bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evidence for tip control of the ‘slug/fruit’ switch in slugs ofDictyostelium discoideum
Authors: Smith Elizabeth , Williams Keith L. 
Published: April 2021

ABSTRACTReciprocal transplants were performed between slugs of two strains of Dictyostelium discoideum. Slugs of one strain (NP84 ‘slugger’) showed prolonged migration, while slugs of the other strain (AX3 ‘fruiter’) migrated for a short period only. The transplant experiments showed that the ‘slug/fruit’ characteristic is tip dependent, since an NP84 tip induced an AX3 rear to migrate for a prolonged period, while an AX3 tip induced the rear of a NP84 slug to fruit without migration. These findings are not consistent with the hypothesis that tips of all stages release only one signal which is interpreted differently by the rest of the cells in the aggregate at different stages. Rather, we propose that the tip of a D. discoideum aggregate may release a number of signals, one of which is stage dependent, and triggers the ‘slug/fruit’ switch.
Changing muscle patterns in a segmental epidermal field
Authors: Williams G. J. A. , Caveney S. 
Published: April 2021

ABSTRACTThe spatial rearrangements that take place during metamorphosis in the abdominal sternites and associated retractor muscles of the beetle Tenebrio molitor are described. This paper provides the descriptive background needed to consider whether a morphogenetic gradient is involved in specifying the position at which adult muscle attachments develop. (Experimental work in support of this gradient hypothesis is published in a companion paper.)The ventral abdominal retractor muscles are extensively remodelled at metamorphosis so that the adult muscles differ considerably in appearance from the larval muscles from which they are derived. In particular, there is a change in both the absolute and relative positions of the sites of muscle attachment. Rearrangement of muscles takes place during both the pre- pupal period and the pupal stage. It is achieved by means of two separate and temporally distinct mechanisms. Epidermal remodelling in the pre-pupal period results in the movement of attached retractor muscles (epidermokinetic muscle movement). In the pupal stage, however, the muscles move over the basal surface of the epidermis (myokinetic muscle movement). Myokinetic movements may be brought about by extension of myoblast processes from the metamorphosing muscles. These findings are considered in terms of Poyarkoff’s theory that the pupa serves as an integumental mould, approximating the shape of the adult, within which certain adult muscles develop.
Cell behaviour and cleft palate in the mutant mouse, amputated
Authors: Flint O. P. 
Published: April 2021

ABSTRACT
Cleft palate with a genetic origin normally arises because of a failure of the palatal shelves to elevate or fuse. Until now attention in studies of palatal development has been focused on two critical phases, those of elevation and fusion. In the mutant mouse, amputated, however, cleft palate arises because of a failure of the palatal shelves to make any significant outgrowth between the 12th day after conception when the palatal shelves are first observed and the 14th day when elevation and fusion normally occur. When cell proliferation (mitotic index) was measured in the palatal shelves on days 12, 13 and 14 no difference was found between mutant and normal. The failure of the mutant palate to grow cannot be accounted for on grounds of reduced cell proliferation. For this reason the palatal mesenchyme in 12·5-day and 14·5-day normal and amputated mice has been studied with the scanning electron microscope. This work shows that the mesenchymal cells in the mutant palate are clumped together and have much greater areas of cell contact than are observed in the normal palate. The abnormal cell behaviour described in mutant palatal mesenchyme is typical of amputated embryonic mesenchyme in general, and in other cases has been shown to cause abnormal morphogenesis. We propose that aberrant cell behaviour causing an aggregation through increased cell adhesion inhibits palatal outgrowth in the mutant, and for this reason the palatal shelves subsequently fail to elevate and fuse.
The retinotectal projections from surgically rounded-up half-eyes in Xenopus
Authors: Straznicky C. , Gaze R. M. , Keating M. J. 
Published: April 2021

ABSTRACT
In Xenopus embryos of stage 32 half of one eye anlage was removed and the remaining half was surgically rounded-up. The visuotectal projections through such half-eyes, recorded after metamorphosis, showed in most cases a deformation of the map which corresponded to the deformation imposed on the half-eye at operation. Some eyes gave normal maps and some showed mirror-reduplication.
Effect of epidermal growth factor on secondary palatal epithelium in vitro: tissue isolation and recombination studies
Authors: Tyler Mary S. , Pratt Robert M. 
Published: April 2021

ABSTRACT
Previous studies have shown that epidermal growth factor (EGF), a peptide of M.W. 6045, can specifically inhibit in organ culture the cessation of DNA synthesis and programmed cell death that normally occur in the presumptive fusion zone (PFZ) of the secondary palatal epithelium. The aim of this study was to determine if EGF acts directly on the epithelium to exert its effect and if there is a requirement for the underlying mesenchyme. Palatal processes from 13- and 14-day Swiss Webster embryonic mice were enzymatically separated into epithelium and mesenchyme which were then cultured alone or in transfilter recombination for up to 72 h. Tissues were examined by transmission- and scanning-electron microscopy and DNA synthesis was monitored autoradiographically using [3H]thymidine incorporation. In isolated epithelium cultured in control medium, cell death occurred in the PFZ and DNA synthesis did not occur in the oral and nasal epithelial regions. EGF (20– 50 ng/ml) did not prevent cell death in the PFZ and failed to stimulate DNA synthesis in the isolated epithelium; EGF, however, did have an effect on epithelial cell morphology. In the presence of mesenchyme and EGF, there was extensive proliferation in the entire epithelium and cell death within the PFZ was not evident. The results indicate that the stimulation of DNA synthesis in the palatal epithelium by EGF requires the presence of the underlying mesenchyme and that EFG alone is not sufficient to inhibit programmed cell death within the PFZ of the isolated palatal epithelium.
The migration of presumptive primordial germ cells through the endodermal cell mass in Xenopus laevis: A light and electron microscopic study
Authors: Kamimura Michiko , Kotani Minoru , Yamagata Kenzo 
Published: April 2021

ABSTRACT
Presumptive primordial germ cells (pPGCs) were examined during migration from their deep endodermal position to the endodermal crest in Xenopus laevis, using light and electron microscopy with Epon sections, and several morphological characteristics of pPGCs, associated with their migration, were revealed. pPGCs displayed polymorphism, with smooth contours. The intercellular space around the pPGCs was large and variable in width and cytoplasmic processes from pPGCs were occasionally observed in it. It was shown quantitatively that pPGCs at the migratory stage had a tendency to move with the leading end, towards which the nucleus was localized, dragging the germinal plasm behind. These polarized pPGCs were frequently associated with large intercellular spaces, both at their leading and trailing ends. Cytoplasmic processes of polarizing pPGCs found in the large intercellular space at the leading end were conspicuous. Ultrastructurally, the nuclei of pPGCs were euchromatic, and the nucleolus was prominent. The germinal plasm at the light microscope level corresponded to the cytoplasmic area near the nucleus where a large number of mitochondria with well-developed cristae and most of the other organelles were aggregated. Centrioles and centriole-associated microtubules observed in the aggregate were thought to be important structures responsible for the cell polarization mentioned above. It was demonstrated quantitatively that the size of mitochondria in pPGCs was larger on average than that of mitochondria in neighbouring somatic endodermal cells. Numerous irregularly shaped small yolk platelets characterized pPGCs. These ultrastructural features suggested that pPGCs were in an activated metabolic state. It was concluded that the migration of pPGCs was attributable to active movement with high cell metabolism, causing the formation of cell processes and intracellular polarization.
Polyploidization of extraembryonic tissues during mouse embryogenesis
Authors: Ilgren E. B. 
Published: April 2021

ABSTRACT
It has recently been shown that visceral yolk-sac endoderm is derived from the primitive endoderm of the 4-5-day mouse blastocyst (Gardner & Papaioannou, 1975; Gardner & Rossant, 1979). During development, primitive endodermal cells acquire nuclei with more than four times the haploid amount of DNA. The finding of metaphases with multiple sets of chromosomes suggests that the diploid precursors of such endodermal giant cells become truly polyploid. Amniotic cells also contain giant nuclei but the mechanism by which these arise is uncertain. The giant-cell transformation therefore appears to be a general feature of mouse extraembryonic development rather than a phenomenom restricted solely to trophoblast. The basis and significance of these findings are discussed in relation to the development of other extraembryonic membranes both of plant and animal origin.
Changes in protein synthesis during differentiation of embryonal carcinoma cells, and a comparison with embryo cells
Authors: Lovell-Badge R. H. , Evans M. J. 
Published: April 2021

ABSTRACT
Two-dimensional electrophoresis was used to find changes in protein synthesis occurring as pluripotent embryonal carcinoma (EC) cells differentiate to give embryoid bodies in vitro. 2-D patterns from other embryonic cell lines, and from the inner cell mass (ICM) cells of mouse embryos, were also analysed for the expression of those proteins showing some change during embryoid body formation and for overall differences between these and the EC cells.
Most changes in protein synthesis occurred before 12 h but endoderm was not discerned morphologically on the outside of EC cell clumps until at least 18 h after their suspension. The number of changes occurring is small compared with the number of polypeptides resolved, but is in line with similar studies. Comparisons with nullipotent EC cells and an endodermal cell line have allowed these changes to be assigned, tentatively, to the different cell types within embryoid bodies, and may allow them to be used as markers of differentiation.
Comparisons between the 2-D patterns derived from ICMs and EC cells reveal substantial differences between the two that might not have been expected from their developmental homology. The importance of these differences to their pluripotentiality is discussed.
Analysis of the effects of encystment and excystment on incomplete doublets of Oxytricha fallax
Authors: Grimes Gary W. , Hammersmith Robert L. 
Published: April 2021

ABSTRACT
Singlet cells of Oxytricha fallax possessing supernumerary rows of dorsally located marginal cirri were encysted, excysted, and observed for retention of the supernumerary rows. Without exception, cells lost the supernumerary rows as a result of cystment processes. (Encystment previously has been shown to result in the total resorption of ciliature.) In contrast, supernumerary dorsally located marginal cirral rows develop true-to-type during prefission morphogenesis and thus are inherited from cell to cell. These (and other) observations suggest that at least two levels of cytotactic control of cell patterning are operative on the ciliate cortex; one is dependent upon visible ciliature whereas the other is dependent upon an as yet ultrastructurally unidentifiable molecular architecture.
Alterations of chondroitin sulfate synthesized by chick embryo cartilage cultured in the presence of 6-aminonicotinamide
Authors: Seegmiller Robert E. , Horwitz Allen L. , Dorfman Albert 
Published: April 2021

ABSTRACT
Treatment of day-4 chick embryos with 6-aminonicotinamide (6-AN) impairs limb chondrogenesis and produces micromelia. Interference with limb cartilage development may be related to decreased NAD-dependent synthesis of ATP due to the fact that chondrogenesis is dependent upon anaerobic metabolism. To better understand the effect of 6-AN on chondrogenesis, isolated cartilage epiphyses from day-11 chick embryos were treated in vitro. Sulfate incorporation into total glycosaminoglycans of treated epiphyses was 30 % of control. Incorporation of [3H]glucosamine was normal. Fractionation by gel chromatography showed that 40 % of the glycosaminoglycans synthesized by treated cells had a molecular weight of less than 15000 compared with 5 % of that of the control. A decrease in amount of chondroitin 6-sulfate, an increase of chondroitin 4-sulfate and no change in amount of unsulfated polysaccharide were observed. These results suggest that, upon exposure to 6-AN, chondrocytes produce shorter than normal chondroitin sulfate chains that are preferentially sulfated in the 4 position. Since endochondral bone formation plays an integral role in growth and development of the limb, a defect in production of chondroitin sulfate, a major constituent of cartilage matrix, appears to be involved in 6-AN-induced micromelia.
Impaired energy metabolism as an initial step in the mechanism for 6-aminonicotinamide-induced limb malformation
Authors: Sheffield Val C. , Seegmiller Robert E. 
Published: April 2021

ABSTRACT
The analogue and antagonist of nicotinamide, 6-aminonicotinamide (6-AN), impairs cartilage formation and results in shortening of the limbs when administered to chick embryos. Studies have shown that 6-AN forms an abnormal NAD analogue which inhibits the activity of NAD-dependent enzymes associated with production of ATP. To determine if an effect on ATP synthesis might be associated with the mechanism of teratogenesis in the chick embryo, ATP levels of cartilage from day-8 chick embryos treated in vitro were assayed in relation to biosynthesis of protein, DNA and chondroitin sulfate. Incorporation of 35SO4= was inhibited by 6 h of treatment with 10μg/ml of 6-AN, whereas incorporation of [3H]thymidine and [3H]amino acid was not inhibited until 12 h. Incorporation of [3H]- glucosamine was increased at all treatment times. A decrease in the level of ATP preceded any detectable inhibition of precursor incorporation. These results are consistent with the hypothesis that 6-AN inhibits chondroitin sulfate synthesis through a reduction in the level of ATP in chondrocytes.
Coaggregation and formation of a joint myocardial tissue by embryonic mammalian and avian heart cells
Authors: Nag Asish C. , Cheng Mei , Healy Christopher J. 
Published: April 2021

ABSTRACTIntercellular adhesion and tissue reconstruction from homologous dissociated embryonic cells from two species were studied. Dissociated 12-day-old embryonic rat heart cells and 50-h-old embryonic chick heart cells were labeled with tritiated thymidine and allowed to aggregate in Erlenmeyer flasks during rotation culture on a gyratory water-bath shaker. The cultures were continued for 72 h. Cell aggregates were examined microscopically for evidence of contractility and subsequently processed at intervals between 1 and 72 h for transmission electron microscopic autoradiography. Rat and chick hearts used in this study appeared comparable in their stage of development and cellular composition. With the exception of mature blood cells and some fibroblastic non-muscle cells, all chick cardiac muscle cells were labeled with tritiated thymidine. As the cultures continued, aggregates increased in size by continuous accretion of cells and joining of small clusters. The cells within these mixed aggregates exhibited synchronous contractility from 1 h until the cultures were terminated. Most of the aggregation in both control and mixed aggregates was completed within 24 h. Control aggregates consisted of cells from a single species, either chick or rat. Approximately 18 % of labeled chick cardiac muscle cells established intercellular contacts and junctions with unlabeled rat cardiac muscle cells after 6 h of culture. This increased to 72 % after 72 h in culture. The junctions observed between chick and rat cardiac muscle cells were desmosomes and hemidesmosomes. Approximately 13 % of the cardiac muscle cells of one species either chick or rat were found scattered within clusters which contained .15 % of the cells from the other species after 72 h of culture. These scattered cells did not form junctions with monospecific cell groups. The implications of these intercellular adhesions between the same and different species are discussed, bearing two hypotheses in mind: (1) Moscona and collaborators, (2) Burdick and Steinberg. This study suggests that cellular as well as species identity plays an important role in the determination of intercellular adhesion among the embryonic cells from different species.
Sterility in mutant (t
Lx
/t
Ly
) male mice : I. A morphological study of spermiogenesis
Authors: Hillman Nina , Nadijcka Mary 
Published: April 2021

ABSTRACT
The results from a comparative ultrastructural study of spermiogenesis in 6-, 10-, 14- and 17-month-old sterile t6/tw32, and fertile T/t6, T/tw32 and BALB/c, mice are reported. The studies show that all of the males contained the same types of defective spermatids and that defects were not limited to specific spermatid stages. Younger males had fewer abnormal spermatids than older males of the same genotype and at each age the BALB/c and t6/tw32 males appeared to contain more abnormal spermatids than the other males. No unique spermatid defect or increased frequency of a specific defect was found which can be correlated with infertility of the t6/tw32 males.
Vitamin A alters the internal viscosity of fragments of limb-bud mesenchyme
Authors: Kwasigroch T. E. , Kochhar D. M. 
Published: April 2021

ABSTRACTTwo techniques were used to examine the effect of vitamin A compounds (vitamin A acid = retinoic acid and vitamin A acetate) upon the relative strengths of adhesion among mouse limb-bud mesenchymal cells. Treatment with retinoic acid in vivo and with vitamin A acetate in vitro reduced the rate at which the fragments of mesenchyme rounded-up when cultured on a non-adhesive substratum, but these compounds did not alter the behavior of tissues tested in fragment-fusion experiments. These conflicting results indicate that the two tests measure different activities of cells and suggest that treatment with vitamin A alters the property(ies) of cells which regulate the internal viscosity of tissues.
The Behaviourin vitroof Dissociated Embryonic Pituitary Tissue
Authors: Sobel H. 
Published: April 2021

ABSTRACTA method for the partial or complete disintegration of the pituitary tissue of the 8-day embryonic chick is described. The anterior lobe, after being partially disintegrated by incomplete dissolution of the intercellular substance, developed in vitro into typical glandular tissue. After dissociation of the anterior lobe into a suspension of discrete cells, the epithelial cells reaggregated under suitable conditions in vitro. The epithelial aggregate remained in a quiescent but apparently healthy state during further cultivation. The addition of perichondrial connective tissue to the aggregates caused them to resume growth and development and to differentiate into typical anterior lobe tissue. The mutual relationship of the connective and epithelial tissues in developing glands is discussed.
The behaviour of embryonic chick and quail tissues in culture
Authors: Bellairs Ruth , Ireland G. W. , Sanders E. J. , Stern C. D. 
Published: April 2021

ABSTRACT
Pieces of tissue were dissected from early chick and quail embryos (Stages XTII and XIV of Eyal-Giladi & Kochav, 1976; and stages 3–5 of Hamburger & Hamilton, 1951).
These tissues were taken from three different regions of the early embryos, and from eight different regions of the older ones, and were derived mainly from the lower layer. Epiblast tissues were also used. The experiments were designed to test the ability of one tissue to penetrate another.
A single tissue was grown in culture in a Falcon dish for 18–24 h until it had formed a coherent sheet of cells (Explant I). A second tissue was then combined with it in one of two ways:
A small piece of tissue (Explant II) was explanted on top of Explant I. In most cases Explant II penetrated through Explant I and spread on the Falcon dish. Another small piece of tissue (Explant III) was explanted beside (in confrontation with) Explant I. Usually, Explant III penetrated into Explant 1 rather than vice versa.
The results were analysed to see if there were any variations in behaviour of the different tissues. The main result was that important differences were found to exist between certain types of chick and quail cells when grown in culture; the implications of this finding for the widely used technique of xenoplastic grafting are mentioned.
Another result was that Explant I was more likely to be penetrated when the second tissue was placed on top of it (Explant II) than when it was confronted with it (Explant III). The significance of these results is discussed.
Effects of L-phenylalanine on somite formation in the early chick embryo
Authors: Palén K. , Thörneby L. 
Published: April 2021

ABSTRACT
Chick embryos were treated in ovo and in vitro with L-phenylalanine from the intermediate streak stage (Hamburger & Hamilton stage 3, 12–13 h of incubation) to the 7-somite stage (H&H stage 9, 29–33 h of incubation).
Treatment in ovo resulted in a large number of embryos developing somite blocks, i.e. imperfectly segmented somites. In embryos treated at an early developmental stage (12–21 h of incubation), the blocks of unsegmented somite mesoderm occurred mostly in the somite pairs 1–5, whereas treatment that began at a later stage (24–30 h of incubation) caused blocks in the somite pairs 5–10, i.e. the appearance of blocks of unsegmented somite mesoderm is correlated in time with the onset of the treatment. No difference regarding mitotic indices could be distinguished between normally segmented somites and blocks of unsegmented somite mesoderm. Autoradiography based on tritiated L-phenylalanine showed no regional differences in labelling of the chick embryo body. Electronmicroscopical observations indicate a slightly suppressed formation of microvilli in the cells of the unsegmented mesoderm blocks compared with cells in normally segmented somites. The observed disturbances are probably caused by a suppressed yolk granule decomposition in the developing somite cells.
The experiments in vitro support the findings in the in ovo material; at the same time, they reveal an unexpectedly slow diffusion of L-phenylalanine through the vitelline membrane.
The innervation of dorsoventrally reversed chick wings: evidence that motor axons do not actively seek out their appropriate targets
Authors: Summerbell Dennis , Stirling R. Victoria 
Published: April 2021

ABSTRACT
In normal chick embryos the extensor (dorsal) muscles are innervated by motoneurones lying laterally in the motor horn, while flexor muscles are supplied by more medially placed motoneurones. After reversal of the dorsoventral axis of the forelimb prior to innervation in most cases the opposite pattern is found, the extensors innervated by medial and flexors by lateral motor neurones. In a minority of cases the normal innervation pattern is obtained.
Three hypotheses are discussed, two involving specific target affinity between motor axon and target and one involving passive deployment of axons to targets. We conclude that our results favour the latter hypothesis but that we cannot exclude a short-range specific signal.