula stage, when maternal messages have largely been replaced by embryonic transcripts, the number of differences in proteins synthesized in the animal-derived ectoderm and mesoderm, and the vegetal-derived endoderm started to increase rapidly with time of development with many more animal-characteristic proteins than vegetal-characteristic proteins appearing. Comparison of protein synthesis patterns with those obtained when extracted RNA was translated in vitro and run on 2D gels, showed that the asymmetry in protein synthesis along the animal–vegetal axis in the oocyte and early embryo reflected directly the distribution of their mRNAs along the axis. There was no evidence for localized ‘masked’ abundant messages along the animal–vegetal axis of oocytes and cleavage embryos.
Changes in the transferrin requirement of cultured chick embryo mesoderm cells during early differentiation
Authors: Sanders E. J.
Published: April 2021

Mesodermal tissue from the chick embryo at various stages of early differentiation was cultured in hydrated gels of type I collagen in the presence and absence of transferrin. Primary mesoderm expiants from primitive-streak-stage embryos responded to the presence of avian transferrin by significantly improved outgrowth which appeared to be related to the ability of the cells to attach to, and migrate in, the collagen. No evidence was obtained which suggested that this observation was dependent on increased cell proliferation. This outgrowth enhancement was not duplicated by transferrin of human origin. The avian transferrin did not produce this effect on cells cultured on plastic substrata, suggesting that the species-specific effect involves modulation by the extracellular matrix. Mesoderm expiants from somite stages of development showed no increase in outgrowth in the presence of either avian or human transferrin as judged by counting the number of outwandering cells. Ultrastructural immunocytochemistry indicated surface binding of transferrin by cells in the gels, and the presence of endogenous transferrin on the surfaces of mesoderm cells in situ and in their extracellular environment. It is suggested that by binding to cell surface receptors, transferrin may be able to influence the strength of cellular adhesion to collagen and hence the capacity for cell locomotion.
Regulation of stalk and spore antigen expression in monolayer cultures of Dictyostelium discoideum by pH
Authors: Dominov Janice A. , Town Christopher D.
Published: April 2021

The terminal differentiation of Dictyostelium discoideum cells plated as monolayers with cyclic AMP is dramatically affected by developmental buffer conditions. High pH and addition of weak bases induces spore differentiation while low pH and weak acids favour stalk cell formation. In order to analyse the timing and nature of this regulation we have raised and characterized an anti-stalk serum which we have used together with an anti-spore serum to monitor developmental progression in the monolayer system and to detect the phenotypic effects of pH at earlier stages of development. The stalk serum detects both polysaccharide and protein antigens expressed during the terminal stages of normal development. In monolayer culture, the stalk-specific protein antigen appears precociously, while the timing of prespore vacuole appearance is unaffected. Expression of stalk polysaccharide antigens in monolayer cultures occurs as early as 12 h and is localized in a single subset of cells or region of extracellular space within the small cell clumps that form. The effects of pH (and acid/base) on these phenotype-specific antigens can be detected early in development, shortly after their first appearance. In monolayers of wild-type V12 M2 cells, the low pH regimes appear to act more by suppressing the spore than enhancing the stalk pathway, while the high pH regimes both suppress stalk and enhance spore antigen expression. In monolayers of the sporogenous mutant HM29, low pH regimes both enhance stalk antigen and suppress spore antigen expression. These results show that extracellular pH regulates phenotypic expression during a large part of the differentiation process and is not simply restricted to terminal cytodifferentiation.
Cell–matrix interactions: influence of noncollagenous proteins from dentin on cultured dental cells
Authors: Lesot Herve , Smith Anthony J. , Meyer Jean-Marie , Staubli Aline , Ruch Jean Victor
Published: April 2021

Matrix-mediated epitheliomesenchymal interactions control dental cytodifferentiations. Experiments were performed in order to study the effects of noncollagenous proteins extracted from dentin on cultured enamel organs and dental papillae.

Seven noncollagenous protein fractions were prepared from rabbit incisor dentin and used as substrates to coat Millipore filters. Embryonic mouse tooth germs were dissociated and the isolated tissues were cultured for 4 days on these different substrates as well as on noncoated Millipore filters.

When compared to control cultures, only two protein fractions affected the behaviour of epithelial cells. A slight elongation of the cell body and a preferential localization of the nuclei at the basal pole of the cells in contact with the filter was observed with protein fractions 5 and 6.

When dental papillae were cultured on Millipore filters coated either with protein fraction 2 or fraction 6, the mesenchymal cells in contact with the filter elongated, polarized and demonstrated a high metabolic activity. Such modifications in the cell organization, implying changes in the cytoskeleton organization and, or, activity, never occurred spontaneously or in the presence of isolated collagens (I-V), laminin or fibronectin.
Disruption of segmentation in a short germ insect embryo
Authors: Mee Jane E. , French Vernon
Published: April 2021

The effect of heat shock (15 min at 48 °C) on segmentation has been investigated in the short germ embryo of the locust (Schistocerca gregaria). Prior to formation of the germ anlage and at the disc stage heat shock considerably reduced the survival of eggs but appeared to have little effect upon segmentation. At later stages heat shock had no effect on survival but resulted in disruptions of the segmental pattern. The location of abnormal segments depended upon the stage at heat shock and the number affected depended on its severity. A constant number of normal segments developed between the last segment visible at the time of heat shock and the first abnormal segment. These results are similar to the disruptions observed in amphibian somites following heat shock. However, different parts of the segment pattern varied in their response; the head segments were very rarely affected, and disrupted regions rarely started in the middle abdomen (segments A5 and A6).

The results are discussed in relation to two models (the clock and wavefront and progress zone models) that have been proposed as an explanation for the specification of the somite pattern in amphibians.
Electrical properties of the otic vesicle epithelium in the chick embryo
Authors: Represa J. J. , Barbosa E. , Giraldez F.
Published: April 2021

The electrophysiological properties of the epithelium of the otic vesicle were studied in the chick embryo using conventional microelectrode techniques. A preparation is described that allows continuous recording of transmural potential and resistance during changes in the composition of the bathing fluid. Vesicles in stages 18 to 22 showed a spontaneous transmural potential (ET) that ranged from 2 to 6 mV, inner positive. This electrical potential difference was abolished after 2h incubation in K+-free strophantidin (10−4M) and it increased by about twofold immediately after addition of the cation ionophore Amphotericin B (250 μM) to the bath. The specific resistance of the wall (RT) was about 80 Ωcm2 between stages 18 and 22 indicating a low-resistance, noncellular, permeation pathway for current flow. The short-circuit current, calculated from ET and RT was about 50 × 10−6 A cm–2 throughout this period. This corresponds to a net flux of 187 ×10−8molcm–2h–1 of a single cation pumped towards the vesicular cavity. Diffusion potentials (salt gradients and single-ion substitutions) showed a selectivity ratio PK:PNa:PCl = 1:0 ·9:0 ·7, which is that of a weakly charged aqueous pathway. Measurements of vesicular volume and surface area showed an increase by a factor of ten in the size of the vesicle with maximal rates of change in volume of 5 μlcm–2h–1. The electrical properties reported here for the epithelium of the otic vesicle resemble very much those of ‘leaky’ epithelia which are known to transport ions and water at a very high rate.
Role of bilateral zones of ingressing superficial cells during gastrulation of Ambystoma mexicanum
Authors: Lundmark Cathy
Published: April 2021

Vital dye staining and cell lineage tracers were used to mark superficial cells of early Ambystoma mexicanum gastrulae. Superficial marks placed between the equator and the blastopore, on the dorsal midline, stained notochord, whereas marks or injections made at similar animal–vegetal levels but 90° to either side of the dorsal midline were later found in somitic mesoderm. Notochord marks remained on the dorsal surface of the archenteron throughout gastrulation, though they became elongate and narrow by the morphogenetic movements of extension and convergence. Marked somitic mesoderm disappeared from the superficial epithelial layer soon after passing over the blastoporal lip and could not be found on the archenteron surface. A possible mechanism for this de-epithelialization is proposed on the basis of correlated SEM. The significance of a method of gastrulation so distinctly different from that of certain other amphibians is discussed in terms of amphibian phylogeny.
The regulation of dna synthesis and mitosis in multinucleate frog eggs
Authors: Graham C. F.
Published: April 2021

The timing of DNA synthesis and mitosis in normal eggs, in activated eggs, and in eggs containing several accessory nuclei has been studied in Xenopus. DNA synthesis was followed by injecting [3H] thymidine into the egg and detecting its subsequent incorporation into DNA by autoradiography.

It was found that the accessory nuclei which were introduced into the egg during different phases of the cell cycle incorporated label and entered mitosis in synchrony with the resident egg and sperm nuclei if the introduced nuclei were released from the intact sperm. In eggs activated by pricking, the egg nucleus had synthesized DNA at a time when it would have done so during normal fertilization.