bluuebunny/crossref_metadata_2025_split huggingface dataset:
The synthetic activity of primordial germ cells in normal and irradiated neonatal male rats
Authors: Lett I. C. 
Published: April 2021

ABSTRACT
Exposure of the testes of rats to 100 r of X-rays at birth inhibits the division of gonocytes but does not prevent them from differentiating into transitional cells. The latter, however, fail to divide to form spermatogonia type-A, but increase markedly in size so that by 8 days post partum (p.p.) the testes of irradiated animals contain numerous giant transitional cells which are destined to degenerate. The metabolic activity of germ cell nuclei in normal and irradiated rats has been studied by the technique of autoradiography, using radioactive precursors of DNA, RNA and protein. The results have demonstrated that synthetic processes continue in cells whose division has been blocked. The synthesis of RNA is largely unaffected by irradiation. DNA synthesis may be prolonged after exposure, but the amount of 3H-thymidine incorporated by the nucleus declines from 5 days p.p. and does not keep pace with nuclear growth. The synthesis of nuclear protein, on the other hand, increases from 5 days after irradiation and the quantity of phenylalanine taken up by giant cells seems to be proportional to nuclear size. Thus the accumulation of nuclear protein appears to be the main factor in nuclear enlargement.
Métabolisme des acides nucléiques et des protéines et formation de cytasters dans les œufs d’amphibiens sous l’action de l’eau lourde
Authors: Assel S. Van , Brachet J. 
Published: April 2021

ABSTRACT
The formation of cytasters and the metabolism of nucleic acids and proteins in amphibian eggs treated with heavy water
Amphibian eggs (Pleurodeles and Xenopus) form cytasters, which are made of astral fibres and probably centrioles, upon treatment with concentrated heavy water (D2O). A study of the importance of nucleic acid and protein synthesis for the formation of cytasters was undertaken; both precursors and inhibitors of these syntheses were used. It was found that D2O completely inhibits the synthesis of nuclear DNA. Hydroxyurea (an inhibitor of DNA synthesis) and X-rays do not inhibit the appearance of the cytasters, which is clearly independent of nuclear DNA replication. Actinomycin D, a classical inhibitor of RNA synthesis, has no effect on cytaster formation. Eggs treated with D2O incorporate 14C-leucine in the nucleus as well as in the cytoplasm, including the cytasters. However, puromycin, which inhibits protein synthesis, has no effect on the formation of cytasters in Pleurodeles and Xenopus eggs. Another inhibitor of protein synthesis, cycloheximide, prevents the formation of cytasters in the eggs of Pleurodeles but not in those of Xenopus. Mercaptoethanol also blocks the appearance of cytasters in the eggs of Pleurodeles without affecting those of Xenopus. The possible reasons for the discrepancies in the results obtained with different species are discussed.
A time-lapse photographic study of chick embryos exposed to teratogenic doses of hypoxia
Authors: Grabowski Casimer T. , Schroeder Robert E. 
Published: April 2021

ABSTRACT
Continuous, long-term observations of amniote embryos have always been difficult. Special culture techniques for young avian and mammalian embryos have been developed (New, 1967) and these have helped to visualize the early stages of development. But studies of normal and abnormal development during the major period of organogenesis have been made largely by tedious indirect methods, such as the examination of a series of embryos preserved at different time intervals. Transitory responses to toxic stimuli have been particularly difficult to detect in this manner. To observe the visible initial effects of terato-genic agents, a photographic time-lapse study of chick embryos in their natural, in ovo, state was initiated. This report compares the changes in normal and hypoxia-treated embryos during the third day of development.
The role of sodium chloride in the process of induction by lithium chloride in cells of the Rana pipiens gastrula
Authors: Barth Lester G. , Barth Lucena J. 
Published: April 2021

ABSTRACT
A study of the effects of a series of monovalent cations, Li+, Na+ and K+, and a series of divalent cations, Mn2+, Ca2+ and Mg2+, upon small aggregates of cells taken from the presumptive epidermis of Rana pipiens gastrulae re-vealed that these ions induce nerve and pigment cells (Barth, 1965). The effec-tiveness of both series of ions as inductors was similar to their effects on decreasing the electrophoretic mobility of DNA as determined by Ross & Scruggs (1964).
A cytological study of Mauthner’s cells in Xenopus laevis and Rana temporaria during metamorphosis
Authors: Moulton J. M. , Jurand A. , Fox H. 
Published: April 2021

ABSTRACT
This paper discusses cytological changes which occur during anuran meta-morphosis in a pair of large hind-brain neurones, the Mauthner cells or M-cells which, in many teleosts and amphibians, innervate the tail musculature via ventral horn cells. The M-cells of fishes, urodeles and anuran larvae are un-usually large neurones of particular interest, and according to Stefanelli (1951) they constitute a ‘true functional system of nervous activity’. The value of a cytological study is enhanced by the fact that amphibian M-cells have not yet been extensively analysed biochemically (Deuchar, 1966).
Gene loss and gain in the evolution of the vertebrates
Authors: Ruddle Frank H. , Bentley Kevin L. , Murtha Michael T. , Risch Neil 
Published: April 2021

ABSTRACT
Homeobox cluster genes (Hox genes) are highly conserved and can be usefully employed to study phyletic relation ships and the process of evolution itself. A phylogenetic survey of Hox genes shows an increase in gene number in some more recently evolved forms, particularly in verte brates. The gene increase has occurred through a two-step process involving first, gene expansion to form a cluster, and second, cluster duplication to form multiple clusters. We also describe data that suggests that non-Hox genes may be preferrentially associated with the Hox clusters and raise the possibility that this association may have an adaptive biological function. Hox gene loss may also play a role in evolution. Hox gene loss is well substantiated in the vertebrates, and we identify additional possible instances of gene loss in the echinoderms and urochordates based on PCR surveys. We point out the possible adaptive role of gene loss in evolution, and urge the extension of gene mapping studies to relevant species as a means of its sub stantiation.
The evolution of arthropod segmentation: insights from comparisons of gene expression patterns
Authors: Patel Nipam H. 
Published: April 2021

ABSTRACT
The comparison of gene expression patterns in a number of insect and crustacean species has led to some insight into the evolution of arthropod patterning mechanisms. These studies have revealed the fundamental nature of the parasegment in a number of organisms, shown that segments can be generated sequentially at the molecular level, and suggested that pair-rule pre-patterning might not be shared by all insects.
Symmetry systems and compartments in Lepidopteran wings: the evolution of a patterning mechanism
Authors: Nijhout H. Frederik 
Published: April 2021

ABSTRACT
The wing patterns of butterflies are made up of an array of discrete pattern elements. Wing patterns evolve through changes in the size, shape and color of these pattern elements. The pattern elements are arranged in several parallel symmetry systems that develop independently from one another. The wing is further compartmentalized for color pattern formation by the wing veins. Pattern development in these compartments is largely independent from that in adjacent compartments. This two-fold compartmentalization of the color pattern (by symmetry systems and wing veins) has resulted in an extremely flexible developmental system that allows each pattern element to vary and evolve independently, without the burden of correlated evolution in other elements. The lack of developmental constraints on pattern evolution may explain why butterflies have diverged so dramatically in their color patterns, and why accurate mimicry has evolved so frequently.
This flexible developmental system appears to have evolved from the convergence of two ancient patterning systems that the butterflies inherited from their ancestors. Mapping of various pattern types onto a phylogeny of the Lepidoptera indicates that symmetry systems evolved in several steps from simple spotting patterns. Initially all such patterns were developmentally identical but each became individuated in the immediate ancestors of the butterflies. Compartmentalization by wing veins is found in all Lepidoptera and their sister group the Trichoptera, but affects primarily the ripple patterns that form the background upon which spotting patterns and symmetry systems develop. These background pattern are determined earlier in ontogeny than are the symmetry systems, and the compartmentalization mechanism is presumably no longer active when the latter develop. It appears that both individuation of symmetry systems and compartmentalization by the wing veins began at or near the wing margin. Only the butterflies and their immediate ancestors evolved a pattern formation mechanism that combines the development of a regular array of well-differentiated symmetry systems with the mechanism that compartmentalizes the wing with respect to color pattern formation. The result was an uncoupling of symmetry system development in each wing cell. This, together with the individuation of symmetry systems, yielded an essentially mosaic developmental system of unprecedented permutational flexibility that enabled the great radiation of butterfly wing patterns.
The hedgehog gene family in Drosophila and vertebrate development
Authors: Fietz Michael J. , Concordet Jean-Paul , Barbosa Robert , Johnson Randy , Krauss Stefan , McMahon Andrew P. , Tabin Cliff , lngham Philip W. 
Published: April 2021

ABSTRACT
The segment polarity gene hedgehog plays a central role in cell patterning during embryonic and post-embryonic development of the dipteran, Drosophila melanogaster. Recent studies have identified a family of hedgehog related genes in vertebrates; one of these, Sonic hedgehog is impli cated in positional signalling processes that show interest-ing similarities with those controlled by its Drosophila homologue.
The evolution of echinoderm development is driven by several distinct factors
Authors: Wray Gregory A. , Bely Alexandra E. 
Published: April 2021

ABSTRACT
We analyzed a comparative data base of gene expression, cell fate specification, and morphogenetic movements from several echinoderms to determine why developmental processes do and do not evolve. Mapping this comparative data onto explicit phylogenetic frameworks revealed three distinct evolutionary patterns. First, some evolutionary differences in development correlate well with larval ecology but not with adult morphology. These associations are probably not coincidental because similar developmental changes accompany similar ecological transformations on separate occasions. This suggests that larval ecology has been a potent influence on the evolution of early development in echinoderms. Second, a few changes in early development correlate with transformations in adult morphology. Because most such changes have occurred only once, however, it is difficult to distinguish chance associations from causal relationships. And third, some changes in development have no apparent phenotypic consequences and do not correlate with obvious features of either life history or morphology. This suggests that some evolutionary changes in development may evolve in a neutral or nearly neutral mode. Importantly, these hypotheses make specific predictions that can be tested with further comparative data and by experimental manipulations. Together, our phylogenetic analyses of comparative data suggest that at least three distinct evolutionary mechanisms have shaped early development in echinoderms.
Neural Activation and Transformation in Explants of Competent Ectoderm under the Influence of Fragments of Anterior Notochord in Urodeles
Authors: Nieuwkoop P. D. , Nigtevecht G. V. 
Published: April 2021

ABSTRACT
The inductive influence of presumptive notochordal tissue (neurula stage) upon competent ectoderm was tested in sandwich-experiments, for which eggs of Triturus alpestris, T. taeniatus, and Ambystoma mexicanum were used. Strong activating and rather weak transforming influences emanate from the anterior portion of the notochord. Both activating and transforming influences have the character of field actions and spread with decrement, probably from cell to cell, in the overlying ectoderm. Both influences, but especially the activation, can spread over an area much larger than the area in which a direct contact between inductor and ectoderm occurs. It is therefore suggested that the more lateral portions of the archenteron roof merely support the activation spread from the dorsal midline, probably as a form of double assurance. The activation leads to a segregation into neural, mesectodermal, activated epidermal, and indifferent epidermal zones, each of which is characterized by a certain threshold value. In the activated epidermal zone differentiation tendencies for prosencephalic placodal development arise. They can be transformed by additional transforming influences into those for rhombencephalic or spinal placodes.
The yolk of Holostean fishes
Authors: Kilarski Wincenty , Grodziński Zygmunt 
Published: April 2021

ABSTRACT
Eggs of some archaic fishes, such as Polypterus, sturgeon or the holosteans, resemble amphibian eggs. Not only has the similarity been found in the amount of yolk (mesolecithal types of eggs), which indicates the manner of egg cleavage (holoblastic) in these vertebrates, but also in the morphological composition of yolk. Fat droplets, yolk platelets and an unidentified fluid in which they are suspended, in fishes sometimes called ichthulin, are three main components of yolk in these eggs.
Myocardial cell death in the embryonic chick ventricle
Authors: Manasek Francis J. 
Published: April 2021

ABSTRACT
The degeneration and death of cells is a normal occurrence in renewing cell systems in mature animals. Cell death is also a frequent event during embryonic development and appears to be a normal, and perhaps necessary constituent process of morphogenesis (see Glucksmann (1951) and Saunders (1966) for reviews). The events of cell degeneration and death during ontogenesis have been observed in many developing tissues, even those which have a relatively static cell population in the adult, such as the nervous system (Hamburger & Levi-Montalcini, 1949).
Development of luxoid (lu) skeletal defects in vitro
Authors: Burda D. J. , Center E. M. 
Published: April 2021

ABSTRACT
Skeletal abnormalities in the hind limb of the homozygous luxoid mutant mouse (lu/lu) have been described by Green (1955) and Forsthoefel (1958, 1959). These defects include a reduction in the size of the tibia, a slight thickening of the fibula and a failure to form normal condyles on the distal portion of the femur. Chondrogenesis and ossification are also slightly retarded in these limbs.
Morphogenesis in hydra: I. Peduncle and basal disc formation at the distal end of regenerating hydra after exposure to colchicine
Authors: Corff Sondra C. , Burnett Allison L. 
Published: April 2021

ABSTRACT
The regenerative ability of hydra has been frequently demonstrated since Trembley (1744) first witnessed the regeneration of a hydranth from the proximal half of an excised animal. Under normal conditions, the hypostome and tentacles always regenerate from the distal cut end, and proximal structures, the peduncle and basal disc, from the proximal cut end. This pattern of regeneration reflects the rigid polarity of hydra. Normal polarity and regeneration can be altered, however, by several techniques. Various graft combinations induce distal structures from regions destined to produce peduncle (Wetzel, 1898; King, 1903; Browne, 1909; Koelitz, 1911; Mutz, 1930; Burnett, 1961). An interspecific graft between the peduncle region of Hydra oligactis and the distal end of Hydra pirardi can result in the production of tentacles at the proximal end of the peduncle, which normally would form a base, and the inversion of polarity (Burnett, 1961). An extract prepared from an homogenate of hydra can induce multiple head and tentacle formation and inversion of polarity in gastric annuli (Lesh & Burnett, 1964; Lentz, 1965a; Lesh & Burnett, 1966). It appears therefore that regions proximal to the hypostome and tentacles are not irreversibly determined, but susceptible to redirection under appropriate stimuli. Although distal structures have been produced from proximal regions, no report exists of peduncle and basal disc formation at the distal end of an excised hydra.
Analysis of follicle cell patterns in dextral and sinistral Limnaea peregra
Authors: Ubbels Geertje A. , Bezem J. J. , Raven Chr. P. 
Published: April 2021

ABSTRACT
Several experiments done in our laboratory make it likely that in the egg of Limnaea stagnalis there is a cortical morphogenetic field (Raven, 1949, 1952, 1966). One of us (Raven, 1963,1964,1967) has studied the origin of this morphogenetic field. In the newly laid egg cell there is a vegetative pole plasm, occupying a sector of about 110 degrees with its apex near the centre of the egg. It is situated somewhat obliquely with respect to the longitudinal axis of the first maturation spindle. Moreover, a circle of six lenticular subcortical patches of cytoplasm are found in the equatorial region of the egg. These ‘subcortical accumulations’ (SCA) are arranged according to a regular pattern. Four of them are situated close together on one side, occupying about 180 degrees of the egg circumference; two somewhat larger SCA lie on the opposite side. The SCA, together with the obliquity of the vegetative pole plasm, define a pattern which is polar, dorsoventral and nearly symmetric, though a slight asymmetry seems to be present.
Aspects of the tabby-crinkled-downless syndrome : II. Observations on the reaction to changes of genetic background
Authors: Sofaer J. A. 
Published: April 2021

ABSTRACT
Two alleles of the sex-linked gene tabby, Ta and Tac, and two autosomal mimics of tabby, crinkled, cr, and downless, dl, each produce a similar mutant syndrome involving the coat and dentition of the mouse. Certain aspects of the development of the mutant defects have already been studied, and some comparisons between tabby and crinkled have been made. The present investigation is concerned with a comparison of all four genes, and with further analysis of the developmental basis for the dental abnormalities.
The measurement of cell adhesiveness by an absolute method
Authors: Curtis A. S. G. 
Published: April 2021

ABSTRACT
The development of a quantitative method for measuring cell adhesion would allow tests to be made of a variety of hypotheses concerning the role of cell adhesiveness in many morphogenetic processes, such as segregation (Steinberg, 1963; Curtis, 1960, 1967), contact inhibition of movement (Abercrombie, 1961), malignancy, etc. Furthermore, the development of a quantitative method giving absolute measurements of cell adhesiveness would be of considerable value in that it would allow critical experiments to be made to test hypotheses about the mechanism of cell adhesion. Basically, two methods exist for the measurement of cellular adhesiveness: (i) a measure of the force or energy required to reseparate two cells or a group of cells from one another or from a non-cellular substrate; (ii) a measure of the forces or energies of interaction involved in bringing two cells or cell groups into adhesion. The first method was introduced as a qualitative test of adhesiveness by Dan (1936). Recently, Brooks, Millar, Seaman & Vassar (1967) have made ingenious calculations of the probable magnitude of the adhesive energies which have to be overcome in dispersing a tissue by mechanical means into single cells. Measurement of the forces that have to be used to disperse the tissue can be used to derive a value of the adhesiveness of the cells as Brooks et al. (1967) have done. But there are difficulties in this method since intercellular materials, such as collagen, may contribute to the average resistance of a tissue to dispersion by mechanical forces, and if the hypothesis advanced by Weiss (1961) is correct, the measurement is not of the adhesiveness of cells but of the mechanical resistance of the cells to being broken. With the first of these considerations chiefly in mind, it seemed desirable to develop a method for measurement of adhesiveness using the formation of adhesions between cells.
Etude comparative des effets de l’ypérite azotée sur les constituants, mésodermique et ectodermique, des bourgeons de membres de l’embryon de Poulet
Authors: Salzgeber Berthe 
Published: April 2021

ABSTRACT
Des recherches récentes (Salzgeber & Pinot, 1968) ont montré que les ébau-ches de membres d’embryons de 3 à jours d’incubation (stades 18 à 20 de Hamburger & Hamilton, 1951) traitées in vitro à l’aide d’une solution d’ypérite azotée et de liquide de Tyrode, et greffées après lavage à l’embryon de Poulet, évoluent en membres micromèles, phocomèles ou ectromèles. Le type de mal-formation obtenue dépend de la durée du traitement et de la concentration de la solution. Ces expériences apportent la preuve d’une action directe de l’ypérite azotée sur les ébauches de membres.
The effect of trypan blue on the growth of the rat embryo in vivo
Authors: Berry Colin L. 
Published: April 2021

ABSTRACT
In a previous paper (Berry, 1968) it has been demonstrated, by comparison of in vivo and in vitro growth of the rat foetus, that it is possible to dissociate growth and differentiation in the rat. In a series now exceeding 1000 embryos it is evident that for a given somite number the protein content of an animal developing in vitro might be less than half that of the normal control, suggesting that a considerable reduction in growth rate might be found without necessarily inducing death or malformation. The rate of somite formation is not reduced in vitro in the rat; it has been shown by Herrman & Schultz (1958) that the rate of somite formation is not interfered with by different explant conditions in the chick embryo. These findings suggest that the increase in somite number is more rigidly determined than the increase in growth rate.