bluuebunny/crossref_metadata_2025 huggingface dataset:
In vitro studies on skeletogenic potential of membrane bone periosteal cells
Authors: Thorogood Peter
Published: April 2021

In the avian embryo ectomesenchyme cells, derived from the mesencephalic level of the cranial neural crest, migrate into the presumptive maxillary region and subsequently differentiate into the membrane bones and associated secondary cartilage of the upper jaw skeleton. The cartilage arises secondarily within the periosteum at points of articulation between membrane bones and provides an embryonic articulating surface. The stimulus for the differentiation of secondary cartilage is believed to be intermittent pressure and shear created at the developing embryonic movement. The development of one such system - the quadratojugal, has been analysed using organ and explant culture techniques and studied with particular reference to the differentiation of periosteal cells into secondary cartilage. A number of conclusions were reached.

Normally only cells at discrete loci express a chondrogenic potential in vivo: the periosteal cells at these sites of future articulation become committed to chondrogenesis during stage 35, more than 24 h before cartilage is identifiable in vivo. However, cells with a ‘latent’ chondrogenic potential are widespread in membrane bone periosteum and occur over most, if not all, of the surface area of the bone. This potential is expressed in the ‘permissive’ environment created by submersion of the tissue in explant culture or in submerged organ culture. This chondrogenic potential exists long before the time at which commitment of cartilage-forming cells occurs and even presumptive maxillary ectomesenchyme at stage 29 has a limited ability to form cartilage in vitro.

It is suggested that spatial position is a principal factor controlling the differentiation of secondary cartilage. Ectomesenchyme cells with the potential to form secondary cartilage are widespread but it is only those cells whose migration from the neural crest positions them and their progeny at the site of a presumptive joint which subsequently express this potential. This epigenetic interpretation is discussed in the general context of development mechanisms underlying the spatial and temporal patterns in which neural crest-derived cells differentiate to produce bone and cartilage during the formation of the head skeleton.
Immunofluorescence studies on deoxyribonuclease from mouse teratocarcinoma cells during cell differentiation
Authors: Soriano L. , Paulin D.
Published: April 2021

Specific anti-DNase-I IgG have been used to detect deoxyribonuclease in teratocarcinoma cells by an indirect immunofluorescence method. All the cells studied show fluorescence staining. However, the patterns are quite different in embryonal carcinoma cells (amorphous cytoplasmic fluorescence and absence of nuclear staining) as compared to differentiated cell lines (diffuse, bright granular nuclear and fibrillar cytoplasmic fluorescence). It is possible by this method to distinguish different cell types derived from the same origin. Deoxyribonuclease from teratocarcinoma cells can therefore be considered as a marker of cell differentiation in this system.
Localization of cytoskeletal proteins in preimplantation mouse embryos
Authors: Lehtonen E. , Badley R. A.
Published: April 2021

The immunofluorescence technique was used to detect the presence and distribution of actin, alpha-actinin, tubulin and 10 nm filament protein in early mouse embryos. Actin and alpha-actinin stainings showed a distinct concentration to a peripheral layer in the cleavage-stage blastomeres and in trophectoderm cells. Dots of fluorescence appeared in this cortical staining pattern. The distribution of tubulin staining in the blastomere cytoplasm was relatively even with apparent concentration at the perinuclear region and frequently at wide intercellular contact areas. 10 nm filament protein was distributed evenly in the blastomere cytoplasm without cortical concentration of the label. At the blastocyst stage, the trophectoderm cells in blastocyst outgrowths in vitro developed well organized cytoskeletons including both microfilament, microtubule and 10 nm filament elements. Comparable structures were not observed in blastocysts in vivo, or in late hatched blastocysts cultured in suspension. The morphogenetic significance of the observations is discussed.
Studies on the female-sterile phenotype of 1(1)su(f)ts76a; a temperature-sensitive allele of the suppressor of forked mutation in Drosophila melanogaster
Authors: Wilson Thomas G.
Published: April 2021

A new allele of the suppressor of forked [su(f)] mutation in Drosophila melanogaster has been found and designated 1(1)su(f)ts76a. It is temperature-sensitive for suppression of forked (f) and has additional temperature-sensitive phenotypes of lethality, female sterility, and abnormal bristle formation at 29 °C. It closely resembles two other conditional alleles of su(f), 1(1)su(j)s67g and 1(1)ts726. Female sterility at 29 °C is characterized by both disorganized egg chambers in the ovarioles and also chorion-deficient oocytes. Both of these abnormalities may be the result of premature follicle cell death. The observations on 1(1)su(f) ts76a are consistent with the proposal that the similar allele, 1(1)ts726, is a cell-lethal mutation specifically affecting mitotically active cells.
An experimental analysis of somite segmentation in the chick embryo
Authors: Bellairs Ruth , Veini Marianne
Published: April 2021

In a previous paper it was suggested that collagen fibrils play an important role in the process of somite segmentation. This paper was designed mainly to test that concept. In one series of experiments, embryos were treated with either α, α′-dipyridyl or L-azetidine-2-carboxylic acid, which are analogues that interfere with the formation of normal collagen. The reagents led to a reduction in the numbers of somites that formed, as well as to the production of other anomalies such as overall diminution in size and retardation. The older the embryo at the time of treatment, the further posteriorly were the major anomalies located. It is concluded that these results lend some support to the concept.

In a second series of experiments an incision was made along one side of the neural tube and notochord to separate it from the segmental plate on one side. The result was that many more somites formed on the unoperated (control) side of the embryo than on the operated side. It is concluded that these results also lend support to the concept; but that they are of interest also in relation to the mechanisms involved in the control of somite numbers. In a third group of experiments, attempts were made to obtain somites in the absence of endoderm. Although this was not possible using surgery, it was achieved by treating the young embryos with u.v. irradiation. It was concluded that the presence of endoderm is not essential for the segmentation of mesoderm.
Effects of culture conditions on the developmental programme of mouse blastocysts
Authors: Sellens Martin H. , Sherman Michael I.
Published: April 2021

We have investigated the developmental potential of mouse blastocysts cultured under a variety of conditions. A number of parameters were used as criteria for development and differentiation, namely hatching of blastocysts from the zona pellucida and their adhesion to the substratum, outgrowth and polyploidization of trophoblast cells, increase in cell number, protein content, β-glucuronidase activity, appearance of lactate dehydrogenase A subunits, plasminogen activator production, and Δ5,3βhydroxysteroid dehydrogenase activity. Under optimal culture conditions, embryos grew relatively rapidly and expressed all the differentiative markers for which they were tested. Under less supportive conditions, the production of the markers was usually reduced quantitatively; the expression of some markers could also be considerably delayed or even totally prevented. In fact, embryos cultured in the least nutritive medium (one designed to support development only through pre-implantation stages) appeared to be in a state of metabolic quiescence closely resembling that of blastocysts in ovariectomy-induced delay. Overall, the results of our investigations lead us to propose that the expression of each of the aforementioned markers is probably under independent control and subject to intrinsic programming. Finally, the observation that some markers are produced by embryos in suboptimal media whereas others are not, suggests that the minimum metabolic level necessary for expression varies from one marker to another.
The metabolism of exogenous fatty acids by preimplantation mouse embryos developingin vitro
Authors: Flynn Thomas J. , Hillman Nina
Published: April 2021

The utilization of fatty acids from the culture medium has been examined in preimplantation mouse embryos developing in vitro.

Incorporation of exogenous fatty acid into embryo lipids was examined by culturing 8-cell mouse embryos for 2 h in a medium containing 0·1 mM [9, 10-3H]palmitic acid (900 mCi/ mmol). Lipids were extracted from the embryos, and the total lipid extract was fractionated into various neutral lipid and polar lipid classes by thin-layer chromatography. Most of the radioactivity, over 93%, was recovered in neutral glycerides (monodi-, and triacylglycerols). About 2% of the total radioactivity was recovered in other neutral lipid species including fatty acids, fatty alcohols, and sterol esters. The remainder of the radioactivity was recovered in polar lipids. Seventy-four per cent of the polar lipid radioactivity was present in the choline phosphatides. Other labelled phospholipid and glycolipid species included ethanolamine phosphatides, inositol and/or serine phosphatides, sphingomyelin, choline lysophos-phatides, sulfatides, cerebrosides, and monoglycosylglycerides. Chemical degradation studies of labelled embryo lipids indicated that the tritium label was entering into embryo lipids as the fatty acid and not via metabolic recycling.

The oxidation of exogenous fatty acids by mouse embryos was assessed by incubating variously staged embryos for 4h in medium containing 0·1 mM [U-14C]palmitic acid (50 mCi/mmol) and quantitating the production of 14CO2. The rate of fatty acid oxidation was found to be relatively constant from the unfertilized egg up to the 8-cell stage and then increase significantly between the 8-cell and late blastocyst stages. The results suggest that preimplantation mouse embryos developing in vitro can utilize fatty acids from the medium both for incorporation into embryo lipids and for energy production via oxidation.
Localisation and characterization of acid mucopolysaccharides in the early chick blastoderm
Authors: Vanroelen Ch. , Vakaet L. , Andries L.
Published: April 2021

Acid mucopolysaccharides in the extracellular compartment of early chick blastoderms (16 h of incubation) were labelled with tritiated glucosamine and/or [35S]sulphate. The incorporation pattern was studied autoradiographically. Treatment with testicular hyaluronidase revealed a testicular hyaluronidase-sensitive fraction, mainly at the periphery of Middle Layer and Deep Layer cells, and a testicular hyaluronidase-resistant fraction, mainly at the ventral side of the Upper Layer.

A biochemical analysis, utilizing chondroitinase ABC and nitrous acid, followed by cellulose acetate electrophoresis, demonstrated the synthesis of a non-sulphated fraction, i.e. hyaluronic acid and/or chondroitin, and a sulphated fraction, comprising two undersulphated components, i.e. chondroitin sulphate, and heparan sulphate or heparin. The appearance of different AMPS in specific areas of the early chick blastoderm is regarded as an early specialization of the extracellular compartment.
Correlative scanning electron, transmission electron, and light microscopic studies of the in vitro development of mouse embryos on a plastic substrate at the implantation stage
Authors: Gonda Matthew A. , Hsu Yu-Chih
Published: April 2021

Correlative scanning electron, transmission electron, and light microscopy were utilized to study the morphogenic events occurring during mouse blastocyst outgrowth and earlyegg-cylinder development in vitro. After hatching and attachment of blastocysts on the plastic surface, the blastocoelic cavity collapses as the mural trophoblasts spread and migrate outward. The inner cell mass is covered with a differentiated endoderm on the blastocoelic cavity side and by the polar trophoblasts on the medium side at this stage. As the endodermcovered inner cell mass proliferates, being physically restricted from further downward expansion by the plastic coverslip and by lack of space in the collapsed blastocoelic cavity, it migrates upward and protrudes into the culture medium in a break between the polar and mural trophoblast cells. Polar trophoblast cells apposed to the base of the egg cylinder continue to proliferate forming the ectoplacental cone. Thus, the early egg cylinder lacking a trophoblast barrier begins inverting its growth pattern from towards the culture dish surface to a more upright position. Egg-cylinder development in vitro from the inner cell mass and polar trophoblast cells closely paralleled in vivo. The functional nature of various embryonic cell types observed in these embryos was revealed by scanning electron microscopy. These studies as well as those of Wiley and Pedersen (1977) suggest that blastocysts can serve as a source of in vitro developing early mouse egg cylinders that appear to resemble their in vivo counterparts and can be used in experimental studies of mouse embryogenesis.
Effect of follicular steroids on the maturation and fertilization of mammalian oocytes
Authors: Moor R. M. , Polge C. , Willadsen S. M.
Published: April 2021

Pronuclear development was used to measure the effects on ovine oocytes of altering follicular steroidogenesis during maturation in vitro. Follicular steroid secretion was altered using enzyme inhibitors and exogenous steroid supplementation. Abnormalities induced during maturation were measured 24 h after transfer of oocytes to the oviducts of inseminated hosts.

The presence throughout maturation of aminoglutethimide, an inhibitor of the conversion of cholesterol to pregnenolone, reduced steroid secretion to 7% of that in controls and decreased from 77% to 33% the number of normal oocytes. Abnormalities were substantially reduced by the addition of aminoglutethimide during the final 8 h of maturation only.

The inhibition of 17 α -hydroxylase enzymes with SU10603 reduced oestrogen and testosterone secretion to about 10% of control levels but had no effect on progestin secretion. Only 13% of oocytes matured in the continual presence of SU10603 underwent normal fertilization. The number of oocytes undergoing normal fertilization was increased to about 50% by (i) delaying the addition of SU10603 until the last 8 h of the maturation period or (ii) adding exogenous steroids to follicles cultured with inhibitor from explantation.

It is concluded that oocytes require a specific intra-follicular steroid environment for the completion of the full maturation process. Alterations to the steroid profile during maturation induce changes in the oocyte which are expressed as gross abnormalities at fertilization.
Intercellular bridges in the embryo of the Atlantic squid, Loligo pealei
Authors: Cartwright Joiner , Arnold John M.
Published: April 2021

In the post-gastrulation embryo of the Atlantic squid, Loligo pealei, the cells of the developing blastoderm are joined to each other by intercellular bridges which may provide a means of cytoplasmic communication between the cells. This paper describes an electron microscope survey of bridges in the developing blastoderm just prior to, and during, the onset of differentiation. The bridges are similar to those described in the gonadal tissue of many animal species and appear to result from incomplete cytokinesis followed by the disappearance of the spindle remnant. The bridges persist and chains of cells result which are generally branched and coiled. In the undifferentiated blastoderm the chains of cells show no apparent orientation to each other. However, in the apical blastoderm undergoing differentiation, chains of bridged cells appear to coincide closely with the developing mantle and shell gland primordia.

The configuration a chain of cells assumes depends upon the degree of branching (i.e. the number of cells having three bridges) and the degree of coiling of the chain. Whereas coiling is probably affected by the crowding of neighboring cells, both branching and coiling appear to be functions of spindle orientation relative to previous bridges. During mitosis the bridges appear to become occluded by systems of transverse membranous cisternae, and mitotic nuclei are thus isolated. However, the bridges apparently re-open during G1, and during periods of protein synthesis the cells within a group share a common cytoplasm. It is suggested that gene products are shared and protein synthesis of the entire bridged group may be synchronized. As the sharing of control molecules may also be facilitated, these essentially syncytial groups may respond uniformly to inducers from the yolk syncytium, or other tissues and differentiation may be synchronized within the group.
Regional variation of cell proliferation within the facial processes of the chick embryo: a study of the role of ‘merging’ during development
Authors: Minkoff Robert
Published: April 2021

Variation in rates of cell proliferation along the long axis of the maxillary process, within the lateral nasal process and in the zone of attachment between these structures was analyzed employing DNA labeling indices. Chick embryos were labeled with [3H]thymidine for 1 h and processed for histology and autoradiography. The percentage of labeled mesenchymal cells was determined in delineated areas.

Analysis of labeling indices indicated that rates of cell proliferation varied within each of the facial processes. Regions where rates of proliferation were maintained at elevated levels were the boundary areas of the facial processes (e.g. the anterior tip of the maxillary process) and the zones of attachment between the facial processes (e.g. between the maxillary process and the lateral nasal process). Despite the presence of elevated rates of proliferation in selected regions within the facial processes, however, the percentage of labeled cells in all areas declined with advancing developmental age.

These findings support the hypothesis, proposed by Streeter and Patten, that the ‘merging’ of adjacent facial primordia, suchas the maxillary and lateral nasal processes, is accomplished by elevated rates of cell proliferation within the zones of attachment compared to the rates of proliferation in adjacent regions.
Polar granules and pole cells in the embryo ofCalliphora erythrocephala:ultrastructure and [3H]leucine labelling
Authors: Lundquist Anders , Emanuelsson Hadar
Published: April 2021

The polar granules in Calliphora undergo a gradual fragmentation during early cleavage, but reaggregate after pole-cell formation. Autoradiographic analysis showed that the pole cells in Calliphora acquire a higher [3H]leucine label than the rest of the embryo during the blastoderm stage. Such an increased label was not seen in the pole plasm before pole-cell formation or in the pole cells during gastrulation. Electron microscopic autoradiography revealed that the polar granules are substantially labelled during the blastoderm stage. At the same time, characteristic nuclear blebs appear in the pole cells. The observations are consistent with the hypothesis that polar granules contain maternal messenger RNA, which is released and translated into proteins.
Tunicamycin inhibits mouse tooth morphogenesis and odontoblast differentiationin vitro
Authors: Thesleff Irma , Pratt Robert M.
Published: April 2021

Tunicamycin (TM), an antibiotic that selectively inhibits dolichol-mediated protein glycosylation, inhibited morphogenesis and differentiation of odontoblasts in the molar tooth germ in vitro. These effects of TM are reversible and dose-dependent, and in advanced teeth the effect of TM was not complete unless the basement membrane was removed prior to culture. TM did not prevent secretion of predentin or enamel when added to the cultures after initiation of predentin secretion. TM dramatically inhibited protein glycosylation and the accumulation of labeled proteoglycans and glycoproteins in the basement membrane. Our previous studies indicated that odontoblast differentiation is triggered by an interaction between the basement membrane and mesenchymal cells. We suggest that TM inhibits odontoblast differentiation by causing alterations in the basement membrane which prevent the necessary cell-matrix interaction required for odontoblast differentiation.
The role of divalent cations in the metabolic response of mouse blastocysts to serum
Authors: Fishel S. B.
Published: April 2021

Uptake and incorporation of [3H]uridine by mouse blastocysts was measured in response to serum under various conditions of Ca2+ and Mg2+ availability. Previous studies (Fishel & Surani, 1978) showed that serum stimulated uptake and incorporation of uridine in blastocysts. Here it is shown that in Ca2+-deficient medium ( < 20 μM-Ca2+) cell metabolism was also inhibited and increasing [Ca2+] resulted in increased uptake and incorporation. Maximum stimulation required an extracellular [Ca2+] of 0·25 mM. The effects of low Ca2+ were reversible and could also be alleviated by 15 and 20mM-Mg2+. Magnesium greater than 20 mM was deleterious. Inorganic phosphate (Pi) was used to complex free Mg2+ in order to maximize the effects of Mg2+ deficiency. Inhibition was reversed by increasing [Mg2+] or by 15–20 mM-Ca2+. Calcium concentrations greater than 20 mM inhibited maximum stimulation. Inhibitors of Ca2+ influx D600 and papaverine, inhibited stimulation at concentrations above 5 and 20 μM respectively. Magnesium concentration of 15 mM alleviated the inhibitory effects of 50 μM D600. The effect of Ca2+-deficient medium was also alleviated by Sr2+. The results suggest that both Ca2+ and Mg2+ are required for blastocysts to respond maximally to serum; their initial role appeared to involve the binding of stimulatory serum molecules to the cells of the blastocyst followed by an influx of these cations.
Erratum; The role of extra-cellular matrix in the formation of the sclerotome
Authors: Solursh Michael , Fisher Marilyn , Meier Stephen , Singly Karl T.
Published: April 2021

J. Embryol. exp. Morph. 54, 75– 98 (1979)

The Editors regret that Figures 2–6 of the above paper contained inaccuracies. The revised version of this plate is published here.
Distal regeneration in proximal fragments of the wing disc ofDrosophila
Authors: Karlsson Jane
Published: April 2021

The rules governing proximo-distal regeneration in the wing disc of Drosophila were investigated. It was found that proximal fragments confined to either anterior or posterior compartments could not regenerate distally, although many fragments having tissue from both compartments could do so even in the absence of circumferential regeneration. Fragments containing the ventral but not the dorsal end of the anterior-posterior border were able to regenerate distally. The use of a cuticular marker in the posterior compartment very close to the border permitted precise localization of the tissue required to cause anterio fragments to regenerate distally; in anterior fragments cut close to the border, there was an almost perfect correlation between possession of this marker and distal regeneration. It was found however, that distal regeneration was not an all-or-none phenomenon; its extent was dependent on the total amount of tissue present from both compartments.
The changes in lectin activity during the development of embryonic chick skin
Authors: Kitamura Kunio
Published: April 2021

Changes in lectin activity during development of embryonic chick skin were studied. In the dorsal skin of the chick embryo in which feathers were formed, lectin activity first increased, during the period of dermal condensation, and then it decreased during the development of feathers. A similar change in lectin activity was also found in the anterior shank skin, the prospective scale region of the chick embryo. The embryonic cornea, in which no mesenchymal condensation took place, had lectin activity and did not show any developmental changes in lectin activity. Apteria regions of the dorsal skin, experimentally formed by treatment with hydrocortisone, gave low lectin activity. The lectin found in the embryonic skin showed specificity for lactose. The relationship found between lectin activity and dermal condensation in the embryonic chick skin is discussed.
Preimplantation development of microsurgically obtained haploid and homozygous diploid mouse embryos and effects of pretreatment with Cytochalasin B on enucleated eggs
Authors: Modliński Jacek A.
Published: April 2021

Haploid embryos were obtained by microsurgical removal of one pronucleus, followed by doubling of the haploid chromosome set with Cytochalasin B (CB), either at the first or second mitosis. This procedure provides a source of fully homozygous diploid embryos, which were grown in vitro or in vivo. The effect of CB treatment before and during operation on the course of enucleation and further development of embryos was studied. Out of 81 eggs made diploid at 2-cell stage and transplanted into the oviducts of immature or pseudopregnant recipients 27 morulae and blastocysts were recovered, but not a single case of implantation occurred by the eighth or ninth day of development. After 72–80 h of in vitro culture, most of the homozygous embryos were morulae but after an additional 24 h the majority of them transformed into blastocysts. The rate of development of homozygotes was markedly better than that of haploids, which progressed beyond morula stage. The immediate survival rate of operated eggs was dependent on whether or not the eggs were pre-incubated and the enucleation was performed in the presence of CB. In the former case the immediate survival rate was nearly twice as high as in the absence of CB, but more of the treated eggs underwent fragmentation and early developmental arrest.
The cellular basis of epiboly: An SEM study of deep-cell rearrangement during gastrulation in Xenopus laevis
Authors: Keller R. E.
Published: April 2021

Measurements of several indices of shape, contact, position and arrangement of deep cells in the late blastula and gastrula were made from scanning electron micrographs of carefully staged, fractured embryos in order to describe the cellular processes which account for the increased area of the deep region of the gastrula during extension of the dorsal marginal zone and epiboly of the animal region. At the onset of gastrulation, the deep cells of the dorsal marginal zone become elongated, extend protrusions between one another along radii of the embryo and interdigitate to form fewer layers of cells of greater area in a process of radial interdigitation. When interdigitation is complete, the deep region consists of one layer of columnar cells which then flatten and spread and thus account for additional increase in area of the deep region. During epiboly of the animal region, interdigitation occurs and the number of cell layers decreases without the changes in cell shape seen in the dorsal marginal zone. These differences may be related to the anisotropy of expansion (extension and convergence) in the dorsal marginal zone as opposed to uniform spreading in the animal region, or they may reflect an active cell motility in the dorsal marginal zone as opposed to a passive behavior in the animal region. A cellular and mechanical model is presented in which active (autonomous) spreading is brought about by active, force-producing interdigitation and subsequent flattening of deep cells. A model of passive spreading (stretching) is also presented. These observations suggest experiments that would determine the relationship of cell behavior to the mechanics of gastrulation.
Induction of supernumerary tracheal buds and the stimulation of DNA synthesis in the embryonic chick lung and trachea by epidermal growth factor
Authors: Goldin Geoffrey V. , Opperman Lynne A.
Published: April 2021

Epidermal growth factor (EGF) has been found to stimulate DNA synthesis in both the trachea and bronchial tree of 5-day-old chick embryo lung rudiments in organ culture. After 20 h culture in the presence of 10 ng/ml EGF, the incorporation of tritiated thymidine into DNA is stimulated two- to three-fold following a 2 h labelling period, as revealed by scintillation counting. Autoradiographic data indicate that this stimulation is most marked in the epithelial tissue component of both the trachea and bronchial tree. Supernumerary ‘lung’ buds have been induced in the normally unbranched tracheal epithelium by agarose pellets containing EGF, such buds having been previously induced only by grafting a variety of mesenchymal tissues alongside the tracheal epithelium. Since EGF has been shown to be a potent stimulator of tracheal DNA synthetic activity it is suggested that the induction of supernumerary buds by the EGF-agarose pellets is achieved through a localized stimulation of cell proliferation in the tracheal epithelium. These data would further suggest that the induction of supernumerary tracheal buds by various mesenchymal tissues is similarly due to a localized increase in mitotic activity resulting from the action of some mitotic stimulator substance(s) emanating from the inducing mesenchymal tissue. This conclusion may be extended to include normal bud formation which occurs during branching morphogenesis in everal developing organ systems.
Correlative light and electron microscopy of dissociated immature rat testicular cells undergoing morphogenesis in vitro
Authors: Erickson L. A. , Davis J. C. , Burton P. R. , Snyder J.
Published: April 2021

Immature rat testicular cells undergo morphogenesis in primary culture (Davis, 1978). Depending upon the number of dissociated testicular cells added to the culture dish, spherical or tubular aggregates were formed. Spherical aggregates resulted from movement of cells into centers of aggregation and the detachment of these cells from the substratum; on the other hand, tubular aggregates resulted from detachment and retraction of the cell monolayer at certain points along its outer edge. In this investigation, the different methods of formation of aggregates by immature rat testicular cells in primary culture were examined with the scanning electron microscope (SEM). The cell types involved in such morphogenesis and their associations within completely formed structures were examined by transmission electron microscopy (TEM). In addition, the rates of formation of aggregates were established by time-lapse cinemicroscopy. During formation of spherical aggregates, the rate of recruitment of cells into centers of aggregation (0·04 ± 0·006 μm/min; x̄ ± S.E.M., n = 78) was much slower than the rate of cell detachment during formation of tubular aggregates (11·7 ± 1·8 μm/sec; x̄ ± S.E.M., n = 110).

Although specific roles for each cell type in formation of aggregates have not been determined, the associations of cells within the two types of reformed aggregates appeared to be similar. Myofibroblast cells were located in outer cell layers and Sertoli cells were observed to underlie the layers of myofibroblasts in both types of aggregates. Germinal cells, however, were found on the outer surface of spherical aggregates, but in tubular aggregates they were located on the inner surface. Since spherical and tubular aggregates are formed by different methods, this observation suggests that rearrangement of cells within the aggregates takes place and contributes to the internal morphology of newly-formed aggregates.
Evidence that the premature death mutation (p) in the Mexican axolotl (Ambystoma mexicanum) is not an autonomous cell lethal
Authors: Mes-Hartree Mary , Armstrong John B.
Published: April 2021

Cell-lethal developmental mutations, which are presumed to affect the viability of all cells in a mutant embryo, have been distinguished from other developmental lethals on the basis of the results of parabiosis and transplant experiments. Premature death (p), previously classified as a cell lethal, does not survive parabiosis. However, transplants involving mutant eye, flank epidermis and primordial limb tissue all survived on a normal recipient. The mutant, therefore, cannot be considered a true cell lethal, though it suffers from serious and widespread abnormalities that cannot be corrected by parabiosis. In addition, transplants of mutant branchial mound tissue did not develop into normal gills on a normal recipient. These transplants were the only ones involving mutant endoderm, and their failure supports our hypothesis that the mutation leads to a specific endoderm defect.
Paternal gene expression in developing hybrid embryos of Xenopus laevis and Xenopus borealis
Authors: Woodland H. R. , Ballantine J. E. M.
Published: April 2021

We have studied protein synthesis in the viable hybrid Xenopus laevis (♀) × Xenopus borealis (♂) using 2D gel electrophoresis. Fourteen borealis-specific proteins were studied. Two of these proteins appeared by the gastrula stage, five in the gastrula and the rest later. Where homologous laevis proteins were tentatively identified, androgenetic haploid hybrids were used to study whether the protein was encoded by stored maternal mRNA, and how long this mRNA persisted. The two proteins appearing in blastulae were probably initially coded by stored maternal mRNA. This was not detectable by the tailbud-tadpole stage, and presumably had been destroyed.
Hormonal control of head-wart development in the snail, Euhadra peliomphala
Authors: Takeda Naokuni
Published: April 2021

The terrestrial snail, Euhadra peliomphala, has a peculiar organ between the optic tentacles named the head-wart, which releases a sex pheromone just before courtship. The development of the head-wart was closely correlated with the sexual maturity of the snail. Castration led to the atrophy of the head-wart. Subsequent injection of hermaphrodite gland homogenate into the body cavity of castrated individuals induced the development of the head-wart. The peripheral regions of the acini in the hermaphrodite gland showed a positive reaction for 3β-hydroxy steroid dehydrogenase. Furthermore, preliminary radioimmunoassay also showed that the hermaphrodite gland of the snail contained testosterone and estradiol. When the immature head-wart was cultured for 10 days in a medium containing testosterone and estradiol respectively, development of the head-wart was found only in medium containing testosterone. From these results, it is concluded that head-wart development in the snail, Euhadra peliomphala, is under direct control from the hermaphrodite gland, probably by means of testosterone.
Role of the kidney in foetal erythropoiesis: Erythropoiesis and erythropoietin levels in newborn mice with renal agenesis
Authors: Hågå Per , Kristiansen Stein
Published: April 2021

The role of the kidney in foetal erythropoiesis was studied in newborn SD mice on the day of birth. Some of the homozygotes and heterozygotes of this strain are born anephric. Red cell production was evaluated by haematocrit levels, reticulocyte counts, and Fe59-uptake in liver and RBC, the isotope given to the mothers during pregnancy.

Erythropoiesis of the newborn with renal agenesis was not different from that of animals with intact kidneys. When the mothers were exposed to hypoxia during pregnancy, significantly higher haematocrit- and reticulocyte levels were observed, and there was no difference in erythropoiesis of anephric newborn compared with newborn with intact kidneys. Red cell production was also similar in those with and without kidneys when the mothers were hypertransfused.

Plasma erythropoietin levels in the offspring of normal pregnancies were determined. Detectable concentrations of the hormone were found, and the levels were the same in anephric and normal newborn. Exposure to hypoxia (0-5 atm for 6 h) significantly increased plasma erythropoietin levels. This increase was of the same magnitude in animals with and without kidneys.

This study indicates that murine foetal erythropoiesis is regulated by erythropoietin in the same way as later in life. Since abolition of the erythropoiesis of the mothers through hypertransfusion, did not influence the red cell production of the foetuses, Ep seems not to cross placenta. Erythropoietin is, therefore, produced extrarenally during this period.
Evidence for a metameric pattern in the development of the chick humerus
Authors: Stephens Trent D. , McNulty Teresa R.
Published: April 2021

It has been proposed that the wing bud is induced by some axial influence at a specific confined location and that the ZPA is the residual influence of such induction. The purpose of the present investigation was to test this hypothesis. Tantalum foil barriers were placed lateral to the mesonephric duct and parallel to the long axis of the embryo in the wing field of stage-12 to -15 chick embryos. These barriers blocked the somatopleure’s communication with more medial tissues at specific somitic levels. The results of these experiments demonstrate that (1) the limb is not induced at one specific point, (2) portions of the humerus appear to be induced segmentally along the entire limb field and (3) the ZPA is not induced by axial structures. We propose a model of wing development suggesting that the humerus is induced as several separate components which then fuse to form the definitive bone.
Ionic induction of the frog cement-gland cell from presumptive ectodermal tissues
Authors: Yoshizaki Norio
Published: April 2021

Cells of the superficial layer which had been explanted from the presumptive ectoderm of Rana japonica early gastrulae at stage 10 differentiated into cement-gland cells (CGCs) when cultured in Barth’s solution containing 90–130 mM-NaCl., and into common epidermal cells and cilia cells when cultured in a solution containing 20–40 mM-NaCl. They failed to differentiate, however, when cultured in a solution in which NaCl is 15 mM or lower.

The optimum condition for inducing the differentiation of CGC was stimulating them with a solution containing 130 mM-NaCl for 6–10 h at 18 °C, followed by culturing in a solution containing 15–40 miu-NaCl for 7 days. The greatest ability to react to the CGC-inducing stimuli resided in the superficial layer of the presumptive ectoderm of the embryo at stages 10–11. Under the optimum condition, the total volume of CGCs induced amounted to about 85% of the explanted tissue. High percentage comparable to this was obtained with stimulation by KC1, RbCl, sucrose or mannitol.
The distribution of regenerative potential in the wing disc ofDrosophila
Authors: Karlsson Jane
Published: April 2021

The distribution of regulative potential was investigated in the wing disc of Drosophila. Ten complementary pairs of fragments were tested for their capacity to regenerate or duplicate. The distribution of positional values resulting from this data was found to be very unequal; six of the twelve clockface values were tightly clustered round the anterior-posterior compartment boundary. Despite this, complementarity between regeneration and duplication was generally maintained.
Morphogenetic analysis of changing cell associations following release of 2-cell and 4-cell mouse embryos from cleavage arrest
Authors: Kimber S. J. , Surani M. A. H.
Published: April 2021

Two-cell and four-cell mouse embryos were cultured in Cytochalasin D (CD) for 40–48 h. They were fixed for light and electron microscopy at various times after washing off the CD. Cleavage-arrested embiyos in CD had well separated blastomeres but by 1 h from washing the embryos had compacted, in most cases without undergoing cell division. By 2 h after release from arrest one blastomere of the 2-cell arrested embryos had become crescent shaped and at 4–5 h the crescent-shaped blastomere had started to spread over the surface of the other rounded blastomere. This process continued until by 16–24 h from explantation to fresh medium one blastomere had almost completely engulfed the other. A similar process occurred in 4-cell arrested and released embryos. At this stage the embryos had accumulated fluid and become blastocyst-like vesicles. In 20% of 2-cell and 4-cell embryos one or two blastomeres underwent one cell division after release from arrest. Serial sections of these embryos lead to the conclusion that one or both progeny of the first cell to divide tended to be engulfed by the later dividing or non-dividing cell(s). These results are discussed in relation to the differentiation of ICM and trophectoderm in blastocysts.
Blastokinesis in embryos of the bug, Pyrrhocoris apterus.: A light and electron microscopic study 1. Normal blastokinesis*
Authors: Enslee Eugenie C. , Riddiford Lynn M.
Published: April 2021

In the bug, Pyrrhocoris apterus, blastokinesis (a reversal of the position of the embryo within the egg) is seen to involve contraction of the serosa that is attached to the embryo’s head. As the serosal cells change from squamous to columnar in the course of blastokinesis, a dense zone of microfilaments appears just under the apical surface. Many apical protrusions develop above this zone. After the embryo is in its final position the zone disappears and later the cells degenerate.

Laterally, the serosal cells are connected by belt desmosomes, septate junctions and gap junctions. As blastokinesis progresses, more lateral surface is recruited below them from the original basal surface.

Microtubules running parallel to the plasma membrane are seen near the apical microfilaments and along other surfaces of the cell. Secretory granules are evident both within serosal cells and along the apical surface, probably providing a lubricant for movement against the chorion. Yolk cells are common basal to the serosa, possibly mobilizing nutrients for it.

This study of blastokinesis in Pyrrhocoris provides a dramatic example of cell shape change that is correlated with the appearance of microfilaments. In its details blastokinesis is comparable to morphogenetic events such as amphibian neural tube formation and ascidian metamorphosis.
The age-dependent loss of cells from the rear of aDictyostelium discoideumslug is not tip controlled
Authors: Smith Elizabeth , Williams Keith L.
Published: April 2021

Young slugs of the cellular slime mould Dictyostelium discoideum drop small numbers of individual amoebae (∼ 10/mm) in the slime trail. With increased time of migration, slugs develop trailing tails and leave clumps of cells in their slime trails. Using reciprocal transplants between tips of young and old slugs and between a wild-type strain and an ‘aged” mutant it was shown that this age-dependent cell loss is due to changes in the bulk of cells comprising the slug, rather than to changes in the effectiveness of the tip (organizer region). Another property of the slug, the decision to continue migrating or form a fruiting body which is controlled by the tip, was less affected by age. This raises the possibility that cell autonomous properties of the slug are more subject to ageing than is the tip.
The development of the retinotectal projections from compound eyes in Xenopus
Authors: Straznicky C. , Gaze R. M. , Keating M. J.
Published: April 2021

The retinotectal projections from double-nasal (NN), double-temporal (TT) and double-ventral (VV) compound eyes in Xenopus were studied autoradiographically and electrophysiologically during development. Early TT projections were confined to rostrolateral tectum and spread with advancing age to cover most of the tectum by shortly after metamorphosis. Early VV projections showed a decreased density of label on lateral tectum. Early NN projections appeared to extend across the entire rostrocaudal length of the available tectum at all stages of development, but showed a decrease in label density on rostral tectum. The results are discussed in relation to various hypotheses about the formation of retinotectal connexions.
Effects of biochemical inhibitors on positional signalling in the chick limb bud
Authors: Honig Lawrence S. , Smith J. C. , Hornbruch Amata , Wolpert L.
Published: April 2021

In 3- to 4-day embryonic chick limb buds, a region at the posterior margin of the limb, the zone of polarizing activity, appears to be responsible for signalling positional information along the anteroposterior axis. Our experiments were designed to test which biosynthetic processes are required for polarizing activity. We have treated polarizing regions with biochemical inhibitors, and then assayed their abilities to induce limb reduplications when grafted into anterior sites on host limb buds, and also measured their capacities for protein, RNA, and DNA synthesis. DNA synthesis, and possibly oxidative phosphorylation, do not seem to be required for polarizing activity. But, glycolysis and protein and RNA synthesis are necessary, although not sufficient, for polarizing region activity. Activity seems particularly sensitive to inhibitors (actinomycin D and a-amanitin) of RNA synthesis.
Cytoplasmic polarity develops at compaction in rat and mouse embryos
Authors: Reeve W. J. D.
Published: April 2021

Cells of both rat and mouse morulae can be stained vitally to reveal an asymmetry in the organization of their cytoplasm. In each cell of the rat 8-cell embryo a column of organelles develops between the nucleus and the embryo periphery as revealed by toluidine blue, acridine orange and horseradish peroxidase (HRP). Although cells of the mouse morula lack the blatant asymmetric distribution of organelles observed in rat cells, a long pulse (> 3 h) of HRP to compact 8-cell mouse embryos revealed a distinct restricted localization of the enzyme not evident at earlier pre-compaction stages. The cytoplasmic polarity generated in these embryos can be demonstrated in cells of intact embryos, and also in cells disaggregated from embryos before vital staining.
Temporal pattern of cleavage and the onset of gastrulation in amphibian embryos developed from eggs with the reduced cytoplasm
Authors: Kobayakawa Yoshitaka , Kubota Hiroshi Y.
Published: April 2021

Fertilized eggs of the Japanese newt, Cynops pyrrhogaster, were divided into two or four equal-sized parts with fine glass rods before the first cleavage. In such cases one of the egg fragments, at least, proceeds to cleavage and gastrulates.

The temporal pattern of cell division and the onset of gastrulation in such half or quarter embryos were investigated and compared with normal development. The following results were obtained: (1) desynchronization starts two divisions earlier in quarter embryos and one division earlier in half embryos compared with whole embryos, (2) the time from the first cleavage to the onset of gastrulation does not widely vary among quarter, half and whole embryos and (3) the numbers of blastomeres which constitute embryos at the pigment stage decrease in proportion to the diminution of egg volume.