bluuebunny/crossref_metadata_2025 huggingface dataset:
The interaction of the organizing regions in hydra and its possible relation to the role of the cut end in regeneration
Authors: Newman Stuart A.
Published: April 2021

Regeneration in hydra does not necessarily involve cell division, so that the problem of pattern regulation is essentially one of finding the processes by which a given population of cells are assigned appropriate functions in the correct positions. The restoration and nature of the organizers or ‘dominant regions’ must also be explained.

Lateral transplants of the two different organizer tissues (hypostome and basal disc) into the digestive regions of host animals unexpectedly antagonize one another’s inductive ability, suggesting that the heretofore separately studied distal and proximal developmental fields may in fact be interconnected. A model based on this idea, incorporating the extinction results with classical findings, leads to the hypothesis of a role for leakage from the cut surface as a trigger for the regenerative process. This is tested using a ligature technique in which the cut surface is minimized when the hypostome is removed, and the degree of regeneration is found to be significantly lowered, in agreement with prediction.

These results are discussed in relation to ‘positional information’ and ‘special substance’ models for pattern formation.
Cell redundancy in the zona-intact preimplantation mouse blastocyst: a light and electron microscope study of dead cells and their fate
Authors: El-Shershaby A. M. , Hinchliffe J. R.
Published: April 2021

In the zona pellucida-intact 95 h post coition mouse blastocyst, electron-microscopic studies reveal the presence, as a part of normal development, of 1–2 dead cells lying free on the surface of the inner cell mass (1CM) or trophoblast cells, and of 4–5 dead cells phago-cytosed by I.CM cells. Such dead cells are electron-dense and show characteristic chromato-pycnosis of the nucleus, and swelling of the endoplasmic reticulum. In addition, 1–2 digestive vacuoles with granular contents and myelin figures are found, principally in ICM cells, and corresponding with basophilic bodies observed with the light microscope. The results are interpreted as indicating that a relatively large number (i.e. a minimum of 6–8, or approximately 10%) of blastocyst cells die and are phagocytosed and digested, usually by the ICM cells, but probably also by trophoblast cells. This process does not, however, affect the future differentiation of the ingesting cell. Simultaneously a small number of epithelial cells adjacent to the blastocyst die, either singly or in small groups. These findings confirm the view that previous reports of penetration of the uterine epithelium by ‘primary invasive cells’ originating in the ICM were due to confusion between two separate groups of dead cells, namely the embryonic dead cells of the ICM and the single dead cells in the adjacent uterine epithelium, which appear to be phagocytosed by trophoblast cells following loss of the zona pellucida.
Polarizing and maintenance activities in two polydactylous mutants of the fowl: diplopodia
1 and talpid
2
Authors: Maccabe Jeffrey A. , Abbott Ursula K.
Published: April 2021

In two polydactylous mutants, talpid2 and diplopodia1, polarizing activity appears to be present only in the normal location in the posterior corner of the limb-bud. There is, thus, a preaxial extension of maintenance activity without an accompanying extension of demon-strable polarizing activity. Experiments involving apex exchanges between normal and talpid2 wing-buds suggest that the movement of ‘maintenance factor’ per se from preaxial talpid2 limb tissue into a normal apex does not occur.
Some aspects of the development of the notochord in mouse embryos
Authors: Jurand A.
Published: April 2021

Prenotochordal cells are derived by proliferation from the pluripotential ectoderm in the Hensen’s node area, and they migrate in the cephalic direction to be incorporated into the roof of the archenteron. Later, after separation from the archenteron, the notochord probably includes some endodermal cells. Topographically it occupies an intermediate position between the ectoderm and endoderm. In this way it assumes a mesodermal-like character. After separation fiom the archenteron, the differentiation of the organ and its cells follows a cranio-caudal gradient. At the time of separation the basal lamina, originally covering the dorsal side of both the prenotochordal and endodermal cells, remains continuous between the endoderm and the notochord. Its presence from the earliest stages of morphogenesis of the notochord presumably indicates that it plays an important formative role.

The cells of Hensen’s node contain numerous microtubules, centrioles and cilia. In later stages fibrillogenesis in the prenotochordal and notochordal cells and excortication (ecdysis) occur. The intracellular fibrillar material in the notochordal cells may first form the basal lamina and later the perichordal sheath. In 12 to 13-day-old embryos, during excortication of the fibrillar material, the basal lamina undergoes disruption and eventually disappears. From the 10th day onwards, the outer plasma membrane shows an active endocytosis, by the formation of micropinocytic vesicles. Vacuolization occurs in the later stages of morpho-genesis and it is suggested that this is due to dilation of endoplasmic reticulum and mito-chondria.

There is no evidence of a syncytial stage in the development of the notochord in mouse embryos.
Effects of X-rays on nucleic acid metabolism during cleavage and gastrulation inPleurodeles waltliieggs
Authors: Alexandre H.
Published: April 2021

X-irradiation produces a rapid and substantial decrease in DNA synthesis in cleaving eggs of Pleurodeles, as shown by thymidine incorporation experiments; this decrease is presumably due to the arresting of the cell cycle in many blastomeres. DNA replication is partly resumed at the late blastula stage after irradiation at the 2- to 4-cell stage.

The present work demonstrates a high radiosensitivity of the metabolic pathway leading to the incorporation of uridine into DNA; this could be the result of the inhibition of the activity or the synthesis of such enzymes as ribonucleotide reductase, thymidylate synthetase and CTP synthetase. The radiosensitivity of this metabolic pathway becomes lower after gastrulation.

Finally, irradiation strongly inhibits the synthesis of new RNA species at gastrulation, but seems to have no effect on heterodisperse RNA (mRNA) synthesis during cleavage.

The results are discussed in relation to the biochemistry of early stages of development in Amphibians.
The cellular basis of movement of the migrating grex of the slime mouldDictyostelium discoideum:chemotactic and reaggregation behaviour of grex cells
Authors: Garrod D. R.
Published: April 2021

The chemotactic behaviour of cells of the migrating grex of D. discoideum has been studied by observing the responses of small groups of cells placed near to aggregation streams, agar blocks containing cyclic AMP or migrating grexes. Grex cells placed near aggregation streams were not attracted to the streams initially; after about I h, however, some cells were attracted to the streams. Similarly, grex cells placed near agar blocks containing cyclic AMP were not initially attracted towards the blocks, but some attraction was observed after about 1 h; the most effective cyclic AMP concentration was 10_4 M. Grex cells which were placed in heaps against the sides of aggregation streams, instead of a short distance away, were often incorporated into the streams within . Grex cells were not attracted towards migrating grexes.

Because of these results it is suggested that (1) migrating grex cells are not chemotactically sensitive to cyclic AMP, but they acquire chemotactic sensitivity after separation from the grex for about 1 h ; (2) chemotaxis is probably not involved in the movement of the migrating grex; (3) grex cells retain the adhesive property found in aggregating cells, which is involved in the formation of end-to-end contacts necessary for the behaviour known as contact following.

Reaggregation of dispersed grex cells was studied by time-lapse photography. Reaggregation was found to be a two-stage process: first, an adhesive phase dependent on the development of intercellular contacts at the expense of adhesions with the substratum; secondly, a chemotactic phase which begins about 1 h after dispersal of the grex cells. It is suggested that the first phase may be accounted for by assuming that the cells are more cohesive than adhesive.
Extent and properties of the regeneration field in the larval legs of cockroaches (Leucophaea maderae): III. Origin of the tissues and determination of symmetry properties in the regenerates
Authors: Bohn Horst
Published: April 2021

Previous papers dealing with the regeneration field of cockroach (Leucophaea maderae) legs have shown that two elements of the leg surroundings are indispensable for regeneration of a leg: the basal sclerites and the ‘]eg-inducing membrane’ (LIM). The experiments of this paper partly clarify the way in which these two tissues interact; the origin of the regenerative tissues and the determination of polarity and symmetry in the regenerated legs were studied.

By combination of sclerites and LI M of different species or segments it has been shown that each of the tissues makes up half of a leg regenerate -the sclerite tissues the anterior longitudinal half, the LIM the posterior longitudinal half.

The trochantin was implanted in four different orientations (normal, turned 90° clockwise or anti-clockwise, turned 180’) into a normally orientated field of LIM. The anterior-posterior and medio-lateral axes of the regenerates had the same orientation as those of the sclerites. Therefore, the sclerites alone determine symmetry of the regenerate; the LIM has no influence in this respect. Neither of the two axes is fixed irreversibly in the cells of the LIM; the cells seem able to accept any polarity which is forced upon them by the sclerites. The symmetry properties are more strongly fixed in the cells of the sclerites, but an inversion of polarity (through 180°) is possible for both axes.

Regeneration of a leg from the level of the trochantin seems to be initiated by or dependent on a small medial region of the trochantin. A tiny fragment of the medial wedge of the trochantin, when transplanted to a field of LIM, can form a complete leg regenerate; a lateral half of the trochantin never does. As long as this small medial part of the trochantin is prevented from making contact with LIM by a praecoxa fragment, no regeneration takes place at the anterior border of the trochantin, even when the greatest part of the border has contact with LIM.

The regenerative capacities of the praecoxal sclerite are different at the anterior and posterior cut surfaces, irrespective of the level of the cut and the orientation of the sclerite. An anterior cut surface never forms a leg regenerate, but a posterior cut surface does.
Biochemical control of fresh-water sponge development : effect on DNA, RNA and protein synthesis of an inhibitor secreted by the sponge
Authors: Rozenfeld Francine
Published: April 2021

During their growth, fresh-water sponges release into the medium a dialysable inhibitor (gemmulostasin) which reversibly blocks development of the gemmules at an early phase, prior to the first mitoses.

The incorporation of [3H]labelled precursors into DNA, RNA and proteins has been measured throughout development, in the presence or absence of inhibitor. Autoradiographic controls of the nuclear incorporation of [3H]thymidine have been made. Gemmulostasin erases the peak of [3H]thymidine incorporation that otherwise occurs just before the first mitoses. Its overall effect is to bring about, either directly or indirectly, a high peak in the incorporation of [3H]uridine and [3H]leucine at a time when the incorporation of these precursors is low in the controls.

It is suggested that a causal relation exists between these phenomena.
Dedifferentiation, redifferentiation and bundle formation of smooth muscle cells in tissue culture : the influence of cell number and nerve fibres
Authors: Chamley Julie H. , Campbell Gordon R. , Burnstock Geoffrey
Published: April 2021

Smooth muscle from newborn guinea-pig vas deferens was enzymically dispersed into single cells or small clumps and grown in culture in the presence or absence of sympathetic ganglion explants.

Most single smooth muscle cells gradually lost their typical ultrastructural features and contractile properties during the first few days in culture. At 7 days of culture these de-differentiated smooth muscle cells underwent extensive proliferation. If sufficient cells were present in the culture inoculate, a continuous monolayer formed at about 9 days of culture and redifferentiation of smooth muscle began. At 11–12 days of culture the cells reaggregated into clumps, began to contract spontaneously, and formed into well-organized muscle bundles in two layers at right angles, resembling the muscle layer organization of the in vivo NZS deferens. In cultures where a continuous monolayer was not formed at 9 days, isolated cells did not redifferentiate. The process of dedifferentiation and proliferation was delayed in those smooth muscle cells which had sympathetic nerve fibres in close association.

Clumps of vas deferens tissue which were not fully dispersed by the enzyme treatment did not dedifferentiate with time in culture but muscle bundles were disrupted and asyn-chronous contractions resulted. After 8–12 days of culture the muscle bundles reformed and foci of synchronous contractions developed. Nerve fibres appeared to accelerate bundle and nexus formation in this situation, with synchronous contractions resuming at 3–5 days.

The relation of these findings to the process of wound healing in smooth muscle tissues in vivo is discussed.
A block to cross-fertilization located in the egg jelly of the frog Rana clamitans
Authors: Elinson Richard P.
Published: April 2021

The egg of Rana clamitans enrobed in its native jelly was not fertilized by sperm of R.pipiens. However, when R. clamitans eggs were enrobed by R. pipiens jelly, they were fertilized by R. pipiens sperm. Male pronuclei were found in the eggs, and most of the resulting embryos were diploid. The embryos gastrulated, but most arrested at mid-to late gastrula stages. Some begun neurulation, but none survived longer than 4 days. When R. clamitans eggs in R. pipiens jelly were fertilized by R. clamitans sperm, the embryos developed normally except that they failed to hatch.

In the reciprocal experiment, R. pipiens eggs were enrobed in R. clamitans jelly. The eggs were not fertilized by R. pipiens sperm but were fertilized by R. clamitans sperm. Therefore, the R. clamitans jelly plays a major role in preventing fertilization by sperm of other species.

The R. clamitans jelly’s block to cross-fertilization was not a block to sperm migration. Further, the R. clamitans jelly contained factors which permitted R.pipiens sperm to fertilize dejellied R. pipiens eggs. Dejellied eggs are usually not fertilizable in the absence of jelly factors.
Structure and development of ommatidia in Oncopeltus fasciatus
Authors: Shelton P. M. J. , Lawrence P. A.
Published: April 2021

The structure and development of ommatidia has been examined in Oncopeltus fasciatus (Lygaeidae). Each ommatidium is composed of 18 cells comprising four crystalline cone cells, two primary pigment cells, four secondary pigment cells and eight retinula cells. Ommatidia are of the apposition type and the retinula cells are arranged on the open rhabdomere plan.

During the five larval stages the retina grows anteriorly to provide a 12-fold increase in numbers of ommatidia. Grafts of presumptive eye epidermis show that the proliferating anterior border of the developing retina is an area of epidermal cell recruitment rather than a special budding zone.

Mosaic retinae were formed by grafting epidermis from near the eye of wild-type donors into the corresponding region of mutant hosts. Ommatidia which developed at the borders of the graft contained mixtures of wild-type and mutant cells in variable and unpredictable combinations. Similar mosaic structures were seen in retinae generated by irradiation at early stages of development. The suggestion that each ommatidium is clonally derived from a single epidermal stem cell is thus disproved.

The frequent occurrence of mosaic ommatidia containing only one cell of a different genotype from the rest suggests that the formation of ommatidial clusters follows the main proliferative phase of eye growth. We conclude that cell determination within ommatidia is not connected with lineage but is dependant upon cell position within the developing ommatidium.
A quantitative study of blastemal growth and bone regression during limb regeneration in Triturus cristatus
Authors: Smith A. R. , Lewis J. H. , Crawley A. , Wolpert L.
Published: April 2021

Soft X-ray photographs show both the outlines of the soft parts of the regenerating limb and the bones. This enables one to make quantitative studies on bone regression and the growth of the regenerate, since good reference points are available. Bone regression of about 0·5 mm was observed to occur within about 20 days following amputation. Growth curves of regenerates cut at different levels confirm Spallanzani’s old observation that the total time for regeneration is fairly constant for different levels of amputation -regenerates from proximal levels regenerate faster. However, the intrinsic growth rate curves are remarkably similar for different levels of amputation; the difference in final length arises because the short period of high intrinsic growth rate continues for slightly longer in regenerates from proximal levels.

In terms of the progress zone theory of limb development, three phases of regeneration are recognized: the formation of the blastema and progress zone; the laying down of the skeletal rudiments by the rapidly proliferating progress zone; and the subsequent slower growth of the rudiments. A quantitative model is put forward and it is shown that it can provide a good description of the observed growth curves. An important assumption is that the various skeletal rudiments are the same size when they leave the progress zone and the final differences in size reflect differences in the final growth phase. The progress zone model provides new quantitative insights into the relationship between the growth of the limb as a whole and the behaviour of individual cells.
Participation of cartilage grafts in amphibian limb regeneration
Authors: Wallace H. , Maden M. , Wallace B. M.
Published: April 2021

Irradiated axolotl arms bearing grafts of pure cartilage obtained from the non-irradiated humerus of other specimens show a variable response to amputation of the hand. Some arms grow spikes with little morphogenesis, others produce one or more digits, and some regenerate small and defective but recognizable hands. Identically irradiated control arms which carry no grafts or grafts of irradiated tissue show none of these features. The cartilage grafts must therefore be responsible for the limited amount of regeneration observed. The origin of the regenerated tissues could not be independently determined in this experiment, although grafts were made reciprocally between white and dark genotypes, as all the regenerates were either very pale or completely unpigmented. A previous demonstration that grafted tissue does not reactivate irradiated host cells, however, permits the conclusion that the grafted cartilage provides all the mesodermal tissues of these regenerates.

The grafts consisted exclusively of chondrocytes, while the regenerates contained cartilage, muscle, blood vessels, nerve sheaths and general connective tissue. It is concluded that chondrocytes dedifferentiate into pluripotent blastemal mesenchyme cells which can re-differentiate into all other internal tissues of the limb. The concepts of modulation and neo-blasts (undifferentiated reserve cells) thus have no basis in amphibian limb regeneration.
Regional developmental capacities of the rat embryonic endoderm at the head-fold stage
Authors: Švajger A. , Levak-švajger B.
Published: April 2021

Three areas, composed of all three germ layers, were isolated from Fischer strain rat embryonic shields at the head-fold stage, and grafted separately under the kidney capsule of adult male rats of the same strain. The areas were from the neural plate, Hensen’s node and the primitive streak. The resulting teratomas were examined histologically for the presence of derivatives of the primitive gut.

The grafts differed strikingly in their capacity to develop into different segments of the gut. Endoderm underlying the neural plate developed into derivatives of the foregut, while endo-derm underlying the primitive streak developed mainly into derivatives of the mid-and hindgut.

It was concluded that, at the head-fold stage, the capacities to develop into different segments of the definitive gut are already roughly limited to particular areas of the endoderm.
The effect of excess vitamin A on the development of rat embryos in culture
Authors: Morriss Gillian M. , Steele C. E.
Published: April 2021

Primitive streak stage rat embryos were cultured in serum containing added vitamin A alcohol at concentrations ranging from 0·5 to 20 μg/ml. At the higher concentrations there was an overall growth retardation, and differentiation was inhibited. This was thought to be due to inhibition of DNA synthesis. At 0· 5 μg/ml the embryos developed abnormally in a manner similar to that previously seen in vivo. This result, which was supported by an ultra-structural study, provides evidence that the teratogenic effects of vitamin A are due to a direct action on the embryos.

Comparison of embryonic development in vitro at different concentrations of vitamin A with the results obtained in vivo suggests that in the latter, only a very small proportion of the amount injected was reaching the embryos in an active form. The maternal factors involved are discussed, and excess vitamin A is defined as an excess of free and non-specifically bound retinol. The levels of vitamin A which affected differentiating embryos in vitro are lower than the minimum levels previously shown to affect differentiated tissues. This suggests that relatively minor increases in serum levels during pregnancy may cause malformations without affecting the maternal organism. Since raised serum vitamin A levels have been shown to be associated with impaired liver function in man, these factors may be significant in human teratogenesis.
Synthesis of RNA in oocytes of Xenopus laevis during culture in vitro
Authors: Colman A.
Published: April 2021

RNA synthesis can be maintained in large oocytes of Xenopus laevis during periods of in vitro culture of at least 10 days. A simple salt medium, modified Barth’s solution, is found to be as effective a culture medium for these oocytes as several other complex media. The newly synthesized RNA is characterized electrophoretically and shown to consist predominantly of ribosomal RNA precursor, 28S and 18S ribosomal RNA, and 4S RNA. The distribution of this RNA within the oocyte is detected autoradiographically, where it is found to be greatly concentrated over the nucleoli. No qualitative alterations in either of these parameters are found during culture, within the limits of sensitivity of the assay procedures.
Studies on the locomotion of primordial germ cells from Xenopus laevis in vitro
Authors: Heasman Janet , Mohun Tim , Wylie C. C.
Published: April 2021

The mechanism of embryonic cell movement is poorly understood. Primordial germ cells (PGCs) of the anuran amphibian Xenopus laevis migrate individually from their site of determination in the embryonic endoderm to their site of differentiation, in the developing gonad. PGCs have been isolated during their migratory phase from tadpoles, and their movement studied in vitro on a variety of natural and artificial substrates.

On all artificial substrates used, including acid-washed glass, tissue-culture plastics, poly-L-lysine-coated glass, and collagen, the PGCs move by amoeboid extrusion of hemispherical lobopodia. Several considerations make it unlikely that this is the mechanism employed in vivo.

On living cellular substrates, e.g. monolayers of Xenopus laevis embryonic cells, adult kidney cells, and adult mesentery cells, PGCs become firmly attached and undergo phases of elongation and contraction. They move by elongation, coupled with the extrusion of filopodia, followed by waves of contraction, and ultimately by retraction of the trailing end of the cell. Evidence is presented that this is the mode of locomotion normally employed by PGCs in vivo.
Tractus uro-génital des chimères chez l’amphibien modèle Triturus alpestris Laur
Authors: Houillon Charles
Published: April 2021

Urogenital tract in chimaeras of the urodele amphibian Triturus alpestris

Embryonic grafting in Triturus alpestris allows homosexual (♀-♀ and ♂-♂) and heterosexual (♀-♂ and ♀ ♂) connexions of anterior and posterior part of two different tail-bud-stage embryos. Most of the 46 chimaeric animals obtained have been shown to possess two pairs of gonads. Among homosexual chimaeras, females (♀-♀) possess four ovaries and males (♀-♂) four testes. Among heterosexual chimaeras, some animals (♂-♂) show two sterile anterior ovaries and two normal posterior testes, other heterosexual chimaeras (♂-♀) possess normal anterior testes and sometimes well-differentiated posterior ovaries. These results confirm those obtained in Pleurodeles waltlii by the same author.

Final sex differentiation of the gonads seems likely to be an effect of their reciprocal position down the longitudinal axis of the chimaera : an anterior ovary is entirely inhibited by a posterior testis, but a posterior ovary may differentiate and reach sexual maturity notwithstanding a well-developed anterior testis. These kinds of adult heterosexual chimaeras (♂-♀) can be accounted as hermaphrodites.

Statistically, the number of homosexual chimaeras ♂-♂ is significantly greater than the other homosexual ♀-♀ or heterosexual ♀-♂ and associations. This fact may be due to the total inhibition of anterior ovaries in some heterosexual chimaeras, but also, to a phenotypic sex reversal of the female part.
Precocious evagination of the embryonic chick thyroid in ATP-containing medium
Authors: Hilfer S. Robert , Palmatier Bernice Y. , Fithian Eileen M.
Published: April 2021

The identification of actin and myosin in many cell types other than muscle has given support to the hypothesis that contractile proteins are involved in cell shape changes. However, there is no direct evidence that a contractile process participates in morphogenetic movements during organogenesis. As a first step in testing this possibility, thyroid placodes of chick embryos were treated with an incubation medium containing Triton X-100 and ATP. Pharyngeal regions, isolated in Medium 199, were photographed at timed intervals. At a concentration of 10−3 M ATP, the thyroid region formed a deep pit within minutes after addition of this ‘contraction medium’, whereas evagination requires approximately 7 h in ovo. Treatment with Medium 199 containing either Triton X alone, ATP alone, or Triton X and pyrophosphate did not result in evagination of the thyroid. Substitution of other nucleotides for ATP suggested a specific requirement for ATP. Surgical removal of selected portions of the pharyngeal floor and examination of sectioned material by light microscopy indicated that the cells involved in the shape change were located at the periphery of the thyroid placode before treatment. The sharp bends that were formed in ‘contraction medium’ cannot be explained entirely by pinching of cell apices at the point of folding; rather the effect of several forces is indicated in the evagination.
The onset of phosphatase activity in early mammalian embryos
Authors: Ishiyama V. , Izquierdo L.
Published: April 2021

The onset of acid and alkaline phosphatase activity is determined by means of Burstone’s azo dye coupling methods in oocytes and embryos of the mouse, rat and hamster, and in mouse embryos cultured in vitro. Acid phosphatase activity is detected in all cases while alkaline phosphatase activity begins during the 4-cell stage and is always present thereafter. The method is sensitive regarding detection of activity but does not permit the quantification nor a precise localization of the enzymes.
Vitesse de croissance et renouvellement des dents chez les Amphibiens
Authors: Chibon Pierre
Published: April 2021

Growth rate and replacement of teeth in Amphibians

The growth rate of teeth depends on age: it varies from 5 days for the first teeth, functional at hatching time, to 2 months for 2-year-old animals. The life time of a functional tooth is 20 days in the young larva and in the young post-metamorphic individual; it is not precisely known in adults. The proteins of organic matrices are elaborated in ergastoplasm, transported through the Golgi apparatus and Golgian vesicles, and deposited outside the cells within 1 h. Destruction of old teeth begins before metamorphosis; it is performed by pulp cells necrosis, and intervention of macrophages and osteoclasts; teeth are completely destroyed in situ, allowing growth of the replacement teeth. Thyroxine hastens tooth replacement.
Feedback inhibition of erythropoiesis induced in anaemic Xenopus
Authors: Aleporou Vassiliki , Maclean Norman
Published: April 2021

Serum from normal Xenopus, when injected into anaemic Xenopus, causes reduction in both DNA and protein synthesis in erythroid cells as indicated by in vitro culture of the blood cells. Experiments with erythrocyte-conditioned medium, reveal that this inhibitory substance can be recovered from mature erythrocytes. Sephadex G-25 fractionation of normal serum and haemolysate demonstrates that the inhibitory factor consists of molecules of low molecular weight, and experiments with cells of Xenopus kidney reveal that the feedback inhibition may be tissue specific to erythroid cells.
Measurement of metabolites in single preimplantation embryos; a new means to study metabolic control in early embryos
Authors: Barbehenn Elizabeth K. , Wales Raymond G. , Lowry Oliver H.
Published: April 2021

The preimplantation mammalian embryo offers many unique research opportunities. Among these is the possibility of studying the progression of metabolic systems during the transition from the single, free-living, migratory germ cell to the multicellular blastocyst, ready for sessile existence and dependence on second-hand nutrition.
Teratological evaluation of 5-fluorouracil and 5-bromo-2-deoxyuridine on hamster fetuses
Authors: Shah Ravindra M. , MacKay Robert A.
Published: April 2021

A single intraperitoneal injection of 5-bromo-2-deoxyuridine (BUDR) between days 9 and 11 and a single intramuscular injection of 5-fluorouracil (FU) between days 8 and 11 of gestation were teratogenic in hamster. The malformation frequencies were related to the dose and time of BUDR and FU treatment but the pattern and types of malformations and their frequencies were different. BUDR showed lower embryotoxic effect than FU. Both drugs impaired general fetal growth. It is suggested that the differences between FU and BUDR may be related to the chemical nature and metabolism of the drug and their eventual effect on the species-specific target tissue.
Regeneration and compartments inDrosophila
Authors: Szabad Janos , Simpson Pat , Nöthiger Rolf
Published: April 2021

A clonal analysis was performed in order to study the process of regeneration in wounded wing discs of Drosophila. Regeneration was induced either by cutting the disc in situ, or by shifting gynandromorphic larvae whose male tissue was hemizygous for a temperature-sensitive cell lethal to the restrictive temperature. Fast growing M+ clones, labelled with y and/or mwh, were produced by X-irradiation of the following genotypes: y; scJi(y+)M(3)i55/ mwh jv M+ (series I), and l(1)ts 504 sn3l(1)ts 5697/ In(1)wvC; M(3)i55/mwh M+ (series II). The clones were induced either before or after the experimental lesion. Clones initiated one day prior to the lesion were able to cross compartment boundaries whereas clones initiated one day after the lesion did not do so. It is concluded that cells involved in the process of regeneration lose their compartmental commitment, but that later on the growing population of cells again becomes subdivided into the same compartments.
Myotypic Respecification of Regenerated Nerve-fibres in Cichlid Fishes
Authors: Arora H. L. , Sperry R. W.
Published: April 2021

The mandibular portion of cranial nerve V of the teleost fish, Astronotus ocellatus, was totally severed and allowed to regenerate into its distal nervestump in a series of ten cases. In a second series of fourteen cases, the two nerve branches supplying the elevator and depressor muscles of the mandible were sectioned separately and the nerve of the depressor muscles was crossed into the levator muscles and vice versa. In both series, return of function in the re-innervated muscles was first detected about 8 days after nerve-section, and full recovery was achieved by the 18th to 21st day save for two exceptions in Series II in which the surgical crossunion proved faulty. The recovered mandibular action was properly timed and co-ordinated from the beginning with the mandibular muscles of the opposite side. It is inferred (a) that the regenerating motor-fibres establish functional connexions with foreign mandibular muscles, (b) that the muscles induce a local muscle specificity in the regenerated motor axons, and (c) that this ‘myotypic’ specificity determines in some way not yet analysed the central timing of motoneuron discharge in the trigeminal motor nucleus.
The Morphogenetic Influence of Innervation on the Ontogenetic Development of Muscle-spindles
Authors: Zelená J.
Published: April 2021

The development of muscle-spindles in the calf-muscles of the rat was followed under normal conditions and after section of n. ischiadicus. The first differentiation of muscle-spindles in the muscles of the hind limb of the rat was observed on the 19th day of intra-uterine development and their morphogenesis is complete by the 25th day after birth. After section of n. ischiadicus in rat foetuses on the 19th-20th day of intrauterine development, differentiation of muscle-spindles does not take place; neither intrafusal fibres nor the connective tissue capsule are formed. Since only proprioceptive fibres have innervated the normal muscle at this time, it is the loss of the morphogenetic influence of these nerve-fibres, that prevents differentiation. Similar results were obtained in rabbits denervated 7 days before birth. When section of n. ischiadicus is performed in new-born rats, disintegration of intrafusal fibres in which the equatorial segment was already differentiated at the time of denervation occurs within 10 days. Denervation in a 20-day-old rat, the muscle-spindles of which are already morphologically mature, leads after the same interval, to a slight atrophy in the equatorial zone of the intrafusal fibres. The mechanism of the morphogenetic influence of the nervous system and its changes during ontogenesis are discussed.
Contribution à l’étude de la maturation et de la segmentation de l’œuf d’Aplysie
Authors: Fautrez J.
Published: April 2021

Study of the maturation and the beginning of segmentation of the egg of Aplysia punctata by vital staining with toluidine blue demonstrates the appearance of a ‘colourless plasm’ and its unequal distribution between the various blastomeres. It may be a component analogous to the pole plasms of other Spiralia, correlated with the inequality of the cleavage divisions and with morphogenesis.
The temporal stability of the Drosophila oocyte
Authors: Wyman Robert
Published: April 2021

Individual female Drosophila melanogaster were maintained without yeast for up to 18 days. Some of the females did not lay any eggs during this holding period. The females produce mature oocytes (stage 14) by day 3 and from day 5 onward the females each held about 60 mature oocytes. The nulliparous females were mated and it was shown that the first egg produced by females held up to 18 days before mating could be viable and develop into a normal, fertile adult. On day 2 each female contained about 500 oocytes in post-oogonial stages of oogenesis. The first 500 fertilized eggs were collected from females that had been held nulliparous for 7−10 days before mating. No period of significantly reduced viability was found. It is concluded that the developmental program of Drosophila eggs can be interrupted between oogenesis and fertilization for at least 15 days without loss of the ability to produce normal, fertile adult progeny.
Waves propagated during vertebrate development: observations and comments
Authors: Robertson Anthony
Published: April 2021

The status and possible roles of propagated waves occurring during vertebrate embryogenesis are discussed. Some preliminary data for waves observed in time-lapse films of early chick (Gallus domesticus) and Medaka (Oryzias latipes, a teleost) are given. The general similarities between these phenomena and wave propagation during cellular slime mold aggregation are pointed out and it is suggested that the control of development by propagated waves in regulative embryos is not only widespread but also depends on a common cellular mechanism.
Neurotrophic and X-ray blocks in the blastemal cell cycle
Authors: Maden M.
Published: April 2021

Using microdensitometry techniques the points in the cycle where blastemal cells become blocked after X-irradiation or denervation of the regenerating amphibian limb have been identified. X-irradiation blocks the cells in both G1 and G2 and those cells that were in S at the time of irradiation presumably proceed to G2. After denervation, however, cells accumulate only in Gx and those that were in S or G2 continue through the cycle to the next Gx. The latter results are clearly contradictory to a recent theory proposing a G2 neurotrophic control of blastemal cells and a solution to the contradiction is presented in the light of recent results.
Ontogeny and localization of the crystallins during lens development in normal and Hy-1 (hyperplastic lens epithelium) chick embryos
Authors: McDevitt David S. , Clayton Ruth M.
Published: April 2021

A strain of chickens selected for high growth rate has been found to exhibit an anomalous eye lens morphology indicating a failure of the normal process of growth regulation. Hyper-plasia of the lens epithelium and annular pad, often with fiber formation, has recently been described in day-old chicks of this strain, termed Hy-1 (Clayton, 1975). The earliest evidence of this condition in this study has been found in the 11-day embryonic Hy-1 lens. Before this time, no definitive lens abnormality could be detected histologically in the Hy-1 embryos. However, the indirect immunofluorescence technique had revealed early temporal and spatial differences with regard to the lens crystallins. Antibodies, specific for δ, cathodal β, anodal β and α crystallins, were applied to sections through the lens of , 3-, , 4-, 5-, 8- and 16-day embryonic and 1-day post-hatch normal and Hy-1 chicks. δ crystallin appears precociously in the external layer, and α crystallin in the prospective fiber region, of the lens rudiment of Hy-1 embryos. Both anodal and cathodal β crystallins are retarded, however, in their appearance in the external layer/epithelium of Hy-1 lenses. Localization of the crystallin classes within the lenses of the two strains continues to vary during lens differentiation until 1 day post-hatch, at which time and during late embryogenesis annular pad and epithelium abnormalities can be frequently be seen in the Hy-1 lens. This inability to control normal lens histogenesis thus manifests itself early as alterations in the appearance of an organ-specific gene product, the crystallins.
The specification of metameric order in the insect Callosobruchus maculatus Fabr. (Coleoptera) : I. Incomplete segment patterns can result from constrictioninduced cytological damage to the egg
Authors: Meer Jitse M. Van Der
Published: April 2021

Eggs of the pea-beetle Callosobruchus were divided into two at different stages of development. Both fragments were allowed to develop into partial larvae. The segment patterns of normal and partial larvae are described using cuticular markers of cell differentiation. To study the contribution of cytological damage to the segment gap phenomenon three different types of constriction were performed : complete and incomplete permanent constriction and complete temporary constriction.

Changes in the structure of the egg can produce absence of segments resulting from two different effects. First, partial absence of segments results from a decreased egg circumference in the constriction region and involves the disturbance of a morphogenetic process (dorsal closure). Secondly, cytological damage can result in a gap between two arrays of segments. The loss of segments in the gap occurred in two different ways. In a spatial segment gap the two arrays of segments were physically discontinuous, whereas in a non-spatial gap the segments bordering the gap were juxtaposed in a physically continuous cuticle.

The extent to which the gap phenomenon can be attributed to cytological damage is discussed. We also discuss, on the basis of certain dorsal defects, a possible stepwise specification of the dorsal transverse cuticular pattern.
The ultrastructure of the dorsal yolk-free cytoplasm and the immediately surrounding cytoplasm in the symmetrized egg of Xenopus laevis
Authors: Herkovits Jorge , Ubbels Geertje A.
Published: April 2021

Cytoplasmic segregation and subsequent dorsad displacement of the segregated cytoplasm lead to symmetrization of the egg of Xenopus laevis. At 60 min post-fertilization (p.f.) the ‘dorsal yolk-free cytoplasm’ (DYFC) is located in the dorso-animal part of the egg. Its ultrastructure and that of the immediately surrounding cytoplasm have been studied with transmission electron microscopy (TEM).

The endoplasmic reticulum (ER) within the DYFC consists of single or paired cisternae and many small vesicles, both with moderately dense contents. Numerous particles, presumably ribosomes and glycogen, are present together with many mitochondria and some Golgi structures. The fraction of total yolk-free area occupied by mitochondria in the DYFC is about three times that in the adjacent cytoplasm. The number of cytoplasmic vesicles per unit area of cytoplasm is far larger in the DYFC than in the surrounding area.

The morphological characteristics of the DYFC at 60 min p.f. suggest that it represents a region of high metabolic activity. Since it is located in the dorso-animal quadrant of the uncleaved egg, it may be partly responsible for a difference in metabolism between the dorsal and the ventral side of the egg, and hence may play an essential role in the determination of dorso-ventrality.
Somitogenesis in amphibian embryos: I. Experimental evidence for an interaction between two temporal factors in the specification of somite pattern
Authors: Pearson Murray , Elsdale Tom
Published: April 2021

Somitogenesis is described in two species of anuran amphibians, Xenopus laevis and Rana temporaria, in which the cellular mechanics of somite formation are distinctly different. Heat shocks are employed to demonstrate a wave of cellular change which precedes somite formation down the body axis. This prior wave is shown to be kinematic. It is not a propagated wave. It is a consequence of the temporal activities of the cells laid out in space, but there is no evidence that these activities depend upon an interpretation of their position.

Heat shocks cause characteristic segmental abnormalities over a zone of somites which is formed several hours after the shock. Evidence from double heat shock experiments suggests that the pattern of abnormality is the result of (i) a disturbance of co-ordination between pre-somitic cells, and (ii) the time available to those cells for recovery before they are recruited into a segmental pre-pattern at the time of passage of the prior wave. It is a temporal coordination that is disturbed and subsequently recovered following a heat shock. This temporal co-ordination of pre-somitic cells does not depend upon position along the axis.

The evidence for two physiologically independent temporal patterns of cellular processes, which interact to specify the segmental pattern of somites (their size, shape and number), gives experimental support for the theoretical account of somitogenesis proposed by Cooke & Zeeman (1976).
Effects of colchicine on spermiogenesis in the mouse
Authors: Handel Mary Ann
Published: April 2021

The effects of colchicine on spermiogenesis in the mouse were examined. Mice were injected intratesticularly with colchicine in concentrations of 10−4M to 10−6M for various periods of time. The ultrastructure of the testes was examined and abnormal sperm in the epididymis were scored. Colchicine degraded microtubules in the testis and the treatment caused abnormalities of the head and acrosome of testicular spermatids and also resulted in an increase on the number of epididymal sperm showing abnormal head structure by 5 days after treatment of the testes. These results suggest that structurally intact microtubules are essential for the normal morphogenetic processes of spermiogenesis.
Latent effects on in vitro development following cytochalasin B treatment of 8-cell mouse embryos
Authors: Granholm N. H. , Brenner G. M. , Rector J. T.
Published: April 2021

Eight-cell mouse embryos when treated with 4·0μg/ml cytochalasin B (CB) in vitro undergo a reversible developmental arrest. Upon rinsing of embryos and subsequent culture in control medium, normal morphogenetic processes such as compaction of 8-cell embryos, cavitation, and post-blastocyst attachment and outgrowth are restored. However, the effects of CB on mouse embryos are not completely reversible; latent post-blastocyst defects become increasingly more prevalent as CB treatment duration increases.

The present study was conducted to quantitatively determine latent effects of CB on post-blastocyst embryos by comparing their ability to attach and to sustain the growth and differentiation of 1CM and trophoblast tissues. Groups of 8-cell embryos were cultured in Brinster’s BMOC-3 medium containing 4·0μg/ml cytochalasin B for 6, 12, 18, and 24 h. Following treatment, embryos were rinsed and cultured until 190 h post coitum (h.p.c.) in Eagle’s MEM/10% fetal calf serum modified to contain optimal levels of essential amino acids. Blastocysts generally attached to the surface of the plastic substratum by 120 h.p.c. At selected time periods after attachment (130, 160, and 190 h.p.c.), embryos were scored for outgrowth size, ICM size, extent of peripheral hyaloplasmic fan, and number of trophoblast nuclei per outgrowth. Analyses of variance (ANOVAs) were conducted for each of the four parameters listed above. Rates of attachment were analyzed by χ2 test.

Results show that the treatments affect (P < 0·01) embryo attachment, number of trophoblast nuclei per outgrowth, hyaloplasmic fan production, and ICM growth in a durationdependent manner. Interestingly, since treatment effects on outgrowth areas are nonsignificant apparently CB does not significantly change total outgrowth area. But CB tieatment does cause abnormal fan production and decreased trophoblast nuclei numbers. However, trophoblast cells are apparently more resistant than ICM to CB as is evident by the high incidence of trophoblast outgrowths devoid of ICM.

CB (4·0μg/ml) treatments at 8-cell stages for relatively short durations (6 and 12 h) induce latent effects on post-blastocyst embryos. Finally, there exists a definite 4·0μg/ml CB duration response over the 68–190 h.p.c. observation interval.