bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the ‘clock’ mechanism determining the time of tissue-specific enzyme development during ascidian embryogenesis
Authors: Satoh Noriyuki 
Published: April 2021

ABSTRACT
During ascidian embryogenesis a tissue-specific enzyme, muscle acetylcholinesterase (AChE) may first be detected histochemically in the presumptive muscle cells of the neurula. In order to investigate the ‘clock’ or counting mechanism that is determining the time when AChE first appears, Whittaker’s experiment (1973) has been repeated using eggs of the ascidian, Halocynthia roretzi.
Embryos that had been permanently cleavage-arrested with cytochalasin B were able to differentiate AChE in their muscle lineage blastomeres. The time of first AChE occurrence in embryos that had been cleavage-arrested in the 32-cell stage with cytochalasin B was about the same as in normal embryos. This result indicates that the clock is not apparently regulated by the events of cytokinesis.
The early gastrulae which had been arrested with colchicine or with colcemid could develop AChE activity, although no histochemically detectable AChE activity was observed in the cleavage-stage embryos that had been arrested with either drug. Therefore the clock does not seem to be controlled by the mitotic cycle of the nucleus. It is suggested that the cycle of DNA replication may be related to the regulation of the clock that is determining the time of development of histospecific protein.
Muscle-forming potential of the non-somitic cells of the early avian limb bud
Authors: McLachlan John C. , Hornbruch Amata 
Published: April 2021

ABSTRACT
It has recently been shown that the musculature of the chick wing arises by migration of cells from the somites, and that on morphological grounds this process begins at about stage 14.
We have carried out grafts of wing anlagen separate from the somites from quail donors to the extra-embryonic coelom of chicks, and find that anlagen from as early as stage 10 (11 pairs of somites) can give rise to muscle. We discuss the possible reasons for this finding, and conclude that in the absence of the cells normally giving rise to the musculature, mesodermal cells themselves can give rise to muscle.
The differentiation and proliferation of follicle cells during oocyte growth in Lacerta sicula
Authors: Filosa S. , Taddei C. , Andreuccetti P. 
Published: April 2021

ABSTRACT
The follicular epithelium of the lizard oocytes undergoes structural and morphological modifications throughout oocyte growth. During this process the number of follicle cells increases and the epithelium acquires a multilayered and polymorphic organization which is characterized by the appearance of large follicle cells (intermediate and pyriform’cells). The number of large cells also increases during oocyte growth and this increase parallels that of small cells. However, only the small cells become labelled one hour after [3H-]thymidine administration. Large cells have been found labelled after a longer period of time, i.e. 4–5 months after isotope injection.
All these results together indicate that large follicle cells arise from the differentiation of small cells.
The role of extracellular matrix in the formation of the sclerotome
Authors: Solursh Michael , Fisher Marilyn , Meier Stephen , Singley Carl T. 
Published: April 2021

ABSTRACTThe development of the sclerotome is considered as a model for the formation of mesenchyme from an epithelium. In early epithelial somites, transmission and scanning electron microscopy indicate considerable ultrastructural similarity between the future sclerotome and dermamyotomal regions. Subsequently, these two regions diverge in their development. In the forming dermamyotome, junctional complexes become more extensive and the cells become elongated, closely applied to each other, and have angular surface contours. In the forming sclerotome, there is an early reduction in apical junctions. The cells elongate, keeping their original polarity, and acquire numerous filopodia which contain punctate junctions at sites of cell-to-cell contact. Associated with cellular extension is an expansion of the intercellular spaces which do not contain any ultrastructurally recognizable material.Evidence for a role of hyaluronic acid in the expansion of the intercellular spaces is presented. As identified by the susceptibility of cetylpyridinium chloride precipitates to Streptomyces hyaluronidase and chromatographic separation of chondroitinase ABC digestion products, as much as 64 –68 % of the [3H]glucosamine-labeled glycosaminoglycans synthesized by explanted somites is hyaluronic acid. In addition, hyaluronidase-sensitive label is localized in the intercellular spaces of the sclerotome, as demonstrated by autoradiography. When Streptomyces hyaluronidase is injected in ovo into living embryos, the sclerotomal mesenchyme differentiates morphologically, but intercellular spaces are drastically reduced. It is hypothesized that the sclerotomal cells produce a hyaluronate-enriched extracellular matrix which is inflated by hydration to mediate the expansion of the sclerotomal mass towards the notochord.
The formation of muscles in regenerating limbs of the newt after denervation of the blastema
Authors: Grim Miloš , Carlson Bruce M. 
Published: April 2021

ABSTRACT
The purpose of this experiment was to examine the relationship, if any, between nerve fibers and the formation of muscle pattern in the regenerating amphibian limb. During embryogenesis, nerve fibers grow into the limb bud at the time when the common muscle blastemas subdivide into individual muscle primordia, whereas in regeneration nerve fibers are always present. In order to learn whether or not the muscle pattern could be laid down in the absence of nerves we amputated 58 limbs of newts (Notophthalmus viridescens) at the mid humeral level and allowed them to regenerate to the medium-bud or late-bud stage. The limbs were then denervated. The majority of limbs denervated at the medium-bud stage either regressed or failed to regenerate further. Regeneration after denervation failed in 9 of 25 limbs denervated at the late-bud stages.
In those limbs that continued to regenerate after denervation, the formation of individual muscle primordia did occur, following the same sequence with respect to the gross stage of regeneration as innervated regenerates. In comparing these results with our previous results on the development of muscular pattern in aneurogenic limbs of the axolotl, we conclude that in neither the embryonic nor the regenerating amphibian limb are nerve fibers directly involved in the subdivision of common muscle blastemas into the primordia of individual muscles.
Histochemistry of the developing notochord, perichordal sheath and vertebrae in Danforth’s short-tail (Sd) and normal C57BL/6 mice
Authors: Paavola Laurie G. , Wilson Doris B. , Center Elizabeth M. 
Published: April 2021

ABSTRACT
The development of the notochord, perichordal sheath and vertebrae was studied in C57BL/6 and Danforth’s short-tail (Sd) mutant mice on days 9–14 of gestation, using histochemical stains to detect possible extracellular matrix (ECM) components or precursors. Stains used were periodic-acid Schiff (PAS) after diastase treatment (glycoproteins, neutral polysaccharides) and alcian blue (glycosaminoglycans). Embryos from C57BL/6Sfd mice were analyzed to establish a normal baseline. In 9-day normal (C57BL/6Sfd; +/ + ) embryos the notochord is an uninterrupted structure and contains PAS-positive, diastaseresistant granules, whereas in abnormals (Sd/+ ; Sd/Sd) the notochord is discontinuous and exhibits few, if any, granules. A notochordal sheath is present in normal and abnormal embryos on day 10 and stains with PAS, alcian blue and aniline blue; subsequently, it increases in thickness in normal, but not defective, embryos. In normal embryos, the notochord shows dilatations, and notochordal cells become vacuolated from 13 to 14 days. In contrast, the notochordal fragments of abnormals never develop dilatations, nor do the cells vacuolate. Organization of mesenchymal cells into specific patterns is observed initially in 11-day normal embryos; further mesenchymal organization into vertebral and intervertebral disc analgen occurs during days 12–14. In abnormal embryos, disturbance of mesenchymal cell organization is evident as early as day 11, and by day 12 aberrant patterns of organization have emerged. Mesenchymal cells of abnormal embryos also lack the typical distribution of PAS-positive, diastase-resistant granules that occurs in normal specimens. The possible relationship of these granules in notochordal and mesenchymal cells to ECM materials is discussed.
Embryonic axis orientation in the mouse and its correlation with blastocyst relationships to the uterus: Part 1. Relationships between 82 hours and days
Authors: Smith L. J. 
Published: April 2021

ABSTRACT
Up until at least days p.c., the orientation of all axes in the mouse conceptus, embryonic axis included, is directly correlated with two orientations of the 82 h blastocyst within the lumen. These two are: the almost horizontal position of the blastocyst’s inner cell mass-abembryonic pole axis and the fixation of its abembryonic pole to either the right wall of the uterine horn (type-R orientation) or to the left (type-L orientation). At 88 h and at and days equal numbers of conceptuses are found in type R and L orientations. Axes of symmetry also are recognizable in some developmentally advanced 82 h blastocysts and in all older conceptuses. For example, when the inner cell mass-abembryonic pole axis has become vertically oriented within the lumen by days, the inner cell mass is oblique to this axis. It is concluded that the 82 h blastocyst’s orientation to the uterine walls and floor provides it with positional information used in the location of its axes.
Acetylcholinesterase development in extra cells caused by changing the distribution of myoplasm in ascidian embryos
Authors: Whittaker J. R. 
Published: April 2021

ABSTRACTThis research shows that myoplasmic crescent material of the ascidian egg has both functional autonomy and functional specificity in establishing the differentiation pathway of muscle lineage cells. The cytoplasmic segregation pattern in eggs of Styela plicata was altered by compression of the embryos during third cleavage. This caused a meridional division instead of the normal equatorial third cleavage; first and second cleavages are meridional. Since eggs of S, plicata have a pronounced yellow myoplasmic crescent, one observes directly that third cleavage under compression resulted in a flat 8-cell stage with four cells containing yellow myoplasm instead of the two myoplasm-containing cells that would be formed by normal equatorial division at third cleavage. If such altered 8-cell-stage embryos were released from compression and kept from undergoing further divisions by continuous treatment with cytochalasin B, some embryos eventually developed histospecific acetylcholinesterase in three and four cells instead of in just the two muscle lineage cells found in cleavage-arrested normal 8-cell stages. The wider myoplasmic distribution effected by altering the division plane at third cleavage apparently caused a change in developmental fate of the extra cells receiving myoplasm. This meridional third cleavage also resulted in a changed nuclear lineage pattern. Two nuclei that would ordinarily be in ectodermal lineage cells after third cleavage were now associated with yellow myoplasm. Acetylcholinesterase development in these cells demonstrates that nuclear lineages are not responsible for muscle acetylcholinesterase development in the ascidian embryo.
Specification of retinotectal connexions during development of the toadXenopus laevis
Authors: Sharma S. C. , Hollyfield J. G. 
Published: April 2021

ABSTRACTThe specification of central connexions of retinal ganglion cells was studied in Xenopus laevis. In one series of experiments, the right eye primordium was rotated 180° at embryonic stages 24 – 32. In the other series, the left eye was transplanted into the right orbit, and vice versa, with either 0° or 180° rotation. After metamorphosis the visual projections from the operated eye to the contralateral optic tectum were mapped electrophysiologically and compared with the normal retinotectal map. In all cases the visual projection map was rotated through the same angle as was indicated by the position of the choroidal fissure. The left eye exchanged into the right orbit retained its original axes and projected to the contralateral tectum. These results suggest that retinal ganglion cell connexions are specified before stage 24.
Effects of juvenile hormone, ecdysterone, actinomycin D, and mitomycin C on the cuticular proteins ofTenebrio molitor
Authors: Roberts P. Elaine , Willis Judith H. 
Published: April 2021

ABSTRACTJuvenile hormone (JH), ecdysterone and some antibiotics cause Tenebrio molitor to form a second pupa or pupal-adult intermediate. Incorporation of labelled leucine into the cuticular proteins of JH-induced second pupae did not differ from incorporation in normal pupae, and the soluble cuticular proteins from these young second pupae were identical to those extracted from normal pupal exocuticle when analysed by SDS-polyacry lamide gel electrophoresis. However, as these second pupae aged, the major early bands did not undergo a normal decrease in staining intensity, indicating a JH effect on protein insolubilization (sclerotization). The transport of protein into the cuticle may also have been altered by JH; electrophoretic analysis of the new cuticle of treated animals showed intense staining of bands with RF’s similar to those of blood proteins.The new exocuticle produced after treatment of pupae with ecdysterone had soluble proteins which were typical of normal pupae, but extracts from such animals aged prior to cuticle removal yielded bands characteristic of normal adults. Pupae treated with actinomycin D occasionally form new abdominal cuticle with characteristic pupal morphology. These cuticles yielded soluble proteins which, upon analysis, had pupal, pupal and adult, or adult banding patterns. Animals treated with mitomycin C, although retaining vestiges of pupal abdominal characters, had adult cuticular proteins.
Fibroblast progenitor cells of the embryonic chick limb
Authors: Newman Stuart A. 
Published: April 2021

ABSTRACT
A population of mesenchymal cells derived from the stage-25 chick wing tip gives rise to progeny of a similar morphology and to authentic fibroblasts when grown in low density culture. Mixed clones containing both cell types are often observed. As the more rapidly proliferating fibroblasts begin to predominate in these cultures, collagen biosynthesis rises from the basal mesenchymal level to a level characteristic of mature fibroblasts. The fibroblast progenitor is discussed relative to the other cell types of the mesodermal lineage of the developing limb.
Ribonucleic acid synthesis in embryonic chick muscle, rates of synthesis and half-lives of transfer and ribosomal RNA species
Authors: Nwagwu Mark , Nana Mohammed 
Published: April 2021

ABSTRACT
In this study the term ‘rates of synthesis’ does not refer to rates of transcription but to rates of accumulation of newly synthesized RNA.
The rates of synthesis and half-lives of tRNA, 18S and 28S rRNA of 14-day and 17-day embryonic chick muscle were determined by following the accumulation of radioactive AMP in RNA after administration of [3H]8-adenosine to chick embryos and correcting for the average specific activity of the precursor ATP pool. Transfer RNA of 14-day embryonic chick muscle is synthesized at a rate of 2·4 × 105 molecules per min per 2 N DNA content and decays with a half-life of 50 h. Transfer RNA of 17-day embryonic chick muscle is synthesized, and decays, at similar rates. Ribosomal RNA, 18S and 28S, are synthesized at a rate of 9·94 × 103 and 8·48 ×103 molecules per min per 2N DNA, respectively, in 14-day embryonic chick muscle. The rates of rRNA syntheis in 17-day embryonic muscle are also similar. In both 14-day and 17-day embryonic muscle, 18S and 28S rRNA each decays with a half-life of 65 h. We conclude that the constant level of tRNA and rRNA in embryonic chick muscle from 14 to 17 days (Nwagwu & Nana, 1974) is maintained also by a constant rate of synthesis and turnover.
The genesis of membrane bone in the embryonic chick maxilla: epithelial-mesenchymal tissue recombination studies
Authors: Tyler Mary S. , McCobb David P. 
Published: April 2021

ABSTRACT
In the present study, the question of whether a relatively non-specific epithelial requirement exists for membrane bone formation within the maxillary mesenchyme was investigated. Organ rudiments from embryonic chicks of three to five days of incubation (HH .18 –25) were enzymatically separated into the epithelial and mesenchymal components. Maxillary mesenchyme (from embryos HH 18 –19) which in the absence of epithelium will not form bone was recombined with epithelium from maxillae of similarly aged embryos (homotypic-homochronic recombination) and of older embryos (HH 25) (homotypic-heterochronic recombination). Heterotypic recombinations were made between maxillary mesenchyme (HH 18 –19) and the epithelium from wing and hind-limb buds (HH 19 –22). Recombinants were grown as grafts on the chorioallantoic membranes of host chick embryos. Grafts of intact maxillae, isolated maxillary mesenchyme, and isolated epithelia from the maxilla, wing-, and hind-limb buds were grown as controls. The histodifferentiation of grafted intact maxillae was similar to that in vivo; both cartilage and membrane bone differentiated within the mesenchyme. Grafts of maxillary mesenchyme (from embryos HH 18 –19) grown in the absence of epithelium formed cartilage but did not form membrane bone. Grafts of maxillary mesenchyme (from embryos HH 18 –19) recombined with epithelium in homotypic-homochronic, homotypic-heterochronic, and heterotypic tissue combinations formed membrane bone in addition to cartilage. These results indicate that maxillary mesenchyme requires the presence of epithelium to promote osteogenesis and that this epithelial requirement is relatively non-specific in terms of type and age of epithelium.
Viability and proliferation of epithelia and the initiation of osteogenesis within mandibular ectomesenchyme in the embryonic chick
Authors: Hall B. K. 
Published: April 2021

ABSTRACTEctomesenchyme, a derivative of the embryonic neural crest, forms the membrane bones of the mandibular skeleton, but will only do so after undergoing an inductive interaction with mandibular epithelium. Previously, non-mandibular epithelia have been shown to act as effective substitutes for the mandibular epithelium in this interaction. The role of epithelial viability was examined by enzymatically separating the mandibular epithelium from its ectomesenchyme, killing the epithelium, recombining the epithelium with vital ectomesenchyme and either organ culturing the recombinant or grafting it to the chorioallantoic membrane of a host embryo. Epithelia killed by distilled water, air drying, 80% ethanol, freeze-thawing or with 2500 rad of gamma irradiation did not elicit osteogenesis from the ectomesenchyme while vital epithelia did. Exposure of epithelia to gamma irradiation at doses between zero and 2000 rad resulted in a progressive reduction in the incidence of osteogenesis in ectomesenchyme. However, the incidence of osteogenesis progressively increased after irradiation of the mandibular epithelium with 3000 to 5000 rad, only to decrease again after 10000 rad. [3H]thymidine autoradiography was used to show that this pattern of induction of bone by irradiated epithelia could be correlated with the proliferative activity of the epithelia. A similar pattern of induced osteogenesis and epithelial proliferation was seen after epithelia were treated with colchicine. It was concluded that the ability of the mandibular epithelium to permit osteogenesis within mandibular ectomesenchyme was correlated with some property of epithelial proliferation. Several possibilities are discussed and related to other instances of induction of heterotopic bone by epithelia.
Dr Elizabeth Marion Deuchar (1927–1979)
Authors: Bellairs Ruth 
Published: April 2021

ABSTRACT
Elizabeth Deuchar, who died of cancer in January 1979 at the age of 52, was an embryologist of distinction. After studying Zoology at Oxford she moved in 1948 to the Institute of Animal Genetics in Edinburgh as a Ph.D. student with the late C. H. Waddington. Her earliest papers, published under his influence, were on embryonic induction, a topic to which she returned many times. These studies culminated in 1975 in a book synthesizing many of her ideas (8).
The effect of chymotrypsin on the development of Dictyostelium discoideum
Authors: Kilpatrick David C. , Schmidt Jerzy A. , Stirling John L. , Pacy John , Jones Gareth E. 
Published: April 2021

ABSTRACT
Development of the cellular slime mould Dictyostelium discoideum strain NC4, in the presence of α-chymotrypsin (3 mg/ml) is reversibly arrested at the tight aggregate stage (10/12 h). Pronase has a similar effect, but trypsin only retards normal development by about five hours. Normally developing cells are susceptible to α-chymotrypsin if they are transferred into its presence at any time up to the tight aggregate stage (10-12 h). Transfer after this stage does not affect the appearance of fruiting body structures in the normal time (24 h).
Electron microscopy showed the ultrastructure of α-chymotrypsin-blocked aggregates after starvation for 24 h to be consistent with a block at 10 –12 h of normal development. Poorly developed prespore vacuoles, having thin incomplete walls and a paucity of electrondense material, are present in some cells. No angular vacuolated cells characteristic of stalk cells are visible. Fruiting bodies formed in the presence of a α-chymotrypsin, either as minority structures when the enzyme is added before 10 –12 h of normal development, or as the majority structures on later enzyme addition, were found to be abnormal. Normal stalks were formed but the spores were immature. Prespore vacuoles were present, though disrupted, and the cells were not encapsulated by spore walls.
The electronegativity of intact slime mould amoebae was significantly reduced, and material containing L-[6-3H]-fucose and [l-14C]leucine was removed from the cell surface on α-chymotrypsin treatment. Few plasma membrane proteins were affected, however, and staining of polyacrylamide gels for glycopeptides using Con A-peroxide binding also showed little change.
Development of amphibian thymus I. Morphological differentiation, multiplication, migration and lysis of thymocytes in the urodelePleurodeles waltlii
Authors: Henry M. , Charlemagne J. 
Published: April 2021

ABSTRACTDifferent stages of thymus morphogenesis and thymocyte differentiation have been studied at the ultrastructural level in the urodele amphibian Pleurodeles waltlii Michah. From stage 38 to 42 the undifferentiated lymphoid stem-cells colonize the epithelial thymic buds. From stage 43 to 45 the lymphoid stem-cells differentiate into lymphoblasts and then transform into typical lymphocytes. A clasmatosis phenomenon seems to be involved in this transformation. From stage 46 to 52, a phase of intense proliferation occurs and relations between dense reticular epithelial cells and lymphocytes are described. At stage 53, numerous lymphocytes die in the thymic tissue and are phagocytosed by macrophages. At the same time, lymphocytes undergo migrations through the intra- and peri-thymic blood vessels. These lymphocytes should populate the peripheral lymphoid organs, according to the previous finding that stage 52 was the last developmental step for an efficient abrogation of cell-mediated immunity by thymectomy in Pleurodeles.