bluuebunny/crossref_metadata_2025 huggingface dataset:
Distal transformation in regenerating double anterior axolotl limbs
Authors: Stocum David L.
Published: April 2021

Previous investigations have shown that axolotl double anterior thighs regenerate only a tapered extension of the femur after simple amputation, but undergo intercalary regeneration of the femur and a symmetrical tibia when a normal wrist blastema is grafted to the thigh. There are two possibilities to account for these results: (1) distal transformation in both terminal and intercalary regeneration depends upon special properties of posterior cells (such as polarizing ability) that are lacking in the anterior half of the limb, but which would be provided by the posterior half of a normal wrist blastema graft, or (2) the pattern of cellular interactions required for distal transformation during terminal regeneration is different from that required for distal transformation during intercalary regeneration.

These alternatives were tested by grafting axolotl double anterior wrist blastemas to double anterior thighs. The host thighs regenerated a femur and symmetrical tibia that structurally were the same as the bones intercalated after grafting a normal wrist blastema to a double anterior thigh. In all cases, the graft developed as a symmetrical hand comprising one to three carpals and one to two digits. These results rule out the necessity of any special properties of posterior cells for distal transformation or polarization of the anterior-posterior axis and suggest instead that distal transformation during intercalary regeneration involves a different pattern of cellular interactions than in terminal regeneration.
Analysis ofvestigialw(vgw): a mutation causing homoeosis of haltere to wing and posterior wing duplications inDrosophila melanogaster
Authors: Bownes Mary , Roberts Sarah
Published: April 2021

vg w is a homozygous lethal mutation killing embryos prior to formation of the syncitial blastoderm. In heterozygous condition it causes duplications of the posterior wing, ranging from very small duplications of the axillary cord and alar lobe to large duplications including much of the wing blade and the posterior row of bristles. No anterior margin structures are ever observed. The thorax is sometimes slightly abnormal, but rarely shows large duplications. The size of the wing is related to the number of pattern elements deleted or duplicated.

Heterozygous vgw flies also show homoeosis of the haltere to wing. This occurs in the capitellum, where wing blade is observed, but no wing margin structures are found. As with the bithorax (bx) mutation which transforms anterior haltere to anterior wing this aspect of the phenotype is repressed by the Contrabithorax (Cbx) mutation. The transformed haltere discs show more growth than wild-type haltere discs.

Flies heterozygous for vgw also show a high frequency of pupal lethality, those forming pharate adults generally show the most extreme vgw phenotype.

No cell death has been observed in the Imaginal discs of third instar larvae, suggesting that if the wing defects result from cell death this must occur early in development. The homoeosis in the haltere discs and duplications of the wing disc are reflected by the altered morphology and growth of these discs.

There are some minor differences in the expressivity of the phenotype when flies are reared at different temperatures. Chromosome substitutions suggested that all aspects of the phenotype related to the vgw mutation and that other mutations had not occurred in the stock. Cytological analysis indicated that vgw is a deletion or inversion on the right arm of chromosome 2 from 47F/48A to 49C.

Complementation studies with various mutants thought to be located within the deletion, or inversion and which affect wing morphology have been undertaken.

Cbx causes transformations of wing to haltere; this occurs in the posterior compartment far more frequently than in the anterior compartment. Cbx; vgw flies have wings where one of the duplicates is no longer present, presumably transformed to haltere, though this is difficult to identify. One copy of the axillary cord, alar lobe etc, the structures commonly duplicated in vgw, are present, but they are the anterior duplicate rather than the original posterior copy of these structures. Thus Cbx acts upon genuine posterior structures but not those posterior structures in vgw which form in anterior wing locations, suggesting that although these structures differentiate into posterior wing, to the Cbx gene product the cells are still ‘anterior’.
Staging the metamorphosis of Drosophila melanogaster
Authors: Bainbridge S. Paul , Bownes Mary
Published: April 2021

A sequence of 51 visible changes is described during the course of metamorphosis in Drosophila melanogaster, and a series of 24 convenient stages is defined for use in the experimental analysis and exploitation of this part of the insect life cycle. The duration of each stage is estimated and times are suggested for batch collections of symphasic animals.
The regeneration of supernumerary cockroach antennae
Authors: French Vernon , Domican John
Published: April 2021

Grafting experiments performed on the basal scape segment of the antenna of Blabera craniifer give very similar results to those of corresponding grafts done on the legs of cockroaches and many other insects. If the antenna is amputated and replaced on the stump, it heals, while a 180°-rotated graft de-rotates and sometimes forms a symmetrical partial supernumerary. If the antenna is grafted on to the contralateral stump, one transverse axis of the graft is reversed relative to the host, and this results in the regeneration of a supernumerary antenna with host orientation from each of the two points of maximum incongruity between graft and host. Sometimes one double supernumerary forms midway between these points, and its orientation suggests that it results from a secondary fusion of the two supernumeraries.

The similarity of these results to those of leg grafts suggests that legs and antennae have a similar general organisation of positional information and similar rules for cellular behaviour. Further, the two appendages may have the same set of positional values but have evolved different ways of interpreting it. Preliminary attempts to test this idea directly (by grafting between leg and antenna) were rather unsuccessful since only a few control grafts healed (poorly) and all rotated and contralateral grafts were eliminated.
Effect of Li+ on preimplantation mouse embryos
Authors: Izquierdo L. , Becker M. I.
Published: April 2021

Two-cell mouse embryos were cultured in vitro for different periods in a medium in which NaCl was partially replaced by LiCl at concentrations ranging from 1 to 30 mM. The relative cell number diminished according to increasing LiCl concentrations but the onset of blastulation was not affected, thus resulting in blastulae with fewer cells than normal and with a reduced or absent inner cell mass. Results are discussed in terms of the possible mechanisms involved and are related with the vegetalization induced by Li+ on early embryos of echinoderms and amphibia.
Morphology of programmed cell death in the ventral nerve cord ofCaenorhabditis eleganslarvae
Authors: Robertson Alison M. G. , Thomson J. N.
Published: April 2021

In the nematode C. elegans, cells undergoing programmed death in the developing ventral nerve cord were identified by Nomarski optics and prepared for ultrastructural study at various times after their birth in mitosis.

The sequence of changes observed suggests that the hypodermis recognizes the dying cell before completion of telophase. The dying cell is engulfed and digestion then occurs until all that remains within the hypodermal cytoplasm is a collection of membranous whorls interspersed with condensed chromatin-like remnants. The process shares several features with apoptosis, the mode of programmed cell death observed in vertebrates and insects. The selection of cells for programmed death appears not to involve competition for peripheral targets.
Pioneer growth cones in virgin mesenchyme: an electron-microscope study in the developing chick wing
Authors: AL-Ghaith L. K. , Lewis J. H.
Published: April 2021

Axons grow out along predictable routes to specific destinations. An EM study of the early development of one of the main chick wing nerves -the interosseous nerve -helps to show how they do it. The growing tip of the nerve appears frayed, consisting of nerve fibres occurring singly or in small bundles, taking slightly divergent paths. Most of these pioneer nerve fibres have the characteristic appearance of growth cones. They are not seen to advance along fibrils of the intercellular matrix (as one might expect from some tissue culture experiments), but instead are generally in close contact over their whole surface either with mesenchyme cells or with other nerve fibres. The same is true of the axons at more proximal levels of the developing nerve: they too are never naked, but always in contact either with other axons or with mesenchyme cells. Later nerve fibres follow the pioneers: their growth cones travel out in contact with the pre-existing axons, within the primitive perineurium formed by the enveloping mesenchyme cells, and most often close to the periphery of the fascicle.
Regulation of meiosis in the foetal mouse gonad
Authors: Evans Clive W. , Robb Diana I. , Tuckett Fiona , Challoner Susan
Published: April 2021

In vitro culture of male and female gonads was found to have significant effects on gonadal structure and development. Culture resulted in a reduction of testicular cord diameter and a reduction in the number of Sertoli cells lining each cord in cross section. In the female, culture increased the percentage of pyknotic oocytes and fewer germ cells per unit of ovary volume reached diplotene. Mixed sex co-culture using different culture methods showed that day 14 p.c. testes inhibited meiosis in day 14 p.c. ovaries when the cultures were continued until the equivalent of day 21 p.c. Day 15 p.c. and mixed age co-cultures of mixed sex provided more equivocal data since meiosis was inhibited in some preparations but not in others. The possibility is suggested that prophase I may proceed irrevocably to diplotene after about day 15 p.c. and thus the inhibitory effects of foetal testes may be a function of female gonadal age. No evidence was found to support the hypothesis that mixed sex co-culture may stimulate meiosis precociously in foetal testes.
Fine structural analysis of limb development in the wingless mutant chick embryo
Authors: Sawyer Linwood M.
Published: April 2021

The fine structure of the normal and wingless chick limb bud was examined with scanning and transmission electron microscopy. The apical ectodermal ridge (AER) of the normal limb bud was composed of pseudostratined columnar cells. These cells contained gap junctions, electron-dense vesicles, and numerous microtubules and microfilaments that were oriented perpendicularly to the basal lamina. Microfilaments were also found coursing transversely in the basal cell cytoplasm.

The ectoderm of the wingless mutant limb bud lacked a well-developed AER and resembled the dorsal and ventral ectoderm of the normal embryo. Gap junctions and electron-dense vesicles found in the AER of the normal limb bud were not apparent in the mutant ectoderm.

The normal-limb bud mesoderm is composed of stellate cells that are oriented at right angles to the overlying ectoderm. There is a prominent subectodermal space that is traversed by numerous mesenchymal cell filopodia. The mesodermal cells of the mutant limb bud are compact and round and have short stubby filopodia, while the cells of the adjacent flank mesoderm are stellate. The subectodermal space is absent and the mesodermal cells are in intimate association with the basal lamina of the overlying ectoderm.

Ruthenium red was employed as an extracellular marker for glycosaminoglycans. No differences were found in the distribution of these substances in normal and mutant limb buds. In several cases the basal lamina of the mutant limb bud ectoderm was discontinuous and the lamina lucida was not apparent. The results indicate that the mutation has an effect on the limb buds’ ability to maintain a well-developed AER and basal lamina. It also suggests that the wingless gene affects the shape and possibly the mobility of the limb-bud mesoderm cells.
The phenotypic expression of a t
6
/t
6
/t
6 genotype
Authors: McGrath James , Hillman Nina
Published: April 2021

In vivo, embryos which are homozygous for the t6 mutation die during egg cylinder development (gestation days 5·5-6·5). In vitro, these mutant embryos can be distinguished from their wild-type littermates by their developmental arrest and by the failure of their tropho-blast cells to transform to giant cells. We have investigated the nature of this lethality by constructing triploid embryos with varying combinations of the t6 mutant chromosome* The phenotypes of outgrowths from these triploid embryos were examined and compared with the phenotypes of outgrowths from 4-/ +, + /t6, and tft6 embryos. The data show 1) that + / t6/ t6 embryos are phenotypically wild-type, while t6/ t6/t6 embryos are phenotypically mutant and 2) that t6/t6/t6 and t6/ t6 embryos are developmentally arrested at the same stage of outgrowth.
Surface changes in the embryonic interdigital epithelium during the formation of the free digits: a comparative study in the chick and duck foot
Authors: Hurle J. M. , Colvee E.
Published: April 2021

The formation of the free digits of the chick is accompanied by conspicuous surface changes of the interdigital ectoderm. These changes were much less pronounced or absent in the duck.

As early as the interdigital grooves were detected in the chick, the morphological features of the ectodermal cells changed from a polygonal shape and flattened appearance to a rounded shape and bulging appearance. These changes were not present in the webbed foot of the duck. On the other hand the development of the interdigital commissures was accompanied by the formation of ectodermal ridges consisting of an accumulation of rounded cells which were in some cases in course of detachment to the amniotic cavity. These ridges were very prominent in all the interdigital commissures of the chick. In the duck they were less pronounced and were only present in the first and third commissure. From these results it is suggested that in addition to the well-known interdigital mesenchymal necrotic process (INZ) the ectodermal tissue of the interdigits might also be actively involved in the formation of free digits.
The Localization of the Presumptive Cerebral Regions in the Neural Plate of the Axolotl Larva
Authors: Jacobson Carl-olof
Published: April 2021

By means of vital staining it has been possible to project the most important areas of the fully developed brain of the axolotl, Siredon mexicanum, upon the neural plate of the larva. The map of presumptive areas is shown in Textfigs. 15-17. The investigation has shown that the presumptive fore-brain occupies space not only upon the foremost part of the neural plate, but also upon the transverse ridge. All material of the presumptive diencephalon and of the more caudally situated brain regions is situated in the plate proper. The position of the eye-forming area has been shown to be more medial than has been proposed by earlier authors. This mapping of the presumptive brain areas makes it possible to judge with greater certainty the question of self-differentiation and regulation in the transplantation experiments of previous authors.
The Development of the Nervous System in Chick Embryos, studied by Electron Microscopy
Authors: Bellairs Ruth
Published: April 2021

An electron microscope study of developing nervous tissue has been made in the chick embryo, correlating the results with those obtained by other techniques. I have been especially concerned with (1) the relationship between ectoderm and mesoderm cells at the time of neural induction, and (2) the formation of the Nissl substance.

Tissue from 73 chick embryos incubated for periods between 1 and 13 days has been studied. Before fixation each specimen was staged according to the normal table of Hamburger & Hamilton (1951). The tissue was fixed either in osmium tetroxide, or in potassium permanganate (Luft, 1956). In either case the pH was buffered to 7·4 with sodium veronal (Palade, 1952) and fixation was at 0° C. In the early stages the whole embryo was fixed.
Metachromasia Observed in the Living Eggs ofArbacia punctulataand its Cytochemical Analysis
Authors: Mulnard Jacques , Auclair Walter , Marsland Douglas
Published: April 2021

The analysis of the egg of Arbacia punctulata by means of vital staining with toluidine blue confirms the results obtained on other species. It shows a primary metachromasia due to tiny a granules scattered throughout the cytoplasm, and the appearance, at the time of the paired pronuclei, of secondary metachromatic β granules in close relation to the nucleo-mitotic apparatus.

High-speed pressure-centrifugation (Marsland’s procedure) shows that the a granules are sedimented in the upper half of the vitelline zone, the ft granules in the lower half of the hyaline zone. These two metachromatic layers remain separated by the mitochondrial band. A third granular, metachromatic material can be detected which may be a precursor of the βgranules.

Cytochemical tests verify the presence of acid phosphatase in all the metachromatic structures and show that all contain mucopolysaccharides, which account for the metachromasia. The Alcian-blue technique reveals that the β granules contain strongly acidic mucopolysaccharides, whereas the a granules contain less acidic mucopolysaccharides.
Immunochemical Studies of Muscle Proteins in Mature and Regenerating Limbs of the Adult Newt,Triturus viridescens
Authors: Laufer Hans
Published: April 2021

Immunochemical procedures were employed to analyse changes in contractile proteins during limb regeneration in the adult newt, Triturus. Methods for the isolation of myosin and actomyosin were modified for use in the newt. After these proteins were characterized biochemically they were shown to be antigenic in the rabbit. The activity and specificity of anti-actomyosin and anti-myosin sera were determined by means of agar diffusion techniques. Purified actomyosin was found to be contaminated by myosin and a second component, a nucleoprotein. The diffusion coefficients increased in the order actomyosin, myosin, nucleoprotein. The injection of myosin into rabbits elicited the formation of antibodies which, when tested in agar diffusion, usually demonstrated a minimum of one band but occasionally, when contaminated by minor quantities of actomyosin, two bands were seen. Some modifications of existing procedures are described for the use of small reagent samples in Ouchterlony plates. The development of muscle during limb regeneration was tested by the agar diffusion method. Actomyosin and myosin can first be detected in the regenerate at the stage of hand formation (‘palette’ stage). Thereafter there is an upsurge of synthesis of these proteins during the ‘early’ and ‘medium’ digital stages. The appearance of these contractile proteins probably coincided with the time of myofibril formation. A rise in nucleoprotein preceded the appearance of muscle protein and later decreased to a concentration characteristic of adult tissues. All tissues which were tested immunologically contained the nucleoprotein component. Infusions of rabbit serum and anti-muscle serum into the regenerate yielded a cytotoxic response which varied according to the serum used, the reaction to the immune serum being more severe. There was a temporary cessation of regeneration for a few days, the duration of which was related to the severity of the reaction. Observations of the histopathology of infused regenerates revealed sarcolysis attributable to the specific effects of the anti-muscle serum. Autoradiograms of limbs infused with I131 gamma globulin demonstrated the course and disposition of labelled protein within the regenerate and stump. There was localization of material about muscle-cells, suggesting a possible specificity of the reaction. The epidermis appeared to be an active organ for the elimination of foreign material.
Interactions of blastomeres suggest changes in cell surface adhesiveness during the formation of inner cell mass and trophectoderm in the preimplantation mouse embryo
Authors: Kimber Susan J. , Surani M. Azim H. , Barton Sheila C.
Published: April 2021

Whole 8-cell morulae can be aggregated with isolated inner cell masses from blastocysts. On examining semithin light microscope sections of such aggregates we found that cells of the morula changed shape and spread over the surface of the ICM, thus translocating it to the inside of the aggregate. Using single cells from 8-cell embryos in combination with single cells from other stage embryos or isolated ICMs we show that 1/8 blastomeres spread over other cells providing a suitably adhesive surface. The incidence of spreading is high with inner cells from 16-cell embryos (56 %) and 32-cell embryos (62 %) and isolated inner cell masses (64%). In contrast, the incidence of spreading of 1/8 blastomeres is low over outer cells from 16-cell embryos (26 %) and 32-cell embryos (13 %). Blastomeres from 8-cell embryos do not spread over unfertilized 1-cell eggs, 1/2 or 1/4 cells or trophectoderm cells contaminating isolated ICMs. When 1/8 cells are aggregated in pairs they flatten on one another (equal spreading) as occurs at compaction in whole 8-cell embryos. However, if 1/8 is allowed to divide to 2/16 in culture one of the cells engulfs the other (51 –62% pairs). Based on the ideas of Holtfreter (1943) and Steinberg (1964,1978) these results are interpreted to indicate an increase in adhesiveness at the 8-cell stage as well as cytoskeletal mobilization. Following the 8-cell stage there is an increase in adhesiveness of inside cells while the outside cells decrease in adhesiveness. The difference in adhesiveness between inside and outside cells in late morulae is probably central to the divergent differentiation of (inner) ICM and (outer) trophectoderm cell populations.
Evidence of male germ cellredifferentiation into female germ cells in planarian regeneration
Authors: Gremigni V. , Nigro M. , Puccinelli I.
Published: April 2021

The source and fate of blastema cells are important and still unresolved problems in planarian regeneration. In the present investigation we have attempted to obtain new evidence of cell dedifferentiation-redifferentiation by using a polyploid biotype of Dugesia lugubris s.l. This biotype is provided with a natural karyological marker which allows the discrimination of triploid embryonic and somatic cells from diploid male germ cells and from hexapioid female germ cells. Thanks to this cell mosaic we previously demonstrated that male germ cells take part in blastema formation and are then capable of redifferentiating into somatic cells. In the present investigation sexually mature specimens were transected behind the ovaries and the posterior stumps containing testes were allowed to regenerate the anterior portion of the body. Along with the usual hexaploid oocytes, a small percentage (3.2%) of tetraploid oocytes were produced from regenerated specimens provided with new ovaries. By contrast only hexaploid oocytes were produced from control untransected specimens. The tetraploid oocytes are interpreted as original diploid male germ cells which following the transection take part in blastema formation and then during regeneration redifferentiate into female germ cells thus doubling their chromosome number as usual for undifferentiated cells entering the female gonad in this biotype.
Analysis of the intermediate size proteoglycans from the developing chick limb buds1
Authors: Vasan Nagaswamisri
Published: April 2021

Limb-bud proteoglycans are heterogeneous molecules which vary in their chemical and physical properties with development. This report describes proteoglycan intermediates (PG-I) that predominate in stage-34 limbs, and compares them with proteoglycan aggregates (PG-A) in stage-38 limbs. We analysed proteoglycans and their components extracted with guanidinium chloride by subjecting them to density gradient centrifugation, molecular sieve chromatography, electrophoretic separation, and selective enzymatic degradation. PG-I and PG-A have similar chondroitin sulphate composition, amino sugars, chondroitin sulphate side-chain length, glycoprotein link factors, and hyaluronic acid binding capacity, and both cross react with antisera prepared against cartilage-specific chick sternal proteoglycans. However, PG-I has lower molecular weight, lower buoyant density, and fewer chondroitin sulphate side chains on the protein core. The PG-I in the developing limb can be considered a mixture of smaller aggregates and cartilage-specific large monomers in which the former predominate.
The spatial pattern of aggregation centres in the cellular slime mould
Authors: Waddell David R.
Published: April 2021

The spatial pattern of aggregation centres of the slime mould Dictyostelium discoideum was analysed by using nearest-neighbour distributions. Both undisturbed cultures, and cultures that were initiated from cells dissociated from cultures that had already aggregated, formed non-randomly spaced patterns. However, the minimal distance between aggregates in undisturbed cultures was approximately ten times that observed in dissociated cultures.

In undisturbed cultures the aggregate size is regulated as a function of cell density (Bonner & Hoffman, 1963): As cell density increases aggregate density decreases and the aggregate size consequently increases. At the same cell density more and smaller aggregates were formed by dissociated cultures than by undisturbed cultures. Nevertheless, the same cell-densitydependent regulation of aggregate density existed in the dissociated cultures.

Here a model is developed to account for both the non-random spacing and the celldensity-dependant regulation of aggregate density. In this model, distance-dependent competition occurs between points in a random prepattern to generate patterns very similar to those observed in experiments. The cell-density-dependent regulation of the aggregate density can be explained by assuming that a constant fraction of the cell population has the capacity to initiate centres at the time of pattern determination regardless of the cell density. As the cell density is increased the fraction of potential centres that survive distance-dependent competition decreases and hence the aggregate size increases. These results suggest that distance-dependent competition may be a mechanism that evolved to control aggregate size at high cell densities.

Results obtained with this model indicate that the decrease in aggregate size in dissociated cultures is due primarily to an increase in the fraction of the cell population capable of initiating centres. This implies that as morphogenesis progresses a greater fraction of the cell population acquire a capacity which they will not normally express. Although this increase may have a function in later stages of morphogenesis, it may also provide a way to ensure aggregation in small populations of amoebae and at low cell densities.
Effects of ultraviolet light on the activity of an avian limb positional signalling region
Authors: Honig Lawrence S.
Published: April 2021

Cells from a region on the posterior margin of the developing avian limb bud (the polarizing region) can signal positional information to responding anterior cells. Polarizing activity may be assayed by disaggregation of the tissue into single cells, followed by reaggregation and grafting of cell pellet. This method enables treatments of the cells while in single-cell suspension. The effects of ultraviolet radiation (254 nm) were studied to determine the role of nucleic acids in polarizing activity. Ultraviolet radiation eliminated quail polarizing activity over the same range of doses as it reduced cell spreading (20-60 J/m2). In contrast to the published effects of γ-radiation in which polarizing activity is affected only at doses much higher than those that are cell lethal, ultraviolet apparently abolishes cell survival and polarizing activity at comparable doses. Compared to other biological systems, polarizing activity is quite sensitive to ultraviolet light: the D37 is 18 J/m2; the extrapolation number, n, is 3·6. From comparison of the effects of ultraviolet radiation to those published for ionizing X- or γ-radiation, one may conclude that ultraviolet and y-radiation abolish limb polarizing activity at equivalent nucleic acid dosages, not at equivalent cell lethal doses.
A quantitative study of hair growth using mouse and rat vibrissal follicles
Authors: Ibrahim Lamees , Wright E. A.
Published: April 2021

The volumes of the dermal papilla, matrix and fully grown hair of vibrissal follicles of rats and mice were measured.

Dermal papillae were surgically removed from rats’ vibrissal follicles and a small new dermal papilla was always reformed. The lower third of rats and mice follicles, containing the whole of the dermal papilla was amputated and very small dermal papillae were reformed.

Follicles containing small dermal papillae produced small hairs and a constant positive linear relationship of 7·0 was found between the volume of the dermal papilla and the volume of the full-grown hair for all cases studied.
Changes in the Protein Content of Yolk during Chick Embryogenesis
Authors: Mcindoe W. M.
Published: April 2021

The original purpose of the present investigation was to determine the rate of degradation of phosphoprotein in the yolk at different times during embryogenesis as a preliminary to examining the mechanism of its assimilation, and to see if phosphoprotein and other proteins were assimilated at different times or at markedly different rates. The early work on the assimilation of yolk protein has been reviewed by Needham (1931) and few pertinent papers have appeared since then (Schenck, 1932; Rupe & Farmer, 1955; Walter & Mahler, 1958). Recently Holoubek & Brada (1956) have made an extensive examination of the distribution of phosphorus compounds in the egg during embryogenesis.
Cortical Grafting inXenopus laevis
Authors: Curtis A. S. G.
Published: April 2021

A technique for the grafting of cortical material from one embryo to another at early cleavage stages is described. This method may also be used for the grafting of cortical material from infertile eggs to early cleavage stages. Grafts transplanted to embryos during first cleavage to the same site as that from which they were derived, resulted in normal development. Grafts obtained from grey crescent material and transplanted to the ventral margin induced the appearance of a secondary dorsal lip and subsequent secondary axis. Those of animal pole or ventral margin material placed in the grey crescent resulted in the failure of invagination during gastrulation at the graft site, and this causes the splitting of the dorsal lip into two and the appearance of double axes. Animal pole material placed at the vegetal pole produces a peculiar form of exogastru-lation. Cortical material from infertile eggs if grafted into embryos during their first cleavage inhibits further development. Cortical material from fertile uncleaved eggs, if placed in embryos in the midst of their first cleavage, appears to cause a lag in cleavage in that half of the embryo which received the graft. These results show that the cortical material definitely possesses morphogenetic properties which may be transferred with it. These are concerned with gastrulation, and the experiments are discussed in relation to the ‘cortical field’ theory of Dalcq & Pasteels. This technique of grafting allows investigation of the organization of the cortical field.
Oocytes and early embryos of Xenopus laevis contain intermediate filaments which react with anti-mammalian vimentin antibodies
Authors: Godsave Susan F. , Anderton Brian H. , Heasman Janet , Wylie Christopher C.
Published: April 2021

Previous studies have shown that Xenopus oocytes possess a cortical shell, which includes actin-containing microfilaments and cytokeratin-containing intermediate filaments. In this paper we show that oocytes of Xenopus laevis also contain filaments throughout their cytoplasm which are stained by several anti-vimentin antibody preparations. We also show that dramatic changes in pattern of these filaments occur during oocyte differentiation, first during vitellogenesis, and then during maturation of the oocyte to form an egg.
Intercellular relationships during cavitation of aggregates of extraembryonic endoderm cells from gastrulating chick embryos
Authors: Milos Nadine , Zalik Sara E. , Sanders Esmond J. , Ledsham Irene M.
Published: April 2021

Extraembryonic endoderm cells from gastrulating chick embryos undergo epiboly and change from a multilayered cell group to a single cell layer surrounding the yolk. Single cell suspensions from this cell layer can aggregate in vitro to form aggregates that cavitate. To study the stages of cavitation aggregates were harvested after different times in culture, and fixed and processed for light and electron microscopy. In aggregates harvested at 75 min of culture cell contact consisted of areas of parallel and close membrane apposition and interdigitation. Desmosomes were occasionally observed. Aggregates in the early stages of cavitation (24 h) contained numerous intercellular spaces bordered by irregularly shaped cells which appeared to be digesting their yolk and releasing material extracellularly. Long cytoplasmic projections were extended into these spaces. In addition to regions of parallel membrane apposition and interdigitation, desmosomes and adherens junctions were observed. Cells closer to the periphery of the aggregates displayed fewer cell projections and also showed signs of release of material extracellularly. After 48 h of culture, a single smooth-walled central cavity was present and cells still exhibited signs of extracellular release of material. These same cell shapes and intercellular junctions were also observed when area opaca tissue dissected from gastrulating embryos was examined. Aggregates of different sizes were created and cultured. The results suggest that a critical tissue mass may be important for cavitation.
An introduction to programmes for development
Authors: Macgregor Herbert C. , Swan Alma P.
Published: April 2021

The symposium of which this book is a record was first suggested in the autumn of 1982. At that time, all members of the BSDB committee were persons who were primarily concerned with studies of animal development, and the initial tendency was to think along these lines.
Switch genes and sex determination in the nematode C. elegans
Authors: Hodgkin Jonathan
Published: April 2021

The development of the nematode C. elegans is highly invariant, and has been described in great detail. Many developmental mutations have been isolated and analysed; some of these identify switch genes, i.e. genes that control the choice between two developmental alternatives. It appears that the genetic controls of development in this animal are discrete, hierarchical and relatively simple. The control of sexual dimorphism provides an example of how a series of switch genes are organized in a regulatory cascade.
Polarity, calcium and abscission: molecular bases for developmental plasticity in plants
Authors: Trewavas A. J. , Sexton R. , Kelly P.
Published: April 2021

This article considers novel aspects to plant development. It starts by outlining the concept of plastic development. It then discusses polarity in plants arguing for the vascular tissue and surrounding cells as a major internal polar axis. The requirement for a change in polarity in this system when regeneration occurs is discussed and molecular mechanisms for specification and changing of polarity are outlined. The process of abscission is then discussed as an example of plastic development and it is concluded that many factors control abscission.

Molecular changes in abscission zone cellulase are summarized and the notion of two phases in abscission are developed and generalized to other systems of development in plants.
Models for positional signalling, the threefold subdivision of segments and the pigmentation pattern of molluscs
Authors: Meinhardt Hans
Published: April 2021

Models of biological pattern formation are discussed. The regulatory features expected from the models are compared to those observed experimentally. It will be shown that: Stable gradients appropriate to supply positional information can be produced by local autocatalysis and long-range inhibition.Spatially ordered sequences of differentiated cell states can emerge if these cell states mutually activate each other on long range but exclude each other locally. Segmentation results from the repetition of three such cell states,S,A and P (and not of only two, as is usually assumed). With a repetition of three states, each segment has a defined polarity. The confrontation of P cells and S cells lead to the formation of a segment border (… P/SAP/ SAP/S …) while the A-P confrontation is a prerequisite for appendage formation. Mutations of Drosophila affecting larval segmentation are discussed in terms of this model.The two models for the generation of sequences of structures in space (positional information including interpretation versus mutual activation) lead to different predictions with respect to intercalary regeneration. This allows a distinction between the two models on the basis of experiments.The pigmentation patterns of certain molluscs emerge from a coupled oscillation of cells (that is, a lateral inhibition in time, instead of space). The oblique lines result from a chain of triggering events.
Subroutines in the programme of Chlamydomonas gene expression induced by flagellar regeneration
Authors: Schloss Jeffery A.
Published: April 2021

The unicellular green alga Chlamydomonas reinhardtii possesses two anterior flagella that are rapidly replaced if they are lost. A cytoplasmic pool of flagellar precursors supports regeneration of partial length flagella, but complete regeneration requires de novo synthesis of flagellar proteins. This increase in protein synthesis is transient and is programmed by changes in the physical abundance of a set of RNAs. These changes were measured using cloned cDNAs. The curves that were generated with probes for a number of different RNAs were variations-on-the-theme of a rapid accumulation following deflagellation of the cells, followed by similarly rapid degradation. Differences in the characteristics of the accumulation curves suggest that several ‘subroutines’ for RNA metabolism appear to run concurrently during flagellar regeneration. A significant portion of the mRNA abundance regulation occurs at the transcriptional level. A group of cDNAs that encode mRNAs whose abundance remains at constant levels during regeneration provides an important internal control for the abundance and transcription measurements. Flagella contain over 200 different proteins, so the possibility exists that the cells coordinately and rapidly alter the transcription of the same number of genes. Chlamydomonas flagellar regeneration thus provides an opportunity to study cellular mechanisms for coordinating the expression of a large set of genes, and correlating these changes with an easily monitored morphogenetic process.
Allocation of mesendodermal cells during early embryogenesis in the starfish, Asterina pectinifera
Authors: Kominami Tetsuya
Published: April 2021

The volume of archenteron tissue (mesendoderm) in the early-to-middle gastrula of the starfish Asterina pectinifera was nearly one-quarter of whole embryo. Treatment with LiCl during 7–10 h increased this volume ratio by about 30 %, whereas the total volume and the total number of cells of whole embryo remained unchanged. Such a relative increase in mesendodermal part and simultaneous reduction in ectodermal part by LiCl treatment was confirmed by counting the number of constituent cells of these parts at early bipinnaria stage. Pulse treatment with LiCl revealed that the effective period of the treatment is limited from 7 to 10 h of development, when tightly packed blastulae are formed through increase in adhesiveness of blastomeres. These results indicate that a fraction of presumptive ectodermal cells can change its fate to mesendoderm during 7–10 h of development. Cellular interactions during a specific stage of development are suggested to be involved in the determination of mesendodermal tissue.
The stages of flank ectoderm capable of responding to ridge induction in the chick embryo
Authors: Carrington Jill L. , Fallon John F.
Published: April 2021

Reports on the stages when chick flank ectoderm can respond to ridge induction are contradictory. Different results have been obtained using presumptive wing or leg bud mesoderm as the inducing tissue with flank ectoderm as the responding tissue. In addition, although incomplete outgrowths have been obtained from recombinants with stage-19 flank ectoderm in a small percentage of cases, no complete outgrowths have been obtained from recombinants with ectoderm older than stage 18. We reinvestigated when chick flank ectoderm can respond to ridge induction and promote outgrowth of complete limbs. To do this, we combined flank ectoderm with in situ chick presumptive wing bud mesoderm using a pre-limb bud recombinant technique. When presumptive wing bud ectoderm was removed from the host and not replaced, wing development was suppressed. When host ectoderm was replaced with stage-15 through -18 chick flank ectoderm, limbs grew out in all cases; 86·4% of these recombinant limbs were distally complete. Stage-19 flank ectoderm formed a ridge and promoted limb outgrowth in 80·9% of recombinants; 52·9% of these were distally complete limbs. Recombinants made by grafting early stage-20 (40-somite donor) flank ectoderm to stage-15 hosts resulted in outgrowths in 60% of the cases and 33·3% of these were distally complete. Graft ectoderm from older donors did not respond to inductive mesoderm.

Our results demonstrate that chick flank ectoderm from stage-15 through early stage-20 donors can respond to inductive signals from presumptive wing bud mesoderm to form an apical ridge. This ridge can promote outgrowth of distally complete wings in a substantial proportion of recombinants. This is two stages beyond when the ability to promote outgrowth of distally complete wings appeared to be lost using other methods.
Microtubules influence compaction in preimplantation mouse embryos
Authors: Maro Bernard , Pickering Susan J.
Published: April 2021

The role of microtubules during compaction of the 8-cell-stage mouse embryo was investigated using the drugs Taxol (which leads to a non-controlled polymerization of tubulin) and Nocodazole (which causes depolymerization of microtubules). Taxol inhibits compaction in most non-compacted embryos and reverses it in already compacted embryos. These effects were observed on both cell flattening (as judged by phase-contrast microscopy) and on cell surface polarization (as judged by scanning electron microscopy and the surface binding of fluorescent concanavalin A). In contrast Nocodazole does not inhibit cell flattening, but rather accelerates its completion. Nocodazole influences the detailed organization of the surface pole and appears to reduce the incidence of surface polarization but does not reverse polarity once established to a significant extent. We conclude that microtubules exercise a constraining role during compaction, influencing cell shape, cell organization and the time at which compaction takes place.
Restoration of the antibody response to sheep erythrocytes in thymectomized Xenopus implanted with MHC-compatible or MHC-incompatible thymus
Authors: Gearing A. J. H. , Cribbin Frances A. , Horton J. D.
Published: April 2021

These experiments make use of an amphibian model system for investigating the role of the thymus in T helper cell education. Clawed toads (Xenopus laevis), thymectomized at 7 days, are unable to mount an antibody response to thymus-dependent antigens, such as sheep red blood cells (SRBC). When thymectomized larvae are implanted with larval thymuses (either irradiated or non-irradiated), incompatible at the major histocompatibility complex (MHC) or with MHC-compatible or -incompatible ‘adult’ thymuses, their splenic plaque-forming cell response and serum haemolytic antibody production to SRBC are both restored, to some extent. However, levels of mercaptoethanol-resistant antibody were extremely poor in those animals implanted with MHC-incompatible ‘adult’ thymus. Larval thymus implants were shown, by ploidy-labelling studies, to become repopulated with host-derived lymphocytes. Whether or not these lymphocytes acquire their MHC restriction specificities in the thymus awaits clarification.
Formation of the notochord in living ascidian embryos
Authors: Miyamoto David M. , Crowther Robert J.
Published: April 2021

The dynamic behaviour of cells during formation of the notochord in the ascidian, Ciona intestinalis, was examined by means of Differential Interference Contrast (DIC) microscopy and time-lapse videorecording. The initial rudiment is formed in part as a consequence of the pattern of mitotic divisions as the blastopore shifts posteriorly. Vertical and horizontal rearrangements produce an elongate rod of disc-shaped cells stacked end to end. Further elongation is accompanied by a cell shape change. Some cell growth or swelling is indicated to occur later in development, but this growth appears to contribute mostly to an increase in the diameter, and only insignificantly to the length of the notochord. Intracellular vacuoles that appear around 13 h after fertilization increase in size and fuse at about 16 h to form intercellular ones. These in turn merge to form the central matrix core of the notochord at around 18 to 20 h. As the notochord elongates and cells change in shape, the basal surfaces bleb actively. This surface activity may be related to formation of the perinotochordal sheath.
Cautery-induced colour patterns in Precis coenia (Lepidoptera: Nymphalidae)
Authors: Nijhout H. F.
Published: April 2021

Cautery of the dorsal hind wing in the butterfly, Precis coenia, induces the formation of a concentric colour pattern around the site of injury. The induced pattern is identical in pigmentation to the eyespots that normally develop on this wing surface. This response to cautery also occurs, though much less dramatically, on the ventral forewing. In addition to the peculiar response to cautery, the dorsal hindwing of Precis also develops a series of unique pattern aberrations in response to coldshock. These consist of irregular elongation of the anterior eyespot along the proximodistal axis of the wing. In the most dramatic aberrations the eyespot field covers the entire anterior half of the wing surface. An analysis is presented that attempts to reconcile the effects of cautery on the Precis hindwing with the very different morphological effects of cautery on the colour pattern of Ephestia kühniella, described by Kühn & Von Engelhardt. Computer simulations reveal that the finding presented in this paper, as well as the classical work on Ephestia, can both be explained by assuming that the site of cautery becomes a sink for one of the morphogens involved in colour pattern determination. The experimental findings furthermore indicate that minor perturbations of the wing epidermis can evoke the physiological conditions that attend normal eyespot determination. It is shown that this interpretation also helps to explain the unusual pattern modifications following coldshock.