bluuebunny/crossref_metadata_2025_split huggingface dataset:
Differentiation of tropomyosin-containing myofibrils in cleavage-arrested ascidian zygotes expressing acetylcholinesterase
Authors: Crowther Robert J. , Meedel Thomas H. , Whittaker J. R. 
Published: April 2021

Abstract
Two muscle differentiation programs, acetylcholinesterase and tropomyosin-containing filaments and fibrils, occur together in the same cleavage-arrested zygotes (1-celled) of the ascidian Ciona intestinalis. Coexpression in such undivided but developing ‘embryos’ is consistent with the idea that separate elements of muscle differentiation are related at some regulatory level, perhaps through a single multi-gene regulatory factor. Fertilized Ciona eggs were exposed to cytochalasin B for 20 h and then briefly reacted histochemically for acetylcholinesterase activity. Strongly reacting specimens were selected and processed for transmission electron microscopy to reveal regions of muscle ultrastructure. Every acetylcholinesterase-reactive zygote tested contained muscle contractile elements; no example lacking acetylcholinesterase was found with myofilaments and myofibrils. As demonstrated by immunogold labelling, a polyclonal antibody to tropomyosin from Ciona adult body wall reacted differentially with the presumed ultrastructural muscle elements in cleavage-arrested zygotes. Site-specific reactions were also observed in larval tail muscle and the siphon muscles of postmetamorphic zooids.
Using CRISPR to understand and manipulate gene regulation
Authors: Akinci Ersin , Hamilton Marisa C. , Khowpinitchai Benyapa , Sherwood Richard I. 
Published: April 2021

ABSTRACT
Understanding how genes are expressed in the correct cell types and at the correct level is a key goal of developmental biology research. Gene regulation has traditionally been approached largely through observational methods, whereas perturbational approaches have lacked precision. CRISPR-Cas9 has begun to transform the study of gene regulation, allowing for precise manipulation of genomic sequences, epigenetic functionalization and gene expression. CRISPR-Cas9 technology has already led to the discovery of new paradigms in gene regulation and, as new CRISPR-based tools and methods continue to be developed, promises to transform our knowledge of the gene regulatory code and our ability to manipulate cell fate. Here, we discuss the current and future application of the emerging CRISPR toolbox toward predicting gene regulatory network behavior, improving stem cell disease modeling, dissecting the epigenetic code, reprogramming cell fate and treating diseases of gene dysregulation.
Development and maintenance of tendons and ligaments
Authors: Bobzin Lauren , Roberts Ryan R. , Chen Hung-Jhen , Crump J. Gage , Merrill Amy E. 
Published: April 2021

ABSTRACT
Tendons and ligaments are fibrous connective tissues vital to the transmission of force and stabilization of the musculoskeletal system. Arising in precise regions of the embryo, tendons and ligaments share many properties and little is known about the molecular differences that differentiate them. Recent studies have revealed heterogeneity and plasticity within tendon and ligament cells, raising questions regarding the developmental mechanisms regulating tendon and ligament identity. Here, we discuss recent findings that contribute to our understanding of the mechanisms that establish and maintain tendon progenitors and their differentiated progeny in the head, trunk and limb. We also review the extent to which these findings are specific to certain anatomical regions and model organisms, and indicate which findings similarly apply to ligaments. Finally, we address current research regarding the cellular lineages that contribute to tendon and ligament repair, and to what extent their regulation is conserved within tendon and ligament development.
Direct repression of Nanog and Oct4 by OTX2 modulates the contribution of epiblast-derived cells to germline and somatic lineage
Authors: Di Giovannantonio Luca Giovanni , Acampora Dario , Omodei Daniela , Nigro Vincenzo , Barba Pasquale , Barbieri Elisa , Chambers Ian , Simeone Antonio 
Published: April 2021

ABSTRACT
In mammals, the pre-gastrula proximal epiblast gives rise to primordial germ cells (PGCs) or somatic precursors in response to BMP4 and WNT signaling. Entry into the germline requires activation of a naïve-like pluripotency gene regulatory network (GRN). Recent work has shown that suppression of OTX2 expression in the epiblast by BMP4 allows cells to develop a PGC fate in a precise temporal window. However, the mechanisms by which OTX2 suppresses PGC fate are unknown. Here, we show that, in mice, OTX2 prevents epiblast cells from activating the pluripotency GRN by direct repression of Oct4 and Nanog. Loss of this control during PGC differentiation in vitro causes widespread activation of the pluripotency GRN and a deregulated response to LIF, BMP4 and WNT signaling. These abnormalities, in specific cell culture conditions, result in massive germline entry at the expense of somatic mesoderm differentiation. Increased generation of PGCs also occurs in mutant embryos. We propose that the OTX2-mediated repressive control of Oct4 and Nanog is the basis of the mechanism that determines epiblast contribution to germline and somatic lineage.
Immunology of nervegrowth factor (NGF). The effect of NGF-antiserumon sensory ganglia in vitro
Authors: Hoffman H. 
Published: April 2021

ABSTRACT
The properties of the ‘Nerve Growth Factor’ (NGF) have been described extensively (Levi-Montalcini & Booker, 1960; Levi-Montalcini, 1965) and reviewed recently (Levi-Montalcini, 1966). This factor is a protein of molecular weight about 130000 in its aggregated form (Varon, Nomura & Shooter, 1967, 1968) but may be active in lower molecular weight forms (Cohen, 1959, 1960; Banks et al. 1968). It is widely distributed in the adult organism (Bueker, Schenkein & Bane, 1960) and exerts a controlling influence on the differentiation of sensory and sympathetic ganglia in developing chick embryos. In newborn mammals its administration influences sympathetic ganglion growth only. A possible role in the adult nervous system is suggested by Scott, Gutmann & Horsky (1966), who showed that injected NGF will increase protein synthesis in regenerating sensory neurons in vivo.
Accumulation of an organ-specific protein duringdevelopment of the embryonic chick brain
Authors: Friedman Harvey P. , Wenger Byron S. 
Published: April 2021

ABSTRACT
In an earlier investigation by the present authors (Friedman & Wenger, 1965) the quantitative development of brain-specific antigens in chick embryos was studied using antisera against whole brain homogenates. The antisera employed were made brain specific by absorption with homogenates of various chicken tissues. Based on this study, the period between and 12 days of incubation, stages 28 and 38 of the Hamburger & Hamilton (1951) stage series, was considered to be critical for neural differentiation.
Sterility and partial sterility in the South African clawed toad following the pricking of the egg
Authors: Buehr Mia L. , Blackler Antonie W. 
Published: April 2021

ABSTRACT
Bounoure (1934) first described the presence in the egg of the frog Rana temporaria of a special cytoplasmic differentiation, which he termed the ‘germinal cytoplasm’. He was able to trace the developmental history of this plasm as it moved from its original position just under the cortex of the vegetal pole of the fertilized egg, to its inclusion in a number of cells of the early gastrula endoderm, and also mapped the migration of these cells into the gonad rudiments. Bounoure believed that the germinal cytoplasm is the definitive germcell determinant, and that its presence in a cell is a prerequisite for the cell to undergo meiosis and differentiate into a gamete.
Behaviour of germ cells and sexual differentiation in late embryonic and early postnatal mouse chimeras
Authors: Mystkowska Ewa T. , Tarkowski Andrzej K. 
Published: April 2021

ABSTRACT
The purpose of the present study was to trace the fate of primordial germ cells in mouse chimeras of XX/XY constitution. In this type of research one hopes to obtain knowledge of the role of intrinsic genetic factors and of environmental factors (the environment provided by the gonads) in initiating and directing the course of gametogenesis in mammals.
The effect of exogenous RNA extract on chick embryo fibroblasts in vitro
Authors: Sann A. , Sharp D. , McKenzie J. 
Published: April 2021

ABSTRACT
It is extremely difficult, if not impossible, to reconcile the conflicting claims of those who have treated different cells and tissues with exogenous RNA. Some authors (e.g. Niu, Cordova & Niu, 1961 ; Niu, Cordova & Radbill, 1962) maintain that RNA extracts alter the course of cell differentiation to conform in morphological terms to the source of the RNA; in the same vein, Amos, Askonas & Soeiro (1964) have shown that, under certain conditions, RNA from mouse and bacterial cells can stimulate chick embryo fibroblasts to synthesize protein related antigenically to the origin of the RNA. Shepley, Ambrose & Kirby (1965), however, obtained stimulation of growth with permanent morphological changes in baby hamster kidney fibroblasts by the addition of RNA from a variety of sources.
On the other hand, Holoubek, Fanshier & Crocker (1966) showed that nuclear RNA synthesis in Ehrlich ascites cells was inhibited for 6–8 h by the addition of homologous or rat liver RNA and our results are similar in that rat liver RNA extract has been shown to have an adverse effect on the growth and survival of chick embryo fibroblasts.
Cell populations in skeletal muscle after regeneration
Authors: Church J. C. T. 
Published: April 2021

ABSTRACT
Much is known of the processes involved in the regeneration of skeletal muscle after injury. Yet in most accounts, the results are expressed in general or relative terms. Thus Adams, Denny-Brown & Pearson (1962) state that provided the architecture of the muscle survives, the reconstruction of ‘considerable lengths’ of muscle fibre is feasible. Wright (1963) makes a plea for the applica-tion of quantitation, with the choice of ‘some muscle that is sufficiently small for counting and measuring techniques to be reasonably applicable…’ The web of the fruit bat Eidolon helvum (Kerr) contains a number of small muscles which have proved very suitable for the detailed study, in light and electron micro-scopy, of muscle regeneration (Church & Noronha, 1965; Church, Noronha & Allbrook, 1966) (Fig. 1 A – D), and for the quantitation of recovering lesions (Church, 1968).
Etude ultrastructurale des stades précoces du développement du membre postérieur dePleurodeles waltliiMichah. (Amphibien, Urodèle)
Authors: Lauthier M. 
Published: April 2021

ABSTRACTAn ultrastructural study of the early stages of development of the hind limb-bud has been carried out in Pleurodeles waltlii Michah. The most interesting results concern the structure of the epidermis and the evolution of the dermo-epidermal boundary in the limb-bud.At every level of the limb-bud, the mesoderm draws near to the epidermis due to filopodia that penetrate the basal fibrous layer which becomes progressively disorganized; this can be considered as the establishment of interactions between epidermis and mesoderm. Some subepithelial cells with dense bodies participate in the disorganization of the basal fibrous layer.There is no special epidermal feature at the limb-bud apex. However, the ultrastructural uniformity of the epidermis (which can be related to its histoenzymological uniformity) does not exclude a morphogenetic role of that epidermis.The absence of any apical differentiation of the Pleurodeles hind limb-bud as well as the absence of a strictly localized disorganization of the basal fibrous layer and the closeness of the mesoderm and epidermis, are discussed. It is suggested that, if in Urodela the epidermis of the limb-bud plays a morphogenetic role, the whole epidermis is concerned and not only its apical part as in Amniotes. The differences observed at the level of the hind limb-bud between Urodela and the other Tetrapods could be related to the strikingly different chronological appearance of the toes in the two groups.
Recent findings on oogenesis of Drosophila melanogaster: I. Ultrastructural observations on the developing ooplasm
Authors: Giorgi F. , Jacob J. 
Published: April 2021

ABSTRACT
The ultrastructure of the developing ooplasm has been examined in 2–3-day-old flies of Drosophila melanogaster with a view to clarifying the origin of the yolk platelets.
Previtellogenic ovarian chambers have been shown to exhibit a number of cytolysosomes; these are first formed in the nurse cells and are later brought to the ooplasm after having passed through the ring canals.
Just prior to the beginning of vitellogenesis some of the cytolysosomes in the ooplasm acquire in places a yolk-like appearance. As vitellogenesis commences, in ‘early stage-8 chambers, the central ooplasm comes to exhibit a number of inclusions which combine in themselves features of both yolk platelets and cytolysosomes.
The onset of vitellogenesis at stage 8 is marked by the appearance of several structural entities on the plasma membrane of the oocyte. At this site, there appear a number of depressions or pits in between the microvilli. Deeper in the cortical ooplasm there are also present a number of coated vesicles and tubules. While the former exhibit a typical threelayered structure similar to that of the pits, the tubules lack the outer spiked layer.
Mature yolk platelets appear to be made up of three major components. These are a central homogeneous dense body, an outer superficial layer with a number of small spherules and a rounded body therein, and an external limiting membrane.
Instances of fusion between vesicles of sizes progressively larger have been observed with frequency. This observation is discussed in relation to the formation of yolk platelets by means of pinocytotic uptake. A contribution made by the nurse cells to the formation of the yolk platelets is also taken into account.
Preleptotene chromosome condensation stage in human foetal and neonatal testes
Authors: Lucian J. M. , Devictor Monique , Stahl A. 
Published: April 2021

ABSTRACTA preleptotene stage of chromosome condensation analogous to that already described in various plants and in the oocytes of several animal species has been observed in the human foetal testis. Contrary to what has been previously described, this stage in the testis is not followed by decondensation leading to leptotene filaments. This observation underlines the problem of the precise significance of this stage and its relation to initiation of meiosis. It is suggested that meiosis may be initiated during this condensation phase and that the male germ cell, despite its XY chromosome constitution, tends to evolve towards meiosis. This proposal pleads in favour of both the role of somatic cells in the inhibition of meiosis in the male foetus and the role of environmental factors rather than genetic constitution of the germ cell in meiotic induction.
Immunohistochemical studies of vitellogenin during embryogenesis in the cockroach Blattella germanica
Authors: Tanaka Akira 
Published: April 2021

ABSTRACT
The fate of vitellogenin, vitellogenic female-specific protein, during embryogenesis in the German cockroach was investigated by an immunofluorescent technique. The period of the embryonic development of this insect is about 25 days at 25 ± 1 °C, and it has been divided into 18 stages (Tanaka, 1976).
Vitellogenin-specific fluorescence was evenly distributed among yolk spheres until stage 4. The intensity of the fluorescence of each yolk sphere, however, began to be uneven at stage 5, and the unevenness became more distinct in stages 6 – 7 to reach a mosaic appearance with respect to fluorescence. After stage 8, the mosaic appearance disappeared, and the intensity of fluorescence of the yolk region decreased on the whole as the stage advanced.
In vitellophages, no specific fluorescence was observed until stage 6. Very strong fluorescence, however, became observable in some vitellophages at stage 7. All vitellophages became fluorescent after stage 8. Some vitellophages, however, lost the fluorescence after stage 12, though the strong fluorescence still persisted in others until a fairly late stage when the cells became shrunken.
The specific fluorescence was observed in the yolk region only until stage 10. The nuclei of the body region of the embryo, however, began to fluoresce very strongly at stage 11 when dorsal closure had occurred. It persisted during stages 11 – 13, and abruptly declined after stage 14. The cytoplasm of the body region also had comparatively weak fluorescence at these stages. In the appendageal region including the antennae and pleuropodia, the specific fluorescence was not observed at all either in the nuclei or cytoplasm during development.
Differentiation of primordial germ cells in the embryonic development ofThermobia domestica. Pack.(Thysanura):an ultrastructural study
Authors: Klag Jerzy 
Published: April 2021

ABSTRACTThe primordial germ cells (PGCs) of Thermobia domestica undergo some morphological changes during the embryonic development. Most conspicuous are the changes in the ultrastructure of the nucleus, whose envelope shows a high degree of activity. Two types of vesicles bleb off from the nucleus; the ones with the light interior are called the accessory nuclei, the others, with electron-opaque contents, have been termed the dense bodies. The nucleolus, initially clustered at the nucleus centre, undergoes dispersion and assembles again towards the end of embryonic development. At the same time, the sex differentiation of PGCs takes place. It is preceded by an increase in the activity of Golgi complexes and in the volume of lysosomes and lamellar bodies, the latter giving rise to lipid droplets. At the early stages of postembryonic development, preoogonia and prespermatogonia can readily be distinguished. Preoogonia have a wavy-surfaced nucleus and their cytoplasm contains dense bodies. In prespermatogonia, the nucleus is spherical with smooth envelope and there are no dense bodies in the cytoplasm. Throughout the period studied there occur nucleolus-like bodies and nuage material considered to be the germ-cell determinants in this species.
Ontogeny of lens crystallins in marine cephalopods
Authors: Brahma Samir K. 
Published: April 2021

ABSTRACT
The ontogeny of the lens crystallin antigens throughout development of three marine cephalopod embryos, Loligo vulgaris, Sepia officinalis and Octopus vulgaris has been investigated using the indirect immuno-cytochemical staining against respective homologous anti-total lens protein antiserum.
The cellular mechanism of lens development appears to be the same in all species investigated and so does the ontogeny of the lens crystallins. The first positive immunofluorescence reaction appears simultaneously and in equal intensities over the lens and lentigenic area confirming the relationship between the two.
Electron microscopic studies on the structure of motile primordial germ cells of Xenopus laevis in vitro
Authors: Heasman Janet , Wylie C. C. 
Published: April 2021

ABSTRACT
Primordial germ cells (PGCs) of Xenopus laevis have been isolated from early embryos and kept alive in vitro, in order to study the structural basis of their motility, using the transmission and scanning electron microscope. The culture conditions used mimicked as closely as possible the in vivo environment of migrating PGCs, in that isolated PGCs were seeded onto monolayers of amphibian mesentery cells.
In these conditions we have demonstrated that: (a) No significant differences were found between the morphology of PGCs in vitro and in vivo.(b) Structural features involved in PGC movement in vitro include (i) the presence of a filamentous substructure, (ii) filopodial and blunt cell processes, (iii) cell surface specializations. These features are also characteristic of migratory PGCs studied in vivo.(c) PGCs in vitro have powers of invasion similar to those of migrating PGCs in vivo. They occasionally become completely surrounded by cells of the monolayer and, in this situation, bear striking resemblance to PGCs moving between mesentery cells to the site of the developing gonad in stage-44 tadpoles.
We conclude that as far as it is possible to assess, the behaviour of isolated PGCs in these in vitro conditions mimics their activities in vivo. This allows us to study the ultrastructural basis of their migration.
In vivo and in vitro studies on the hypoblast and definitive endoblast of avian embryos
Authors: Sanders E. J. , Bellairs Ruth , Portch P. A. 
Published: April 2021

ABSTRACT
An unusual example of the invasion of one tissue by another occurs during gastrulation in the chick embryo when the definitive endoblast becomes inserted into the hypoblast. The two tissues were examined morphologically by SEM and TEM. They resemble each other in being of an epithelial type, though neither possesses a basal lamina. The definitive endoblast cells are flatter than the hypoblast cells and more closely attached to one another. When they were explanted in hanging drop cultures, the two tissues were found to exhibit differences in their behaviour. In comparison with the definitive endoblast, the hypoblast cells attached more readily to the glass, produced larger ruffle membranes, moved more rapidly, showed poorer contact-inhibition of locomotion and showed a greater tendency to break away from the main explant.
When a hypoblast explant was confronted with a definitive endoblast explant, the hypoblast cells became displaced by the definitive endoblast. The hypoblast explant tended to fragment into smaller groups of cells, many of which migrated around the definitive endoblast, thus mimicking the situation in vivo. Control experiments comprised confronting hypoblast with hypoblast, hypoblast with somites, definitive endoblast with definitive endoblast, and definitive endoblast with somites. The hypoblast explants behaved in a consistent manner, always fragmenting when coming into contact with cells from a confronting explant. The definitive endoblast explants showed more contact inhibition of locomotion when confronted with definitive endoblast or with somites than when confronted with hypoblast. It is suggested therefore that the ability of the hypoblast cells to separate from one another may play an important role in the penetration of the hypoblast by the definitive endoblast both in vitro and in vivo.
Différenciation cytophysiologique régionale de l’épithélium uropygien chez l’embryon de canard Anas platyrhynchos
Authors: Bride Jacqueline 
Published: April 2021

ABSTRACT
The uropygial gland (preen gland), an epidermal derivative, is a bilobed, lipid-secreting gland located over the base of the tail of most birds.
In the duck embryo Anas platyrhynchos, the internal branching morphogenesis of preen gland is set up at the 17th day of incubation. Each glandular lobe is made of numerous epidermal columns each of which is terminated by a bulb or end-bud. The functional differentiation of the end-buds and the development of the cellular columns into collecting ducts were investigated. The ductal epithelium, separated from the mesoderm by a continuous basal lamina, is keratinized just as in normal embryonic avian epidermis. The features which indicate glandular differentiation in the end-buds were described. Lipogenesis results from progressive cellular differentiation characterized by proliferation and development of smooth membranes. The direct ecto-mesodermal contacts, which were observed at the endbuds after the establishment of morphogenetic pattern and before the onset of glandular secretory activity, suggest that a new interaction mechanism would be required to initiate the functional differentiation.