bluuebunny/crossref_metadata_2025_split huggingface dataset:
The spatio-temporal framework of melanogenic induction in pigmented retinal cells of Xenopus laevis
Authors: Hoperskaya Olga A. , Golubeva Olga N. 
Published: April 2021

ABSTRACT
Using methods involving transplantation of neuroectoderm and eye rudiments between ap/ap mutants and + / + embryos of Xenopus laevis, new aspects of melanogenic induction have been ascertained. The possibility of separate induction of a melanocyte cell type and of the product of terminal differentiation in it - melanosomes, has been demonstrated. Melanogenic induction starts at the late gastrula stage. It has an irreversible character which has been shown using the technique of double transplantation. Melanogenic factor (MgF) is produced only by the region of endomesoderm which is adjacent to eye rudiments in the course of normal development. Competence for melanogenic induction lasts till stage NF 30. Melanogenic induction appears to be species-specific; at least after transplantation of eye vesicles from ap/apXenopus laevis to Rana temporaria the melanoprotein synthesis cannot be switched on. L-Tyrosine, under the conditions of the experiments, is not a factor in the induction of melanogenesis.
Immunosurgical studies on inner cell mass development in rat and mouse blastocysts before and during implantation in vitro
Authors: Spielmann Horst , Jacob-Müller Ursula , Beckord Werner 
Published: April 2021

ABSTRACT
Eighty per cent of rat blastocysts (Wistar, SW72) cultured for 96 h in NCTC-109 supplemented with fetal calf serum (FCS) hatched from the zona pellucida and developed a trophoblast giant cell layer. Thirty seven per cent of the rat blastocysts developed an inner cell mass (ICM) which, in about 7 %, consisted of two germ layers (ectoderm and endoderm), compared to 84% in NMRI mice. A significantly better ICM development was obtained with cultured rat blastocysts that had hatched in vivo. Similar to the in vivo situation LDH-5 was present in rat blastocysts after implantation in NCTC-109-FCS. Differentiation of C57BL mouse blastocysts in NCTC-109-FCS proceeded as poorly as in the rat.
ICM development of rat and mouse blastocysts in NCTC-109-FCS was studied in detail. ICMs of the two species were isolated immunosurgically using complement from different species, e.g. human, rat and rabbit complement, since guinea-pig complement did not lyse trophectoderm cells of rat blastocysts. All immunosurgically isolated rat ICMs degenerated within 48 h, but mouse ICMs isolated with rat or rabbit complement developed significantly better than mouse ICMs isolated with guinea-pig complement. Determinations of the blastocyst total cell number (BTCN) and of the cell number of immunosurgically isolated ICMs were performed in rat and mouse blastocysts to investigate growth kinetics of the ICM before implantation in vitro. In the mouse an exponential increase in both BTCN and cell number of the ICM was observed during the 48 h before implantation in NCTC-109-FCS and also during the 16-24 h before implantation in vivo. In the rat, doubling of the BTCN was found only during the first 24 h in NCTC-109-FCS and there was hardly any increase in the cell number of the ICM during the first 48 h in culture. ICM growth of blastocysts in NCTC-109-FCS is, therefore, stimulated in the mouse before and after implantation and. in the rat it is inhibited already before implantation.
Membrane sterols and the development of the preimplantation mouse embryo
Authors: Pratt Hester P.M. , Keith Jo , Chakraborty Jyotsna 
Published: April 2021

ABSTRACT
The role of membrane sterols in the compaction and subsequent development of the preimplantation mouse embryo was studied by incubating embryos in 7-ketocholesterol and other oxygenated sterols. These sterols have been shown to inhibit sterol synthesis and deplete membranes of cholesterol in a variety of other cell types.
Compaction and subsequent blastocyst formation were normal when embryos were incubated in physiological sterols but were inhibited by oxygenated sterols to a degree which depended upon the concentration of sterol, duration of incubation and developmental age of the embryos. Precompaction 8-cell embryos were most susceptible to the action of these sterols and failed to compact (as assessed by cell flattening and increased intercellular adhesion) but continued to divide, whilst later stage embryos developed normally. 7-keto-cholesterol had a specific effect on the ultrastructure of the smooth endoplasmic reticulum of treated embryos. The developmental and ultrastructural effects induced by the oxygenated sterols could be reversed or prevented by the use of products of the blocked reaction (i.e. mevalonate, desmosterol or cholesterol).
These results substantiate the evidence that preimplantation mammalian embryos are capable of synthesizing membrane sterols from the 8-cell stage onwards and emphasize the importance of the sterol composition of membranes for normal cytokinesis and compaction of the mouse embryo.
Pattern regulation and the origin of extra parts following axial misalignments in the urodele limb bud
Authors: Thoms Stephen D. , Fallon John F. 
Published: April 2021

ABSTRACT
Pattern regulation following axial misalignments in the stage-38 + to stage-40 urodele limb bud was studied on one newt and two salamander species. Grafts of the distal tip of the limb bud were made to the stump of a host limb bud from which a similar piece had been removed. The grafts were positioned with either their anteroposterior, dorsoventral, or both of these axes reversed with respect to the host axes. Mirror-imaged duplications, positioned posteriorly or both anteriorly and posteriorly, occurred nearly all (96%) of the time when the anteroposterior axis was reversed. Dorsoventral axial misalignment rarely promoted the generation of mirror-imaged duplications (8%) but did affect the organization along the anteroposterior axis by causing a serial repetition of either digit 2 or digit 3. Regulation, therefore, does not always occur along each axis independently of the others. Consistent with the data derived from reversing individual axes, most of the duplications which occurred when both axes were reversed were in the anteroposterior plane. Some were in the dorsoventral plane, and a few had intermediate positions. Of these duplications a few were neither right nor left hands, rather they were of mixed handedness with a change in the dorsoventral polarity from the anterior border to the posterior border.
Whether extra parts which result from axial misalignments arise from the graft, the host, or both the graft and the host was investigated using heteroplastic grafts and grafts exchanged between triploid and diploid axolotls. Duplications were found to have cellular contributions from both the graft and the host. In some cases one source would dominate but usually both made a substantial contribution. The diploid-triploid material suggests that a considerable mixing of host and graft cells may occur in duplications. Additionally, some digits of the graft sequence of digits can be derived from host tissue. The extra digit in those hands displaying a serial repetition was derived from host tissue in some cases and graft tissue in other cases.
Commitment of stem cells to nerve cells and migration of nerve cell precursors in preparatory bud development in Hydra
Authors: Berking Stefan 
Published: April 2021

ABSTRACT
Budding in Hydra starts as an evagination of the double-layered tissue in the parent animal’s gastric region. Five hours later the density of nerve cells in the bud’s tissue doubles, representing the first detectable difference from the cellular composition of the surrounding tissue. These new nerve cells derive from multipotent stem cells which are in S-phase one day before evagination starts. Some of the bud’s new nerve cells derive from stem cells which have migrated into the future bud’s tissue after their commitment, apparently attracted by the bud anlage. The bud anlage recruits precursors of nerve cells even during starvation, during which nerve cell production ceases in other parts of the body. Furthermore, the bud anlage controls the duration of the development from commitment to final differentiation of the resulting nerve cells.
Experiments with an inhibitor purified from hydra tissue indicate a tight correlation between stages of preparatory bud development and stages of recruitment of nerve cells for the bud. Whether or not precursors of nerve cells are involved in the control of bud formation in normal hydra, as compared to epithelial hydra which still bud though consisting of epithelial cells only, will be discussed.
The control of trophoblastic growth in the guinea pig
Authors: Ilgren E. B. 
Published: April 2021

ABSTRACT
The growth of mouse trophectoderm depends upon the presence of the inner cell mass. Whether this applies to other species of mammals is not known. To investigate this problem, the guinea pig was selected for two reasons. Firstly, the growth of guinea-pig trophoblast resembles that of man. Secondly, earlier studies suggest that the proliferation of guinea-pig trophectoderm may not be under ICM control. Therefore, in the present study, the guinea-pig blastocyst was cut microsurgically to yield two tissue fragments. These contained roughly equal numbers of trophectodermal cells, one fragment being composed only of trophectoderm and the other containing ICM tissue as well. Subsequently, the growth of these mural and polar fragments was followed in vitro since numerous technical difficulties make an in vivo analysis of this problem impracticable. In a manner similar to the mouse, the isolated mural trophectoderm of the guinea pig stopped dividing and became giant. In contrast, guinea-pig polar fragments formed egg-cylinder-like structures. The latter contained regions structurally similar to two presumptive polar trophectodermal derivatives namely the ectoplacental and extraembryonic ectodermal tissues. These findings suggest that guinea-pig trophectodermal growth may occur in a manner similar to the mouse and thus be under ICM control.
The effect of microtubule- and microfilament-disrupting drugs on preimplantation mouse embryos
Authors: Siracusa G. , Whittingham D. G. , De Felici M. 
Published: April 2021

ABSTRACT
The sensitivity of early preimplantation mouse embryos to drugs which disrupt microfilament function (cytochalasin B-CB and cytochalasin D-CD) and microtubule assembly (colchicine, colcemid, vinblastine and griseofulvin) was examined. CD inhibited cleavage at a concentration 35-fold lower than CB (3 × 10–7 M v. 1 × 10−5 M). Treatment of 2-cell embryos for 6 h with 1 × 10−5 M CB or 1 × 10−6 M CD or continuous exposure to lower concentrations of CB or CD did not affect development to the blastocyst stage in vitro. Vinblastine inhibited cleavage at a concentration tenfold lower than colcemid or colchicine (1 × 10−8 M v. l × 10−7 M). The continuous presence of colcemid at 10−8 M did not affect the development of 2-cell embryos to the blastocyst stage, but development was reduced with vinblastine at 1 × 10−9 M and completely inhibited with colchicine at 1 × 10−8 M. The drugs produced similar responses when 2-cell embryos were treated for 6 h with concentrations that inhibited cleavage. Complete inhibition of cleavage was obtained after only a 2 h exposure to 2 × 10−7 M colchicine. A similar concentration of lumicolchicine did not affect cleavage or blastocyst formation. Embryos were less sensitive to griseofulvin; the first cleavage division was unaffected by concentrations as high as 3 × 10− 4M and only 50% of 2-cell embryos failed to cleave in 1 × 10 1 and 3 × 10 −4M griseofulvin. At these concentrations a small proportion of 1-cell embryos and the majority of the 2-cell embryos showed unequal cytoplasmic division probably caused by the formation of multipolar spindles. The continuous exposure of 2-cell embryos to 3 × 10−5 M griseofulvin did not affect blastocyst formation.
A method for visualizing the chromosomes of the second polar body of the mouse egg
Authors: Modliński J. , McLaren Anne 
Published: April 2021

Abstract
A second-polar-body nucleus inserted by microinjection into a different mouse egg entered into mitosis synchronously with the pronuclei of the host egg. The extent to which the karyotype of the polar body can yield information on the karyotype of the donor egg is discussed.
Disproportionate micromelia (Dmm): an incomplete dominant mouse dwarfism with abnormal cartilage matrix
Authors: Brown Kenneth S. , Cranley Robert E. , Greene Robert , Kleinman Hynda K. , Pennypacker John P. 
Published: April 2021

ABSTRACT
This paper describes a new autosomal incomplete dominant dwarfism, disproportionate micromelia, which has been characterized genetically and phenotypically, and the cartilage of homozygotes, and heterozygotes has been examined by histochemical, immunofluorescence and biochemical methods. Homozygotes, which die at birth, are disproportionately short and have cleft palates. The heterozygotes appear normal at birth but beginning at 1 week of age dwarfism is apparent and increases during growth. Histochemical and biochemical analyses of the cartilage rudiments of homozygotes at day 18 of gestation demonstrate that the cartilage growth plate is disorganized and that the matrix components, collagen and proteoglycan, are altered. Total collagen synthesis is reduced by approximately 30% and the amount of type II collagen is greatly reduced. By immunofluorescence staining with collagen antibodies, it appears that type II collagen is located primarily near the cell surface of chondrocytes but is poorly distributed throughout the remainder of the matrix. The amount of proteoglycan in the cartilage matrix is reduced by approximately 70% as determined by chemical analysis of hexosamines and by [35S]sulfate incorporation. Although the proteoglycans synthesized by the mutant are normal in size and in glycosaminoglycan composition, they were more easily extractable from the matrix than were normal cartilage proteoglycans. Heterozygotes had reduced cartilage matrix proteoglycan by histochemical methods, but the organization of the epiphyseal cartilage was not abnormal. These data suggest that a reduced or abnormal cartilage matrix is the cause of the dwarfism.
Biochemical studies of intrauterine components of the tammar wallaby Macropus eugenii during pregnancy
Authors: Thornber Elizabeth J. , Renfree Marilyn B. , Wallace Gregory I. 
Published: April 2021

ABSTRACT
The in vitro uptake and incorporation of [3H] uridine by blastocysts of the tammar wallaby showed a 16- and 30-fold increase from day 0 to day 10 after removal of pouch young, respectively. Two of the six non-expanded blastocysts recovered on day 5 showed a tenfold increase in incorporation. During the first ten days after removal of pouch young the diameter of the blastocyst increased threefold. Endometrial exudate from gravid uteri had a higher protein concentration than exudate from nongravid uteri (39·5 ±0·9 and 320 ± 2·0 mg/ml (mean + s.E.M.), respectively). Endometrial exudates from uteri where the blastocyst was actively growing were found to contain six uterine-specific proteins. These were separated by gradient polyacrylamide gel electrophoresis. Two of the proteins were prealbumins and the others were larger molecules (M.W. 153000-670000). Two proteins were only present at particular stages of pregnancy: the other four were present at all stages from diapause to birth, in exudate from gravid and nongravid uteri. The specific binding of progesterone and androstenedione to proteins in endometrial exudates or uterine flushings from pregnant wallabies was less than one per cent of the value obtained from day-5 pregnant rabbits. The ability of mouse blastocysts to take up and incorporate [3H] uridine into acidinsoluble material increased threefold in the presence of day-10 endometrial exudates from wallabies. However, this was less than ten percent of the values obtained in the presence of bovine serum albumin.
The concentration of calcium in endometrial exudates increased from 23·6 to 45·2μg/ml during pregnancy; in endometrium it remained at 88·7μg/g (wet weight) throughout pregnancy, and in plasma it was 53·3 μg/ml. The concentration of zinc in endometrial exudates was 4·5 μg/ml; in endometrium it decreased from 21·8 to 13-3μg/g (wet weight) during pregnancy and in plasma it was 0·6 μg/ml.
Dictyostelium amoebae can differentiate into spores without cell-to-cell contact
Authors: Kay Robert R. , Trevan David J. 
Published: April 2021

ABSTRACT
Amoebae of sporogenous mutants of Dictyostelium discoideum can differentiate into stalk cells and spores in the absence of normal morphogenesis when spread on agar containing cyclic-AMP. The efficiency of differentiation is improved when the amoebae are incubated as submerged monolayers in plastic petri dishes. Under these conditions spore formation is density dependent and hence requires some form of cellular interaction. To determine whether this interaction involves direct cell-cell contact we have made time-lapse films of cells differentiating at intermediate density. These films show that amoebae can develop into spores without making contact with any other cells. In addition, although some cells do divide during incubation, division is not necessary for spore formation. At higher densities small aggregates form which give rise to mixtures of stalk cells and spores. There is no detectable patterning of the two cell types within such aggregates.
Differentiation within the gonads of Drosophila revealed by immunofluorescence
Authors: Brower Danny L. , Smith R. J. , Wilcox Michael 
Published: April 2021

ABSTRACT
The antibody produced by the hybrid cell line DA.1B6 binds to the diploid epithelial cells of Drosophila. In this paper, we describe the immunofluorescence-binding pattern of the antibody to the gonads. A bright sheath of fluorescence extends from the seminal vesicle onto the most proximal part of the adult testis. The only other significant binding to the organ is to the apical cells of the germinal proliferation centre, which fluoresce brightly in testes from adults and from third instar larvae. In the adult ovary, there is strong binding to the cells of the follicular epithelium, although this binding is reduced in the latter stages of follicle development. Soon after the formation of a follicle, a pair of epithelial cells at each pole of the follicle can be seen to fluoresce much more brightly than the other cells. This early differentiation is reflected in the morphogenetic behaviour of these polar cells as the follicle develops. The anterior pair are among the ‘border cells’ which migrate between the nurse cells to the anterior pole of the developing oocyte; and, when the follicular epithelium around the oocyte becomes columnar, the posterior pair of cells do not elongate as much as the surrounding cells.
Neural crest formation in the head of the mouse embryo as observed using a new histological technique
Authors: Nichols David H. 
Published: April 2021

ABSTRACTA histological technique is described which results in the differential staining of neural crest cells. This is used to describe the formation and early migration of crest cells in the head of the mouse embryo. The first indications of crest formation are seen in the midbrain/anterior hindbrain at 3–4 somites where crest cells accumulate in the basal surface of the ectodermal epithelium near the future margin of the neural plate. Shortly thereafter (4–6 somites) these cells disrupt the basal surface of the epithelium and escape as mesenchyme. The apical epithelial cells in this region become the surface ectoderm adjacent to the neural plate. Subsequently, crest is formed from neural plate rather than surface ectoderm. In addition, mesenchyme is formed from presumptive surface ectoderm in a groove in the lateral portion of the fold between the forebrain and the midbrain. By 5–7 somites, crest mesenchyme is formed at all levels of the midbrain, hindbrain, and from the margins of the forebrain adjacent to the optic pits. Because of the bending of the embryonic axis, forebrain crest cells appear to migrate dorsally over the presumptive eye where they are met by ventrally migrating midbrain crest cells. Crest formation continues in the region of the midbrain and hindbrain during, and for an undetermined period after closure of the head folds at between 8 and 16 somites.These results demonstrate differences in the origin and timing of crest formation between chick and mouse. From this may be inferred different patterns of crest migration as well.In addition, the ability to directly observe early crest formation should aid in the analysis of the mechanisms by which epithelial cells are converted into mesenchyme.
The induction of neural crest-derived cartilage and bone by embryonic epithelia: an analysis of the mode of action of an epithelial-mesenchymal interaction
Authors: Hall Brian K. 
Published: April 2021

ABSTRACTThe formation of membrane bone from neural crest-derived mesenchyme of the maxillary and mandibular processes of the embryonic chick depends upon prior interactions between the mesenchyme and maxillary or mandibular epithelia. The present study explores the specificity of these interactions using tissue recombinations between heterotypic epithelia and mesenchyme. Mandibular and maxillary mesenchyme responded to maxillary and mandibular epithelia by forming bone. A third osteogenically inductive epithelium, the scleral epithelium with its specialized scleral papillae, also allowed mandibular mesenchyme to form bone, indicating that mesenchyme can form bone in response to osteogenic epithelia other than its own. Epithelia which normally do not induce membrane bone formation in situ (wing and leg bud, back and abdominal epithelia) also allowed mandibular epithelia to ossify as did mandibular epithelia from the 10-day-old foetal mouse. Thus this tissue interaction is neither site nor species specific.Mandibular epithelium allowed bone to form in osteogenic mesenchyme from the maxilla and the sclera of the chick and from the mouse mandible but would not induce bone formation from normally non-osteogenic mesenchyme of the limb buds, chorioallantoic membrane or trunk neural crest.The results obtained with all of the tissue recombinations were consistent with the epithelial-mesenchyme interactions that initiate osteogenesis in both the mandibular and the maxillary processes being permissive interactions. The distinction between permissive and instructive interactions is discussed.
Sequence of regeneration in the Drosophila wing disc
Authors: Karlsson Jane 
Published: April 2021

ABSTRACT
The sequence of appearance of different structures during regulation was ascertained for three wing disc fragments. It was found that structures were added sequentially from the cut edge. Regeneration in one fragment was very fast and successful, and it is suggested that this is difficult to explain in terms of wound healing being responsible for the decision to regenerate rather than duplicate. In another fragment, regeneration appeared to proceed from one part of the cut edge only, this being the region through which the anteroposterior compartment boundary runs. Compartment boundaries have been implicated in both proximodistal and circumferential regeneration, and it is suggested that regeneration is controlled at these sites. The decision to regenerate rather than duplicate may be made on the basis of which compartment boundaries are exposed at the cut edge, and their preferred direction of regeneration. The implications of this interpretation for the control of growth are discussed.