bluuebunny/crossref_metadata_2025_split huggingface dataset:
A high frequency of fertilization in premature and mature coelomic toad eggs after enzymic removal of vitelline membrane
Authors: Katagiri Chiaki 
Published: April 2021

ABSTRACT
The jelly-less coelomic eggs of the toad, Bufo bufo, even if chromosomally mature and reactive to parthenogenetic stimuli, are not fertilized or fertilized in a low frequency under the conditions which assure the sperm entry into dejellied uterine eggs. A high frequency of fertilization was obtained, however, when coelomic eggs from which the vitelline membrane had been digested away by pronase or hatching enzyme were inseminated in the presence of polyvinylpyrrolidone (PVP) or the diffusible egg-jelly component. Experimental evidence is presented to show that the conditions important for inducing this success in fertilization arc the complete removal of the vitelline membrane and insemination in the presence of one of the following sperm ‘capacitating’ substances: the diffusible jelly component, the non-dialysable jelly component, PVP, dextran, or Ficoll. Fertilization obtained by this method was monospermic, as defined both by cytological examination and by the mode of early cleavage. However, the eggs invariably ceased development at the gastrula stage, because of the lack of the mechanical support normally provided by the egg envelopes. These results indicate that toad eggs acquire the full ability, without any influences from the oviduct, both to react to a penetrating sperm and to prevent polyspermy.
When eggs undergoing maturation (premature eggs) were demembranated and inseminated in the presence of PVP, they did not show a genuine cleavage. Cytological examination proved the occurrence of highly polyspermie fertilization in these premature eggs, together with a tendency for the rate of pronucleus formation by the incorporated sperm to increase as the eggs were closer to the stage of full nuclear maturity.
On the basis of these results, a possible role of the oviduct in affecting the vitelline membrane-egg surface interrelationship is discussed, as well as the changing reactivity of maturing oocytes to spermatozoa, and vice versa.
Behavioural transformation in chick yolk-sac cells
Authors: Downie J. Roger 
Published: April 2021

ABSTRACT
During the first 3 to 4 days of development in the chick, the extraembryonic part, the yolk-sac, expands to encompass the yolk mass. The yolk-sac, initially a two-layered epithelial sheet, is pulled out by the action of a specialized band of cells at its periphery. These attach to the overlying vitelline membrane and move out over it.
However, unincubated blastoderms are not attached to the vitelline membrane, and each comprises a loose assemblage of rounded cells, not an epithelial sheet.
The transformation of the unincubated blastoderm into an actively expanding epithelial sheet has been followed in culture, using hanging-drop cultures of fragments to observe large-scale behaviour, and disaggregated blastoderms to observe individual cell behaviour. The timing of events in culture accords well with related events in ovo, and the possibility that in vitro changes are merely a response to culture conditions has been largely excluded.
0–6 h in ovo. No cells attached to the vitelline membrane. All cells loosely attached to one another.
0–6 h in vitro. Cells do not attach to the glass. The cells of disaggregated blastoderms are rounded and stationary.
6–10 h in ovo. Cells at the blastoderm periphery attach to the vitelline membrane inner surface, but expansion does not start. The cells remain loosely attached to one another.
6–10 h in vitro. Cells begin to stick to the glass surface. Cells from disaggregated cultures move around as individuals. They remain rounded with long, narrow filopodia. If two cells collide, the adhesion tends to be brief.
10+h in ovo. The blastoderm starts to expand rapidly as a cohesive epithelial sheet, pulled by its specialized ‘edge’ cells. All yolk-sac cells become tightly attached to one another.
10+h in vitro. Blastoderm fragments start to spread rapidly as flattened epithelial sheets. There is no sign of specialized ‘edge’ cells. Cells at the periphery of any fragment take on the role of the edge. Cells from disaggregated cultures flatten out on the glass with wide lamellae all round. When two cells collide, they now tend to stick permanently together.
The role of these changes in the mechanics of blastoderm expansion is briefly discussed.
‘Spontaneous’ sex reversal in organ cultures of the embryonic male gonad of the bird
Authors: Erickson Gregory F. 
Published: April 2021

ABSTRACT
The left embryonic testis of the bird (4–8 days of incubation) was organ cultured in medium that contained 10% foetal calf serum. Under these conditions, the germinal epithelium (GE) of the 4-day gonad differentiates into an ovarian cortex and the male primordial germ cells (PGCs) complete a developmental sequence similar to normal oocytes, i.e. they divide mitotically, develop a Balbiani body, divide synchronously in groups of two, four, and eight germ cells, and some enter pre-leptotene. No medullary tissue develops in the 4-day explants. The pieces of 6-and 8-day gonad differentiate into true ovotestes in which the GE develops into a cortex and the medulla develops into seminiferous cords. The PGCs in the cortex differentiate as oocytes and those in the seminiferous cords differentiate as spermatogonia. The possibility that biologically active oestrogens are present in the growth medium is discussed.
Diploid and haploid mouse parthenogenetic development following in vitro activation and embryo transfer
Authors: Kaufman M. H. , Gardner R. L. 
Published: April 2021

ABSTRACT
Parthenogenetic mouse embryos were selected following in vitro activation, and transferred to the oviducts of pseudopregnant recipients. Decidua was evoked by 50–56 % of diploid parthenogenones compared to 35·1 % of haploid embryos with a single pronucleus, 37·5 % of immediate cleavage eggs and 77 % of fertilized eggs (controls). On day 4, 58·7 % of diploid parthenogenones were morphologically normal morulae or blastocysts; over 90 % of these ‘normal’ embryos evoked decidua when retransferred to recipients compared to 8·9 % of abnormal embryos flushed from the ‘transfer’ sides, suggesting that only ‘normal’ embryos could evoke decidua. Potentially diploid parthenogenones remained diploid on chromosomal examination on day 4.
Serum variants causing the formation of double hearts and other abnormalities in explanted rat embryos
Authors: Steele C. E. , New D. A. T. 
Published: April 2021

ABSTRACT
Rat embryos explanted before organogenesis ( days gestation) were grown in culture in homologous serum. When the serum was prepared from blood centrifuged after clotting, the embryos developed double hearts. In serum prepared from blood centrifuged before clotting had occurred, and in plasma, the embryos developed normal single hearts. The delayed-centrifuged (D.C.) serum also supported less growth of older embryos than the immediately-centrifuged (I.C.) serum. The harmful properties of D.C. serum appeared rapidly in contact with a normal blood clot but did not develop in contact with separated blood cells and fibrin clot. Mixtures of D.C. and I.C. sera gave results intermediate between those from the two sera alone. No significant differences were found between D.C. and I.C. serum in calcium or complement content but both supported better embryonic development after pre-heating.
Induction de la maturation sexuelle chez la Planaire scissipare Dugesia gonocephala (Turbellarié, Triclade)
Authors: Lender Th. , Briançon C. 
Published: April 2021

ABSTRACT

Induction of sexual maturity in a fissiparous Planarian, Dugesia gonocephala
The planarian Dugesia gonocephala reproduces either sexually, or asexually by fission, according to the presence or absence of a genital apparatus.
The experimental induction of sexual maturity in a fissiparous planarian can be obtained by grafting a piece of a planarian with a genital pore containing mature testes, whether they are testes existing in the graft before the operation (grafts of testes) or testes differentiated in the piece after grafting (grafts of ovaries). Grafts of cephalic or caudal region, and pieces of a planarian without genital pore, cannot induce this maturation and cannot differentiate testes.
The induction of testicular structures seems to be dependent on hormones.
The development of a genital apparatus in a planarian without genital pore is accompanied by the disappearance of fission.
An ultrastructural study of sex differentiation in the teleostOryzias latipes
Authors: Satoh Noriyuki 
Published: April 2021

ABSTRACTElectron-microscopic observations on sex differentiation during normal development in the medaka, Oryzias latipes, are presented in this report.Primordial germ cells in embryos 6-10 days after fertilization are clearly distinguishable from somatic cells by the presence in the cytoplasm of the former of germinal dense bodies, closely associated with large aggregations of mitochondria. The gonadal primordium is composed of the primordial germ cells and the enveloping somatic cells; no special ultrastructural relationships have been detected between these two cell types. The sex of an embryo cannot be decided by means of the electron microscope.The newly formed ovary is distinguishable in newly hatched fry of about 5 mm total body length. In the ovary, a layer of cells forming the ovarian wall encloses the ovarian matrix, consisting of oogonia and their surrounding follicle cells. There are often observable desmosomes between two neighbouring follicle cells. Although marked rearrangement of somatic cells takes place during sex differentiation of the gonad, few visible changes are observed in the ultrastructure of the primordial germ cells during their transition to oogonia. The transition from the oogonium to the oocyte is, however, characterized by a distinctive change in the nucleus, associated with the onset of meiosis. In the young ovary of 5-day-old fry, ooctye chromatin is visibly organized into electron-dense axial elements at the leptotene stage of meiotic prophase. But in the ovary of 10-day-old fry (about 6 mm body length), many oocytes at zygotene or pachytene stages are found, with synaptonemal complex configurations essentially the same as those described in numerous other meiosing plant and animal cells.In contrast, the testis of newly hatched male fry remains in an undifferentiated state, with the somatic cells simply enveloping the spermatogonia.No cells with the ultrastructural characteristics of Leydig cells (as observed in adult testis) can be distinguished in the young ovary or in the undifferentiated testis 10 days after hatching. Cells with the ultrastructural characteristics of adult Leydig cells are detectable for the first time in the matrix of the testis of 25-day-old young, about 8 mm in total length. When proliferation of spermatogonia has occurred, to form the typical testis of 45-day-old (about 15 mm), young, these cells appear in the interstitial region of the testis.Observations from the present study indicate that sex differentiation of germ cells and somatic cells in the gonad precedes the differentiation of steroid-secreting cells. Therefore, the hypothesis that sex hormones are natural sex-inducers is not supported by the present results. The possibility is emphasized that some intracellular mechanisms may be involved in the natural course of sex differentiation of the germ cells and the gonad in this fish.
X-inactivation pattern in the epididymis of sex-reversed mice heterozygous for testicular feminization
Authors: Drews Ulrich , Alonso-Lozano Valentin 
Published: April 2021

ABSTRACT
Female mice heterozygous for testicular feminization were sex-reversed by means of the autosomal sex reversal mutation (Sxr). Due to X-inactivation, the blastemata for male sex organs in these animals are composed of a mixture of cells, carrying either the wildtype X chromosome or the X chromosome affected with Tfm in an active state. Thus, the two types of cells are sensitive to androgens or insensitive to androgens, respectively. This mosaic could be demonstrated in the epididymis on a cellular level. Segments of undifferentiated Tfm cells were found alternating with normally differentiated wild-type cells. The ultras truc tura] appearance of the mosaic is described.
Mesenchyme specificity in rodent salivary gland development: the response of salivary epithelium to lung mesenchyme in vitro
Authors: Lawson Kirstie A. 
Published: April 2021

ABSTRACT
Lung mesenchyme is able to support budding and cytodifferentiation of salivary epithelial rudiments in vitro. No difference in response was found between submandibular and parotid epithelium from mouse or rat.
There are several further features of this result, which is contradictory to previous findings. (1) Lung mesenchyme is quantitatively less effective than submandibular mesenchyme for supporting submandibular morphogenesis. At least part of this difference is attributed to the inability of submandibular epithelium to replace lung epithelium in supporting the growth of lung mesenchyme. (2) Rat lung mesenchyme is quantitatively more effective than mouse lung mesenchyme when recombined with mouse submandibular epithelium. This may be at least partly due to mouse lung being more easily damaged by the procedures used. (3) Whereas the response of submandibular epithelium to submandibular mesenchyme is equally good on an agar or Millipore filter (MF) substratum, the response to lung mesenchyme is severely reduced or eliminated on MF. This difference is interpreted in terms of different mesenchymal cell densities necessary for submandibular or lung mesenchyme to support branching morphogenesis.
Salivary buds formed in lung mesenchyme after 6 days are smaller and more closely packed than in salivary mesenchyme. In these heterotypic recombinates, the accumulation of amylase-resistant, PAS-positive material in the buds is initially accelerated and the tubular epithelium accumulates glycogen.
Protein synthesis in the early Drosophila embryo; analysis of the protein species synthesized
Authors: Roberts David B. , Graziosi Giorgio 
Published: April 2021

ABSTRACT
The soluble proteins were extracted from Drosophila eggs which had been permeabilized and incubated in medium containing [35S]methionine. These proteins were analysed on immunoelectrophoresis plates and on SDS polyacrylamide gels both by staining for total protein and by autoradiography. The radioactive proteins must have been synthesized during the period of incubation with [35S]methionine. In the period covered by this study (0–3 h) there was much protein synthesis but no new proteins were synthesized which had not already been synthesized during oogenesis. We conclude that the considerable protein synthesis that occurs in early Drosophila development is translated from maternal mRNA which is activated both by egg deposition and fertilization. Translation of protein from either masked maternal mRNA, which had not been previously translated, or from mRNA transcribed from the zygote genome must occur after blastoderm formation.
Etablissement de l’axe dorso-ventral dans le pied de l’embryon de poulet
Authors: Pautou Marie-Paule 
Published: April 2021

ABSTRACT

Establishment of the dorso-ventral axis in the foot of the chick embryo
The experiments were performed on 3·5-day and 5·5-day chick embryo leg-buds. Homo-and heterochronic heteropolar ecto-mesodermal recombinants were prepared in which the dorso-ventral (d-v) axis of the ectoderm was rotated by 180° with respect to that of the mesoderm. The mesodermal component of the associations consisted either of the intact mesodermal core or of a reaggregate of dissociated mesodermal cells. Recombinants were grafted onto a host wing stump and grown to day 16–20 of incubation.
The resulting feet display a d-v polarity in their integument and skeleton. This polarity conforms to that of the mesoderm in the proximal part of the foot (roughly basipod and metapod) and to that of the ectoderm in its distal part (roughly acropod) in the case of recombinants containing 3·5-day mesoderm. With 5·5-day undisrupted mesoderm, the polarity conforms entirely to that of the mesoderm.
In the recombinants containing 3·5-day or 5·5-day disrupted reaggregated mesoderm, the d-v polarity of the resulting feet, on the whole, conforms to that of the ectoderm. However, a high frequency of unpolarized integumentary and skeletal abnormalities occurs with 5·5-day disrupted mesoderm.
It is concluded that the ectoderm is polarized along its d-v axis. It exerts a d-v polarizing activity on the mesoderm during the 48 h period necessary for the segregation of the presumptive territories of the autopod. The ectodermal polarizing effect is expressed in the morphology of the integument and skeleton. At the end of the 48 h period, the d-v axis of the mesoderm is irreversibly laid down.
Effect of the brachypod mutation on cell adhesion and chondrogenesis in aggregates of mouse limb mesenchyme
Authors: Duke Jackie , Elmer William A. 
Published: April 2021

ABSTRACTTwelve-day normal and brachypod mouse limb mesenchyme was studied in rotation culture. Over a h period the rate of decline of single cells was significantly greater in mutant than in normal cultures, probably because the brachypod cells were more adhesive. However, the final size of the aggregates and their cell densities were the same by 24 h of incubation. On the other hand their pattern of chondrogenesis was different. Normal aggregates contained condensations with typical histotypic cartilage by 24 h of incubation, and were entirely chondrified by 4 days in culture. The condensations in brachypod aggregates were fewer, smaller, and delayed in their chondrogenesis. Never more than 50% of the brachypod aggregate exhibited chondrogenesis. The importance of cell contact and cell density to the chondrogenic process are discussed.
La cinétique cellulaire au cours de la segmentation du germe d’Axolotl: proposition d’un modèle statistique
Authors: Signoret J. 
Published: April 2021

ABSTRACT
The present work is based on the study of individual cell cycle times for a given category of cells. The material considered in detail is the Axolotl embryo during the eleventh cleavage cycle. In spite of the exceptional homogeneity of this population, individual cycle times show a remarkable variation from cell to cell, coinciding with a characteristic statistical distribution.
To describe the kinetics of cell proliferation, we propose a model for which the theoretical distribution of cycle times fits with the distribution observed in our material. Numerous observations allow us to generalize the model to other types of populations. According to this concept the notion of cell cycle time disappears in favour of the notion of a statistical distribution of individual cycle times.
This variability is integral to the cell division process itself. We suggest that in the cycle there is a particular event the probability of occurrence of which is constant beginning with a critical state. The cells would therefore remain a certain time in this state, overcoming it at a characteristic rate.
To this exponential distribution variability would be added the variability of other events whose cumulative effects would result in a normal distribution. The resultant of both factors conforms to the frequency distribution implicated in our kinetic model.
Discussing in a more general way the distributions of the cycle times of each cell division during cleavage, we propose the following interpretation of this development. The introduction of new events in the cyclic process would imply the switching on of certain essential genetic activities. The final consequences would be the desynchronization and the lengthening of the cycles observed at the blastula stage.
Thus considered, this period of embryonic development would be eminently suitable for the study of the factors of cell division control.
Anomalous ipsilateral optic fibre projection in Xenopus induced by larval tectal ablation
Authors: Straznicky Charles , Glastonbury John 
Published: April 2021

ABSTRACT
Unilateral left tectal ablation was carried out in Xenopus between stage 48 and 1 month after metamorphosis. Six to 12 weeks after metamorphosis the retinal projection from the right eye was examined with the use of [3H]proline autoradiography. The autoradiographs indicated that optic fibres whose tectal target was destroyed recrossed to the ipsilateral tectum and basal optic nucleus via the posterior and pretectal commissures. No anomalous recrossing occurred if the tectal ablation was carried out at stage 58 or later. The aberrant optic fibres were restricted to the rostrolateral and central parts of the ipsilateral tectum and they terminated in a discontinuous manner. It is concluded that available surfaces serving as contact guidance cues are needed to direct aberrant optic fibres to the ipsilateral tectum.
The role of irradiated tissue during pattern formation in the regenerating limb
Authors: Maden M. 
Published: April 2021

ABSTRACT
The amphibian limb regeneration blastema is used here to examine whether irradiated, non-dividing tissue can participate in the development of new patterns of morphogenesis. Irradiated blastemas were rotated 180° on normal stumps and normal blastemas rotated on irradiated stumps. In both cases supernumerary elements developed from the unirradiated tissue. The supernumeraries were defective but this did not seem to be due to a lack of tissue. Rather it suggested that this could be a realization of compartments in vertebrate development or simply reflect the limited regulative ability of the blastema. The results are also discussed in relation to a recent model of pattern formation.
Differentiation capacity of unincubated chick blastoderm in culture
Authors: Zagris Nicholas 
Published: April 2021

ABSTRACT
Unincubated (stage X) chick blastoderms cultured in plain Dulbecco’s modified Eagle medium in the absence of serum, synthesize haemoglobin and melanin 2·5−3·0 and 607·0 days, respectively, after the beginning of culture. The capacity of unincubated blastoderm to form haemoglobin and melanin is a response to intrinsic genotypic instructions rather than to the active intervention of substances continuously supplied by the yolk. 5-Bromo-deoxyridine, applied during the first and second days of unincubated blastoderm in culture, is incorporated into DNA and perturbs the formation of haemoglobin and melanin, perhaps, by modifying gene expression.
An analysis of the aggregation and morphogenesis of area opaca endoderm cells from the primitivestreak chick embryo
Authors: Milos Nadine , Zalik Sara E. , Phillips Robert 
Published: April 2021

ABSTRACT
The aggregative behaviour and subsequent morphogenesis of extra-embryonic endoderm cells from primitive-streak chick embryos have been investigated. A relatively pure population of area opaca endoderm cells was obtained by differential dissociation, which involves partial separation of epiblast and endoderm cell clumps by sieving through Nitex mesh. For aggregation studies cells were cultured in rotating flasks in Leibovitz (L-15) medium, in saline or in saline supplemented with glucose (1 mg/ml). Aggregation was monitored using the Coulter Counter. In these three media aggregation is rapid; by 10 min an average of 61% of the population had aggregated, to reach a plateau at 30 min when an average percent adhesion value of 83 % was obtained. The aggregates in L-15 medium were large and compact. After several days in culture, they cavitated and formed smooth hollow vesicles with thin walls composed of one or a few cell layers. Aggregates formed in PCS were smaller and looser in appearance; the addition of glucose resulted in a certain degree of compaction. Some morphogenesis occurred under these conditions with the aggregates developing numerous irregular cavities. These experiments suggest that some of the factors that affect cell adhesion in early embryonic cells can be studied in vitro. The results also indicate that the ability to cavitate is an intrinsic property of the endoderm cells of the area opaca since this occurs in the absence of epi blast or mesoderm.