bluuebunny/crossref_metadata_2025 huggingface dataset:
A study of the growth cones of developing embryonic sensory neurites
Authors: Roberts Alan , Taylor J. S. H.
Published: April 2021

The scanning electron microscope was used to examine the growth cones of sensory neurites on the basal lamina of the trunk skin and on the myotomes in dissected embryos of the amphibian, Xenopus laevis. On the myotomes growth cones are large and flat with extensive lamellipodia and many filopodia. On the skin growth cones are smaller and have simpler processes particularly in more ventral positions. Where growth cones contact each other or other neurites they are very intimately apposed and show many indications of strong mutual adhesion. Fasciculation and separation of growing neurites is described and the conditions leading to fasciculation are considered. Measurements of growth cones on the myotomes and different dorsoventral regions of the skin are interpreted in terms of possible differences in the adhesiveness of these substrates. We conclude that many of our observations can be explained by differences in substrate adhesion to the growth cones but that the skin may have some special, unknown attraction for them.
Size dependence during the development of the amphibian foot. Colchicine-induced digital loss and reduction
Authors: Alberch P. , Gale Emily A.
Published: April 2021

Localized treatment of the limb buds of the frog, Xenopus laevis, and the salamander, Ambystoma mexicanum, with the mitotic inhibitor colchicine results in limbs that, when compared with the contralateral control, are smaller in size and have lost skeletal elements. There is a very well defined pattern in terms of what elements are most likely to be lost. For example, frogs that have lost a toe always lose the first toe, while salamanders always lose the fifth. These differences correspond to qualitative differences in developmental sequence of digital differentiation in anurans as compared to urodeles. We propose a hypothesis in which the digital pattern is indirectly affected by reduction in the number of mesenchymal cells in the embryonic field.
Genetic and developmental characteristics of the homeotic mutationbx1 ofDrosophila
Authors: Sánchez-Herrero Ernesto , Morata Ginés
Published: April 2021

The mutations at the bithorax locus produce a transformation of anterior haltere into anterior wing. The bx1 allele presents unusual features when compared with other bx alleles. The phenotype of bx1 homozygotes is temperature sensitive but only with regard to the distal and not to the proximal transformation, thus suggesting two different components in the bithorax transformation. The phenotype of bx1 homozygotes is stronger than that of bx1 over the deletion of the gene, suggesting a trans interaction of the bx1 chromosomes which results in mutual partial inactivation. We show by temperature shift and clonal analysis experiments that the decision on whether to differentiate haltere or wing structures is taken at the end of the proliferation period of the mutant disc.
Development of the lateral line system in Xenopus laevis
Authors: Winklbauer Rudolf , Hausen Peter
Published: April 2021

During development of Xenopus laevis, the supraorbital lateral line system (i.e. the parietal and supraorbital lines of organs and the anterior auditory group of organs) is all derived from a single primordium located in the ear region of the epidermis. The primordium elongates first by active movement along the dorsal margin of the eye. Individual primary organs are then formed by progressive fragmentation of the streak-like primordium. After fragmentation, passive displacement of the organs due to skin growth seems to play the main role in altering the arrangement of the line system. Transplantation experiments confirmed that non-placodal epidermal cells are not incorporated into the developing system. The active elongation of the primordium is due to cell multiplication, and not due to cell rearrangement or change in cell shape or size. Cell multiplication is not confined to a growth zone, but dividing cells are randomly distributed throughout the primordium. All cells of a primordium have to change position during its elongation.
Morphological and molecular modifications induced by heat shock in Drosophila melanogaster embryos
Authors: Graziosi Giorgio , Cristini Franco De , Marcotullio Angelo Di , Marzari Roberto , Micali Fulvio , Savoini Adriano
Published: April 2021

The early embryo of Drosophila melanogaster did not survive treatment at 37°C (heat shock) for 25 min. The histological analysis of eggs treated in this way showed that the heat shock caused disintegration of nuclei and of cytoplasmic islands, displacement and swelling of nuclei and blocked mitoses. These effects were not observed in embryos treated after blastoderm formation. After this stage, we noticed that development was slowed down. The heat shock proteins (hsp 83,70 and 68) were, under shock, synthesized at all developmental stages. There was little or no synthesis of hsp 70 and 68 in unfertilized eggs, but synthesis increased in proportion to the number of nuclei present. Most probably, hsp 70 synthesis was directed by zygotic mRNA. DNA synthesis was not blocked by the heat shock though the overall incorporation of pH]thymidine was substantially reduced, presumably because of the block of mitoses. We did not find a direct relation between survival pattern and hsp synthesis. We concluded that some, at least, of the heat shock genes can be activated at all developmental stages and that heat shock could be used for synchronizing mitoses.
Regeneration of the retinotectal projection following compression onto a half tectum in goldfish
Authors: Schmidt John T.
Published: April 2021

This study tested whether regeneration of the optic nerve following half-tectal compression in goldfish leads to the immediate reestablishment of the compressed projection or to an initial half map followed by the gradual compression. Half of the tectum was removed and the optic nerve crushed in large 12–18 cm goldfish which were kept at 20 °C and later mapped either in air or in water. At 35 to 41 days, the maps showed the presence of the nasal field projection and only the first 27 degrees of the temporal field. Most of the temporal field was represented after 200 days or more. After 253 to 343 days when the compression was largely complete, the optic nerve was recrushed. The projections mapped 35 to 41 days later were always compressed with up to 99 % of the temporal field represented, as were projections regenerated at 28°C and mapped at 23–25 days. Regeneration after compression restores the compressed projection, consistent with the concept of altered tectal markers.
Fine structure of the regressing interdigital membranes during the formation of the digits of the chick embryo leg bud
Authors: Hurle J. M. , Fernandez-Teran M. A.
Published: April 2021

There is recent evidence showing that in addition to the well-known mesenchymal necrotic mechanism involved in the disappearance of the interdigital membranes, the ectodermal tissue may also play an active role in the formation of the free digits of most vertebrates. Ultrastructural study of the regressing interdigital membrane of the chick leg revealed significant changes at the epitheliomesenchymal interface. Disruptions of the ectodermal basal lamina and an intense deposition of collagenous material were the most conspicuous changes observed in the extracellular matrix. In addition the basal ectodermal cells showed prominent cell processes projected into the mesenchymal core of the membrane, and mesenchymal macrophages appeared to migrate through the epithelial tissue to be detached into the amniotic sac. It is concluded from our results that the elimination of the interdigital membranes is a complex process requiring the interaction of all the tissue components of the membrane.
The effects of the pink-eyed unstable gene on the retinal pigment epithelium of the mouse
Authors: Deol M. S. , Truslove Gillian M.
Published: April 2021

Pink-eyed unstable (pun), an autosomal gene in the mouse, causes variegation of the coat. In some melanocytes it functions as the normal allele p+, producing dark pigment, and in others as the mutant p, producing light pigment. As a study of another unstable gene at a different locus had shown that the instability was strongly influenced by the tissue environment, it seemed desirable to find out whether this also applied to pun.

An examination of the retinal pigment epithelium, the only structure in mammals in which it is practicable to determine the position of individual melanocytes, showed that the distribution of dark and light cells in punpun animals was not random. The dark cells increased in frequency with the distance from the optic nerve, suggesting that the tissue environment was a factor in the instability of the gene (i.e. in its rate of mutation), although the increase was less striking than in the other mutant.

It is generally assumed that when pun behaves as p+ it is a case of reversion, and that reversion can also occur in germ cells, the revertant p+ allele subsequently behaving as a stable gene. It is here argued that it is unlikely to be a case of reversion, and that the evidence for the involvement of the germ line is inconclusive. Further, it is suggested that the phenotype of punpun animals is probably an instance of Position Effect variegation, the instability resulting from some chromosomal alteration, which is too small to be cytologically detectable.
Transcription and polyadenylation processes during early development of quail embryo
Authors: Olszańska B. , Kludkiewicz B. , Lassota Z.
Published: April 2021

Transcription of tRNA and mRNA occurs in quail as early as during cleavage while rRNA transcription becomes measurable during blastulation. The polyadenylated fraction content in newly synthesized RNA amounting to 6 % during cleavage and blastulation decreases to 3 % during gastrulation. Up to 3/4 adenylic residues incorporated into RNA during cleavage are accumulated in the polyadenylated molecules mainly in the form of RNAse-resistant tracts.
Labelling of basement membrane constituents in the living chick embryo during gastrulation
Authors: Sanders Esmond J.
Published: April 2021

The basement membrane of the living chick embryo epiblast has been labelled with ultrastructural markers in order to study the movement and turnover of this structure during gastrulation. Two problems were addressed in these experiments. Firstly, to what extent does the basement membrane move medially with the epiblast during morphogenesis? Secondly, what is the relationship to the basement membrane of the so-called interstitial bodies? The ultrastructural markers used were concanavalin A conjugated to ferritin and fibronectin antibodies conjugated to peroxidase. Embryos were cultured using the technique of New, and the label was applied to the periphery of the basal surface of the epiblast through a hole in the endoblast at the early primitive streak stage of development. The embryos were then allowed to develop to the full primitive streak stage in the presence of the label. When the position of the label was determined after incubation, it was found to have accumulated in large amounts at the edge of the primitive streak at the point where the basement membrane is disrupted. This indicates that constituents of the basement membrane are transported medially with the epiblast cells and are sloughed off as the latter pass through the primitive streak. This movement of basement membrane constituents is counter to the direction of migration of the underlying mesoderm cells. When embryos are exposed to label for only 1 h, then washed and incubated for a further three hours, the marker was found in the interstitial bodies and not distributed throughout the basement membrane itself. This suggests that the interstitial bodies, which have been implicated in influencing the migration of the mesoderm cells, are turnover products of the basement membrane to which they are attached.
Experimental analysis of control mechanisms in somite segmentation in avian embryos II. Reduction of material in the gastrula stages of the chick
Authors: Bellairs Ruth , Veini Marianne
Published: April 2021

A new theory of control of somite segmentation in chick embryos is proposed. This supposses that tiny clusters of already programmed cells are present throughout the presumptive somite area at stage 4, but that in order to fulfill their destiny they probably depend on the addition of further cells from the primitive streak. Evidence is based on the two groups of experiments:

a) Experiments involving transection across the primitive streak at various stages, (which results in a ‘tail’ which possesses mesodermal derivatives) and across the segmental plate (which results in a ‘tail’ lacking mesodermal derivatives).

b) Experiments in which parts of embryos have been explanted with or without their primitive streak.

It is suggested that the initial clusters of pre-programmed cells move further and further posteriorly, developing into somitomeres (the precursors of true somites) only as they receive re-inforcements from the primitive streak or, ultimately, from the tail bud.
Differentiation of Argyrophil and Argentaffin Cells in Organotypic Cultures of Embryonic Chick Intestine
Authors: Monesi Valerio
Published: April 2021

Argyrophil, Bodian positive cells, and argentaffin, Masson-Hamperl positive cells differentiate in vitro in organotypic cultures of intestine of chick embryos explanted before argyrophil and argentaffin cells are known to differentiate, which is at the 14th and the day of incubation, respectively. During culture in vitro, argyrophil and argentaffin granules differentiate simultaneously; the number of cells demonstrable with either method does not show any significant difference throughout the duration of the cultures, which were incubated up to a maximum of 6 days. This result is at variance with what occurs in vivo, where argyrophil cells differentiate earlier than argentaffin cells and are in earlier stages 3 or 4 times as frequent as the latter, becoming only twice as numerous at a later stage. As in development in vivo, argyrophil and argentaffin cells differentiating in the intestine of the chick embryo are mainly situated in the epithelium. Only very few are found in the connective tissue of the lamina propria. Simard & van Campenhout (1932) and Ghidini (1940) showed that enterochromaffin granules differentiate in chorioallantoic grafts of intestine of chick embryos and they disproved in this way any kind of derivation of the enterochromaffin substance (enteramine) from the lumen of the gastrointestinal tract, as well as its formation under the influence of normal nervous connexions. It is now shown that the specific granules differentiate also in intestine cultivated in vitro and therefore in conditions which exclude any other possible mode of correlation with the whole organism, and particularly any uptake of enteramine from the blood, thus strongly supporting the conclusion that it is synthesized in situ.
Factors Responsible for the Abnormal Development of Embryos Obtained by Nuclear Transplantation inXenopus laevis
Authors: Gurdon J. B.
Published: April 2021

An analysis has been made of factors which can cause abnormal development of embryos derived from transplanted nuclei in Xenopus laevis. A distinction is made between innate and technical factors, and between those which affect donor nuclei and recipient eggs. The innate developmental potentialities of endoderm donor nuclei do not appear to be limited, at least up to the early gastrula stage. Abnormalities known to be due to differentiated donor nuclei from later donor stages are described elsewhere. The technical treatment of donor nuclei can be carried out so as not to damage them, even if this is purposely made more severe than usual. The innate capacity for development of recipient eggs was found to vary considerably from one spawning to another; this variation seems to be due to an inability of the eggs of any one frog to withstand technical treatment which may be shown to be harmless to the eggs of other frogs. As the quality of recipient eggs can only be judged from results, experiments using Xenopus eggs should be accompanied by control transplantations, using donor nuclei the developmental capacity of which is already known. With these control transplantations for comparison, the technique is suitable for testing unknown developmental potentialities of different kinds of donor nuclei or recipient eggs.
The Development of Anucleolate Embryos ofXenopus laevis
Authors: Wallace H.
Published: April 2021

A Mutation of Xenopus has been found which reduces the maximum number of nucleoli per diploid nucleus from 2 in the wild-type to 1 in heterozygotes. Homozygous mutants possess no true nucleoli, hence being termed anucleolate. They do, however, possess pyronine-staining intranuclear organelles that are smaller and more numerous than typical nucleoli. The mutation can be considered as a recessive larval lethal, unlinked to sex: heterozygotes of both sexes are fully viable, but anucleolate larvae die at about the time their sibs begin to feed. These points have been recorded in two preliminary reports (Elsdale, Fischberg & Smith, 1958; Fischberg & Wallace, 1960). The development of anucleolate embryos is described here as a basis for the design of an experimental analysis of the ways in which the mutation acts. The description rests mainly on the progeny of a single mating of heterozygous toads, conforming with notes made on other such matings, from which additional data are drawn when required. As no developmental differences have been detected between the wildtype and heterozygotes, they are treated together as nucleolate (+n) controls, to which the anucleolate (On) embryos are compared. Nieuwkoop & Faber’s (1956) stages of normal development are used here to indicate age, made independent of temperature. After stage 40, the retarded On larvae are assigned to the stage of their controls.
Embryonic Responses to Structurally Related Inhibitors
Authors: Liedke Kathe , Gillespie H. B. , Graff Samuel
Published: April 2021

The effects of variously substituted quinoxalines, benzimidazoles, and benzotriazoles on Rana pipiens embryos of 2-cell (S. 3), blastula (S. 8), neurula (S. 14) and tail-bud stage (S. 18) were studied. It was found that: Toxicity is variably increased by double substitution with two nitro groups (diN) or a nitro group and a chlorine atom (N+Cl). The relative toxicity of the single N-substituent is diminished by the addition of a hydroxy group, and generally also by a methoxy group, but not by addition of a methyl group; still greater is the diminishing effect of the carboxyl group which nullifies all activity. Cl-substitution in place of N is less toxic except at stages 3 and 8 with benzimidazoles.Susceptibility to benzo triazoles increases with age of embryo from 2-cell to tail-bud stage 18, while the reverse is true for quinoxalines and benzimidazoles. The diN-or N+Cl-substituted compounds are exceptions, as they are highly toxic at all developmental stages under the experimental conditions.In young tadpoles (S. 25) N-substitution increases the toxicity of quinoxaline or benzimidazole approximately 10 times, and of benzotriazole as much as 40 times.
Culturein vitrode blastèmes de régénération de Planaires
Authors: Sengel Catherine
Published: April 2021

Young regeneration blastemata of Planarians have been cultivated in vitro on an agar-embryo extract culture medium which is a modification of the organ culture medium devised by Wolff & Haffen. Transverse cuts were made in whole worms and 3 days later the blastemata were isolated on the culture medium, where they survive for 10–15 days. There is no visible growth, but the observations reveal pigment formation by the third day, the appearance of muscles on the fourth or fifth day, and the presence of the eyes and brain by the tenth day. All three types of differentiation have been observed in the cultures of head blastemata, but only pigment and muscles are present in the cultures of tail blastemata. When two or more head blastemata are cultured together they differentiate into a larger head with supplementary eyes. The association of two or more tail blastemata does not result in the differentiation of eyes or brain. The combination of one head blastema with one or two tail blastemata in such cultures gives rise to a small planarian with a pharynx and a gut. The method of culturing regeneration blastemata in vitro reveals that the fate of the blastemata is determined quite early. A head blastema can differentiate cephalic structures, whereas a tail blastema cannot. However, if a head blastema is associated with a tail blastema in culture, then they differentiate into a complete planarian.
L’action inductrice du chordo-mésoblaste au cours de la gastrulation et de la neurulation et les effets de la culturein vitrosur ses manifestations
Authors: Gallera J.
Published: April 2021

One species of Urodele, Trituras alpestris, was used. The inducing capacities of the anterior chordal zone of the archenteron roof were studied in vitro by the ectoblastic ‘sandwich ‘method. The inducing material was taken from different stages of gastrulae and neurulae. The duration of induction (16–24 hours) had been determined by the results of the author’s previous experiments: it was sufficient to provoke a clear reaction in the ectoblast, but too short for the chordomesoblast to exert fully its specific regional inductive capacity.

When the period of induction was at an end, the two layers of the ‘sandwich ‘were separated to remove the inductor, and the layers were allowed to develop separately in Holtfreter’s solution. No difference was found in the inductive capacities of the dorsal and ventral surfaces of the archenteron roof.

Histological examination of the neural structures produced by the expiants confirmed the results obtained previously in analogous experiments involving transplants to the embryo. The inductive power of the chordomesoblast becomes considerably modified during gastrulation and neurulation. Its feeble power of inducing a forebrain is a more or less delayed acquisition, which only comes into action at the time when the process of neural induction is almost achieved in the embryo. It always possesses, however, a predominant power of inducing deutencephalon and spinal cord. The induction by the chordomesoblast of cerebro-sensory complexes which are exclusively acrencephalic becomes possible only when one dissociates the effects of the two activities manifested by the inductor.

A comparison of these results with those of the author’s previous experiments shows that it is easier for the chordomesoblast to induce a forebrain in ectoblast cultivated in vitro than in grafts implanted on the archenteron roof and then transplanted to the ventral surface of another embryo. In the first case, not only are acrencephalic formations much more frequent, but one can obtain them with a younger chordomesoblast. The saline solution of Holtfreter has a feeble acrencephalogenic action on the neural structures which have resulted from an insufficient induction and which are still labile in the direction of their development.

The author reviews the conception of neural induction held by Nieuwkoop, and the similar interpretation adopted by Johnen to explain the results of her experiments.
The role of the glycoconjugates in the migration of anuran amphibian germ cells
Authors: Delbos M. , Gipouloux J.-D. , Saidi N.
Published: April 2021

The presence of a large amount of glycoconjugates on the anuran amphibian germ cells was demonstrated using fluorescein isothiocyanate lectins binding specifically to D-galactose and at a lower level, by other lectins binding specifically to N-acetyl-galactosamine. Glycoconjugates including D-galactose were found near the pseudopodial expansions and in the extracellular space, between germ cells and follicular cells. They were also disseminated in the cytoplasm. The injection of PNA lectin (from Arachis hypogea) into the endoderm inhibited the migration of 90% of the germ cells. This inhibition was lectin-concentration dependent. Ultrastructural study of germ cells, the migration of which was inhibited, showed that they were degenerating. These results suggest that glycoconjugates are related to the migratory activity of germ cells.
Intestinal cyto differentiation in vitro of chick stomach endoderm induced by the duodenal mesenchyme
Authors: Ishizuya-Oka Atsuko , Mizuno Takeo
Published: April 2021

The inductive action of duodenal mesenchyme on the cytodifferentiation of stomach endoderm in chick embryos was investigated in vitro with electron microscopy and immunofluorescence. Morphologically undifferentiated endoderm of the stomach of a 4-day embryo could differentiate only into a mucous secretory epithelium when cultured in the absence of mesenchyme. However, when cultivated in recombination with 6-day duodenal mesenchyme, most cells of 4-day stomach endoderm differentiated into intestinal absorptive cells possessing striated border and sucrase, and goblet cells, but not into stomach-type mucous secretory cells. In contrast, when 4-day stomach endoderm was cultured recombined with mesenchyme of embryonic digestive organs other than intestine, none of the stomach endoderm cells differentiated into intestinal epithelial cells. The competence of stomach endoderm for intestinal cytodifferentiation decreased rapidly with development, but remained until relatively later stages in the gizzard region. The present investigation demonstrates that duodenal mesenchyme can induce stomach endoderm, which has acquired the potency for self-differentiation into stomach-type epithelium, to cytodifferentiate into intestinal epithelium.
Regeneration of surgically created mixed-handed axolotl forelimbs: pattern formation in the dorsal—ventral axis
Authors: Holder Nigel , Weekes Charleston
Published: April 2021

The regeneration of surgically created mixed-handed limb stumps is examined in the axolotl. Operations were performed in the lower arm and upper arm regions and grafts were allowed to heal for approximately one month prior to amputation or were amputated immediately. In the lower arm group both anterior and posterior limb halves were inverted, whereas only posterior halves were inverted in the upper arm group. Almost all the limbs regenerated were normal in the anterior-posterior axis, whereas a range of limb types were found when the dorsal-ventral axis was analysed using the metacarpal muscle pattern and epidermal Leydig cell number as positional markers. The carpal and forearm muscle patterns were also analysed in order to assess whether the pattern determined from analysis at the metacarpal level reflected that seen at more proximal levels. The results are discussed in terms of the possible role of cell contribution from the stump to the blastema and the relevance of the study to models of pattern regulation.
Muscle gene activation by induction and the nonrequirement for cell division
Authors: Gurdon J. B. , Fairman S.
Published: April 2021

We are investigating the mechanism by which animal cells of an amphibian blastula are induced to differentiate as muscle after contact with blastula vegetal cells. After briefly summarizing previous work on this system, we have asked whether this response of animal cells to vegetal induction requires cell division. Animal and vegetal parts of a blastula were placed in contact with each other, and the resulting conjugates cultured in medium containing a sufficient concentration of colchicine or cytochalasin B to inhibit cell division. Muscle differentiation, as indicated by cardiac actin gene transcription, is induced when cell division is inhibited, though at a substantially reduced rate. However, cytoskeletal actin gene transcription, which does not depend on induction, is also much reduced under the same inhibitory conditions. We conclude that, although the cell division inhibitors seem to reduce all gene transcription, they have no preferential effect on the response to induction, and therefore that this process does not require cytoplasmic or nuclear division.
The phenotypic interdependence of the musculoskeletal characters of the mandibular arch in mice*
Authors: Kay Elizabeth D.
Published: April 2021

Evidence from studies of craniofacial anomalies and the evolutionary transition from reptiles to mammals suggests that the temporomandibular joint (TMJ), bony zygomatic arch, middle ear ossicles and mandibular muscle pattern may form a correlated suite of characters. To test the degree of phenotypic interdependence among these features, mandibular arch defects were analysed in prenatal mice. Retinoic palmitate was administered to pregnant mice on day 8-7 to produce test foetuses with malformations of the mandibular arch. A rating scale was developed for each of the four characters so that numerical values could be assigned to each phenotype encountered. Control animals were used to establish normal phenotypes for each character which were assigned a value of 1. Data from each test age, 16, 18 and 19 days postconception, were pooled and Spearmann rank correlation coefficients between each of the traits were calculated.

Coefficients (R) range from a high of 0·87, between the TMJ and zygomatic arch, to a low of 0-67 between the zygomatic arch and the mandibular musculature showing highly significant correlations (P< 0·0001) among all characters. Therefore, the data suggest that the musculoskeletal features of the mandibular arch are phenotypically interdependent during development.
The effect of replacing different regions of limb skin with head skin on regeneration in the axolotl
Authors: Wigmore Peter , Holder Nigel
Published: April 2021

Head skin was used to replace different halves of limb skin from the upper and lower arms of axolotls. Replacement of upper arm posterior skin caused the regeneration of a high proportion of single-digit limbs while replacement of dorsal, ventral or anterior skin caused only minor defects to the normal skeletal pattern. When dorsal or ventral skin was replaced, however, regenerates often lacked dorsal or ventral muscle. Results from the lower arm were different in that replacement of any half of limb skin failed to cause defects either in the skeletal or muscular pattern. These results are used in conjunction with previous work (Wigmore & Holder, 1985; Wigmore, 1986) to suggest that posterior skin is essential for regeneration of the anteroposterior axis and dorsal and ventral skin is necessary for the differentiation of the muscle pattern in regenerates from the upper arm. In the lower arm no localized region of skin appears to be essential for regeneration of the normal pattern and the patterning mechanism may have a different spatial organization.
Dynamics of the control of body pattern in the development of Xenopus laevis: IV. Timing and pattern in the development of twinned bodies after reorientation of eggs in gravity
Authors: Cooke Jonathan
Published: April 2021

The mesendodermal anatomy of twinned larval axes is described in relation to the normal single pattern, when twinning has been caused by experimental tilting of eggs before first cleavage. The formation of two origins for gastrulation movements (dorsal lips) and their relatively rapid spread and coalescence to give a circular blastopore, is a predictor of twin formation in individual embryos after treatment. The anatomy of twins where development has been disturbed from the outset in this way is appreciably different from that induced by the later operation of second dorsal lip implantation. It is also variable in a systematic way. The total sizes of cellular allocations to individual notochords and prechordal head patterns are enhanced above normal if they arise relatively close together in the tissue, but significantly reduced if they arise far apart. These and other features of twinned patterns due to precleavage disturbance are discussed in terms of what they might indicate about the physicochemical nature of the body positional system. The results confirm that by a variety of rather simple, nonsurgical manipulations the relative amounts of territory in the egg devoted to different parts of the body can be greatly influenced.
Topographical control of cell behaviour: I. Simple step cues
Authors: Clark P. , Connolly P. , Curtis A. S. G. , Dow J. A. T. , Wilkinson C. D. W.
Published: April 2021

The photolithographic techniques of the microelectronics industry have allowed us to fabricate patterned plastic substrata to investigate contact guidance of animal tissue cells. The reactions of cells to single steps on a substratum were examined using time-lapse videorecording and scanning electron microscopy. BHK cells and chick embryonic neural cell processes exhibited gradual inhibition of crossing steps with a concomitant increase in alignment at steps dependent on increasing step height. Comparison of these cells’ reactions, with those of chick heart fibroblasts and rabbit neutrophils, at a 5 fim step revealed that the influence of topography is also dependent on cell type, the neutrophils being relatively unaffected. The presence of an adhesive difference at a series of steps altered BHK cells’ reactions such that the frequency of crossing was dependent on the direction of approach to a step. Although our data are consistent with Dunn & Heath’s proposal (1976) that the inflexibility of the cytoskeleton of a moving cell’s protrusion is the cellular property determining such reactions to topography, we have found that, on encountering a topographical feature, the response of a cell may be predictable on a probabilistic basis, i.e. the topographical feature reduces the probability of a cell making a successful protrusion and contact in a given direction, that even the largest features tested did not act as absolute barriers to cell locomotion since a small proportion of a population of cells were able to overcome them, and that other guidance cues could significantly alter a cell’s response. Even in situations where it is not the primary cue in directing cell locomotion, topographical control may be an important factor during morphogenesis since it must, at the very least, influence the efficiency of other cues.
Differential deposition of basement membrane components during formation of the caudal neural tube in the mouse embryo
Authors: O’Shea K. Sue
Published: April 2021

The distribution of basement membrane and extra-cellular matrix components laminin, fibronectin, type IV collagen and heparan sulphate proteoglycan was examined during posterior neuropore closure and secondary neurulation in the mouse embryo. During posterior neuropore closure, these components were densely deposited in basement membranes of neuro-epithelium, blood vessels, gut and notochord; although deposition was sparse in the midline of the regressing primitive streak. During secondary neurulation, mesenchymal cells formed an initial aggregate near the dorsal surface, which canalized and merged with the anterior neuroepithelium. With aggregation, fibronectin and heparan sulphate proteoglycan were first detected at the base of a 3- to 4-layer zone of radially organized cells. With formation of a lumen within the aggregate, laminin and type IV collagen were also deposited in the forming basement membrane. During both posterior neuropore closure and secondary neurulation, fibronectin and heparan sulphate proteoglycan were associated with the most caudal portion of the neuroepithelium, the region where newly formed epithelium merges with the consolidated neuroepithelium. In regions of neural crest migration, the deposition of basement membrane components was altered, lacking laminin and type IV collagen, with increased deposition of fibronectin and heparan sulphate proteoglycan.
Developmental and spatial patterns of expression of the mouse homeobox gene,Hox2.1
Authors: Krumlauf Robb , Holland Peter W. H. , Mcvey John H. , Hogan Brigid L. M.
Published: April 2021

The H ox 2.1 gene forms part of a cluster of homeo-box -containing genes on mouse chromosome 11. Analysis of Hox2.1 cDNAs isolated from an -day p.c. mouse embryo library predicts that the gene encodes a 269 amino acid protein (Mr, 29432). This deduced protein contains a homeobox 15 amino acids from the carboxy terminus and is very rich in serine and proline. A second partially conserved region present in several other genes containing homeo-boxes, the hexapeptide De-Phe-Pro-Trp-Met-Arg, is located 12 amino acids upstream of the homeodomain and is encoded by a separate exon. Analysis of Hox 2.1 gene expression reveals a complex and tissue-specific series of RNA transcripts in a broad range of feta] tissues (lung, spinal cord, kidney, gut, spleen, liver and visceral yolk sac). Comparison of the temporal patterns of gene expression during development and in the adult suggests that Hox2.1 is regulated independently in different tissues. Evidence is also presented that transcripts from other loci have extensive homology to the Hox2.1 gene in sequences out-side of the homeobox. In situ hybridization shows that Hox2.1 transcripts are regionally localized in the spinal cord in an apparent anterior–posterior gradient extending from the hind brain. The distribution of RNA also displays a cell-type specificity in the. lung, where mesodermal cells surrounding the branching epithelial cell layer accumulate high levels of Hox2.1 transcripts.
Chemotaxis of Chinese hamster ovary cells expressing the human neutrophil formyl peptide receptor: role of signal transduction molecules and α5β1 integrin
Authors: Miettinen Heini M. , Gripentrog Jeannie M. , Jesaitis Algirdas J.
Published: April 2021

Activation of the N-formyl peptide receptor (FPR) of human neutrophils by ligands such as N-formyl-methionine-leucine-phenylalanine (fMLP) induces mobilization of intracellular calcium, cell adhesion, chemotaxis, superoxide production and degranulation. Chinese hamster ovary (CHO) cells are normally devoid of FPR and unresponsive to fMLP, but when stably transfected with a human FPR cDNA, exhibited some of these same responses. Specifically, stimulation with fMLP resulted in release of intracellular calcium and chemotactic migration toward a gradient of fMLP. As in neutrophils, both processes were inhibited through receptor desensitization by prior exposure to a higher or equal concentration of ligand or by treatment with pertussis toxin. Soluble and membrane-bound fibronectin greatly increased fMLP-induced chemotaxis of CHO cells expressing FPR, but not of wild-type CHO cells, suggesting a role for FPR in activation of integrin function. Evidence for this hypothesis was obtained by demonstrating that CHO cells expressing FPR rapidly increased their adhesion to a fibronectin-coated surface after stimulation with fMLP. Both chemotaxis and adhesion were largely inhibited by RGDS peptide and a function-blocking antibody against α5 integrin. FPR-mediated chemotaxis of the CHO transfectants was partly inhibited by a tyrosine kinase inhibitor, herbimycin A, and blocked by a phosphoinositide 3-kinase inhibitor, wortmannin. These data suggest that stimulation of CHO FPR transfectants with a gradient of fMLP results in phosphoinositide 3-kinase-dependent chemotactic migration, which is enhanced by binding of activated α5β1 to fibronectin. This non-myeloid, non-lymphoid fibroblastic cell line will thus serve as a useful model to investigate additional requirements of signal transduction molecules, adhesion molecules and cytoskeletal elements in FPR-mediated chemotaxis.
Apparent H+ Excretion and CO2 Dynamics Accompanying Carapace Mineralization in the Blue Crab (Callinectes Sapidus) Following Moulting
Authors: Cameron James N. , Wood Chrism M.
Published: April 2021

Just after moulting the blue crab, Callinectes sapidus, is soft and defenceless, but in the following days, a hard calcareous shell is formed for support and protection. The carapace of intermoult (hard) crabs constitutes 27% of the wet weight and 53% of the dry weight, with 14% of the body water contained in a carapace fluid compartment. The pH of the shell fluid compartment is maintained at 0·3 to 0·5 pH units above that of the blood. The mineral portion of the carapace is primarily CaCO3, with minor components of Mg2+ and PO4−3 plus traces of other ions. The formation of a new shell after moulting is accomplished by apparent H+ excretion and Ca2+ uptake at remarkable rates, averaging 12·5 and reaching as high as 21 mequiv kg−1 h−1. Direct bicarbonate uptake from the sea water appears to be an important component of the apparent H+ efflux, since CO2 is deposited in CaCO3 at a rate greater than metabolic production, and the animals show a net CO2 uptake for several days.
A Quantitative Description of Flagellar Movement in Golden Hamster Spermatozoa
Authors: Ishijima Sumio , Mohri Hideo
Published: April 2021

Flagellar movement of golden hamster spermatozoa obtained from the testis and the caput and cauda epididymides was observed by a light microscope while holding them at their heads with a micropipette. Flagellar movement of capacitated spermatozoa and of reactivated spermatozoa demembranated with Triton X-100 was also observed. Testicular and caput epididymal spermatozoa showed weak movement in Tyrode’s solution, whereas cauda epididymal spermatozoa showed vigorous movement. The flagellar bends of the’ cauda epididymal spermatozoa were almost planar. Capacitated spermatozoa moved with waves of a large amplitude. Demembranated spermatozoa reactivated with ATP only had a latent period before the initiation of flagellar movement, and beat at low frequency, whereas demembranated spermatozoa reactivated with both ATP and cAMP began to move immediately at high frequency. Thrust and hydrodynamic power output were calculated using the parameters for the typical waveforms of cauda epididymal spermatozoa before and after capacitation. The possible role of the large amplitude beat in capacitated spermatozoa is discussed. A comparison of the ‘principal’ and ‘reverse’ bends in golden hamster sperm flagella as defined by Woolley (1977) with those in sea urchin sperm flagella suggests that the so-called ‘principal’ bend in golden hamster sperm flagella corresponds to the reverse bend in sea urchin sperm flagella and vice versa.
Motor Programme Switching in the Crayfish Swimmeret System
Authors: Heitler W. J.
Published: April 2021

Intracellular and extracellular recordings have been made from neurones of the swimmeret system in the semi-isolated abdominal ganglion of the crayfish during rhythmic activity. Extracellular recordings commonly reveal a motor programme (MP1) consisting of low-amplitude symmetrical power and return stroke activity with phase-constant posterior-to-anterior intersegmental coordination. Occasionally a different motor programme (MP2) is expressed. MP2 has higher amplitude episodic activity, with return stroke duration greater than power stroke, and with latency-constant anterior-to-posterior or near synchronous intersegmental coordination. Preparations may switch spontaneously between the two motor programmes. Intracellular recordings show that interneurones whose membrane potentials oscillate during MP1 and which can reset its rhythm usually cease to oscillate during MP2. During production of MP1, current injected into any one of a small number of interneurones can induce MP2. The polarity of current required is usually such as to drive the membrane potential towards the level normally associated with return stroke during MP1. During MP1 many motor neurones receive synaptic input with approximately sinusoidal waveform. During MP2 they may receive an episodic input with approximately sawtooth waveform, and/or input consisting of large, unitary EPSPs. The unitary EPSPs drive a ‘bursty’ mode of MP2 activity that is sometimes seen. The bursts of unitary EPSPs in MP2 appear to derive from a different source to that of the sinusoidal input in MP1. These sources are probably caudally-conducting through-interneurones and non-spiking local interneurones respectively. Thus experimental perturbation of a single neurone can induce a motor programme switch such as to change the activity of some hundreds of neurones in at least three ganglia. Neurones with this property would be convenient targets for controlling influences in the intact animal.
Contractile and Metabolic Characteristics of Muscle Fibres From Antarctic Fish
Authors: Johnston Ian A. , Harrison Paul
Published: April 2021

Contractile properties were determined for muscles from three species of Antarctic fish with broadly similar activity patterns: Trematomus hansoni, Notothenia rossii and Chaenocephalus aceratus. C. aceratus differs from the other species in that the genes for the respiratory pigments are not expressed.

Red and white fibres were isolated from the pectoral fin adductor and trunk muscles, respectively. Fibre segments were chemically skinned with the nonionic detergent Brij-58. All experiments were carried out at 0°C. Maximum isometric tensions (P0) were 6·6–7·1 Ncm−2 for red, and 21·4–25·1 N cm−2 for white muscle fibres. The force-velocity (P-V) characteristics of muscle fibres were determined by step isotonic releases. Unloaded contraction velocities (muscle lengthss−1, L0S−1) were 0·7 for red, and 0·9–1·1 for white fibres. Maximum mechanical power outputs (Wkg−1 muscle for white muscle), calculated using Hill’s equation for muscle shortening, were 26·7 (T. hansoni), 15·7 (A. rossii) and 22·7 (C. aceratus). Corresponding values for red pectoral muscle fibres were around 4·2Wkg−1 for all three species.

Maximum activities of enzymes of carbohydrate utilization (hexokinase, phosphofructokinase, lactate dehydrogenase), fatty acid metabolism (carnitine palmitoyl transferase, 3-OH acyl CoA dehydrogenase) and aerobic mitochondrial metabolism (cytochrome oxidase) were measured in muscle homogenates from C. aceratus and N. rossii at 0°C. Red pectoral muscle fibres from C. aceratus and N. rossii had similar activities of cytochrome oxidase, carnitine palmitoyltransferase and glycolytic enzymes. Hexokinase activities were two times higher in the red fibres of C. aceratus than N. rossii, suggesting a greater capacity for aerobic glucose utilization in the former species.

In spite of the lack of respiratory pigments, the metabolic and mechanical characteristics of the swimming muscles in C. aceratus apppear to be similar to those of other Notothenioids. Power outputs and enzyme activities of Antarctic fish muscle measured at 0 °C are comparable to those for temperate species measured at 15 or 25 °C, indicating a high degree of cold-adaptation of both energy-producing and energy-utilizing pathways.
The Ventilation Cycle in Octopus
Authors: Wells M. J. , Smith P. J. S.
Published: April 2021

Pressure measurements made at various points inside the mantle show that the ventilatory stream of the resting animal is driven by very small (often less than 0·5 cmH2O) pressure differences. Inspiration occupies less than one-third of the total cycle time, while flow across the gills is evidently continuous, since there is always a pressure differential between the prebranchial and postbranchial parts of the mantle cavity. The fact that branchial heartbeats do not correlate with ventilatory movements is further evidence that water flow through to the gills is both steady and continuous.