bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cytokeratin filament assembly in the preimplantation mouse embryo
Authors: Chisholm Julia C. , Houliston Evelyn 
Published: April 2021

ABSTRACT
The timing, spatial distribution and control of cytokeratin assembly during mouse early development has been studied using a monoclonal antibody, TROMA-1, which recognizes a 55 000 Mr trophecto-dermal cytokeratin (ENDO A). This protein was first detected in immunoblots at the 4-cell stage, and became more abundant at the 16-cell stage and later. Immunofluorescence analysis revealed assembled cytokeratin filaments in some 8-cell blastomeres, but not at earlier stages. At the 16-cell stage, filaments were found in both polarized (presumptive trophecto-derm; TE) and apolar (presumptive inner cell mass; ICM) cells in similar proportions, although polarized cells possessed more filaments than apolar cells. By the late 32-cell, early blastocyst, stage, all polarized (TE) cells contained extensive filament networks whereas cells positioned inside the embryo tended to have lost their filaments. The presence of filaments in inside cells at the 16-cell stage and in ICM cells was confirmed by immunoelectron microscopy. Lineage tracing techniques demonstrated that those cells in the ICM of early blastocysts which did possess filaments were almost exclusively the progeny of polar 16-cell blastomeres, suggesting that these filaments were directly inherited from outside cells at the 16- to 32cell transition. Inhibitor studies revealed that proximate protein synthesis but not mRNA synthesis is required for filament assembly at the 8-cell stage. These results demonstrate that there are quantitative rather than qualitative differences in the expression of cytokeratin filaments in the inner cell mass and trophectoderm cells of the mouse embryo.
The wall of the chick embryo aorta harbours M-CFC, G-CFC, GM-CFC and BFU-E
Authors: Cormier Françoise , Dieterlen-Lièvre Françoise 
Published: April 2021

Abstract
In the 3-to 4-day avian embryo, after the first wave of haemopoiesis which derives in the yolk sac from haemopoietic stem cells formed in situ, haemopoietic cells emerge in an intraembryonic site, the wall of the aorta. In this paper, we demonstrate that this site harbours M-CFC, G-CFC, GM-CFC and late and early BFU-E. In serum-free medium, the growth of M-CFC and GM-CFC was strictly dependent on CSF present in fibroblast-conditioned medium (FCM). The growth of G-CFC was improved when FCM was replaced by a minute quantity of chicken and fetal calf serum. Like erythroid progenitors from bone marrow, BFU-E detected here required anaemic chicken serum to differentiate into haemoglobinized cells. The frequency of the different types of haemopoietic progenitors in the aortic population was very high: 80 M-CFC, 25 G-CFC, 4 GM-CFC and 70 BFU-E for 12 500 aorta cells, i.e. two to eight times more frequent than in the bone marrow population, depending on the type of progenitors.
Abbreviations: ACS, anaemic chicken serum; ANAE, alpha-naphthyl acetate esterase; BFU-E, burst-forming unit, erythroid; CAE, naphthol AS-D chloro-acetate esterase; CFU-E, colony-forming unit, erythroid; CFU-GEMM, colony-forming unit, granulocytic, erythroid, monocytic, megakaryocytic; CSF, colony-stimulating factor; FCM, fibroblast-conditioned medium; G-CFC, granulocytic, colony-forming cell; GM-CFC, granulocytic monocytic, colony-forming cell; M-CFC, monocytic, colony-forming cell.
Tectal pathways of regenerating goldfish optic axons after nasal or temporal half retinal removal
Authors: Humphrey Martin F. , Stuermer Claudia A. O. 
Published: April 2021

AbstractThe tectal pathways of regenerating goldfish optic axons are abnormal but not random. The relative proportion of temporal axons is highest in rostral tectum (65 %) drops in midtectum (31 %) and is very low in caudal tectum (4%). By contrast, nasal axons proceed into caudal tectum and are therefore relatively evenly distributed throughout the tectum. In this study, we have tested whether temporal axons are confined to rostral tectum by the presence of nasal axons in caudal tectum or whether they have a preference for rostral tectum regardless of other axons. We similarly tested whether nasal axons would grow preferentially into caudal tectum in the absence of temporal axons.At the time of optic nerve section either the nasal or temporal half retina was removed. Either 35 or 70 days after nerve section, the regenerating optic axons were labelled with HRP and both their pathways and distribution determined in DAB-reacted tectal wholemounts.In the absence of nasal axons, the relative density of temporal axons in rostral, mid and caudal tectum was 70 %, 28 % and 2 %, respectively. The corresponding values for nasal axons, in the absence of temporal axons, were 30 %, 40 % and 30 %, respectively. Thus, the overall distribution of nasal and temporal axons in the half retinal regenerates was similar to that of whole retinal regenerates, demonstrating that the retinotopic preferences of the axons were not dependent upon interaxonal interactions.Thus, nasal and temporal axons obviously discriminate between rostral and caudal tectum despite pathway disorganization and the absence of axons from the opposite hemiretina. This is consistent with axonal growth being under the influence of positional markers in tectum.
Meiosis reinitiation in the mollusc Patella vulgata. Regulation of MPF, CSF and chromosome condensation activity by intracellular pH, protein synthesis and phosphorylation
Authors: Néant I. , Guerrier P. 
Published: April 2021

Abstract
The dependency of some key events of the cell cycle upon pH, phosphorylation and protein synthesis was investigated during meiosis reinitiation of Patella vulgata oocytes stimulated by ammonia. In this report, we show, through heterologous microinjection experiments, that a stable maturation promoting factor (MPF) is actually produced under these conditions. This factor, which may be amplified in recipient germinal vesicle (GV)-blocked oocytes of the starfish Asterias rubens, but not of Patella, remains present in the metaphase-1-blocked oocytes for at least 2·5 h. Using effective concentrations of the protein synthesis inhibitor emetine, we further demonstrate that the appearance of this factor does not depend on newly made proteins, whereas the maintenance of metaphase-1 conditions and chromosome condensation activity (CCA), which has been related to the simultaneous presence of a cytostatic factor (CSF), requires a continuous supply of new short-lived proteins.
Without this, the chromosomes decondense and the nuclear envelope reforms. Finally, we show that the entry into M-phase is accompanied by extensive protein phosphorylation, while the drug 6-dimethylami-nopurine (6-DMAP), which induces protein déphosphorylation without affecting protein synthesis or phosphoprotein phosphatase activity, produces the same cytological effects as emetine. The fact that the effect of 6-DMAP, both on protein phosphorylation and chromosome structure, is perfectly reversible indicates that Patella CSF activity must also be controlled at the posttranslational level, possibly through the activation of relevant protein kinases.
The appearance of glycoconjugates associated with cortical granule release during mouse fertilization
Authors: Lee S. H. , Ahuja K. K. , Gilburt D. J. , Whittingham D. G. 
Published: April 2021

Abstract
For the first time, we have shown with appropriately labelled lectins that fucosyl- and sialyl-rich glycoconjugates are released into the perivitelline space of the mouse oocyte after activation by the fertilizing spermatozoon or artificial activation by the calcium ionophore A23187 or ethanol. The glycoconjugates show a punctate distribution over the oocyte surface except for the microvilli-free area overlying the second meiotic spindle from which they are absent. Their appearance in the perivitelline space is associated with the release of the cortical granules suggesting that they represent part of the cortical granule exudate. Soon after the glycoconjugates appear, they begin to aggregate. The process continues until the beginning of cytokinesis at first cleavage when a single large aggregate is found within the cleavage furrow. Most of the labelled glycoconjugates disappear by the late 2-cell stage and no evidence was found for their presence during the later preimplantation period. This technique is suitable for monitoring the kinetics of the cortical reaction in mammalian oocytes and investigating the importance of the glycoconjugates in early preimplantation period.
Small eye (Sey): a mouse model for the genetic analysis of craniofacial abnormalities
Authors: Hogan Brigid L. M. , Hirst Elizabeth M. A. , Horsburgh Gwynn , Hetherington Colin M. 
Published: April 2021

ABSTRACT
Small eye (Sey) is a dominant mutation in the mouse affecting the embryonic development of the eyes and nose. In homozygous Sey/Sey embryos, the optic vesicles grow out but there is no lens induction and the nasal pits fail to develop. Scanning electron microscope studies of Sey/ Sey embryos show that the maxillary processes develop normally and fuse with ridges of ectoderm in the frontonasal position. In Sey/ + heterozygotes, the vacuolated lens is smaller than normal, and there is folding of the margins of the optic cup and ingrowth of mesodermal cells. Evidence is presented that Sey is not allelic with Coloboma (Cm), another mutation affecting eye development on chromosome 2.
XY follicle cells in ovaries of XX↔XY female mouse chimaeras
Authors: Burgoyne Paul S. , Buehr Mia , Mclaren Anne 
Published: April 2021

Abstract
Oocytes with adhering follicle cells were sampled from ovaries obtained from 11 GPI-1A↔GPI-1B chimaeras, comprising 10 females and 1 hermaphrodite. GPI analysis of individual oocytes revealed a marked bias towards the GPI-1B component in the germ line of this chimaeric combination. GPI-IB XY oocytes were identified in the ovary from the hermaphrodite, the bias towards the GPI-1B germ line perhaps helping to counterbalance the normally severe selection against XY oocytes. GPI analysis of follicle cells revealed a much more balanced contribution of the two components to this ovarian cell type. Importantly, GPI-1A follicle cells were identified in more than half the follicles from an XX↔XY female in which the GPI-1A component was XY, supporting an earlier conclusion of Ford et al. (1974) that XY cells can contribute to the follicles of XX↔XY female mice.
It is suggested that XY cells can be recruited to form follicle cells in XX↔XY chimaeras when there is a developmental mismatch between the two components, such that an ovary-determining signal produced by the XX component pre-empts the testisdetermining action of the Y.
Segmentation in frogs
Authors: Davidson Duncan 
Published: April 2021

ABSTRACT
This paper reviews evidence relating to the question, at what stage in the development of the frog embryo are segment boundaries specified? Current evidence leads to the hypothesis that a spatiotemporal series of cell states leading to segmentation is continuously initiated at a position 200 to 300 μm from the posterior end of the presomitic mesoderm, about nine somite intervals before the formation of a definitive somite. The evidence suggests, though by no means proves, that segment boundaries are specified close to this time. This hypothesis relies critically on evidence concerning the effects of disruptive agents, the extent of cell mixing prior to the early gastrula stage, fate map data, and a comparison with development in the mouse where a similar fate map can be related to morphological evidence of somitomeric segmentation.
Evidence regarding the organization of the posterior, undifferentiated zone of the mesoderm in the frog embryo indicates that the cells are not proliferating rapidly, but are undergoing cell movements and rearrangements associated with caudal extension. The speculation that the segment pattern derives from inductive interactions in this region is discussed.
Involvement of oocyte-coded message in cell differentiation control of early human embryos
Authors: Tesařík Jan 
Published: April 2021

ABSTRACT
Considerable evidence indicates that the first phenotypical diversification of embryonic cells during mammalian preimplantation development is achieved in two successive steps: (i) generation of cell asymmetry and (ii) unequal cell division. This paper shows that ultrastructural signs of blastomere surface regionalization in human preimplantation embryos are evident as early as the 2-cell stage when modifications of the plasma membrane (loss of microvilli and endocytotic activity, formation of cell junctions) are induced in places of blastomere contact. The capacity of the plasma membrane to undergo these cell-contact-dependent changes precedes any detectable activity of the embryonic genome. The area of the modified plasma membrane shows a continuous increase during the first three cleavage stages. The progression of these membrane modifications is the same in embryos that have properly enhanced their transcriptional activity at the 8-cell stage and in those that have not. In spite of the failure of this early-cleavage-progressed-cleavage transition of gene activity, the formation of zonula adherens and gap junctions goes on apparently normally in the respective embryos and morphologically distinct inner cell mass and trophectoderm cell lineages are subsequently segregated in 16-cell morulae. However, tight junctions do not develop under these conditions. The occurrence of the progressed-cleavage pattern of gene activity in the majority of embryonic cells is a necessary prerequisite for the appearance of the blastocyst cavity. Thus, oocyte-coded message is apparently involved in the control of relatively late stages of human preimplantation development including the differentiation of the first two embryonic tissues, but the embryonic genome is required for the full achievement of this early differentiative event.
Maintenance and regulation of cellular handedness in Tetrahymena
Authors: Nelsen E. Marlo , Frankel Joseph 
Published: April 2021

ABSTRACT
The left-handed phenotype of Tetrahymena thermophila (LH) is a global mirror image of its right-handed counterpart (RH). LH cells are ‘wound’ in the opposite direction from that of RH cells with respect to the placement of all structures that are asymmetrically disposed on the cell circumference. However, the local geometry of ciliary rows, including the asymmetrically placed microtubule bands and other accessory structures, is identical in RH and LH cells. Populations of LH cells grow more slowly than those of RH cells, probably because of nutritional problems due to faulty construction of the cell mouth. LH cells, like RH cells, conjugate in a homopolar configuration, while LH cells mate with RH cells in a heteropolar union which suffices to initiate the conjugal nuclear events but is insufficient to allow survival of progeny. Subclonal analyses indicate that reversion of the LH to the RH form is relatively rare. However, the frequency of reversion is greatly increased by conditions that promote the formation of doublets by fission arrest. An analysis of intermediate doublet forms in such cultures strongly suggests that reversion takes place through a specific pathway, with LH-LH doublets regulating to LH-RH forms that then may give rise to RH singlets. The origin and fate of the LH-RH intermediate forms can be explained by applying a modified polar coordinate model of positional information with the proviso that there is a preferred direction for the intercalation of new positional values.
Relationship between vasculogenesis, angiogenesis and haemopoiesis during avian ontogeny
Authors: Pardanaud Luc , Yassine Fouzia , Dieterlen-Lievre FranÇoise 
Published: April 2021

ABSTRACT
Quail-chick intracoelomic grafts of organ rudiments were used to study the origin of endothelia and haemopoietic cells during avian organogenesis in conjunction with the monoclonal antibody QH1 which recognizes the quail haemangioblastic lineage. Results differed according to the germ-layer constitution of the grafted rudiments. In the case of the limb buds, endothelial cells from the host invaded the graft through an angiogenic process. Haemopoietic progenitors from the host also colonized the grafted bone marrow.
In contrast, rudiments of internal organs provided their own contingent of endothelial precursors, a process termed vasculogenesis. Nevertheless, haemopoietic cells in these organs were all derived from the host. In the lung, this extrinsic cell population appeared regularly scattered around the parabronchi and had a macrophage-like phenotype. In the pancreas, the granulocytes which differentiate as dense aggregates located in the wall of the largest vessels were extrinsic. Similarly in the spleen, a mesodermal primordium that develops in close association with the pancreatic endoderm, endothelial cells were intrinsic and haemopoietic cells host-derived.
This study demonstrates that, in ontogeny, vascularization obeys different rules depending on which germ layer the mesoderm is associated with: in mesodermal/ectodermal rudiments angiogenesis is the rule; in mesodermal/endodermal rudiments, vasculogenesis occurs. However, in these internal organs undergoing vasculogenesis, endothelial and haemopoietic cells have separate origins.
We put forward the hypothesis that the endoderm induces the emergence of endothelial cells in the associated mesoderm. Formation of blood stem cells may also involve interactions between endoderm and mesoderm, but in this case the responding capacity of the mesoderm appears restricted to the paraaortic region.
Pattern formation in the Drosophila embryo: allocation of cells to parasegments by even-skipped and fushi tarazu
Authors: Lawrence Peter A. , Johnston Paul 
Published: April 2021

ABSTRACT
The first sign of metamerization in the Drosophila embryo is the striped expression of pair-rule genes such as fushi tarazu (ftz) and even-skipped (eve). Here we describe, at cellular resolution, the development of ftz and eve protein stripes in staged Drosophila embryos. They appear gradually, during the syncytial blastoderm stage and soon become asymmetric, the anterior margins of the stripes being sharply demarcated while the posterior borders are undefined. By the beginning of germ band elongation, the eve and ftz stripes have narrowed and become very intense at their anterior margins. The development of these stripes in hairy−, runt−, eve−,ftz− and engrailecT embryos is illustrated. In eve− embryos, the ftz stripes remain symmetric and lack sharp borders. Our results support the hypothesis (Lawrence et al. Nature 328, 440-442, 1987) that individual cells are allocated to parasegments with respect to the anterior margins of the eve and ftz stripes.
Differential gene expression in the anterior neural plate during gastrulation of Xenopus laevis
Authors: Jamrich Milan , Sato Sheryl 
Published: April 2021

ABSTRACT
We have isolated three cDNA clones that are preferentially expressed in the cement gland of early Xenopus laevis embryos. These clones were used to study processes involved in the induction of this secretory organ. Results obtained show that the induction of this gland coincides with the process of neural induction. Genes specific for the cement gland are expressed very early in the anterior neural plate of stage-12 embryos. This suggests that the anteroposterior polarity of the neural plate is already established during gastrulation. At later stages of development, two of the three genes have secondary sites of expression. The expression of these genes can be induced in isolated animal caps by incubation in 10mm-NH4Cl, a treatment that is known to induce cement glands.
Spatial and temporal variation in the structure of the basal lamina in embryonic grasshopper limbs during pioneer neurone outgrowth
Authors: Anderson Hilary , Tucker Richard P. 
Published: April 2021

Abstract
The pioneer neurones of the embryonic grasshopper limb use the basal lamina underlying the limb ectoderm as a substratum over which to grow from the periphery to the CNS (Anderson & Tucker, 1988). In this paper we use transmission electron microscopy to describe the structure of this substratum before, during, and after the time of axon navigation.
The organization of the basal lamina varies considerably in different regions and at different times of development of the embryonic limbs, and is unlike that of the fully developed limb at the time of hatching. We suggest that this spatial and temporal variation could play a role in regulating the direction of outgrowth of pioneer neurones.
Anin situtransgenic enzyme marker for the midgestation mouse embryo and the visualization of inner cell mass clones during early organogenesis
Authors: Beddington Rosa S. P. , Morgernstern Jay , Land Hartmut , Hogan Aileen 
Published: April 2021

AbstractIn order to study the deployment of cells during gastrulation and early organogenesis, it is necessary to have an in situ cell marker which can be used to follow cell fate. To create such a marker a transgenic mouse strain, designated Tg(Act-lac Z)-1, which carries 6 copies of the Escherichia coli lac Z gene under the control of the rat β-actin promoter, was made by pronuclear injection of DNA. Staining early postimplantation hemizygous mouse conceptuses, during gastrulation and early organogenesis, for β-galactosidase activity shows that lac Z expression is ubiquitous and constitutive in all epiblast derivatives of the 10th day conceptus. No activity is seen in trophectoderm and primitive endoderm derivatives.Postimplantation grafts of [3H]thymidine-labelled transgenic cells establish the cell autonomy of this transgenic marker. Preliminary observations on the distribution of inner cell mass (ICM) descendant clones, identified in situ in midgestation conceptuses, confirm the pluripotency of individual ICM cells. The implications regarding patterns of cell growth in nascent fetal primordia are discussed.
A set of cell surface glycoproteins forms an early marker of cell position, but not cell type, in the root apical meristem of Daucus carota L.
Authors: Knox J. Paul , Day Susan , Roberts Keith 
Published: April 2021

Abstract
A monoclonal antibody (JIM4) has been derived that recognizes a series of glycoproteins associated with the plasma membrane of a suspension-cultured carrot cell line and also an arabinogalactan proteoglycan secreted by the cultured cells. Immunocytochemistry indicated that the plasma membrane antigen(s) recognized by JIM4 are specific to certain cells of Daucus carota L. seedlings. In the root apex JIM4 labelled two segments of the stele. These were centred upon the poles of the protoxylem. An axis of unlabelled cells connected the two phloem regions. Two sections of the pericycle with characteristic oblique longitudinal divisions were particularly reactive with JIM4. This pattern of reactive cells, reflecting cell position rather than a specific future cell type, would appear to be a unique observation in plants. The association of JIM4 antigens with these vascular tissues is maintained through the transition from root to the shoot tissue of the cotyledons and the mature plant. Examination of JIM4 labelling upon ultrathin frozen sections of the carrot seedling root apical meristem indicated that the expression of the antigen is a very early event in root development. Cells express the surface epitope, within one or two cells of the dome of apical initials, before the pattern of future vascular tissue can be discerned and well before its actual differentiation.