bluuebunny/crossref_metadata_2025_split huggingface dataset:
Differentiation potentiality of rat visceral yolk sac in organ culture
Authors: Lu Y. L. , Sobis H. , Hove L. Van , Vandeputte M. 
Published: April 2021

ABSTRACT
Visceral yolk sacs removed at day 12 of pregnancy in the rat were kept in organ culture for as long as 28 days. During this in vitro culture, proliferation of the endoderm and the mesoderm as well as of poorly differentiated cells was observed. The latter displayed neither the characteristics of endodermal nor mesodermal cells and their presence was frequently associated with the development of giant trophoblast cells. The hypothesis is proposed that these trophoblast cells originate from these poorly differentiated cells that acquire in vivo and in vitro the potentiality to differentiate.
Experimental analyses of cytoplasmic rearrangements which follow fertilization and accompany symmetrization of inverted Xenopus eggs
Authors: Neff Anton W. , Wakahara Masami , Jurand Arthur , Malacinski George M. 
Published: April 2021

ABSTRACT
Cytoplasmic rearrangements which follow fertilization were monitored in inverted eggs. A set of yolk compartments was resolved by cytological analyses of both normally oriented and inverted eggs. Those compartments were characterized by their yolk platelet compositions and movement during egg inversion. In addition to the major yolk masses which contain either small, intermediate or large platelets, minor cytoplasmic compartments which line the egg cortex were also identified.
During egg inversion the yolk compartments shift. Those yolk mass shifts occurred only after the inverted egg was activated (by sperm, electrical or cold shock). The direction of shift of the major yolk components, rather than the sperm entrance site (as in normal orientation eggs), determines the dorsal/ventral polarity of the inverted egg. Among different spawnings the rate of shift varied. Eggs that displayed the fastest rate of shift exhibited the highest frequency of developmental abnormalities during organogenesis.
Isopycnic density gradient analysis of yolk platelets and blastula blastomeres showed that isolated yolk platelets and mid-blastula blastomeres are not of uniform buoyant density. Three major yolk platelet density bands were resolved. Large, intermediate, and small yolk platelets were found in all bands. The high density band had the largest proportion of the large yolk platelets and the low density fraction showed the largest proportion of the small yolk platelets.
Interpretation of novel observations on cytoplasmic organization provided criticisms of some earlier models. A new ‘Density Compartment Model’ was developed and presented as a coherent way to view the organization of the egg cytoplasm and the development of bilateral symmetry.
Structural basis of the activation wave in the egg of Xenopus laevis
Authors: Takeichi Tetsuo , Kubota Hiroshi Y. 
Published: April 2021

ABSTRACT
A series of changes in the surface of activated Xenopus eggs was observed. Within a few seconds of prick activation a light area appears near the pricking point and expands as a circular light zone (light wave). Some 60s later this is followed by a dark area expanding as a circular dark zone (dark wave). Both waves travel at a rate of about 9 μm/s at 21 °C. In the light zone, cortical granules are breaking down, microvilli are elongating, and the egg surface is expanded. On the other hand, the elongated microvilli are reshortening to become globular and the egg surface is contracted in the dark zone.
Cell relationships during aggregation between preimplantation embryos and teratocarcinoma-derived cells
Authors: Lehtonen E. , Wartiovaara J. , Reima I. 
Published: April 2021

ABSTRACT
Cleavage-stage mouse embryos aggregate and form chimaeric blastocysts with embryonal carcinoma (EC) cells. We used scanning and transmission electron microscopy to study cell relationships during aggregate formation between 8-cell-stage embryos and F9 EC cells. Relations between heterotypic cells were similarly studied in aggregation experiments with embryos and teratocarcinoma-derived visceral (PSA5-E) and parietal (PYS-2) endoderm cells and in experiments with EC cells and endoderm cells.
The embryos and F9 cells always adhered to each other and rapidly formed compacted aggregates. Numerous microvilli and cell processes, originating from both embryo and EC cells, extended between the two cell types during adhesion and early phases of aggregation. The aggregation process involved spreading of the blastomeres on the EC cells. Frequent adherent junctions and close contacts, including possible focal gap or tight junctions were observed between the embryo and F9 cells after 3 h of culture. Apparent gap or tight junctions were infrequent during the early phases of aggregation but during further culture, extensive typical gap junctions were also seen between embryo and EC cells.
The embryos adhered only irregularly and loosely to PSA5-E and PYS-2 cells; this interaction never led to aggregate formation comparable to that seen in the experiments with embryos and EC cells. Close contacts but no gap or tight junctions could be observed between the embryo and endoderm cells. On the other hand, both PSA5-E and PYS-2 cells readily adhered to and aggregated with EC cells.
The present results suggest that microvilli and cell processes mediate membrane interactions during adhesion and early phases of aggregation between embryos and EC cells. During aggregation, blastomeres spread over the EC cells, and rapid formation of adherent junctions and close contacts, including possible focal gap or tight junctions is involved during the early phases of this process. After this initial phase, typical gap junctions are also seen between the embryo and EC cells. Interestingly, adhesive properties of embryo and EC cells differ: the former aggregate only with EC cells, whereas the latter do so also with teratocarcinoma-derived visceral and parietal endoderm cells. Mechanisms operating in the morphogenetic movement of cells in this experimental setup may be involved also in the development of the blastocyst in vivo.
The structure of supernumerary leg regenerates in the cricket
Authors: French Vernon 
Published: April 2021

ABSTRACT
In many insects, grafting a larval leg onto the contralateral leg stump reverses one transverse axis and leads to the regeneration of supernumerary legs at each of the two points of maximum discrepancy on the graft/host junction. These operations were performed on the cricket Acheta domesticus, grafting between tibiae of pro- and metathoracic legs, and between tibia and tarsus, in order to deduce the mode of origin of the supernumeraries from their graft type, host type or composite structure.
Supernumerary legs formed after A/P axis reversal are always half- and-half in structure, being of host type on the host side and graft type on the graft side, while supernumeraries formed after M/L axis reversal are variable in structure. These results are generally consistent with the recent Polar Co- ordinate Model (whereby supernumeraries form because the pattern of intercalation between graft and host generates two complete circumferences at the junction), provided that intercalation is restricted by the borders between anterior and posterior leg compartments. However there are features of the structure of the M/L supernumeraries which the Polar Co- ordinate Model does not explain. Medial supernumeraries are often of pure graft type (and lateral ones of host type) or half- and-half with anterior graft type and posterior of host type (while lateral supernumeraries often have the converse structure).
Mapping of cortical histogenesis in the ferret
Authors: McSherry G. M. 
Published: April 2021

ABSTRACT
The columnar organization of forebrain cortical neuron production allows the neuroepithelium to be analysed in terms of a simple growth model. The pattern of neuron release within each column is repeated with great regularity across the surface of the developing cerebral hemisphere, resulting in the accumulation of cortical neurons in radial stacks above the proliferative ventricular epithelium. The time course of recruitment of adjacent tissue into neuron production accounts for the observed rostrocaudal and laterodorsal gradients of cortical neuron release. The present study plots the history of this front of neuron production across the surface of the developing cerebral vesicle in the ferret and interprets the resulting maps of cortical development stages in terms of a unified growth model that links the radial and tangential aspects of neuron production. These observations are discussed in relation to other studies of gradients in developing nervous tissue and their implications for the study of experimentally induced abnormalities of brain development.
The role of endoderm in blood cell ontogeny in the newt Pleurodeles waltl
Authors: Deparis P. , Jaylet A. 
Published: April 2021

ABSTRACT
In order to determine the origin of blood cells we performed embryonic grafts of different portions of mesoderm from various locations between diploid and tetraploid embryos at the tail-bud stage. The tetraploid animals were the hosts. The size differences between tetraploid and diploid cells made identification possible by direct microscopic examination of blood smears. In a previous report we showed the important role of truncal anterior mesoderm in the genesis of blood cells. We now establish that this effect is brought about by the inductive capacity of the hepatic endoderm or by the fact that the environmental conditions are more appropriate for blood stem cell development, whereas in the absence of the hepatic endoderm the blood stem cells fail to appear. Grafting of hepatic anlage containing endoderm and mesoderm gives rise to numerous graft-derived blood cells which last throughout the life span of the hosts. The same result is obtained by grafting truncal posterior ventral or lateral mesoderm onto hepatic endoderm. Heterotopic grafting of truncal anterior mesoderm isolated from its underlying hepatic endoderm leads to the formation of only a few blood cells which last only during larval life. This demonstrates that the whole lateral and ventral truncal mesoderm is able to differentiate into blood cells when associated with hepatic endoderm.
Cell cycle analysis of facial mesenchyme in the chick embryo : I. Labelled mitoses and continuous labelling studies
Authors: Minkoff Robert 
Published: April 2021

ABSTRACT
Cell cycle parameters were analysed in mesenchyme of the maxillary process and the roof of the stomodeum in the chick embryo from stages 19 through 28. The generation times at stages 24 –26 were determined by pulse labelling of embryos with [3H]thymidine, followed by labelled mitosis counts and construction and analysis of percent-labelled mitosis curves employing computer-assisted curve-fitting techniques. The median generation time was approximately 10·6 h in the maxillary process, and 16 h in the roof of the stomodeum; corresponding values for mean generation times were approximately 12 ·0 and 18 ·2 h, respectively. Median values for transit times of G1, S, and G2 were 2·0, 5·4, and 2 ·5 h in the maxillary process and 5 ·2, 6 ·7, and 2 ·7 h in the roof of the stomodeum. The distribution of generation times of cells in the roof of the stomodeum, however, appeared to be more heterogeneous than those of cells in the maxillary process.
The percentage of cells which continue to cycle rapidly (i.e. the ‘growth fraction’) was determined by repeated-labelling experiments with [3H]thymidine in chick embryos from stages 19 through 28. Cumulative labelling of mesenchymal cells in both the maxillary process and roof of the stomodeum approached 100 % at stage 19 but dropped markedly from stage 19 to 25 declining to approximately 60 –70 % in the maxillary process, and to 30 % in the roof of the stomodeum. The decline in cell proliferation rates for these regions, determined in previous studies with labelling indices, appears to be a result of the removal of cells from rapidly cycling cell populations into subpopulations which are cycling more slowly and possibly into subpopulations which have become quiescent; the difference in growth rates between these regions could be attributed to the time of appearance and the size of these emerging slow cycling or quiescent subpopulations.
Cell cycle analysis of facial mesenchyme in the chick embryo
Authors: Minkoff R. , Martin R. E. 
Published: April 2021

ABSTRACT
The spatial distribution and developmental fate of quiescent and/or slow cycling cell populations of the primary palate were studied employing label-dilution techniques. -day-old chick embryos were labelled sequentially for 12 h with [3H]thymidine and then chased with cold thymidine. The embryos were reincubated to continue development and were subsequently sacrificed at intervals from the end of labelling at 4 days to 14 days of incubation (10 days after labelling) and processed for autoradiography. Retention of label was used as the assay for identification of quiescent and/or slow-cycling cells. Grain density over the nuclei of labelled cells was determined in the maxillary process and the roof of the stomodeum. Cells with a label density at later time points comparable to that found in cells immediately after the labelling period were defined as label-retaining cells, i.e. those which had become quiescent or had significantly altered generation times. The location and developmental fate of these cell populations were confirmed using slides containing adjacent sections stained with Nuclear Fast Red, Alcian Blue, and Tartrazine. The results demonstrated an association between label-retaining cells and chondrogenic differentiation in the roof of the stomodeum. Subpopulations of label-retaining cells (quiescent and/or slow cycling) which we believe to be prechondroblasts appeared in the chondrogenic region of the roof of the stomodeum prior to, or coincident with, cartilage formation. The retention of label, as evidenced by comparison of nuclear grain counts at the end of the labelling period with subsequent time points, indicated that a cell cycle block may have occurred in the prechondroblastic cell population. The block lasted until these cells expressed the chondrogenic phenotype, after which they resumed cell division.
Characterization of a cell-surface differentiation antigen of mouse spermatogenesis: timing and localization of expression by immunohistochemistry using a monoclonal antibody
Authors: Bechtol Kathleen B. 
Published: April 2021

ABSTRACT
The XT-1 antigen, bound by monoclonal antibody XT-I, is a differentiation antigen of germ cells in the mouse testis. As seen in immunoperoxidase-stained tissue sections from several juvenile ages and adult, the antigen becomes detectable on early (leptotene/zygotene) spermatocytes and increases in staining during spermatocyte development. During spermatid development the distribution of the determinant shifts from its relatively uniform surface distribution on spermatocytes to a more restricted localization on the base of the head, tail and cytoplasmic lobe of the elongating spermatid. The antigen is not detectable on juvenile or adult Sertoli cells. Detection of the antigen is dependent on the presence of germ cells of appropriate developmental stage. It is, thus, a marker for spermatocytes and later germ cells, for a cell-surface molecule related to spermatogenesis and for redistribution and/or modification of the molecule during spermatid elongation.
Fibre order in the normal Xenopus optic tract, near the chiasma
Authors: Fawcett J. W. , Taylor J. S. H. , Gaze R. M. , Grant P. , Hirst E. 
Published: April 2021

ABSTRACT
In juvenile Xenopus retinotopic fibre order in the optic tract near the chiasma was investigated by labelling small groups of optic fibres from peripheral retina with HRP. This selective fibre labelling with HRP was combined with autoradiography following administration of tritiated thymidine to the eye, so that the HRP-labelled fibres could be located within the borders of the optic tract.
Fibres arising from the periphery of all four retinal quadrants were superficially located in the optic tract near the chiasma, with dorsal retinal fibres showing the greatest tendency to travel deep in the diencephalon. Retinal lesions closer to the optic nerve head labelled fibres which ran deeper in the optic tract. Near the chiasma, fibres from ventral retina tended to group rostrally while fibres from dorsal retina tended to group caudally. However, no obvious localization of fibres arising in temporal or nasal retina was seen in the lower optic tract.
Scanning electron microscopy of wound healing in rat embryos
Authors: Smedley Martin J. , Stanisstreet Martin 
Published: April 2021

ABSTRACT
Wound healing in rat early embryos has been studied by scanning electron microscopy. Initially the wound gapes slightly and cells peripheral to the wound assume a cobble-stone appearance. Wound closure is quite rapid; some small wounds are almost closed within 10 min of incision. Wound closure is accompanied by the appearance of some elongated cells at the wound edge. These features are similar to, although less pronounced than, those which have been observed to accompany wound closure in amphibian and avian embryos. Healing of wounds made in the amnion is also accompanied by changes in the shapes of cells at the wound margins.
Wound healing in embryos cultured in Hank’s saline is similar to wound healing in embryos cultured in serum, suggesting that the macromolecular components of serum are not essential to wound healing. Cytochalasin B, which inhibits wound closure in amphibian embryos, does not inhibit wound healing in rat early embryos unless used at a concentration high enough to cause cell dissociation. Similarly chelation of the free calcium in the medium, which also prevents wound closure in amphibian embryos, does not inhibit wound closure unless the embryo is dissociating. Removal of free calcium does however cause collapse of the elevated neural folds. These observations suggest that the cellular mechanisms involved in wound healing are different in mammalian and amphibian embryos.
Patterns of cell division during visual streak formation in the frog Limnodynastes dorsalis
Authors: Coleman L-A. , Dunlop S. A. , Beazley L. D. 
Published: April 2021

ABSTRACT
The site and extent of cell division were determined in midlarval tadpoles, animals at metamorphic climax and 2-month juvenile Limnodynastes dorsalis using untreated animals and those injected with colchicine or pH]thymidine shortly before sacrifice. Mitosis was restricted to the ciliary margin at all stages and there were significantly more dividing cells nasally and temporally than dorsally and ventrally. In animals injected with [3H]thymidine and killed at a subsequent stage, labelled cells were grouped at a distance from the ciliary margin and were more frequent in nasal and temporal than in dorsal and ventral retina. These results suggest that differing extents of mitosis around the ciliary margin, reflected in the number of cells entering the ganglion cell layer, may largely underlie the postmetamorphic formation of a visual streak observed using wholemounts.
The early development of mystacial vibrissae in the mouse
Authors: Wrenn Joan T. , Wessells Norman K. 
Published: April 2021

ABSTRACT
The initial generation of the pattern of mystacial vibrissae (whiskers) in the mouse is described. The maxillary process is present in 10-day embryos but has a relatively flat surface. Beginning at approximately 11·5 days, the first sign of vibrissal development is the formation of ridges and grooves on the maxillary and lateral nasal processes. The first vibrissal rudiment to form subsequently appears posterior to the most ventral groove on the maxillary process. It is the most ventral whisker of the posterior, vertical row. The next few rudiments appear: (1) dorsal to the first, also in the vertical row; and (2) anterior to the first, on the ventral-most ridge and in the groove beneath it. Formation of vibrissal rudiments continues in a dorsal and anterior progression usually by an apparent partitioning of the ridges into vibrissal units.
The hypothesis that this patterning of mystacial vibrissae might be determined by the pattern of innervation in the early mouse snout was investigated. Nerve trunks and branches are present in the maxillary process well before any sign of vibrissal formation. Because innervation is so widespread there appears to be no immediate temporal correlation between the outgrowth of a nerve branch to a site and the generation of a vibrissa there. Furthermore, at the time just prior to the formation of the first follicle rudiment, there is little or no nerve branching to the presumptive site of that first follicle while branches are found more dorsally where vibrissae will not form until later. Thus, a one-to-one spatial correlation between nerve and follicle sites also appears to be lacking.
The developmental changes in ultrastructure within the neurites of the trunks and branches as well as the apparent rearrangements of the nerve trunks suggest that early innervation of the snout is a labile phenomenon and that the vibrissal pattern begins to be established before the neural pattern is completely developed. The results indicate that vibrissal pattern formation is likely to be a complex process relying on the interplay of the cells and tissues involved, rather than on unidirectional instructions from neurons to other cell types.
Initial phases of the rat testis differentiation in vitro
Authors: Agelopoulou Roxane , Magre Solange , Patsavoudi Evangélie , Jost Alfred 
Published: April 2021

ABSTRACT
Rat gonadal primordia with their supporting mesonephroi were explanted in vitro at the undifferentiated stage (12 days 16 h after fertilization), at the outset of testicular differentiation (13 days 9 h) or when already containing seminiferous cords. The younger foetuses were sexed with the sex chromatin test in the amniotic membrane. The basal medium was CMRL 1066 and the culture period, 1 to 4 days. Testicular differentiation resulted from the appearance of large clear cells, the primordial Sertoli cells, and from their aggregation into seminiferous cords. Addition of 15 % foetal calf serum to the medium prevented the differentiation of seminiferous cords, but large clear cells appeared. In testes from 14- or 15-day-old foetuses, the seminiferous cords disintegrated under the influence of serum. The serum did not prevent the differentiation of Sertoli cells, but impaired organogenesis or maintenance of the early seminiferous cords. The results support previous histological observations on the initial stages of testicular differentiation.
Motor innervation of proximally rotated chick embryo wings
Authors: Laing N. G. 
Published: April 2021

ABSTRACT
Chick embryo wing buds were rotated close to the lateral edge of the somites at stage 19, prior to limb innervation. Despite the abnormal orientation of the resulting limb, the motor pools to biceps and triceps were largely normal, as judged by electrical stimulation and horseradish peroxidase labelling just prior to hatching. The only abnormalities were a few caudal motoneurons innervating biceps and a few rostral motoneurons innervating triceps. This distribution is similar to that seen normally in young embryos before the completion of motoneuron death and it is suggested that the rotation may be keeping alive motoneurons which otherwise would die. The morphology of the brachial plexus supplying rotated wings was abnormal. It is concluded that axons growing into the limb bud from the spinal cord can compensate for reversal of both the limb axes and selectively innervate appropriate muscles. The result is consistent with others in which proximal reversal of one limb axis alone produced normal innervation.