bluuebunny/crossref_metadata_2025_split huggingface dataset:
Proteoglycan synthesis by sternal chondrocytes perturbed with vitamin A
Authors: Vasan N. S. 
Published: April 2021

ABSTRACT
Proteoglycan synthesis by sternal chondrocytes was studied in the presence of excess vitamin A (10 i.u./ml). Proteoglycans synthesized by the treated cells were smaller, and had larger amounts of chondroitinase ABC-resistant materials than control cells. Vitamin A-pretreated cells, when provided with normal feeding medium, failed to revert back to normal morphology and synthetic processes. Chrondrocyte cultures prelabelled with [35S]- sulphate, when maintained in the presence of excess of vitamin A, showed: (1) increased release of labelled proteoglycans into the medium, and (2) increased (19%) degradation of the proteoglycans. The proteoglycans synthesized by the vitamin A-treated chondrocytes are also incapable of binding with exogenous large molecular weight hyaluronic acid. Thus, high levels of vitamin A modulate the differentiation of chondrocytes by altering cellular synthetic processes.
The bursa of Fabricius of the chicken embryo: localization and ontogenic evolution of sex-steroid target cells
Authors: Gasc Jean-Marie , Stumpf Walter E. 
Published: April 2021

ABSTRACT
Androgenic hormones induce inhibition or regression of the bursa of Fabricius in the chick embryo. The high doses of hormones necessary to this involution raises the question of the processes involved and their putative role in the normal development of the bursa. If androgens play a role it is mediated by receptor sites in target cells. Using an autoradiographic technique, receptor sites for androgenic hormones were localized in mesenchymal cells of the bursa from the primordium (7-day embryo) up to the fully differentiated immune organ (15-day embryo). No target cells containing receptor sites in their nuclei were observed in the endodermic epithelium or the follicles. Oestrogen target cells in very small number are found in the mesenchyme of the bursa, in 15-day embryos. The early presence of receptor sites for steroid hormones in the bursa of Fabricius shows that the normal development may be influenced by androgens, but the actual effects are yet to be demonstrated.
An ultrastructural study of the maternal-effect embryos of the ac/ac mutant of Pleurodeles waltl showing a gastrulation defect
Authors: Bluemink John G. , Beetschen Jean-Claude 
Published: April 2021

ABSTRACT
Embryos of the ac/ac maternal-effect mutant in Pleurodeles waltl show disturbed epibolic movement during gastrulation. At the early gastrula stage, ectoderm cells begin to sink in at random sites in the animal half of the embryo. At the advanced gastrula stage the ectodermal pits develop into grooves. Electron microscopical analysis shows that many cells in the bottom of the pits and grooves have narrowed apices and bear many microvilli, while the cortical cytoplasm is dense, filamentous and underlain by a stratum of vesicles. These findings are interpreted as indicating that ectoderm cells contract rather than expand leading to disturbed epibolic movement.
Presence of serotonin in the palate just prior to shelf elevation
Authors: Zimmerman Ernest F. , Wee Elizabeth L. , Phillips Nancy , Roberts Nancy 
Published: April 2021

ABSTRACT
Since serotonin and its antagonists affect shelf rotation in mouse embryo culture, experiments were carried out to determine whether a serotonergic system is present in the palate. Employing [3H]5-HT, day-14·5 embryos incorporated the monoamine into palates. Active uptake of [3H]5-HT was shown since excised palates incorporated 9-fold more radioactivity at 37°C than at 4°C. Synthesis of palatal serotonin was measured. Embryos were cultured in the presence of the serotonin precursor, [3H]5-HTP, and radioactive 5-HT was monitored in the palate by thin-layer chromatography. Furthermore, excised palates were incubated with [3H]5-HTP and radioactive 5-HT was measured. Incorporation was linear for about 6 h. In addition, another radioactive compound was detected which had the same Rf as the methylated derivative, 5-methoxytryptamine. Synthesis of this compound was appreciable, about 30% of that of serotonin. Levels of serotonin in the palate were measured by high pressure liquid chromatography. Palates at day 14·5 of gestation contained 0·40 ng serotonin/ mg protein, which was greater than that of tongue (0·33), body (0·14) but less than that of brain (3 09). Serotonin in palate and other embryonic tissues increased with time of development. Dopamine levels in the palate and other tissues were also determined. The distribution of serotonin in the palate was analyzed by culturing day-14-5 embryos in the presence of [3H]5-HTP, and after aldehyde fixation, paraffin embedment and sectioning, autoradiography was performed. Grains were observed throughout the palate in cells of regions 2 and 3, internal mesenchyme, tooth germ, and epithelium. Surprisingly, the pterygopalatine nerve, maxillary nerve and pterygopalatine ganglion contained an appreciable concentration of grains. Thus, the presence of serotonin in the palate is consistent with the neurotransmitter playing a role in shelf elevation.
Random X-chromosome inactivation in female primordial germ cells in the mouse
Authors: McMahon Andy , Fosten Mandy , Monk Marilyn 
Published: April 2021

ABSTRACT
The pattern of expression of the two X chromosomes was investigated in pre-meiotic germ cells from -day-old female embryos heterozygous for the variant electrophoretic forms of the X-linked enzyme phosphoglycerate kinase (PGK-1). If such germ cells carry the preferentially active Searle’s translocated X chromosome (Lyon, Searle, Ford & Ohno, 1964), then only the Pgk-1 allele on this chromosome is expressed. This confirms Johnston’s evidence (1979,1981) that Pgk-1 expression reflects a single active X chromosome at this time. Extracts of -day germ cells from heterozygous females carrying two normal X chromosomes show both the A and the B forms of PGK; since only one X chromosome in each cell is active, different alleles must be expressed in different cells, suggesting that X-chromosome inactivation is normally random in the germ line. This result makes it unlikely that germ cells are derived from the yolk-sac endoderm where the paternally derived X chromosome is preferentially inactivated. In their pattern of X-chromosome inactivation, germ cells evidently resemble other tissues derived from the epiblast.
The formation of somites and early myotomal myogenesis in Xenopus laevis, Bombina variegata and Pelobates fuscus*
Authors: Kiełbówna Leokadia 
Published: April 2021

ABSTRACT
Myogenesis in Xenopus laevis and in Bombina variegata is similar despite differences in the structure of the nonsegmented mesoderm and in the formation of the myotomes. In X. laevis the nonsegmented mesoderm consists of two cell layers with the premyocoel between them. During somitogenesis the premyoblasts rotate covering subsequently the whole myotome length. In B. variegata the premyocoel is absent. The myotomal cells change their shape and elongate, attaining ultimately the whole myotome length. The morphologically mature mononuclear muscle cells in both species result from myogenesis beginning in similarly arranged myoblasts. The multinuclear myotubes arise in the swimming tadpole (stage 45).
The structure of the nonsegmented mesoderm and of the newly formed myotomes in Pelobates fuscus is similar to that of B. variegata, while the process of myogenesis is different. It begins in the multinuclear myotubes. The stage of morphologically mature mononuclear muscle cells was not observed in the light microscope.
The results suggest that myotomal myogenesis is related neither to any particular type of nonsegmented mesoderm structure nor to any specific mode of myotome formation.
Positioning of inner cell mass determines the development of mouse blastocysts in vitro
Authors: Wu Tsung-Chieh , Wan Yu-Jui , Damjanov Ivan 
Published: April 2021

ABSTRACT
We have explanted mouse blastocysts into culture dishes and studied the positioning of the inner cell mass (ICM) at the time of attachment in order to establish what effect the location of the inner cell mass has on the subsequent development of embryos in vitro. We show that blastocysts may attach to the substrate with any portion of the trophectoderm. The location of ICM within the attaching blastocysts is unpredictable. The directions of egg-cylinder development may be either upward or downward. The axis assumed by a developing egg cylinder in vitro depends to a large extent on the initial positioning of the ICM at the time of attachment. Egg cylinders grown from blastocysts that have the ICM in the lower position (close to the plastic dish) reach advanced stages of development in greater numbers than egg cylinders grown from blastocyst with their ICM’s in the upper lateral or upper position. Only upward-growing egg cylinders can develop further into somitic stage (which is equivalent to 8i-or 9-day in vivo embryos). In contrast, downward growing egg cylinders become thwarted in their further development by the surrounding trophectoderm. If the downward growing egg cylinders are freed of trophectoderm and repositioned to face upwards they will develop in a manner similar to the originally upward growing egg cylinders. These findings indicate that the initial positioning of the ICM at the time of attachment is an important factor in governing the development of blastocysts to somite stage in vitro.
Ectoderm-mesoderm interactions in relation to limb-bud chondrogenesis in the chick embryo: transfilter cultures and ultrastructural studies
Authors: Gumpel-Pinot Madeleine 
Published: April 2021

ABSTRACT
Limb ectoderm induces cartilage differentiation in mesoderm from chick embryo limb buds. Transfilter cultures have shown that this interaction requires ‘contact’ conditions and cannot take place at a distance. In vivo, a basement membrane is always present between ectoderm and mesoderm.
The present paper demonstrates that the relationship between ectoderm and mesoderm is similar in vivo and in transfilter cultures. In culture conditions, the filter appears to be infiltrated by mesodermal cell outgrowths which form a continuous mesodermal cover on the filter. A basement membrane is always present between the mat of mesodermal cell processes and the ectoderm.
Mesodermal cell processes are able to cross the Nuclepore filters (pore size 0-6-0-8 μm) within 15 min. After 2 h in culture, the surface of the filter opposite to the mesodermal explant is completely covered with mesodermal outgrowths.
The extracellular material accumulating at the ectoderm-mesoderm interface appears to be mainly of mesodermal origin.
Regeneration from duplicating fragments of theDrosophilawing disc
Authors: Karlsson Jane , Smith R. J. 
Published: April 2021

ABSTRACTIt is a general rule that of two complementary Drosophila imaginal disc fragments, one regenerates and the other duplicates. This paper reports an investigation of an exception to this rule. Duplicating fragments from the periphery of the wing disc which lacked presumptive notum were found to regenerate notum structures during and after duplication. The propensity for this was greatest in fragments lying close to the presumptive notum, with the exception of a fragment confined to the posterior compartment, which did not regenerate notum. Structures were added sequentially, and regeneration stopped once most of the notum was present.These results are not easily explained by the polar coordinate model, which states that regeneration cannot occur from duplicating fragments. Since compartments appear to be involved in this type of regeneration as in others, it is suggested that a new type of model is required, one which permits simultaneous regeneration and duplication, and assigns a major role to compartments.
The distribution of ingested horseradish peroxidase in the 16-cell mouse embryo
Authors: Reeve W. J. D. 
Published: April 2021

ABSTRACTCells of the 16-cell mouse embryo endocytose horseradish peroxidase (HRP) which becomes localized in most cases to a juxtanuclear position. Cells that have ingested HRP in intact embryos, and cells dissociated from embryos prior to culture in HRP, showed similar patterns of cytoplasmic distribution of the ingested enzyme. Cells in the embryo in situ were incubated in HRP, and then labelled with fluorescent antibody either before (to label the outside surface of the embryo) or after (to reveal populations of outer polar and inner apolar cells) their disaggregation into single cells. The population of polar outside cells from the morula includes more cells with a highly restricted localization of HRP-containing vesicles than does the population of inside cells, and this restricted localization underlies the exposed surface or pole of the cell. A 2/16 couplet formed by division in vitro of a 1/8 cell is comparable to the pairs of cells dissociated from 16-cell embryos; most couplets from either source consisted of a larger cell that showed polarized surface binding of fluorescent ligand (fluorescent pole) and a smaller cell with a uniform distribution of bound ligand. The incidence of restricted patterns of HRP staining was highest among populations of both larger and polar cells. When 1 /8 cells labelled with HRP are observed during division to 2/16, the previously clustered vesicles of ingested HRP become more dispersed throughout the cytoplasm and, although the two cells of some couplets can stain differently very soon after their formation, the patterns of distribution of HRP take about 1 h after division to stabilize. These observations are consistent with cells of the 16-cell embryo inheriting different features of cytoplasmic organization.
Differentiation of the optic cups from an anophthalmic murine strain, in culture and in intrafoetal grafts
Authors: Salaün Josselyne 
Published: April 2021

ABSTRACT
The optic anlage of the anophthalmic murine strain ZRDCT/an has been studied. In this strain, 70% of the adults are anophthalmic, 30% are one-eyed. The eye primordium appears and starts to differentiate at day 9 of gestation, then it degenerates. At 13 days of gestation, it has practically disappeared.
When isolated and cultured in vitro, the 10-day anophthalmic anlage develops in the same way as a control optic-cup culture from a Swiss or C57B16 mouse.
When grafted in the back of a 15 –17 day Swiss foetus, this 10-day anophthalmic anlage also develops: retina and lens differentiate, the structures which grow are very similar to those obtained when C57B16 optic cups are grafted in the same conditions.
It appears from these results that the eye regression of the mutant in situ is not a process intrinsic to the anlage. If withdrawn from its local environmental influences, the eye primordium is able to express its aptitude for differentiation.
The proximodistal determination of skeletal parts in the developing chick leg
Authors: Rowe Donene A. , Fallon John F. 
Published: April 2021

ABSTRACT
Currently the chick leg bud or its components are being used extensively to study questions in development. Although fate maps of the leg, similar to that developed by Saunders (1948) for the wing, have been available (Hampé, 1957 a, 1959), no study of the proximodistal sequence of the specification of leg structures exists. Such a sequence developed for the wing by removal of the apical ectodermal ridge at successive stages (Saunders, 1948 ; Summerbell, 1974), has proven useful to the study of wing development. In this paper, we present a similar proximodistal sequence for the chick leg including the same developmental stage range as that of the wing sequence.
Distribution of osteo- and chondrogenic neural crest-derived cells and of osteogenically inductive epithelia in mandibular arches of embryonic chicks
Authors: Hall Brian K. 
Published: April 2021

ABSTRACTMandibular arches of H.H. stage-22 embryonic chicks were divided into halves (lateral/ medial; cephalad/caudal; or proximal/distal) and grafted to the chorioallantoic membranes of host embryos. All six halves formed both cartilage and membrane bone. Epithelial-mesenchymal recombinations performed between half mandibles showed (a), that the cephalad half of the mandible contained more chondrogenic cells than did the caudal half, (b), that the proximocaudal quarter of the mandible contained more osteogenic cells than the remainder of the mandible, and, (c), that the epithelium of the caudal half was more osteogenically inductive than was the cephalad epithelium. Differential distribution of mesenchymal cells and differentially inductively active epithelia are both components of this epithelial-mesenchymal interaction.
Functional differentiation of chick gonads following depletion of primordial germ cells
Authors: McCarrey John R. , Abbott Ursula K. 
Published: April 2021

ABSTRACT
The endocrine capacity of embryonic chick gonads depleted in germ cells was compared to that of controls to determine whether the somatic elements of germ-cell-depleted gonads will undergo normal functional sex differentiation. Primordial germ cells were removed from early embryos, Hamburger and Hamilton stages 7 – 11, by excision of the anterior germinal crescent. Embryos were sacrificed at 14 days of incubation, and their gonads were analysed for functional differentiation by: (1) electron microscopy to detect ultrastructural cellular morphology characteristic of steroid-secreting cells; (2) growth in cell culture to detect development of characteristic cell morphologies ; (3) radioimmunoassay of cell-culture media to detect androgens and oestrogens (androstenedione and oestradiol 17 β) secreted by gonadal cells; and (4) measurement of steroid levels produced by cultures treated with human chorionic gonadotropin (hCG) to detect the ability of gonadal cells to increase steroid production in response to gonadotropin stimulation. As a bioassay of gonadal endocrine activity, a gross morphological analysis was performed on the genital ducts, the development of which is ovary-dependent in females and testis-dependent in males.
This study demonstrated that both male and female embryonic gonads exhibit normal functional differentiation following a significant reduction in the number of primordial germ cells. These results confirm and extend our previous finding that morphological differentiation of sterile embryonic gonads is normal (McCarrey & Abbott, 1978). It is concluded frofn the present study that a normal complement of germ cells is not essential to either morphological or functional sex differentiation of the somatic elements of the embryonic ovary or testis, thus arguing against any inductive role for the germ cells in this process.
The innervation of a virgin tectum by a double-temporal or a double-nasal eye in Xenopus
Authors: Straznicky C. , Gaze R. M. 
Published: April 2021

ABSTRACT
In Xenopus embryos at stage 32/33 one eye anlage was removed and the other made into a compound double-nasal or double-temporal eye. At metamorphosis the optic nerve was cut and the compound eye was permitted to regenerate fibres both to its own contralateral tectum and to the ipsilateral ‘virgin’ tectum. One month later the projection from the compound eye to the virgin tectum was assessed autoradiographically by use of tritiated proline. Projections from double-temporal eyes were found to be restricted to rostrolateral tectum, whereas projections from double-nasal eyes covered the entire tectal surface. It was concluded that the results did not suggest that positional markers existed on the tectum before the arrival of the optic fibres.
Organization of actin filaments in early chick embryo ectoderm: an ultrastructural and immunocytochemical study
Authors: Wakely J. , Badley R. A. 
Published: April 2021

ABSTRACT
By combining transmission electron microscopy (TEM), scanning electron microscopy (SEM) and immunocytochemistry at both light and TEM levels the organization of actin in early chick ectoderm has been demonstrated. Every cell is encircled by a ring of actin filaments which are associated with apically situated intercellular junctions. In this way the actin ring of each individual cell is connected to that of surrounding cells and a continuous network is formed. As clearly shown by immunofluorescence and SEM studies on intact and Triton X-100 treated whole-mount preparations this network extends throughout the entire layer, interrupted only at the blastoderm margins and the primitive streak. A more diffuse arrangement was sometimes seen at cell bases. It is suggested that the network extending throughout the ectoderm gives it stability and cohesion and is important in gross morphogenetic movements involving the entire layer. The less-organized arrangement at cell bases is associated more with movements of individual cells.
Neurotrophic control of events in injured forelimbs of larval urodeles
Authors: Mescher Anthony L. 
Published: April 2021

ABSTRACT
Denervated forelimbs and contralateral innervated forelimbs of Ambystoma larvae were injured internally distal to the elbow by compression with watchmaker’s forceps. Innervated controls completely repaired the crush injury within one week; denervated limbs failed to repair the injury and exhibited varying degrees of limb regression. Histological examination revealed that the process of tissue dedifferentiation initiated by injury was more extensive in denervated, regressing limbs than in controls. In innervated limbs, both the DNA labelling index and the mitotic index peaked approximately 4-6 days after the injury and returned to baseline levels by 10 days. In denervated limbs, the DNA labelling index also increased and remained at an elevated level for at least 2 weeks after the injury, but significant mitotic activity was not observed. The data indicate that intact nerves are not needed for cellular dedifferentiation, cell cycle re-entry, and DNA synthesis in injured limbs, but are required for the cells to proliferate and repair the injury. These results are discussed together with those of similar experiments on the role of nerves during the initiation of epimorphic regeneration in amputated limbs.
Studies in Embryonic and Larval Development in Amphibia: II. The Spinal Motor-Root
Authors: Hughes Arthur 
Published: April 2021

ABSTRACTThe development of the spinal motor-roots is described in the Anurans Xenopus and Eleutherodactylus, together with observations on the embryonic roots of Bufo, the lizard Sphaerodactylus, and the chick. From a primary motor-cell in the embryo of Xenopus an axon process grows along the surface of the cord and finally turns outwards to traverse a myocommatal plane, thereby forming a ventral root. As in other larval Amphibia, the longitudinal motor-tract and the ventral roots originate together, though not necessarily by identical methods in all. In the recently hatched larva, movement is inhibited by transection of the central nervous system behind the otocyst. At these levels there must be a centre for the co-ordination of swimming movements. In mid-larval stages the ventral roots of Xenopus and Bufo arise from the longitudinal motor-tract of the cord; cell-body and myocommatal terminal of the axon are longitudinally displaced, though the precise arrangement varies at different levels in the cord. The ventral roots of the trunk of Eleutherodactylus are wholly separate and distinct from the longitudinal motor-tract, the fibres of which they cross at right angles. The arrangement of the ventral roots of the tail resembles that in other Anura. In embryos of the lizard Sphaerodactylus the ventral-root fibres arise directly from cells of the basal plate of the cord and run at various angles through the white matter to emerge as spinal motor-roots. In the chick embryo ventral-root fibres run directly at right angles through the white matter. On the basis of observations on the behaviour of nerve fibres in tissue culture, it is suggested that there is a general correlation between the angle of approach of two growing fibres and their chances of permanent anastomosis.