bluuebunny/crossref_metadata_2025 huggingface dataset:
The Formation of the Second Maturation Spindle in the Eggs of Succinea, Physa, and Planorbis
Authors: Raven Chr. P.
Published: April 2021

In a previous communication (Raven, Escher, Herrebout, & Leussink, 1958) the maturation of the egg was described in Agriolimax reticulatus, Limax flavus, and Limnaea stagnalis, with special regard to the formation of the second maturation spindle. In the three species the second maturation spindle arises by direct transformation from the deep centrosphere of the first maturation amphiaster. In A. reticulatus and Limax flavus this centrosphere contains a pair of centrioles which move apart to opposite poles of the developing spindle. This is symmetrical and develops an aster at both ends, arising in the cytoplasm outside the original centrosphere.
The Apparent ‘Corneal Specificity’ of Sensory Neurons
Authors: Székely George
Published: April 2021

Tactile stimulation of a forelimb grafted into the gill region in urodeles (Pleurodeles waltlii and Triturus vulgaris) yields no corneal reflex. If the foot of such a grafted limb has been cut off, stimulation of the resulting regeneration blastema evokes a corneal reflex in the same way as does stimulation of the cornea of an eye transplanted into this region. After complete regeneration of the foot the corneal reflex disappears, butJ. Embryol. exp. Morph. from a new regeneration blastema developing after a second and in some cases even after a third amputation the corneal reflex can again be elicited. These results are considered to be inconsistent with the ‘modulation theory’ of Weiss.
The Effects of Chorioallantoic Grafts on the developing Chick Embryo:II. Studies of Adult Antigens in the Duodenum and Spleen
Authors: Alten Pierson J. Van
Published: April 2021

The development of adult duodenal antigens in the embryonic duodenum was studied by means of the Ouchterlony agar diffusion technique. In 11-, 12-, and 13-day embryonic duodena there were two antigens; by the 14th day three antigens; in the 15-, 16-, and 17-day duodena four antigens; while in 18-, 19-, and 20-day duodena there were only three antigens with a fourth antigen again present in the 21-day duodenum. The disappearance of the fourth antigen found in 15-, 16-, and 17-day duodena was attributed to a change in molecular configuration of the antigen in the process of differentiation. Following grafts of adult duodenum there was an increase of three antigens observed in the host duodenum and an increase of one antigen in the host spleen. When adult spleen was grafted there was no increase in the number of antigens in the host spleen, but an increase of one antigen was observed in the duodenum. The results are discussed in the light of the organ-specific growth stimulation hypothesis, but this is rejected because it cannot account for the generalized effects observed.
The Organ Specific Action of Thyroxin in Visual Pigment Differentiation
Authors: Wilt Fred H.
Published: April 2021

The stimulation of conversion of visual pigment from porphyropsin to rhodopsin in eyes of larvae of R. catesbeiana has been effected by local implantation of thyroxin-cholesterol pellets. An eye which has received a pellet consistently shows a greater increase in the vitamin A-l content, an index of rhodopsin content, than does the contralateral sham-operated eye, or eyes from animals with pellets placed in the abdominal cavity. It is concluded that photopigment conversion is a direct response of the eye to thyroxin or its physiological derivative.
Neural induction and the structure of the target cell surface
Authors: Duprat A. M. , Gualandris L. , Rouge P.
Published: April 2021

Lectins (SBA and PSA) were used to provoke crowding and structural modifications of the presumptive ectoderm cell surface in order to investigate the role of the membrane organization of the competent target cells in neural induction. Are specific characteristics of the cell surface essential for this phenomenon to occur?

From amphibian gastrulae, it is possible to obtain neural induction in vitro by association of presumptive ectoderm (target cells) with chordamesoderm (inductor tissue) : 4 h of contact is sufficient in Pleurodeles waltl for transmission of the inductive signal.

Very quickly, the treatment of the normal ectoderm by lectins (SBA-FITC or PSA-FITC) provoked surface modifications.

Lectin-treatment (50 μg ml-1, 30 min) of presumptive ectoderm did not result in any neural induction.

Lectin-treatment (50 μg ml-1, 30 min) of presumptive ectoderm previous to its association with the natural inductor for 4 h, disturbed the phenomenon : no induction.

Similar treatment followed by association with the inductor for 24 h : induction.

Treatment of SBA or PSA with their respective hapten inhibitors prior to addition to ectodermal cells completely blocked the suppressive effects on induction.

The structural integrity of the membrane of competent target cells is necessary for neural induction to occur. The cell membrane could thus play, directly or indirectly, an active role in the specificity of this process.
Axial organization of the regenerating limb : asymmetrical behaviour following skin transplantation
Authors: Maden M. , Mustafa K.
Published: April 2021

An extensive series of skin grafting operations has been performed to investigate axial organization in the regenerating axolotl limb. Semicircular cuffs of skin from either anterior, posterior, dorsal or ventral surfaces were exchanged between right and left limbs thereby creating limbs with double anterior, double posterior, double dorsal or double ventral skin, all with normal internal tissues. Both fore and hindlimbs were used at both upper and lower limb levels. Following amputation through the grafted region the resulting regenerates were analysed both by whole-mount cartilage staining to observe the pattern of digits and by serial sectioning to observe the pattern of muscles. There were clear asymmetries in ability to produce duplications –posterior to anterior grafts resulted in a consistently high frequency of digital duplications, whereas anterior to posterior grafts produced very few. Similarly, dorsal to ventral grafts resulted in a good frequency of muscle duplications, whereas ventral to dorsal grafts did not. Such asymmetrical behaviour is not predicted by most models involving local cell:cell interactions and the significance of the results for theories of pattern formation is discussed.
The development of the peripheral trigeminal innervation in Xenopus embryos
Authors: Davies Stephen N. , Kitson David L. , Roberts Alan
Published: April 2021

The development of the ophthalmic, maxillary and mandibular nerves has been followed in Xenopus laevis embryos from the first emergence of growth cones from the trigeminal ganglia until the establishment of functional innervation of the skin or cement gland. The course of each main nerve is highly predictable and follows pre-existing openings between blocks of other tissues. The development of the mandibulary nerve was observed most easily. Like that of the other trigeminal nerves it falls into three stages: (1) A pioneer neurite emerges and a nerve forms as other, later neurites fasciculate with this. (2) On reaching the inside surface of the cement gland the neurites separate and penetrate holes in the basal lamina. (3) The neurites grow between the cells they will innervate and form free nerve endings. The scanning EM observations have been confirmed by electrical recordings from trigeminal neurones. The role of pioneer fibres and substrate guidance are discussed.
Protein synthesis during limb regeneration in the axolotl
Authors: Slack J. M. W.
Published: April 2021

A study has been made of limb regeneration in the axolotl using two-dimensional gel electrophoresis of proteins labelled with [35S]methionine.

In the early stages of regeneration seven proteins are identified which are-specific to the mesenchyme and thirteen which are specific to the epidermis. There is very little change in the gel pattern until the onset of overt cytodifferentiation upon which the muscle and cartilage become substantially different both from each other and from the blastemal mesenchyme.

The gel pattern of mesenchyme from the larval limb bud is almost identical to that of the blastemal mesenchyme, while the pattern of the limb-bud epidermis differs somewhat from the blastemal epidermis.

A careful search has been made for differences which might be associated with ‘positional information’ by comparing forelimb with hindlimb, proximal with distal and anterior with posterior. The differences which have been found are all associated with differences in visible cellular composition or in rates of differentiation, rather than with position per se. It is concluded that positional codings cannot be detected by this technique. On the basis of biological experiments, six criteria are proposed by which to assess future searches for positional codings.
Localization of H-2Kk in developing mouse palates using monoclonal antibody
Authors: Melnick Michael , Jaskoll Tina , Marazita Mary
Published: April 2021

Using monoclonal antibodies to H-2Kk antigen, we sought to develop a reproduceable method of in situ localization in embryonic tissue and to determine whether there are specific patterns of H-2 localization in time and space in the developing palatal tissues of B10.A(H-2a) embryonic mice, with and without corticosteroid pretreatment at 12 days gestation. Our procedure employs ethanol-glacial acetic acid fixation, paraplast embedding, and enzymatic predigestion with purified hyaluronidase and neuraminidase. H-2 antigens were detected in palatal mesenchyme as well as basement membranes but not in oral or nasal epithelium. The pattern of distribution in mesenchyme of untreated embryos changed with progressive shelf development: vertical →horizontal →epithelial fusion →epithelial seam degeneration →mesenchymal confluence. Although the palatal shelves of treated embryos remained vertical, corticosteroid treatment does not appear to alter the detectable spatiotemporal distribution of H-2 antigens in developing palates of embryonic B10.A mice.
Ultrastructural immunocytochemical localization of fibronectin in the early chick embryo
Authors: Sanders E. J.
Published: April 2021

Fibronectin was localized using peroxidase and biotin-avidin-ferritin techniques in developmental stages of the chick embryo from laying to primitive streak formation. The primary location of fibronectin at all stages examined was the basal lamina of the epiblast and its associated extracellular material. The remaining tissues showed little or no immunochemical deposit. At the primitive streak stage of development there were some regional differences in the density of the deposit on the basal lamina. Closely adjacent to the primitive streak, where the basal lamina is fragmentary, deposit was sparse or absent. In this, and other regions, mesoderm cell surfaces did not stain except where they closely approached the stained basal lamina or interstitial bodies. Staining was variable in the basal lamina anterior to the primitive streak, but in a number of cases particularly heavy deposit was noted overlying the crescent of late hypoblast. This area seemed to correspond with the anterior fibronectin-rich band reported by others using immunofluorescence localization.
Correlation between blastocyst oxygen consumption and trophoblast cytochrome oxidase reaction at initiation of implantation of delayed mouse blastocysts
Authors: Nilsson B. Ove , Magnusson Claes , Widéhn Sibylle , HIllensjö Torbjörn
Published: April 2021

Delayed blastocysts had an oxygen consumption of 0 ·24 nl/h, while only 4h after an oestrogen injection the respiration had increased nearly two fold, remaining at this level both 8 and 18 h after activation for implantation. The mitochondria of delayed blastocysts exhibited no positive cytochrome oxidase reaction, neither in the trophoblast nor in the embryoblasts. A few mitochondria at 8 h and most of those of blastocysts activated for 18 h were positive. It is suggested that the activation of blastocysts for implantation is initiated by a surge of substrates for glycolysis into the uterine secretion causing an increased energy production by glycolysis which in turn makes possible an increase of the cytochrome oxidase activity of the mitochondria thus getting oxidative phosphorylation into action.
Cell contact and surface coat alterations of limb-bud mesenchymal cells during differentiation
Authors: Zimmermann Bernd , Scharlach Evamaria , Kaatz Roman
Published: April 2021

Measurements of the cell perimeter, cell-cell contact number and length and of the thickness of the surface coat were performed in limb buds of mouse embryos during the process of cell condensation of the chondrogenic cell mass. This study starts with measurements of ‘non-limb’ mesenchyme.of day-9 embryos and ends with the young cartilage of day 13. It is shown that until day 12 all cells in the limb bud are interconnected by cell contacts of the gap-junction type. Contact number and contact length increase during development, but increase about twice as much between central, prechondric cells as between peripheral or distal cells. Later in development, chondroblasts lose their contacts almost completely, whereas between peripheral cells, the amount of cell contacts drops to the initial value of mesenchymal cells. The cell size decreases during chondrogenesis. A decrease in the thickness of the surface coat of the cells during the whole differentiation period is shown. It may be assumed that this ‘wave of cell contacts’ is the last step for the initiation of the chondrogenic differentiation process.
Intestinalization of the area-vitellina endoderm cultured in association with digestive-tract mesenchymes
Authors: Masui Tohru
Published: April 2021

Small-intestine-type differentiation of the area-vitellina endoderm of quail embryos, cultured in association with digestive-tract mesenchymes of chick embryos, was analysed chronologically with special attention to the appearance of a striated border and its enzymes (alkaline phosphatase and α-glucosidase). Undifferentiated endoderm of the area vitellina differentiated first into yolk-sac parenchyma expressing cysteine lyase, then gradually lost the cysteine lyase activity, and eventually manifested small intestine-type differentiation with the expression of the striated border and its enzymes.
Cell lineage of the Drosophila abdomen: the epidermis, oenocytes and ventral muscles
Authors: Lawrence Peter A. , Johnston Paul
Published: April 2021

We use a new cell marker to study cell lineage of the epidermis, oenocytes and ventral muscles in the Drosophila abdomen. We find that while the epidermal cells and the oenocytes share common precursors until late in development, the muscles derive from a separate lineage. Marked clones in the muscles, but not in the epidermis and oenocytes, can occasionally extend between neighbouring segments, supporting a previous hypothesis that mesoderm cells may not be determined as to segment.
Localization of receptors forDolichos biflorusagglutinin in early post implantation embryos in mice
Authors: Noguchi Motoko , Noguchi Takehiko , Watanabe Makoto , Muramatsu Takashi
Published: April 2021

The distribution of receptors for Dolichos biflorus agglutinin (DBA) was studied by histochemical staining of paraffin sections with HRP- or FITC-DBA in mouse embryos at stages ranging from 4·5 to 12·5 days post coitum. Preimplantation blastocysts did not express DBA receptors. The receptors first appeared in primitive endoderm cells in 5-day embryos. In 5·5- to 7·5-day embryos, both the parietal and extraembryonic visceral endoderm cells expressed the receptors. Reichert's membrane was negative for DBA receptors. The columnar cells of the embryonic visceral endoderm (EVE) strongly expressed the receptors, while the flat cells at the antimesometrial pole of the EVE were negative or patchily positive. In 8- to 9-day embryos, the receptors were expressed in the epithelium of the fore- and hindgut. In 9·5- to 12·5-day embryos, the epithelial cells of various regions of the gut expressed the receptors, although the endodermal cells of the liver and the pancreas, both derived from the foregut, did not express them. In 8- to 12·5-day embryos both the visceral and parietal yolk sac endoderm were positive in DBA receptors. The receptors were localized exclusively on the free surface facing the yolk cavity or on the luminal surface and subjacent cytoplasm. All endodermal cells which were positive are known to have absorptive activity. All other tissues in these stages were negative in DBA receptors.
Les Malformations cardiaques obtenues par l’irradiation aux rayons X du cœur de l’embryon de Poulet
Authors: Douarin par Georges Le
Published: April 2021

Dans un travail antérieur (Le Douarin & Le Douarin, 1959), nous avons étudié les répercussions de l’irradiation du cœur de l’embryon de Poulet sur l’évolution des arcs aortiques. Par ailleurs, les rayons X exercent sur le cœur lui-même une action tératogène.
Étude immuno-électrophorétique de l’apparition progressive de quelques constituants caractéristiques de l’adulte dans le foie embryonnaire du Poulet
Authors: Croisille par Yvon
Published: April 2021

Dans le cadre des recherches consacrées à l’étude de l’apparition des constituants spécifiques de l’adulte au cours du développement embryonnaire, les méthodes immunochimiques ont trouvé un emploi toujours grandissant pendant les 15 dernières années. Le nombre de travaux, dont les principaux ont été récemment exposés (Croisille, 1958), permet de juger combien l’emploi de ces méthodes s’est révélé fructueux dans ce domaine. La plupart des auteurs ont utilisé les méthodes immunochimiques classiques: réaction à l’interface, épuisement des anti-sérums, techniques de précipitation en milieu gélifié et réaction de déviation du complément. Mais ces méthodes ne permettent souvent pas, malgré leur spécificité et leur sensibilité, de dénombrer et d’identifier correctement tous les constituants, surtout s’il s’agit de l’analyse d’un mélange complexe. Aussi y a-t-il des résultats contradictoires dus pour la plupart à des difficultés techniques ou d’interprétation, notamment en ce qui concerne l’identification certaine des constituants embryonnaires et adultes.
Acetylcholinesterase Activity in the Regenerating Forelimb of the Adult Newt, Triturus
Authors: Singer Marcus , Davis Marjorie H. , Arkowitz Eleanor S.
Published: April 2021

Acetylcholinesterase activity in the regenerating forelimb of the adult newt, Triturus, was measured during various stages of development with the Hestrin colorimetric and the Warburg manometric method. The activity of the enzyme is low during the early formative phases of development. It then increases, the greatest rate of change being in the stage just preceding that of differentiation of muscle. At the time of muscle differentiation the activity levels off and then returns to normal as regeneration draws to a close. The variation in cholinesterase activity correlates well with the cycle of acetylcholine production during regeneration. The acetylcholine content is very high during early regeneration but then drops to a near normal level as esterase activity rises. Since the nerve is required for the regeneration process and since the nerve effect is most dramatic when the acetylcholine content is very high, the possibility that acetylcholine may be the agent of the nerve influence is assessed. The enzymatic activity during regeneration is compared to that observed in embryonic development.
Generation of spatially periodic patterns by a mechanical instability: a mechanical alternative to the Turing model
Authors: Harris Albert K. , Stopak David , Warner Patricia
Published: April 2021

We have studied the generation of spatial patterns created by mechanical (rather than chemical) instabilities. When dissociated fibroblasts are suspended in a gel of reprecipitated collagen, and the contraction of the gel as a whole is physically restrained by attachment of its margin to a glass fibre meshwork, then the effect of the fibroblasts’ traction is to break up the cell-matrix mixture into a series of clumps or aggregations of cells and compressed matrix. These aggregations are interconnected by linear tracts of collagen fibres aligned under the tensile stress exerted by fibroblast traction. The patterns generated by this mechanical instability vary depending upon cell population density and other factors. Over a certain range of cell concentrations, this mechanical instability yields geometric patterns which resemble but are usually much less regular than the patterns which develop normally in the dermis of developing bird skin. We propose that an equivalent mechanical instability, occurring during the embryonic development of this skin, could be the cause not only of the clumping of dermal fibroblasts to form the feather papillae, but also of the alignment of collagen fibres into the characteristic polygonal network of fibre bundles -which interconnect these papillae and which presage the subsequent pattern of the dermal muscles serving to control feather movements.

More generally, we suggest that this type of mechanical instability can serve the morphogenetic functions for which Turing’s chemical instability and other reaction-diffusion systems have been proposed. Mechanical instabilities can create physical structures directly, in one step, in contrast to the two or more steps which would be required if positional information first had to be specified by chemical gradients and then only secondarily implemented in physical form. In addition, physical forces can act more quickly and at much longer range than can diffusing chemicals and can generate a greater range of possible geometries than is possible using gradients of scalar properties. In cases (such as chondrogenesis) where cell differentiation is influenced by the local population density of cells and extracellular matrix, the physical patterns of force and distortion within this extracellular matrix should even be able to accomplish the spatial control of differentiation, usually attributed to diffusible ‘morphogens’.
Retinoids and pattern formation in a hydroid
Authors: Müller W. A.
Published: April 2021

The retinoids (retinol, retinal, retinoic acid) cause alterations in the pattern of limb elements in vertebrates (Summerbell & Harvey, 1983). As shown here, retinoids also influence pattern specification in hydroid polyps (Hydractinia echinata) in a way suggesting interference with the generation and transmission of signals responsible for the dimension and spacing of structures. A pulse-type application of low doses (e.g. retinoic acid 10−6 to 10−10 M, 4 h) causes metamorphosing primary polyps to develop more tentacles but fewer stolons per unit circumference, to shorten the length of the hydranth while the stolon elongates, and to bud secondary hydranths at high frequency 2–3 days after treatment (Fig. 3). Dose-response curves display optimum peaks. It is argued that the increase in budding rate is due to a reduction of the range of spacing signals emitted by the primary hydranth. In regenerating hydranths, low doses (10−10 to 10−9M) improve the rate of head formation, whilst medium doses (10−8 to 10−6M) result in more tentacles being regenerated. However, prolonged treatment with high doses (10−6 to 10−5 M) causes the animals to reduce all head structures and to transform eventually into stolons, in contravention of the rule of distal transformation that they normally obey (Fig. 8). The effects of the retinoids are counteracted by a putative morphogen, the endogenous inhibitor isolated from Hydra by Berking (1977). The Hydra-derived ‘head-activator’ displayed no stimulating effect on the number of tentacles and buds formed.
Effect of microtubule inhibitors on the expansion of hypoblast and margin of overgrowth of chick blastoderms
Authors: Mareel Marc , Bellairs Ruth , Bruyne Georges De , Van Peteghem Marie Christine
Published: April 2021

The effect of the microtubule inhibitors, Nocodazole and taxol, was studied on the expansion of fragments of chick hypoblast (8 to 10 h incubation) and of margin of overgrowth (24 h incubation) cultured on artificial substrata and on the epiboly in intact blastoderms (24 h incubation).

Immunocytochemical staining of these cells with antiserum against tubulin showed that 1 μg Nocodazole/ml caused disassembly of microtubules, and that 1μg taxol/ml led to increased but unordered assembly. The solvent dimethylsulphoxide had no effect. At these concentrations both microtubule inhibitors led to rapid arrest of the expansion of fragments of hypoblast and of margin of overgrowth in culture, and of the epiboly in intact blastoderms. Time-lapse films showed that inhibition of expansion in both situations was reversible within 2 h after removal of the drugs. Phase-contrast microscopy showed remarkably little difference between the morphology of treated as compared to untreated cultures. Measurements of the height of the cells on sectioned fragments of margin of overgrowth showed no differences between treated and untreated cultures. These results suggest that the cytoplasmic microtubule complex is important both for epiboly and for the migration of hypoblast cells in the chick blastoderm. The mechanisms of this microtubule-related migration are not understood.
Histological studies of the effects of wounding vibrissa follicles in the hooded rat
Authors: Jahoda Colin A. B. , Oliver Roy F.
Published: April 2021

The effects of wounding the lower region of rat vibrissa follicles with a sharp tungsten needle were examined histologically, both shortly after injury and up to one year postoperatively. Following cell damage in the dermal papilla component hair growth ceased, and resumption of fibre production was always preceded by dermal papilla reformation. This papilla healing and regeneration was not associated with the production of scar tissue. In follicles undergoing no cell displacement during wounding (an effect associated with the growth of longer than normal hairs) dermal papillae were reformed from the residual papilla cell population, with recruitment of cells from surrounding mesenchyme. Follicles plucked just prior to wounding revealed little or no original epidermal matrix three days later, confirming that dermal components were primarily affected. Papilla cell counts performed on follicles which had consistently produced longer hairs gave no indication of increased papilla cell numbers. Follicles which underwent displacement of cellular material and displayed distortion of normal follicle morphology shortly after wounding (effects associated with the production of shorter than normal hairs) also revealed abnormalities at long-term biopsy. Moreover these follicles often had a history of altered fibre characteristics from one postoperative generation to the next. It is concluded that gross morphological disruption of the normal cellular relationships in the lower follicle results in a series of reorganizational difficulties with each recurring phase of the hair cycle.
Gibberellins and gene control in cereal aleurone cells
Authors: Baulcombe David , Lazarus Colin , Martienssen Robert
Published: April 2021

The production of hydrolytic enzymes in the germinating cereal grain is considered as a model for plant cell differentiation. Recent literature is reviewed which suggests that gibberellins are involved in this process, but in a less straightforward manner than considered previously. It seems likely that only a subfraction of gibberellin is active and that production of this gibberellin is actually in the hydrolase-producing cells. These include aleurone cells and also the scutellar epithelial cells.

At the intracellular level the action of gibberellin results in the accumulation of α-amylase mRNA and also mRNA for other unidentified proteins, referred to as gibb-ons. The α-amylase mRNAs are transcribed from two distinct gene families. The pattern of expression of α-amylase and gibb-on mRNAs is consistent with a common gibberellin-stimulated mechanism of control of for all of these genes. However it seems likely from experiments with ABA and from observations on gibb-on gene expression in non-aleurone cells that gibberellin does not have a role determining the specificity of gene expression, but rather acts as a general stimulator of mRNA accumulation.
Analysis of transcriptional regulation of the s38 chorion gene of Drosophila by P element-mediated transformation
Authors: Kalfayan Laura , Wakimoto Barbara , Spradling Allan
Published: April 2021

Transcriptional regulation of the s38 chorion gene was studied using P element-mediated germline transformation. A 5–27 kb DNA fragment containing the s38 gene and 5′- and 3′-flanking sequences, was tested for its ability to be transcribed with correct developmental specificity. Five single-insert transformed lines were generated by microinjection of this DNA fragment cloned into a marked P element transformation vector. In each line, the transformed gene was transcribed according to the precise developmental pattern followed by the native s38 gene. The 1– 3 kb at the 5′ end of this tested fragment was fused to the E. coli lac z gene. This fragment was also capable of initiating transcription of E. coli lac Z RNA with the developmental profile of the native s38 gene. In vitro deletion studies are underway to determine which sequences in the 1–3 kb fragment are necessary for regulating the developmental expression of the gene.
Computer modelling of cell division during development using a topological approach
Authors: Ransom Robert , Matela Raymond J.
Published: April 2021

Development in multicellular animals consists of a constant progression of cell division, differentiation and morphogenesis. Our understanding of the relationship between division and the acquisition of shape and form is not well understood, and this paper describes a computer representation of cell division processes with possible applications to the modelling of developmental events. This representation is not itself a model in the true sense, but is a scaffolding onto which a set of model assumptions and parameters can be built. We discuss one such set of assumptions, used to model cell sorting, describe the extension of the framework to represent sheets of cells in three dimensions, and make some observations on the incorporation of mechanical forces into the representation.
A mathematically modelled cytogel cortex exhibits periodic Ca++-modulated contraction cycles seen in Physarum shuttle streaming
Authors: Odell Garrett M.
Published: April 2021

If each of many cells of an embryo (or different zones in a single cell) possess identical active cytogel machinery, having the ‘right’ mechanochemical response properties, then the collective interaction among those identical participants leads automatically to the globally coherent tissue deformations seen in embryogenesis, and to shuttle streaming in the plasmodial slime mould Physarum polycephalum.

Biologically plausible, and experimentally verifiable hypotheses are proposed concerning how the tension generated by a strand of cytogel is determined by the deformation it suffers and by the concentration of a contraction trigger chemical, Ca2+, whose kinetics involve coupling to mechanical strain. The consequences of these hypotheses, deduced by solving the appropriate differential equation systems numerically, and displayed in computer-animated films, closely imitate diverse tissue deformation events seen in developing embryos.

The same hypotheses on cytogel behaviour are used to model a thick-walled Physarum vein segment, and two such segments are set up to be able to pump endoplasm back and forth between them. Under certain conditions, this model exhibits spontaneous rhythmic mechanochemical oscillations, many features of which correlate well with shuttle streaming in Physarum.

Small gradual variations of parameters, presumably under genetic control, are shown to cause abrupt and biologically interesting bifurcations of the qualitative behaviour of the model.
Chromosomes and sex differentiation in eutherians
Authors: Müller Ulrich
Published: April 2021

In order to learn more about the role of sex chromosome-dependent gene products in gonadogenesis, changes in protein patterns were studied during gonadal development. Two-dimensional gel electrophoresis analysis revealed specific proteins in both sexes at all developmental stages. Evidently the gonads are not indifferent by biochemical criteria at any developmental stage and express several specific genes from the onset of differentiation. To correlate these polypeptides with the sex chromosomes, proteins were investigated in human-rodent somatic cell hybrids and in genetically identical cell clones differing in one sex chromosome only. On two-dimensional gels one Y-dependent polypeptide was found with similar characteristics (relative molecular mass and isoelectric point) as an early testicular polypeptide. Its identity, however, remains to be proven.
Chromosome order – possible implications for development
Authors: Heslop-Harrison J. S. , Bennett M. D.
Published: April 2021

Chromosomes are arranged in ordered haploid sets around the centre of the metaphase plate at mitosis in several grass species and hybrids. Each chromosome is in a fixed mean position relative to other, heterologous chromosomes, this order can be predicted using Bennett’s model, and is clearly demonstrated from reconstructions of electron micrographs of serial sections (see Heslop-Harrison & Bennett, 1983a,b,c).

The nucleus contains spatial domains of genes with similar functions. Chromosomes with major effects on nuclear behaviour - division or meiotic pairing - may be at special positions in the order. Changing spatial relationships of chromosomes with respect both to each other and the nuclear envelope (during the cell cycle and during development) may affect cell differentiation and gene activity.

Chromosome order may have implications for the control of development within the nucleus and the organism. Order may constrain karyotype and hence species evolution.
Accumulation and localization of troponin-T in developing hearts of Ambystoma mexicanum
Authors: Fuldner Rebecca A. , Lim Soo-Siang , Greaser Marion L. , Lemanski Larry F.
Published: April 2021

Troponin-T (Tn-T) expression in developing hearts of axolotls, Ambystoma mexicanum, was studied with the use of polyclonal and monoclonal antibodies and SDS-polyacrylamide gel electrophoresis. In precontractile hearts (stage 32β3), Tn-T was present in addition to myosin, actin and tropomyosin as evidenced by the presence of the protein bands in SDS-gels and by indirect immunofluorescence. Tn-T was localized in amorphous collections at the peripheries of these precontractile cells. Hearts of normal and cardiac lethal mutant siblings were also analysed for Tn-T expression. No detectable differences in the quantity of protein present was observed by gel electrophoresis or by indirect immuno-fluorescence. The most striking difference concerned the localization of the protein. In normal hearts, Tn- T was primarily localized in the I-bands of organized myofibrils; however, in mutant cells the Tn-T was localized in amorphous collections at the cell peripheries suggesting a reduction of myofibrillar organization in these cells. No differences were observed in the contractile protein composition between normal and mutant em-bryonic hearts by gel electrophoresis experiments.
Differentiation markers in the Drosophila ovary
Authors: White Robert A. H. , Perrimon Norbert , Gehring Walter J.
Published: April 2021

A library of monoclonal antibodies, raised against imaginal discs of Drosophila melano-gaster, was screened for binding to differentiation antigens in the adult ovary by immuno-fluorescence. Several lectins were similarly assayed. Two antibodies, DOV 1 and DOV 2, and wheat germ agglutinin exhibited binding which was restricted to particular stages of ovarian cell differentiation. DOV 2 also showed a marked preferential binding to the cell surface of germ line cells in the ovary. A differentiation of the portion of the tunica propria covering the anterior part of the germarium was revealed by the monoclonal antibody DOV 3. Another monoclonal antibody, DOV 4, identified a molecular specialization of the chorion at the tip of the micropyle. These markers should provide tools for the molecular analysis of oogenesis.
The acellular stroma of the chick cornea inhibits melanogenesis of the neural-crest-derived cells that colonize it.
Authors: Campbell Steven , Bard Jonathan B. L.
Published: April 2021

Neural crest (NC) cells from the periorbital mesenchyme (POM) invade the acellular stroma of the chick cornea at stage 27 of development (∼6 days). The invading cells become collagen-producing fibroblasts while the NC cells remaining in the POM differentiate into a wide range of cell types, the most easily recognizable of which is the pigment-producing melanocyte. In this paper, we report observations on the differentiation in vitro of cells within and migrating from explants of corneal stroma and compare their behaviour with that of cells within and migrating from explants of the POM. In ∼70 % of cases, POM explants produced black, eumelanin pigmentation within 2–3 days in culture and gave rise to a mixed outgrowth of fibroblasts and melanoblasts that produced brown pigment. In no case, however, did a corneal explant produce black pigment (so demonstrating that any POM contamination was negligible). However, in 28 % of cultures from stage-27 and -28 corneas, some of the cells in the outgrowth contained brown pigment indistinguishable from that produced by the POM control, although the majority of the cells in each case were fibroblasts. Two lines of investigation demonstrated that this pigment was melanin: first, transmission electron microscopy showed that the pigment organelles were incompletely melanized, granular melanosomes; second, tests designed to demonstrate the presence of lipofuscin, an alternative pigment, proved negative. Migrating cells from older corneas, in contrast, showed no evidence of even the first stages of melanogenesis. These results show, first, that some of the NC cells that invade the cornea are at least bipotent and hence representative of the POM population rather than being a unique subgroup and, second, that the acellular stroma of the cornea determines the state of differentiation of the NC cells that colonize it. The results thus provide an unequivocal demonstration that extracellular matrix can induce postmigratory NC cells to differentiate into fibroblasts.
Influence of cyclic AMP and hydrolysis products on cell type regulation in Dictyostelium discoideum
Authors: Weijer Cornelis J. , Durston Antony J.
Published: April 2021

We describe the effect of cyclic AMP on regulation of the proportion of prespore and prestalk cells in Dictyostelium discoideum. Prespore and prestalk cells from slugs were enriched on Percoll density gradients and allowed to regulate in suspension culture under 100 % oxygen. The transition of prespore to prestalk cells is blocked by cAMP, while cAMP phosphodiesterase and caffeine cause a decrease in the number of prespore cells. This suggests that extracellular cAMP plays a role in cell type proportioning by inhibiting the conversion of prespore to prestalk cells.

Low concentrations of cAMP prevent the conversion of prestalk to prespore cells; the same effect is seen with hydrolysis products of cAMP, 5 AMP, adenosine and also adenine. We suggest that, when low concentrations of cAMP are added to regulating cells, the cAMP itself is quickly broken down and the breakdown products thereafter inhibit the prestalk-to-prespore conversion.

The relevance of these findings is discussed in the context of an non-positional double-negative feedback model for cell type homeostasis.
Transferrin in foetal and adult mouse tissues: synthesis, storage and secretion
Authors: Meek Jennifer , Adamson Eileen D.
Published: April 2021

Transferrin is an important growth-promoting serum glycoprotein synthesized chiefly in the liver in adults. The transferrin found in the mouse foetus is thought to be wholly a product of the foetus itself and its synthesis starts at least as early as the 7th day of gestation. The major sites of synthesis in mouse foetuses are the visceral yolk sac (VYS) and liver (Adamson, 1982). We now report that other murine foetal tissues synthesize readily detectable amounts, namely lung, spleen, spinal cord and rib cage. Very low levels are also synthesized by the brain, muscle and pancreas. We can detect no synthesis of transferrin in late foetal thymus, heart or skin although mid-gestation foetal skin may make a very small amount. No synthesis of transferrin can be detected in adult brain, lung and spleen, but approximately equal rates of synthesis are detected in adult liver and adult ear pinna.

Transferrin is accumulated by foetal and adult tissues in widely varying amounts and these have been measured by enzyme-linked immunosorbent assays of extracts. In addition to VYS and liver, high levels of transferrin are found in foetal skin, lung and rib cage with lower amounts in spinal cord, spleen and muscle tissues. Tissues of the 15th day foetus accumulate the highest concentrations of transferrin. A role for the mediation of transferrin in the stimulation of growth and differentiation by interacting tissues is discussed.
Acetylcholinesterase (AChE) and pseudocholinesterase (BuChE) activity distribution pattern in early developing chick limbs
Authors: Falugi Carla , Raineri Margherita
Published: April 2021

The distribution of acetylcholinesterase (AChE) and pseudocholinesterase (BuChE) activities was studied by histochemical, quantitative and electrophoretical methods during the early development of chick limbs, from stage 16 to stage 32 H.H. (Hamburger & Hamilton, 1951).

By quantitative methods, true AChE activity was found, and increased about threefold during the developmental period, together with a smaller amount of BuChE which increased more rapidly in comparison with the AChE activity from stage 25 to 32 H.H.

Cholinesterase activity was histochemically localized mainly in interacting tissues, such as the ectoderm (including the apical ectodermal ridge) and the underlying mesenchyme. True AChE was histochemically localized around the nuclei and on the plasma membrane of ectodermal (including AER) and mesenchymal cells, and at the plasma membrane of mesenchymal cell processes reaching the basal lamina between the ectoderm and the mesenchyme. AChE together with BuChE activity was found in the basal lamina between the ectoderm and the mesenchyme, in underlying mesenchymal cells and in deeper mesenchymal cells, especially during their transformation into unexpressed chondrocytes.

During limb morphogenesis, the cellular and regional localization of the enzyme activities showed variations depending on the stage of development and on the occurrence of interactions.

The possibility of morphogenetic functions of the enzyme is discussed.
Cytoskeletal discontinuities in the cell body cortex initiate basal body assembly and oral development in the ciliate Stentor
Authors: De Terra Noël
Published: April 2021

My previous work has shown that disconnecting the oral apparatus of Stentor into two parts induces mass assembly of basal bodies on the ventral cell surface and thus initiates oral development. This operation severs the extensive microtubule tracts joining the oral membranelles at their bases. To determine whether basal body assembly and oral development are also induced by permanently disconnecting the longitudinal microtubule fibre tracts (mt fibre tracts) of the cell body cortex, I interposed a ring of inverted (heteropolar) cortex between the anterior and posterior halves of interphase stentors. When successful, this operation made it impossible for these fibre tracts to rejoin at the heteropolar boundaries and always induced basal body assembly and oral development in the graft complex. By contrast, tripartite homopolar graft complexes rarely initiated oral development; when they did, it was apparently in response to the presence of disproportionately small oral structures, which is the normal stimulus for oral development in Stentor. The mt fibre tracts of tripartite homopolar grafts also eventually became continuous.

These results support the hypothesis that permanent, extensive discontinuities anywhere within the cortical cytoskeleton can trigger basal body assembly and oral development. Since the onset of these processes is known to initiate cell division in Stentor, the results also suggest that development of discontinuities within the cortical cytoskeleton during interphase growth may be the endogenous stimulus initiating cell division in Stentor.
Gene expression at the pink-eyed dilution (p) locus in the mouse is confirmed to be pigment cell autonomous using recombinant embryonic skin grafts
Authors: Stephenson Dennis A. , Hornby Janet E.
Published: April 2021

Sash (Wsh), a viable and fully fertile allele of the dominant spotting (W) locus (Lyon & Glenister, 1982) has been used in a modified test system to investigate the site of gene expression at the pinkeyed dilution (p) locus. Reciprocal recombinant epidermal//dermal skin grafts were constructed from 13-day embryonic skin of p and Wsh homozygotes. Thus in the reciprocal experiments pinkeyed dilution melanocytes were exposed to any environmental influence from the wild-type allele of the p locus in either the epidermis (when WshWsh) or the dermis (when WshWsh). The hair pigmentation of the grafts recovered after three weeks beneath the testicular tunica of adult male mice was always typical of the p phenotype showing that p is melanocyte autonomous. This result was supported by experiments using a modification of Mayer’s (1965) neural crest grafting technique and the construction of 14-day recombinant skin grafts.

Sash (WshWsh) epidermis can support melanocyte differentiation and pigment production but lacks functional melanocytes. The advantages of Wsh in experimental systems for testing the site of pigment gene expression have been demonstrated.

Control experiments confirmed the dermal influence of agouti (A) over non-agouti (a) epidermis but non-agouti dermis did not overrule agouti pink-eyed dilution (AA pp) epidermis suggesting an epistatic effect of p in the melanocyte.
Use of a monoclonal antibody recognizing a cell surface determinant to distinguish prestalk and prespore cells of Dictyostelium discoideum slugs
Authors: Krefft Marianne , Voet Ludwig , Gregg james h. , Williams keith l.
Published: April 2021

Double labelling experiments on Dictyostelium discoideum cells at different developmental stages were carried out using monoclonal antibodies MUD1 (prespore specific), MUD9 (strong label on prestalk and anterior-like cells) and a fluorescence-activated cell sorter. The monoclonal antibody MUD9, which recognizes the surface of prestalk and anterior-like cells strongly and prespore cells weakly, is also present on the surface of vegetative amoebae and on mature stalk cells but not on the spore surface. Sharing of an antigenic determinant between vegetative, prestalk and anterior-like cells is consistent with these cells being ‘less differentiated’ than prespore cells.
Development of the lateral line system in Xenopus laevis : IV. Pattern formation in the supraorbital system
Authors: Winklbauer Rudolf , Hausen Peter
Published: April 2021

The periodic pattern of the supraorbital lateral line organs forms in the epidermis of Xenopus by the subdivision of a streak-like primordium into a linear series of small cell groups. In normal development, each such organ initially contains about 8 cells (Winklbauer & Hausen, 1983a,b). To see whether this initial organ size depends on the size of the streak-like primordium at the time of organ segregation, primordium size was reduced experimentally before the onset of pattern formation. In such small primordia, the size of the primary organs formed is not adjusted so as to allow the formation of a normal number of organs. Instead, the initial organ size is kept approximately normal, and the number of organs is correspondingly reduced, i.e. the pattern forming mechanism is not capable of ‘size regulation’.