bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulation of the pattern of basal bodies within the oral apparatus ofTetrahymena thermophila
Authors: Bakowska Julita , Frankel Joseph , Nelsen E. Marlo
Published: April 2021

The number and arrangement of basal bodies included in the four compound ciliary organelles making up the mature oral apparatus of Tetrahymena thermophila ordinarily vary only slightly. Severe starvation brings about formation of oral structures with a reduced number of basal bodies within these organelles, and sometimes with a complete loss of one of the component organelles. Such reductions are stringently specified in spatial terms, but they do not represent simple and proportional shrinkage of the organelle complex. Instead, certain spatial features remain essentially unaltered, while others undergo major quantitative reductions, resulting in large changes in the internal proportions of the structures. This selective regulation can be explained in terms of the different parallel and sequential processes taking place during the development of this organelle complex. There is also no strict pro-portionality between the size of the oral apparatus and that of the cell ; instead, oral apparatuses become relatively larger as cells become smaller. This is due in part to the inherent temporal discontinuity of oral development, but there is probably also a real change in the oral/body size relation at the time of oral development. The ‘French flag’ rule fails when applied to the relative sizes and internal proportions of organelle systems in this and in other ciliates.
Studies on the Mode of Outgrowth of the Amphibian Pronephric Duct
Authors: Overton Jane
Published: April 2021

The mode of outgrowth of the pronephric duct has been investigated by examining the mitotic index and migratory propensities of duct cells. There is no indication of duct elongation through terminal proliferation or of high proliferative activity throughout the duct that does not merely reflect the generally high growth rate of the embryo as a whole. Explants of the trunk region cultured in plasma clots showed cylindrical extensions of pronephric duct cords into the clot prior to outgrowth of other cell types. It is concluded that in the species studied, duct outgrowth is an essentially migratory phenomenon, and that the nephric epithelial cells have the ability to form cords of roughly normal diameter in a non-cellular environment.
The Adhesive Properties and Expansion of the Chick Blastoderm
Authors: New D. A. T.
Published: April 2021

Chick blastoderms during the first 2 days of incubation are unable to expand if the blastoderm edge is detached from the vitelline membrane. The edge can, however, reattach, and then expansion continues. The blastoderm edge is very sensitive to the nature of the substrate surface. It did not form normal adhesions with, or expand normally over, vitelline membranes that had been boiled or (with one exception) treated with formalin. Neither will it expand over the outer surface of the vitelline membrane (i.e. the surface which in ovo faces the albumen). It will, however, expand over alcohol-treated vitelline membranes. The blastoderm is sensitive to lines of tension in the vitelline membrane, extending fastest along lines of greatest tension. The marginal cells of the blastoderm adhere to the vitelline membrane as a result of their intrinsic properties, and not because of their peripheral position. Expansion of the blastoderm is dependent on a mechanical tension produced by the outward-moving margin. Expansion can occur without protein synthesis, but if yolk protein is available it will be utilized. Albumen protein is not used at this stage. Cell proliferation is particularly active in the marginal region of the blastoderm (though not at the extreme edge). The ectoderm in the marginal region becomes several cells thick if blastoderm expansion is prevented. Blastoderms inverted on the vitelline membrane develop into hollow vesicles. Blastoderms grown on inverted vitelline membranes adhere abnormally strongly to the membranes and fold the membranes at the region of attachment.
Differentiation of Cells of the Rana pipiens Gastrula in Unconditioned Medium1
Authors: Barth Lester G. , Barth Lucena Jaeger
Published: April 2021

A method has been devised for the culture of gastrular cells of R. pipiens. Histological and functional differentiation of nerve, muscle, and pigment cells is described as well as the differentiation of ciliated, mucus-secreting, and notochord cells. The inner layer of the presumptive epidermis differentiates into nerve-cells, ciliated cells, and ‘giant’ cells, in addition to an unidentified cell type X. Brief lithium treatment of presumptive epidermis results in a permanent transformation into pigment cells and mesenchyme.
The developmental potential of a euploid male teratocarcinoma cell line after blastocyst injection
Authors: Rossant J. , McBurney M. W.
Published: April 2021

A karyotypically normal male embryonal carcinoma (EC) cell line, P19, produced large numbers of chimaeras in midgestation after groups of cells were injected into mouse blastocysts. A wide variety of apparently normal tissues were colonized by the EC cells but most chimaeras were also morphologically abnormal. Few live chimaeras were produced and all contained tumours of EC cell origin as well as EC contributions to normal tissues. This apparently incomplete regulation of the EC cells by the embryonic environment was not due to EC cell variation, since a clonal subline, P19S18, produced similar patterns of colonization. It was also not caused by the inability of the blastocyst to regulate large numbers of injected EC cells, since a single P19S18 cell could contribute to both normal and tumour tissue in the same mouse. Neither a high rate of colonization of the embryo nor a normal karyotype is, therefore, sufficient to ensure reversion of EC cells to normal embryonic behaviour.
The effect of teratogenic antiserum on yolk-sac function in rat embryos cultured in vitro
Authors: Freeman Stuart J. , Brent Robert L. , Lloyd John B.
Published: April 2021

The teratogenicity of rabbit anti-rat visceral yolk-sac antiserum, injected into pregnant rats at either 8 ·5 or 9 ·5 days of gestation, has been confirmed. Normal rabbit serum was found not to be teratogenic.

When conceptuses from 9 ·5-day pregnant rats were cultured for 48 h in heat-denatured homologous serum, to which antiserum was added for the final (or the penultimate) 6 h of culture, embryonic development was normal. The protein contents of embryos and yolk sacs (at harvesting) were however decreased.

When antiserum was present in cultures for the final 6 h, pinocytosis by the yolk sac, as measured by the uptake of 125l-labelled polyvinylpyrrolidone (PVP), was decreased to an extent related to the concentration of antiserum in the culture medium and to a minimum level of about 40%. The presence of antiserum in cultures for the penultimate 6 h only, with 125I-labelled PVP present for the final 6 h only, produced an identical result. No uptake of radioactivity into the embryo was observed, in either the absence or presence of antiserum.

When conceptuses were cultured for the final 6 h in vitamin- and glucose-supplemented dialysed homologous serum whose proteins were [3H]leucine-labelled, the presence of antiserum for either the final or penultimate 6 h again resulted in a decrease in the uptake of radioactivity by conceptuses. Uptake of radioactivity into yolk sac and embryo was decreased by the same amount, indicating that proteolysis in yolk-sac lysosomes was not inhibited.

In parallel control experiments in which normal rabbit serum replaced rabbit anti-rat visceral yolk-sac antiserum, no effects on embryonic development, on protein contents of yolk sacs and embryos at harvesting, or on the uptake of radioactivity by conceptuses were observed.

These results are interpreted as providing evidence that teratogenic antibodies decrease pinocytosis of protein by visceral yolk sac at the early organogenesis stage and consequentially decrease the availability of amino acids and thus protein synthesis in both yolk sac and embryo. It is proposed that this effect constitutes the mechanism of action of teratogenic antisera.
Neuronotrophic effects of skeletal muscle fractions on spinal cord differentiation
Authors: Hsu L. , Natyzak D. , Trupin G. L.
Published: April 2021

Soluble fractions of homogenized skeletal muscle were found to promote neuronal migration and neuritic and glial outgrowth from embryonic chick spinal cord explants. Fractions obtained from skeletal muscle immobilized by prolonged treatment with curare were significantly more effective than normal muscle in accelerating neuronal and glial development. Fractions from other tissues such as brain and lung did not enhance neuronal differentiation, but were effective in stimulating outgrowth of glial cells. Separate measurements of glial and neuronal responses indicate that tissue fractions produce independent effects on the glial and neuronal components.
Incorporation of 5-bromo-2’-deoxyuridine into mesenchymal limb-bud cells destined to die: relationship to polydactyly induction in rats
Authors: Wise L. David , Scott William J.
Published: April 2021

The thymidine analogue, 5-bromo-2’-deoxyuridine (BUdR), given at the proper dose and time to pregnant rats produces preaxial hindlimb polydactyly in a high proportion of near term foetuses. The lack of physiological cell death in an area of preaxial mesenchyme known as the foyer primaire preaxial (fpp) is thought to be important in the pathogenesis of this defect. This study addresses the question of whether BUdR’s well-known antidifferentiative effects, which are due in some way to drug incorporation into DNA, are operative in this in vivo system. The dose and temporal response of BUdR for the induction of preaxial polydactyly inversely parallels the frequency of embryonic hindlimbs with an fpp. Incorporation of BUdR into degenerative fragments within the fpp of these treated limbs is demonstrated with indirect immunofluorescence using an antibody to bromouridine. Hindlimbs exposed to a threshold dose of BUdR at the optimal time for producing polydactyly have incorporated the drug into degenerative fragments within the fpp. This suggests that a higher, teratogenic dose of BUdR might likewise be incorporated. The resulting higher level of incorporation presumably alters the normal course of terminal differentiation for these cells originally destined to die.

Teratogenic doses of BUdR injected at later than the optimal time are also incorporated into dead cell fragments within the fpp, suggesting that presumptive dead cells have additional rounds of DNA synthesis which are BUdR-insensitive. Approximately 12 h prior to overt death presumptive fpp cells no longer incorporate the drug.

Results reported support the hypothesis that incorporation of teratogenic levels of BUdR prevent cell death in the fpp. The extra cells are thought to contribute directly or indirectly to the added digit. Contrary to other views, it is suggested that BUdR-induced teratogenesis can be a result of the drug’s antidifferentiative effects on specific, ‘sensitive’, populations of cells.
Insensitivity to cytochalasin B of surface contractions keyed to cleavage in the Xenopus egg
Authors: Christensen Kathy , Merriam R. W.
Published: April 2021

In fertilized eggs of Xenopus laevis a marked flattening of the pigmented animal hemisphere has been observed. The flattening begins 15 –20 minutes before the appearance of the cleavage furrow. As the furrow develops, the pigmented surface relaxes and rounds up. The initial appearance of the furrow is thus shown to be a combination of furrow deepening and rounding up of adjacent pigmented surfaces.

It is demonstrated that the flattening is not caused by gravity or osmotic mechanisms and that internal pressure is increased during the flattening. The flattening is interpreted to be an isodiametric contraction of the pigmented surface. The contraction is not inhibited by injected cytochalasin B in sufficient concentrations to completely inhibit cleavage furrow formation.

These results are discussed with respect to the presence of two surface contractile systems, distinguishable on the basis of their differing sensitivity to cytochalasin B.
Experimental induction of testicular teratomas in dissociated–reaggregated chimaeric gonads
Authors: Regenass Urs , Friedrich Thomas D. , Stevens Leroy C.
Published: April 2021

Testicular teratomas can be experimentally induced in some strains of mice by grafting 12·5-day male genital ridges to the testes of adults. The grafts develop into testes and most of them have teratomas. The cells of 12·5-day foetal gonads were dissociated and the germ cells and somatic cells were separated. When germ cells were reaggregated with somatic cells and implanted in adult testes, they formed seminiferous tubules with teratomas. The somatic cell populations were contaminated with about 1 % germ cells, and when they were implanted in adult testes, they formed testes with a comparatively low incidence of teratomas. When germ cells of a highly susceptible strain were combined with somatic cells from a resistant strain, they formed chimaeric testes with a high incidence of teratomas. When germ cells from a resistant strain were combined with somatic cells from a susceptible strain they formed chimaeric gonads and the incidence of teratomas was low. This indicates that at 12·5 days the genotype of the germ cells is responsible for susceptibility. When germ cells from older foetal gonads were combined with somatic cells of 12·5-day gonads, the incidence of tera-tomas was low. This showed that 12·5-day somatic cells cannot ‘rejuvenate’ older germ cells in a way to regain their susceptibility. When 12·5-day germ cells of highly susceptible strains were combined with older somatic cells the incidence of tumours was low indicating that the age of the somatic cells influences susceptibility to teratocarcinogenesis.
Development of the optic nerve inXenopus laevis: I. Early development and organization
Authors: Cima Charles , Grant Philip
Published: April 2021

Development of the Xenopus laevis optic nerve was studied by light and electron microscopy from embryonic stage 26, before the retina has formed, to juveniles, 8 months post-metamorphic. Low-power EM photographs of sections through the retinal optic nerve (RON), middle optic nerve (MON) and chiasmatic optic nerve (CON) were prepared at different stages and the areas containing large axons (0·5 μm) were traced in optic nerve reconstructions. Ordering of fibre size along a dorsoventral axis was noted in the embryonic nerve, and this pattern persisted throughout development. Most large fibres, myelinated and unmyelinated, occupy an eccentric dorsoventral position in the MON while small axons are seen in a ventral peripheral crescent. In the CON, the dorsal one third to one half is occupied by large fibres while the ventral CON contains small fibres exclusively. If, as assumed, large axons are older than small axons (0·1 –0·3 μm), then patterns of large and small axons along the nerve might reveal a chronotopic fibre ordering. Chronotopic ordering was confirmed by autoradiographic analysis of the distribution of old, labelled fibres and young, unlabelled newly arriving fibres in optic nerves between stage 51 and 57. The young-old labelling pattern corresponds to the small and large axon patterns respectively, in all sections of the optic nerve. Chronotopic ordering of fibres in the developing optic nerve can be explained, in part, by the dorsoventral asymmetric marginal growth of the developing retina and the phenomenon of fibre following as ganglion cell axons join near neighbour fascicles in the retina, converge at the optic disc and grow through the optic nerve.
Increased adhesiveness at sites of high acetylcholine receptor density on embryonic amphibian muscle cells cultured without nerve
Authors: Moody-Corbett F. , Cohen M. W.
Published: April 2021

In culture, myotomal muscle cells from Xenopus laevis embryos develop discrete patches of high acetylcholine receptor (AChR) density. To examine the relative adhesiveness of these sites, muscle cells having AChR patches on their lower surface (apposed to the culture dish) were identified and were then treated with dibucaine or potassium-Ringer in order to cause the cells to round up. More than 90% of these cells remained attached at an AChR patch after rounding up, and this was the case even when the cells had a single patch on their lower surface. When the cells were torn away from the culture dish by mechanical agitation, small cellular fragments still remained firmly attached to the dish and many of these fragments contained an AChR patch. It is concluded that AChR patches on the lower surface of the cell are often located at sites of increased adhesiveness to the culture dish. The findings are discussed in terms of the formation and maintenance of AChR patches.
Experimental Neoplastic Formation in Embryonic Chick Brains
Authors: Källén Bengt
Published: April 2021

In mammalian teratology, a malformation consisting of ‘overgrowth’ of the neural tube has been described by, among others, Patten (1952,1957) and Ariens Kappers (1956, 1957). Sjodin (1957) thought it to be a post-mortem effect and not a true malformation. The present author (1955) demonstrated that a similar malformation could be produced in the rostral part of the brain of chick embryos by operations at somite stages on the rostral end of the rhombencephalon which damaged underlying notochordal structures. Bergquist (1959 a, b) has discussed this problem further. The overgrowth is made up of an excessive proliferation in the neural epithelium with a reduced cell differentiation, giving rise to only a thin layer of migrated cells but to a marked development of neural epithelium in 4-to 5-day embryos. The vesicles of the hemispheres and mesencephalon are strongly folded, and Bergquist (1959c) has produced evidence that the folding is due to the accumulation of mitoses along the ventricular lining of the vesicles. For further details of this malformation the reader is referred to Bergquist’s papers.
Incorporation de l’adénine-C14 dans l’embryon de Poulet
Authors: Barbieri par Francisco D.
Published: April 2021

Malgré le grand nombre de données déjà publiées sur le métabolisme des acides nucléiques pendant le développement embryonnaire, quelques aspects de cette question complexe méritent d’être reconsidérés, surtout quand on dispose de méthodes de recherche précises.
Volumetric Investigations on Overgrowth (Hypermorphosis) in Chick Embryo Brains
Authors: Bergquist Harry
Published: April 2021

The present paper is intended as a continuation of preceding publications (Bergquist, 1959 a, b) on possible causes of the phenomenon of ‘overgrowth’ (Patten, 1952) in the brain of the chick embryo. Reference should be made to these publications for the relevant literature. In these earlier investigations, it was observed that the mitotic rate in the altered portions of the neural tube seemed higher than in the normal regions, and that the hemispheres and tectum opticum showed marked folding.
Osteolathyrogenic Effects on the Developing Rat Foetus1
Authors: Ferm Vergil H.
Published: April 2021

Skeletal and aortic changes in foetal rats treated with osteolathyrogenic agents via the maternal system throughout pregnancy or very late in pregnancy have been described by Stamler (1955). Developmental changes in Xenopus larvae (Chih, Witschi, & Ponseti, 1954) and in salamander and toad larvae (Levy, 1955) have also been described. The abnormalities produced in these forms by these agents have apparently been related to a direct effect of the agent on the mucopolysaccharide ground substance. No attempt has been made in a mammal to determine if there are specific time-susceptible periods in embryogenesis when this type of stimulus may induce true teratogenic effects. The present study was devised to determine the effect of a known osteolathyrogenic agent during specific stages of gestation and especially to observe the effect of this agent during the early critical stages of embryogenesis.
Development of the apical ectodermal ridge in the chick wing bud
Authors: Todt William L. , Fallon John F.
Published: April 2021

Histological examination of the stage-18 to stage-23 chick wing bud apex revealed the following. Initially, the wing bud was covered by a cuboidal to columnar epithelium with an overlying periderm. Thickening of the apical ectoderm was not obvious until late stage 18 (36 pairs of somites), after the appearance of the wing bud. At late stage 18, cells of the inner layer of ectoderm had elongated slightly along an axis perpendicular to the epithelial-mesenchymal interface. Well-defined apical ectodermal ridge morphology, i.e., pseudostratified columnar epithelium with an overlying periderm, was not apparent until stage 20. Subsequently the ridge lengthened along the anteroposterior perimeter of the wing bud. We demonstrated histologically that the apical ectodermal ridge of the wing bud was asymmetric with respect to the anteroposterior axis, in that there was more ridge associated with posterior mesoderm. Other observations include the spatial and temporal location of a groove in the base of the thickest part of the ridge. The groove can be correlated with the specification of distal wing elements. The groove was first seen at stage 20 and became more prominent through stage 23. An anteroposterior progression of ectodermal cell death was also observed. This began at late stage 18 and continued through each of the stages examined.
Heterogeneous differentiation of external cells in individual isolated early mouse inner cell masses in culture
Authors: Nichols J. , Gardner R. L.
Published: April 2021

Inner cell masses (ICMs) were isolated from early blastocysts by immunosurgery and incubated in a dense suspension of melanin granules for 3h after 21 h in culture. The majority of such labelled ICMs subsequently formed outgrowths in vitro in which either giant cells or small solitary cells contained melanin granules. However, a substantial minority produced outgrowths in which both types of cell were unequivocally labelled. Labelled cells appeared from the results of control experiments to have originated within the external layer of the ICM. The giant cells were indistinguishable morphologically from those formed by authentic trophectodermal tissue. The small cells were identified as belonging to the extraembryonic endodermal lineage on the basis of their distribution in host conceptuses following injection into blastocysts. These findings support the conclusion reached in previous studies that early ICM cells can engage in trophectodermal differentiation under certain conditions. In addition, by providing evidence that both trophectoderm and endoderm cells can differentiate from the outer layer of the same ICM, they argue that loss of cellular lability is not coordinated throughout this tissue. Heterogeneity in the differentiation of external cells may depend on differences in both the stage of the mitotic cycle and the number of such cycles that they have completed since fertilization.

Finally, cell number in isolated early ICMs was found to increase approximately two-fold during the first 24 h of culture in the present experiments. This contrasts with the results of previous experiments in which cell number either increased more modestly or failed to do so altogether.
The pigmentary system of developing axolotls
Authors: Frost S. K. , Epp L. G. , Robinson S. J.
Published: April 2021

A biochemical and transmission electron microscopic description of the wild-type pigment phenotype in developing Mexican axolotls (Ambystoma mexicanunm) is presented. There are three pigment cell types found in adult axolotl skin - melanophores, xanthophores and iridophores. Both pigments and pigment cells undergo specific developmental changes in axolotls. Melanophores are the predominant pigment cell type throughout development; xanthophores occur secondarily and in fewer numbers than melanophores; iridophores do not appear until well into the larval stage and remain thereafter as the least frequently encountered pigment cell type. Ultrastructural differences in xanthophore organelle (pterinosome) structure at different developmental stages correlate with changes in the pattern of pteridine biosynthesis. Sepiapterin, a yellow pteridine, is present in larval axolotl skin but not in adults. Riboflavin (also yellow) is present in minimal quantities in larval skin and large quantities in adult axolotl skin. Pterinosomes undergo a morphological “reversion” at some point prior to or shortly after axolotls attain sexual maturity. Correlated with the neotenic state of the axolotl, certain larval pigmentary features are retained throughout development. Notably, the pigment cells remain scattered in the dermis such that no two pigment cell bodies overlap, although cell processes may overlap. This study forms the basis for comparison of the wild type pigment phenotype to the three mutant phenotypes-melanoid, axanthic and albino-found in the axolotl.
The pigmentary system of developing axolotls
Authors: Frost S. K. , Epp L. G. , Robinson S. J.
Published: April 2021

The melanoid mutant in the Mexican axolotl (Ambystoma mexicanum) is analysed with respect to the differentiation of pigment cells. Pigment cells were observed with the transmission electron microscope in order to determine any unusual structural characteristics and to determine what happens to each of the cell types as development proceeds. Chemical analysis of pteridine pigments was also carried out, and changes in pteridine biosynthesis were found to correlate well with changes in xanthophore morphology and number.

In melanoid axolotls, as development proceeds, melanophore numbers increase, xanthophores decrease, and iridophores fail to differentiate at all. This is considered to result from: (a) conversion of xanthophores (that are present in young larvae) to melanophores; (b) the gradual programming of the majority of chromatoblasts to become, exclusively, melanophores, and (c) the failure of some chromatoblasts (possibly iridoblasts) to differentiate altogether. The ultrastructural and chemical evidence presented in this study is compared to similar data for wild-type axolotls, and a mechanism regarding how the melanoid gene might act is suggested.
Apolipoprotein expression by murine visceral yolk sac endoderm
Authors: Shi Wei-Kang , Heath John K.
Published: April 2021

Apolipoprotein expression was examined in the postimplantation mouse embryo. Antibodies directed against murine Apolipoprotein AI and human low-density lipoprotein (LDL) particles specifically immunoprecipitated metabolically labelled radioactive apolipoproteins from the culture supernatant of 10 ·5 days post coitum (days p.c.) yolk sac visceral endoderm cultured in vitro. No evidence for apolipoprotein expression by other embryonic or extraembryonic tissues at this stage was obtained. Immunohistochemical staining at sectioned 10 ·5 days p.c. embryos with anti-Apolipoprotein AI antibodies revealed specific localization of immunoreactive material in the yolk sac visceral endoderm. We conclude that the yolk sac visceral endoderm is a source of lipoproteins during postimplantation embryonic development.
Development of the iris in the chicken embryo: I. A study of growth and histodifferentiation utilizing immunocytochemistry for muscle differentiation
Authors: Ferrari Patricia A. , Koch William E.
Published: April 2021

The development of the iris was studied in chicken embryos from 4 days of incubation through hatching and in chicks up to 17 days posthatching. Serial sections of the eye were stained routinely or by immunocytochemical methods using myosin antiserum to enhance detection of differentiating muscle by light microscopy. Eyes from embryos at each stage were also examined by scanning electron microscopy.

Outgrowth of the iris occurs in a sequential pattern around the eye, beginning at days of incubation in the region temporal to the choroid fissure and proceeding around the eye. Since differentiation of the iris follows the same pattern, similar areas of the iris were compared at each stage of development.

At days of incubation, pigment granules can be seen in the anterior epithelium at the root of the iris, but it is not until 8 days of incubation that pigment is identified in the same area of the posterior epithelium. As development proceeds, the pigmentation of both epithelial layers progresses from the root of the iris to the pupillary margin.

Early features of the development of the sphincter muscle can first be recognized in the 7day embryo, when epithelial buds form from the anterior epithelium adjacent to the pupillary margin. Cells from these buds detach from the epithelium and populate the entire irideal stroma; these cells are the precursors of the sphincter muscle. The epithelial buds increase in size and distribution, and coalesce into a continuous ridge of cells around the iris by 10 days of incubation. The first muscle cells differentiate at 11 days of incubation when striated fibres can be identified by immunocytochemistry. The first striated fibres of the dilator muscle are seen in the 13-day embryo. Differentiation of the dilator muscle begins near the root of the iris and proceeds toward the pupillary margin, ultimately arising from the entire anterior epithelium except near the pupillary margin. Further differentiation of the sphincter and dilator muscles continues throughout incubation and for several weeks beyond hatching.
Development of the iris in the chicken embryo
Authors: Ferrari Patricia A. , Koch William E.
Published: April 2021

The developmental capabilities of the iris rudiment in the chicken embryo, as well as the role of tissue interactions in the differentiation of the iris, were investigated in vitro.

Sectors of the intact iris from through 9-day embryos (stages 32 through 35) lost their morphological organization in vitro, but were capable of normal histodifferentiation. The pigmentation of the epithelium increased, and muscle differentiation occurred. Developing muscle was identified using immunocytochemistry with antiserum against chicken muscle myosin; this procedure permitted positive identification of myoblasts, myotubes, and muscle fibres in cultures in which histological features alone were equivocal. The proportion of irideal explants which developed muscle increased with the age of the embryo, and correlated with the incidence of epithelial buds and epithelial cells in the stroma.

Irideal mesenchyme from stage-32 through stage-35 embryos was already populated with stromal epithelial cells when isolated, but growth and muscle differentiation in these cultures compared poorly with that in the intact iris in vitro. Isolated irideal epithelium (stages 32 through 37) demonstrated even more limited muscle differentiation in vitro, suggesting reciprocal interaction between irideal epithelium and mesenchyme during development. Irideal epithelium was also cultured in direct association with non-irideal mesenchyme from various embryonic organ rudiments, but muscle differentiation was not enhanced.
Intermediate filaments in the Xenopus oocyte: the appearance and distribution of cytokeratin-containing filaments
Authors: Godsave S. F. , Wylie C. C. , Lane E. B. , Anderton B. H.
Published: April 2021

Cytokeratins have previously been shown to exist in the Xenopus oocyte cortex. Using three monoclonal antibodies against cytokeratins, we follow the appearance of cytokeratin-containing filaments, and their changes in distribution during oocyte differentiation and maturation. Cytokeratin-containing filaments are shown to change dramatically in distribution in the oocyte during its ontogeny.
Characterization of a reduced-eye mutant of the grasshopper, Melanoplus sanguinipes
Authors: Emery D. J. , Bell K. A. , Chapco W. , Steeves J. D.
Published: April 2021

A reduced-eye (re) mutant grasshopper of Melanoplus sanguinipes has been characterized by small flat compound eyes lacking facets, no lateral ocelli and only a remnant of the median ocellus. The re grasshoppers walk, jump, fly and feed in a normal manner, but do not respond to visual and auditory stimuli, suggesting they may be blind and deaf. Extracellular recordings from the ventral nerve cord of re mutants verified the lack of neural activity in response to visual and auditory inputs, yet the mutants detected mechanical and tactile stimuli. Electroretinograms implied that a visual deficit may be within the photoreceptors of the compound eye.

Histological examination of the compound eyes and ocelli indicated that the cells of the mutant compound eye incompletely differentiate. The optic lamina underlying the retina is missing, as is the outer optic chiasma. The medulla and lobula of the mutant optic lobe are present, however, the neuropil of the medulla lacks the characteristic axonal projection patterns of wild-type grasshoppers. The re grasshopper also lacks all ocellar nerves. Ocellar nerves are normally formed from processes of second order ocellar neurons (SONs), suggesting that if the mutant SONs are present within the protocerebrum, their morphology is drastically altered. Comparison of embryos and juvenile nymphs supports the suggestion that the alterations in the re visual system are the result of abnormal differentiation during development.

Even though there is clear evidence of morphological alterations in second and third order optic lobe interneurons, one higher order visual interneuron of the midbrain, the descending contralateral movement detector (DCMD), has the same morphology as the DCMD in a wildtype brain. In this instance, the complete deprivation of the primary sensory input does not appear to alter cellular development.
DNA methylation versus gene expression
Authors: Bird Adrian P.
Published: April 2021

Vertebrate DNA is methylated at a high proportion of cytosine residues in the sequence CpG, and it has been suggested that the distribution of methylated and non-methylated CpGs in a given cell type influences the pattern of gene expression in those cells. Since a DNA methylation pattern is normally transmitted faithfully to daughter cells via cell division, this idea suggests an origin for stable, clonally inherited patterns of gene expression. This article discusses some of the current evidence for a relationship between DNA methylation and gene expression. Although the evidence is incomplete, it appears already that the relationship is variable: transcription of some genes is repressed by the presence of 5-methylcytosine at certain CpGs, and may be controlled by methylation, while transcription of other genes is indifferent to methylation. In attempting to explain this variability it is helpful to adopt an evolutionary perspective.
Cell behaviour in a polygonal cell sheet
Authors: Honda H. , Kodama R. , Takeuchi T. , Yamanaka H. , Watanabe K. , Eguchi G.
Published: April 2021

Cell monolayers on culture dishes were divided into two groups: tensile monolayers and non-tensile ones. In the development of an epithelium, a non-tensile cell monolayer turns into a tightly bound tensile one. Detection of these states was carried out by using the boundary shortening procedure, a computer-based geometrical method to show how much the polygonal cell boundary contracts.

Non-tensile monolayers were divided further into two groups according to their motility: a fluctuating monolayer in which cells move laterally, and a stable monolayer in which cells are immobilized. Quantitative determination of cell motility was performed by analysing timelapse cellular patterns.

These computer-based geometrical analyses enabled us to divide monolayers into three groups: tensile stable monolayers, non-tensile stable monolayers and fluctuating monolayers, and this study therefore gives an insight into the way in which changing conformations of cells may be assayed.
Syndactyly induced by Janus Green B in the embryonic chick leg bud: a reexamination
Authors: Fernandez-Teran M. A. , Hurle J. M.
Published: April 2021

In an attempt to clarify the mechanism of production of the syndactyly induced by Janus Green B (JGB) we have studied the morphology and structural modifications of the chick embryo leg bud after JGB administration by means of (1) neutral red vital staining, (2) whole-mount cartilage staining and β) light microscopy and transmission and scanning electron microscopy. The results show that the well-known inhibition of interdigital cell death is accompanied by a precocious alteration of the epithelial tissue and especially of the epithelial-mesenchymal interface. 24 h after JGB administration the cells of the AER reduce the number of junctions and the basal ectodermal cells are detached into the mesenchymal tissue in zones in which the basal lamina undergoes disruption. In addition the interdigital mesenchymal cells diverted from the dying program are able to undergo a rapid differentiation into cartilage.

It is proposed that the mechanism of production of JGB-induced syndactyly might be due to an alteration of the normal epithelial-mesenchymal interactions rather than to a direct inhibitory effect of the JGB on the dying program.
Changes in antibody and complement production in Xenopus laevis during postmetamorphic development revealed in a primary in vivo or in vitro antibody response
Authors: Lallone R. L. , Chambers M. R. , Horton J. D.
Published: April 2021

Xenopus laevis (G-line) mounts a primary plaque forming cell (PFC) response either in vivo or in vitro following challenge with foreign erythrocytes. Methods are described for generating and assaying the response, which specify criteria such as antigen dose, antigen choice, response kinetics, and complement source. The results suggest that at the peak of the primary response (approximately day 6), animals of different ages produce predomi-nantly different ‘classes’ of antibody which display markedly different complement-fixing characteristics. Antibodies produced by larvae and 4-month-old postmetamorphic animals appear here to be unable to fix either guinea pig complement (GPC′) or adult Xenopus complement, but can readily fix complement from 6-month-old Xenopus. The proportion of spleen PFC’s producing antibody capable of fixing GPC′ progressively increases from about six months to 18 months of age. Possible explanations for such ontogenetic changes are discussed.
Investigation of variability among mouse aggregation chimaeras and X-chromosome inactivation mosaics
Authors: West John D. , Bücher Theodor , Linke Ingrid M. , Dünnwald Manfred
Published: April 2021

Mouse aggregation chimaeras were produced by aggregating C3H/HeH and C3H/HeHa-PgZc-la/Ws embryos. At mid-term the proportions of the two cell populations in these conceptuses and the X-inactivation mosaic female progeny of C3H/HeH ♀ × C3H/HeHa-PgZi-7′7Ws ♂ matings were estimated using quantitative electrophoresis of phosphoglycerate kinase (PGK-1) allozymes. The percentage of PGK-1B was more variable in the foetus, amnion and yolk sac mesoderm of the chimaeras than in the corresponding tissues of the mosaic conceptuses. Positive correlations were found for the percentage of PGK-1B between these three primitive ectoderm tissues in both chimaeras and mosaics and between the two primitive endoderm tissues (yolk sac endoderm and parietal endoderm) of the chimaeras. There was no significant correlation between the primitive ectoderm and primitive endoderm tissues of the chimaeras. The results suggest that unequal allocation of cell populations to the primitive ectoderm and primitive endoderm considerably increases the variability among chimaeras but variation probably exists before this segregation occurs. The variation that arises before and at this allocation event is present before X-chromosome inactivation occurs in the primitive ectoderm lineage and explains why the proportions of the two cell populations are more variable among chimaeras than mosaics. Additional variation arises within the primitive ectoderm lineage, after X-inactivation. This variation may be greater in chimaeras than mosaics but the evidence is inconclusive. The results also have some bearing on the nature of the allocation of cells to the primitive ectoderm and primitive endoderm lineages and the timing of X-chromosome inactivation in the primitive ectoderm lineage.
Morphological and experimental studies of the somitomeric organization of the segmental plate in snapping turtle embryos
Authors: Packard David S. , Meier Stephen
Published: April 2021

The segmental plate mesoderm of snapping turtle embryos (Chelydra serpentina) was examined with stereoscanning electron microscopy imaging. A metameric pattern was detected along the entire length of the segmental plates. This pattern consisted of a tandem sequence of mesodermal units, called somitomeres. Each somitomere was oval to cubic in shape and the processes of the constituent mesodermal cells tended to be arranged in concentric rings about the centre of the somitomere. Several experiments from a previous study (Packard, 1980b) of snapping turtle segmental plates were repeated, but, instead of culturing the explants and observing the numbers of somites that formed, the explants were fixed immediately for scanning electron microscopy and the number of somitomeres was counted. The segmental plates were found to contain an average of 6·5 ± 0·7 somitomeres, which is almost identical to the average number of somites formed by such segmental plates when cultured (6·6 ± 1·2). Furthermore, the number of somitomeres was identical in right and left explants removed from the same embryo, and the number of somitomeres was consistent regardless of the length of the segmental plate. Both of these observations are identical to those made previously for somite formation in culture. This association between numbers of somitomeres and somites strongly suggests that one gives rise to the other. Finally, it was demonstrated that for each somite formed by a segmental plate in culture, the segmental plate contained one less somitomere. This showed in a direct manner that turtle somitomeres become somites. It was concluded that the segmental plate mesoderm of snapping turtle embryos is already segmented, and that the ‘segmentation’ seen under a dissecting microscope is actually the final stage of somitomere differentiation into an epithelial somite.
Development of synapses between identified sensory neurones and giant interneurones in the cockroach Periplaneta americana
Authors: Blagburn J. M. , Beadle D. J. , Sattelle D. B.
Published: April 2021

The cereal afferent, giant interneurone pathway in Periplaneta americana was used as a model for synapse formation. The morphology of the two identified filiform hair sensory neurones (FHSNs) and of two giant interneurones (Gl 2 and Gl 3) was followed throughout embryogenesis by cobalt injection. The FHSN axons enter the CNS at the 45 % stage of embryogenesis, branch at 50 % and form complete arborizations by 70 %. The giant interneurones send out a primary dendrite at 45%. Secondary branches form between 50% and 60% and elaboration of the branching pattern takes place until 80 % embryogenesis. At early stages the FHSN axons are within filopodial range of Gl dendrites which may use these sensory processes as guidance cues.

Synapse formation between the main FHSN axon shafts and Gl dendrites was investigated by injection of the latter with HRP. From 55 % to 65 % the process is initiated by desmosome-like filopodial contacts, with subsequent vesicle clustering and formation of a small synaptic density. Numbers of contacts did not significantly increase after about 70 %, but the number of synapses doubled between 65 % and 75 %, with each Gl process becoming postsynaptic to two FHSN synapses and the presynaptic densities lengthening to become bars. From 75 % embryogenesis to hatching there is a further small increase in synaptic bar length.

In the first instar GI3 is postsynaptic to both FHSN axons, whereas GI2 forms very few synapses with the axon of the lateral FHSN (LFHSN). This imbalance of contacts is present throughout synaptogenesis, apart from some early filopodial contacts. Gl 3 forms synapses with the lateral side of the LFHSN axon from 60 % embryogenesis but these are totally absent at hatching. The growth of glia along this side of the axon during the last 30 % of development appears to be associated with degeneration of synapses in this region.

Thus, as the dendrites of the GIs grow to form a miniature version of the adult without loss of branches, there is little evidence of an initial overproduction of FHSN-GI synapses. Similarly there is no evidence that Gl 2 forms ‘incorrect’ synapses with the axon of LFHSN. However, Gl 3 contacts are removed from an inappropriate region of a correct synaptic partner, LFHSN.
Regeneration of axolotl hindlimbs bearing surgically created discontinuities in the anterior—posterior axis
Authors: Holder Nigel , Weekes Charleston
Published: April 2021

The pattern regulation process in amphibian limbs has been examined with respect to the presence of discontinuities in the anterior–posterior (a–p) axis. Limbs bearing such discontinuities were surgically created by contralateral exchange of either dorsal or ventral half thighs and these limbs were then amputated immediately after surgery. The results demonstrate that a–p discontinuities lead to the formation of extra limb structures during distal outgrowth in contrast to the mosaic behaviour of comparable limb stumps which contain dorsal–ventral (d–v) discontinuities (Holder & Weekes, 1984). It is evident, therefore, that pattern regulation in the transverse limb axes is accomplished by basically different mechanisms.

The structure of the limbs in the present study was examined in Victoria-blue-stained wholemounts and serial sections. The results allow some discussion of the basic mechanisms for pattern regulation in the two transverse limb axes and the relationship between them.
Target cell surface glycoconjugates and neural induction in an amphibian
Authors: Gualandris Lydie , Rouge Pierre , Duprat Anne-Marie
Published: April 2021

The possible involvement of target membrane specific receptor(s) in the transmission of the neural signal leading to activation of the intracellular machinery involved in the process of neural determination, has been examined using lectin probes (Con A, succinylated-ConA, LcA, PsA and SB A). Not only Con A binding sites but many different glycoconjugated molecules (α-D-galactose, N-acetyl-D-galactosamine, α-D-fucose, N-acetyl-D-glucosamine, etc.) would have to be involved, if neural receptor(s) are invoked to explain initiation of neural induction. We show here that the close involvement of such receptor molecules in neural induction is so far hypothetical and remains to be demonstrated. Moreover we are inclined to the view of Barth and others who suggested that ionic fluxes and physicochemical and electrophysiological properties of the target membrane could play a crucial role in neural induction.
Polyneuronal innervation of an adult and embryonic lobster muscle
Authors: Govind C. K. , Stephens Philip J. , Eisen Judith S.
Published: April 2021

Motor innervation of the deep extensor muscle in the abdomen of lobsters (Homarus americanus) was compared in adults and embryos using electrophysiological techniques. There is widespread innervation of the adult muscle by the common excitor and inhibitor axons and regionally restricted or private innervation by three more excitor axons. In the embryo the earliest sign of functional innervation revealed a single inhibitory and two to three excitatory axons thus denoting simultaneous innervation by the full complement of axons. In corroboration, serial-section electron microscopy revealed several axon profiles invading the embryonic deep extensor muscles and giving rise to well-defined neuromuscular synapses with presynaptic dense bars. Innervation patterns to homologous regions of the embryonic and adult muscles were similar, consisting of a few large inhibitory synapses and many small excitatory ones. Consequently the adult pattern of polyneuronal innervation occurs simultaneously and in toto during embryonic development.