bluuebunny/crossref_metadata_2025_split huggingface dataset:
Expression of homeobox gene Hox 1.1 during mouse embryogenesis
Authors: Mahon Kathleen A. , Westphal Heiner , Gruss Peter 
Published: April 2021

ABSTRACT
Many of the genes controlling segmentation and pattern formation in Drosophila contain a conserved 183 bp sequence known as the homeobox. Homeobox sequences have been found in a range of metazoan species, including the vertebrates mouse and man. This striking conservation suggests that homeobox genes may play a fundamental role in developmental processes. If this is the case then it might be expected that vertebrate homeobox genes will be differentially expressed during embryogenesis and that the timing of their expression will coincide with major morphogenetic events. Here the spatial and temporal patterns of expression of murine homeobox genes will be explored, concentrating on the Hox 1.1 gene as an example. Using in situ hybridization to localize RNA transcripts, it has been found that Hox 1.1 is expressed in a region-specific manner during the formation and differentiation of the embryonic anteroposterior axis. Although striking patterns of expression of Hox 1.1 and other homeobox genes are seen in overtly segmented structures of the embryo (i.e. somites, prevertebral elements, neural tube and dorsal spinal ganglia) expression is also seen in tissues with no obvious segmental origin. The results suggest that homeobox genes probably do not play an exclusive role in segmentation in vertebrates, but are consistent with a role in the assignment of positional identity along the axis of the embryo.
Models for maternally supplied positional information and the activation of segmentation genes in Drosophila embryogenesis
Authors: Meinhardt Hans 
Published: April 2021

ABSTRACT
Recent experiments concerned with early Drosophila development require some modification of models proposed earlier. The addition of a positional information system spreading out from the anterior pole (as indicated by the bicoid mutation) allows very good size regulation. Additional steep gradients at both poles (as suggested by the mutations of the torso group) allow simpler mechanisms for the activation of the gap (or cardinal) genes. Simulations of pattern alterations due to mutations in one of these systems agree well with the observed phenotypes. Mechanisms that can lead to bicaudal phenotypes as well as mechanisms that keep the anteroposterior and the dorsoventral axes perpendicular to each other are discussed.
According to the model, the sharpness of the region specific activation of the gap genes results from local competition of the gene products. For the correct activation of the pair-rule genes, cooperation between gap genes is required. Basic features of the pair-rule pattern can be described by two binary sequences whose phase shift contains the polarity information. Segmentation results from the reiteration of at least three, but probably four, cell states. Each of these cell states is induced at two different positions in the pairrule pattern, such that 14 segments are formed from 7 double segments. A computer simulation is provided.
Peptidergic properties expressed in vitro by embryonic neuroblasts after neural induction
Authors: Pituello Fabienne , Deruntz Philippe , Pradayrol Lucien , Duprat Anne-Marie 
Published: April 2021

ABSTRACT
As an immediate consequence of neural induction, some neurectodermal cells acquire the ability to develop a number of characteristic neuronal features, without requiring any subsequent embryonic cues (Duprat et al. 1987). Thus, adrenergic, cholinergic and gabaergic traits are expressed in cultures of neural fold and neural plate isolated from amphibian embryos immediately after induction and grown in a defined medium.
The aim of the present study was to determine, using the same in vitro model, their abilities to develop peptidergic phenotypes.
Using immunocytochemical techniques, we show that substance P-, enkephalin- (leu-enkephalin, met-enkephalin), and somatostatin-like immunoreactivities are expressed in subpopulations of neurones grown in vitro, whereas VIP (vasoactive intestinal polypeptide) is not detected under the same conditions. The appearance and development of the somatostatinergic phenotype has been quantified by RIA both in cell extracts and in the culture medium. Somatostatin-like immunoreactivity (SLI) undetectable at the late gastrula stage, can be measured in cells after 4 days of culture and continues to increase over the next 10 days. In culture medium, SLI is present at a constant level from day 4 up to day 14.
These data reveal that some neuronal precursor cells acquire, during neural induction, the potentiality to biosynthesize, store and release neuropeptides. Furthermore, the expression of these peptidergic phenotypes in distinct subpopulations of neurones suggests that certain neuronal precursors become committed to different metabolic pathways at the earliest steps of neurogenesis.
5-azacytidine affects the programming of expression of the somatic nucleus of Paramecium
Authors: Kwok Fanii W. K. , Ng Stephen F. 
Published: April 2021

ABSTRACT
This report introduces a new system in the study of programming of genomic function during development of the somatic nucleus of Paramecium tetraurelia. Previous works have established a definite, but replaceable, role of the germ nuclei (micronuclei) in oral development in the asexual cycle; their removal from the cell generates viable amicronucleate cell lines, which characteristically suffer a transient period of growth depression marked by abnormal oral development. Such cell lines gradually recover, showing that a compensatory mechanism is activated in the absence of the germ nuclei to bring the cell back to near-normal. To test the notion that the somatic nucleus (macronucleus) is involved in this compensation, cells possessing micronuclei were treated with 5-azacytidine during sexual reproduction when new somatic nuclei develop. These cells were then propagated asexually for a number of fissions in the absence of the drug, and thereafter micronuclei were removed from them. The amicronucleate cell lines generated in this manner clearly did not suffer a depression as severe as the untreated controls did in terms of growth rate and oral development, and they recovered much sooner. This supports the notion that the somatic nucleus is the physical basis of the compensatory mechanism. This study suggests that the stomato-genic sequences in question normally become repressed in the somatic nucleus developing in sexual reproduction, and that 5-azacytidine administered to the cells at this time could alter this programme which then persists during subsequent asexual propagation. The possibility that the somatic nucleus is programmed by methylation of cytosine at the 5’ position is discussed.
Developmental expression of tissue inhibitor of metalloproteinase (TIMP) RNA
Authors: Nomura Shintaro , Hogan Brigid L. M. , Wills Alan J. , Heath John K. , Edwards Dylan R. 
Published: April 2021

ABSTRACT
Single-stranded antisense RNA probes have been used to study the expression of the metalloproteinase inhibitor TIMP (tissue inhibitor of metalloproteinases), during mouse embryogenesis and in adult tissues. Using a sensitive RNase protection assay, low levels of transcript can be detected in a variety of tissues, including maternal deciduum, embryonic kidney, lung and amnion. Higher levels are seen in osteogenic tissues such as calvaria, while the highest level in any tissue is found in the ovary, though even here expression is an order of magnitude below that observed in growth factor-treated fibroblasts in vitro. Using the technique of in situ hybridization, TIMP transcripts can first be detected in osteogenic tissues in the head and limb at about 15-5 days post coitum, and increase in amount until birth. The high levels of TIMP RNA in the ovary are localized to cells of the corpora lutea.
Targeted ablation of α-crystalIin-synthesizing cells produces lens-deficient eyes in transgenic mice
Authors: Kaur Satbir , Key Brian , Stock Jeffrey , McNeish John D. , Akeson Richard , Potter S. Steven 
Published: April 2021

ABSTRACT
Genetic ablation techniques were used to study the role of the lens in mammalian eye development. Ablation was accomplished by microinjecting murine eggs with chimeric DNA constructs in which the aA-crystallin gene regulatory sequence (−366 to +46) was fused to the highly cytotoxic diphtheria toxin gene coding sequence. For genetic ablation to be successful the promoter regulating expression should be specific and completely silent in cells necessary for normal mouse development. In this report, we describe the generation and analysis of transgenic mice with this readily discernible phenotype: aphakia or eyes without lens. Of the 109 live-born pups, eight carried the transgene and could be grouped according to the apparent severity of eye malformations. Lines 4, 5 and 6 founder (F0) mice had the most severe phenotype. Histological analysis revealed: marked reduction in eye size, total absence of lens, increased retinal cell density and extensive whorling of the retinal fibre layers. The line 1 F0 mouse displayed a distinct lens opacity and lines 2, 3 and 8 F0 mice were mosaics with a relatively mild, but most unusual phenotype. Their eyes contained a small, highly vacuolated lens. The progeny of these mosaics that inherited the transgene, however, again exhibited the severe phenotype. The aberrant structures of the eyes in which complete genetic ablation of the lens has been achieved suggest that the lens plays a pivotal role in the development of multiple components of the murine eye.
Computer-aided 3-D reconstruction of interphase microtubules in epidermal cells of Datura stramonium reveals principles of array assembly
Authors: Flander David J. , Rawlins David J. , Shaw Peter J. , Lloyd Clive W. 
Published: April 2021

ABSTRACT
From immunofluorescence microscopy it has been suggested that cortical microtubules form whole-cell arrays. This has been most clearly seen in cylindrical hairs where the existence of helical arrays testifies to the continuity of the array around the side walls of the cell. It is not, however, clear how microtubules pack in ‘typical’ polyhedral cells with multiple, angled facets. In addressing this problem, elongated and isodiametric cells in the epidermis of Datura stramonium L. were subjected to anti-tubulin immunofluorescence avoiding distortion by cellulase treatment and air-drying. Serial focal sections were then deblurred by computer, the information being digitized, reconstructed and then rotated in order to observe the arrangement of microtubules along the anticlinal walls (in the z-axis). This established several things. Microtubules tend to be parallel upon any one cell face; they form transverse, oblique or longitudinal arrays except that some walls bear a crisscross arrangement. In subepidermal cells, microtubules clearly form helices. In the elongated epidermal cells, transversely wound microtubules are confirmed by rotation to be continuous from one face to another and probably, therefore, also constitute helices. Microtubules on oblique end walls can be seen to continue onto the side walls and do not form a separate set. Although microtubules can be ordered upon two adjacent facets, the orientation with respect to the stem’s axis need not necessarily be identical on both facets, i.e. overall alignment can change at the cell edge.
In isodiametric epidermal cells, microtubules can similarly be traced from one cell facet to another. However, where microtubules from two anticlinal walls spill over onto a periclinal wall at divergent angles, a crisscross arrangement is set up. This is attributed to the geometrical problem of fitting parallel lines around irregular polyhedra. Despite crossing over one another, the microtubules on these walls are nevertheless continuous with MTs on the side walls.
In conclusion, in elongated cells the arrays still approximate helices of various pitch: in isodiametric cells (where the walls subtend variable non-orthogonal angles to one another) the integrity of the array appears to be preserved by microtubules crossing over each other upon what is termed a ‘sacrificial’ face. The overriding tendency is for microtubules to form an integral array regardless of cell shape.
Altered expression of spatially regulated embryonic genes in the progeny of separated sea urchin blastomeres
Authors: Hurley David L. , Angerer Lynne M. , Angererf Robert C. 
Published: April 2021

ABSTRACT
We have examined the importance of the extracellular environment on the ability of separated cells of sea urchin embryos (Strongylocentrotus purpuratus) to carry out patterns of mRNA accumulation and decay characteristic of intact embryos. Embryos were dissociated into individual blastomeres at 16-cell stage and maintained in calcium-free sea water so that daughter cells continuously separated. Levels of eleven different mRNAs in these cells were compared to those in control embryos when the latter reached mesenchyme blastula stage, by which time cells in major regions of the intact embryo have assumed distinctive patterns of message accumulation. Abrogation of interactions among cells resulted in marked differences in accumulation and/or turnover of the individual mRNAs, which are expressed with diverse temporal and spatial patterns of prevalence in intact embryos. In general, separated cells are competent to execute initial events of mRNA accumulation and decay that occur uniformly in most or all blastomeres of the intact embryo and are likely to be regulated by maternal molecules. The ability of separated cells to accumulate mRNAs that appear slightly later in development depends upon the presumptive tissue in which a given mRNA is found in the normal embryo. Messages that normally accumulate in cells at the vegetal pole also accumulate in dissociated cells either at nearly normal levels or at increased levels. In one such case, that of actin Cylla, which is normally restricted to mesenchyme cells, in situ hybridization demonstrates that the fraction of dissociated cells expressing this message is 4- to 5-fold higher than in the normal embryo. In contrast, separated cells accumulate significant levels of a message expressed uniformly in the early ectoderm but are unable to execute accumulation and decay of different messages that distinguish oral and aboral ectodermal regions. These data are consistent with the idea that interactions among cells in the intact embryo are important for both positive and negative control of expression of different genes that are early indicators of the specification of cell fate.
Detection of age-related changes in the distributions of keratan sulfates and chondroitin sulfates in developing chick limbs: an immunocytochemical study
Authors: Sorrell J. Michael , Caterson Bruce 
Published: April 2021

ABSTRACT
A panel of four separate monoclonal antibodies, all known to specifically recognize epitopes on keratan sulfate glycosaminoglycans, were employed in an immunocytochemical study of developing chick hind limbs. In addition, two monoclonal antibodies specific for epitopes on chondroitin/dermatan sulfate glycosaminoglycans were employed on equivalent sections to determine the degree of colocalization of keratan and chondroitin/ dermatan sulfates. The spatial distributions of keratan sulfate and chondroitin/dermatan sulfate differed to some extent. In younger embryos, high extracellular concentrations of keratan sulfate occurred in joints and articular cartilages, with diminishing amounts being present in epiphyseal and diaphyseal regions. The high concentration of keratan sulfate in joints and articular cartilage corresponded to equally high concentration of chondroitin-6 sulfate. With advancing age, the above mentioned distribution was modified, most notably by increased amounts of keratan sulfate within diaphyseal regions. Finally, the use of four different anti-keratan sulfate monoclonal antibodies made it possible to compare keratan sulfate epitope expression. Differences in keratan sulfate epitopes were noted in some regions of bones, mostly in diaphyseal regions of younger bones and epiphyseal regions of older bones. This pattern of keratan sulfate expression suggests that different types of keratan sulfate may be present and their expression may be developmentally regulated.
Localized synthesis of the Vg1 protein during early Xenopus development
Authors: Tannahill D. , Melton D. A. 
Published: April 2021

ABSTRACT
The Xenopus Vgl gene encodes a maternal mRNA that is localized to the vegetal hemisphere of both oocytes and embryos and encodes a protein related to the TGF-β family of small secreted growth factors. We have raised antibodies to recombinant Vgl protein and used them to show that Vgl protein is first detected in stage IV oocytes and reaches maximal levels in stage VI oocytes and eggs. During embryogenesis, Vgl protein is synthesized until the gastrula stage. The embryonically synthesized Vgl protein is present only in vegetal cells of an early blastula. We find that Vgl protein is glycosylated and associated with membranes in the early embryo. Our results also suggest that a small proportion of the full-length Vgl protein is cleaved to give a small peptide of Mr= —17×103. These results support the proposal that the Vgl protein is an endogenous growth-factor-like molecule involved in mesoderm induction within the amphibian embryo.
Immunohistochemical localisation of chondroitin sulphate proteoglycans and the effects of chondroitinase ABC in 9- to 11-day rat embryos
Authors: Morriss-Kay Gillian , Tuckett Fiona 
Published: April 2021

ABSTRACT
Studies on cell behaviour in vitro have indicated that the chondroitin sulphate proteoglycan (CSPG) family of molecules can participate in the control of cell proliferation, differentiation and adhesion, but its morphogenetic functions had not been investigated in intact embryos. Chondroitin/chondroitin sulphates have been identified in rat embryos at low levels at the start of neurulation (day 9) and at much higher levels on day 10. In this study we have sought evidence for the morphogenetic functions of CSPGs in rat embryos during the period of neurulation and neural crest cell migration by a combination of two approaches: immunocytochemical localization of CSPG by means of an antibody, CS-56, to the chondroitin sulphate component of CSPG, and exposure of embryos to the enzyme chondroitinase ABC. Staining of the CS-56 epitope was poor at the beginning of cranial neurulation; bright staining was at first confined to the primary mesenchyme under the convex neural folds late on day 9. In day 10 embryos, all mesenchyme cells were stained, but at different levels of intensity, so that primary mesenchyme, neural crest and sclerotomal cells could be distinguished from each other. Basement membranes were also stained, particularly bright staining being present where two epithelia were basally apposed, e.g. neural/surface ectoderms, dorsal aorta/neural tube, prior to migration of a population of cells between them. Staining within the neural epithelium was first confined to the dorsolateral edge region, and associated with the onset of neural crest cell emigration; after neural tube closure, neuroepithelial staining was more general. Neural crest cells were stained during migration, but the reaction was absent in areas associated with migration end-points (trigeminal ganglion anlagen, frontonasal mesenchyme). Embryos exposed to chondroitinase ABC in culture showed no abnormalities until early day 10, when cranial neural crest cell emigration from the neural epithelium was inhibited and neural tube closure was retarded. Sclerotomal cells failed to take their normal pathway between the dorsal aorta and neural tube. Correlation of the results of these two methods suggests: (1) that by decreasing adhesiveness within the neural epithelium at specific stages, CSPG facilitates the emigration of neural crest cells and the migratory movement of neuroblasts, and may also provide increased flexibility during the generation of epithelial curvatures; (2) that by decreasing the adhesiveness of fibronectin-containing extra-cellular matrices, CSPG facilitates the migration of neural crest and sclerotomal cells. This second function is particularly important when migrating cells take pathways between previously apposed tissues.
Molecular characteristics of cytostatic factors in amphibian egg cytosols
Authors: Shibuya Ellen K. , Masui Yoshio 
Published: April 2021

ABSTRACT
In amphibians, zygotes microinjected with cytosol of unactivated eggs are arrested at metaphase of mitosis. The factor responsible for this effect has been designated ‘cytostatic factor, (CSF)’. CSF is inactivated by Ca2+ addition to cytosols. During storage of the Ca2+-containing cytosols, a stable CSF activity develops. Therefore, the first Ca2+-sensitive CSF and the second Ca2+-insensitive CSF have been referred to as primary CSF (CSF-1) and secondary CSF (CSF-2), respectively. We have partially purified CSF-1, which had been stabilized with NaF and ATP, and CSF-2 from cytosols of Rana pipiens eggs by ammonium sulphate (AmS) precipitation and sucrose density gradient centrifugation or gel filtration, and investigated their molecular characteristics. CSF-1 was sensitive to protease, but resistant to RNAse, and inactivated within 2h at 25°C. CSF-1 could be sedimented in a sucrose density gradient from a fresh cytosol or its crude fraction precipitated at 20-30% saturation of AmS, showing the sedimentation coefficient 3S. When analyzed by SDS-polyacrylamide gel electrophoresis (PAGE), all the proteins in partially purified CSF-1 samples entered the gel and were separated into numerous peptide bands. In contrast, CSF-2 was an extremely large molecule, being eluted from Sepharose columns as molecules larger than 2×106, and failed to enter the gel when analyzed by SDS-PAGE. It could be purified 40 times from cytosols. CSF-2 was a highly stable molecule, being neither inactivated nor dissociated at pH 11’5 or by 4m-NaCl and L1C1 and 8 M-urea. It was also resistant to RNAse treatment. However, CSF-2 could be broken down into small peptides of variable sizes by trypsin, a-chymotrypsin, and papain, but not by S. aureus V8 protease, although it was less sensitive to proteases than CSF-1. The dose-dependency test showed that the activity of CSF-2 is independent of its concentration and that an amount of CSF-2 could cause cleavage arrest earlier when injected into a blastomere in a larger volume.
Pair-rule expression of a cell surface molecule during gastrulation of the moth embryo
Authors: Carr Jeffrey N. , Taghert Paul H. 
Published: April 2021

ABSTRACT
The TNI monoclonal antibody recognizes a cell surface epitope that is present on subsets of growing axons in the developing nervous system of moth embryos. This antigen is also found in a variety of other developing tissues: in all cases its expression is cell-specific and transient. Here we show that the first expression of the TNI epitope in moth embryos occurs specifically on the surfaces of mesodermal cells during gastrulation, and that it is limited to alternate segments. Creation of this pair-rule pattern of expression includes indications of an initial 4-segment periodicity, and transient immunoreactivity in ‘off’ segments. The alternating pattern is most dramatic at the end of gastrulation. It changes rapidly such that, during organogenesis, the TNI antigen(s) is expressed in many developing tissues of all segments, with little segment-specific variation. Immunolabelling of living embryos under culture conditions demonstrated that the TN1 epitope(s) is associated with cell surfaces, both during neurogenesis and during the earlier period of gastrulation. These observations indicate that pair-rule gene functions operate in insects other than Diptera and suggest that cell surface molecules may be utilized early in insect embryogenesis in the initial establishment of large body regions.