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At least 253 records · Page 14Linked to original sources
PubMed1999

Patterns of programmed cell death in populations of developing spinal motoneurons in chicken, mouse, and rat.

During embryonic development, approximately one-half of the spinal motoneurons initially generated are lost during a wave of programmed cell death (PCD). Classical studies in this system laid the basis of much work on the role and control of neuronal cell death during development. However, we have little information concerning the timing of cell death in motoneuron pools at different rostrocaudal levels, especially in rodents. We developed a novel protocol for whole-mount TUNEL labeling that allows apoptotic nuclei to be visualized in whole-mount preparations of embryonic spinal cord; double labeling with antibodies to Islet 1/2 showed that nearly all TUNEL-positive cells were motoneurons. In chicken and mouse embryos, the density of TUNEL-positive nuclei was specifically increased following target ablation. The pattern of naturally occurring motoneuron PCD was studied in spinal cords from different species and ages: chick (E4.5-E9.0), mouse (E11.5-E15.5), and rat (E13.5-E16. 5). In all species, motoneuron PCD is first apparent at cervical levels and last at sacral levels. However, motoneuron PCD does not follow a strict rostrocaudal sequence. Following cervical motoneuron PCD, TUNEL profiles are first observed at lumbar levels in chick but at thoracic levels in rat. At a given rostrocaudal level, medial motoneurons tend to die before lateral populations, but here too there are exceptions. Motoneuron cell death is thus regulated in a highly stereotyped manner during development of vertebrate spinal cord. Our technique will provide a basis for the monitoring even localized changes in this pattern.

Animals↗
PubMed2001

Distinct enhancer elements control Hex expression during gastrulation and early organogenesis.

In the mouse, embryological and genetic studies have indicated that two spatially distinct signalling centres, the anterior visceral endoderm and the node and its derivatives, are required for the correct patterning of the anterior neural ectoderm. The divergent homeobox gene Hex is expressed in the anterior visceral endoderm, in the node (transiently), and in the anterior definitive endoderm. Other sites of Hex expression include the liver and thyroid primordia and the endothelial cell precursors. We have used transgenic analysis to map the cis-acting regulatory elements controlling Hex expression during early mouse development. A 4.2-kb upstream region is important for Hex expression in the endothelial cell precursors, liver, and thyroid, and a 633-bp intronic fragment is both necessary and sufficient for Hex expression in the anterior visceral endoderm and the anterior definitive endoderm. These same regions drive expression in homologous structures in Xenopus laevis, indicating conservation of these regulatory regions in vertebrates. Analysis of the anterior visceral endoderm/anterior definitive endoderm enhancer identifies a repressor region that is required to downregulate Hex expression in the node once the anterior definitive endoderm has formed. This analysis also reveals that the initiation of Hex expression in the anterior visceral endoderm and axial mesendoderm requires common elements, but maintenance of expression is regulated independently in these tissues.

Animals↗
PubMed1998

Embryonic stem cells and embryoid bodies express lymphocyte costimulatory molecules.

Despite the importance of the costimulatory proteins B7-1 (CD80), B7-2 (CD86), and their counterreceptors CD28 and CTLA-4 (CD154) in the regulation of T cell proliferation in the adult immunological system, the initial appearance of these proteins during embryonic development has not been investigated. Using in vitro cultures of undifferentiated mouse embryonic stem (ES) cells and differentiating embryoid bodies as a model of very early embryonic development, we examined these cells for the presence of mRNA and protein corresponding to the B7 and CD28 families of costimulatory molecules. By flow cytometry, a stochastically regulated subpopulation of B7-1+ cells comprising 33% of total cells was detected in ES cell cultures, while negligible staining was found for B7-2, CTLA-4, and CD28. When ES cells were differentiated into embryoid bodies for 12 days, a CD45+ subpopulation of embryoid body cells were found to stain positively for B7-1, B7-2, and CD28. RT-PCR confirmed cell staining data by revealing amplification products corresponding to B7-1, B7-2, and CD28 in corresponding samples. Very low levels of CTLA-4 amplification products were found in all samples; however, surface staining of CTLA-4 was never detected. The functional capacity of ES cell B7-1 to bind its ligand was verified by the ability of the soluble fusion protein CTLA-4-Ig to bind ES cells and the ability of this reagent to block anti-B7-1 antibody binding in cell based competition assays. These results demonstrate that expression of costimulatory molecules arises very early during in vitro development and suggests that the early embryonic environment may utilize cellular signaling systems analogous to those seen in the immune system.

Abatacept↗
PubMed2000

Thymus organogenesis and molecular mechanisms of thymic epithelial cell differentiation.

In the mature thymus, thymocyte maturation depends on interactions with different thymic epithelial subtypes in a three-dimensional thymic architecture. However, the molecular mechanisms that generate these epithelial subtypes are not well understood. Evidence is accumulating that during fetal thymus development, epithelial cells differentiate by successive interactions with differentiating thymocytes. This review presents fetal thymus development as a process of organogenesis, the main function of which is to promote thymic epithelial cell differentiation and the generation of a functional thymic microenvironment. In this model, endoderm-derived epithelial cells are the driving force in generating the thymic primordium, with hematopoietic cells providing later signals that organize and pattern the developing thymus.

Body Patterning↗
PubMed1995

Bone morphogenetic protein-6 expression in normal and malignant prostate.

Bone morphogenetic proteins (BMPs) have multiple biologic functions, including bone formation and embryonic induction. One of these proteins, BMP-6, was reportedly expressed at high levels in human prostate cancers that had also metastasized to bone. This study investigated both BMP-6 mRNA and protein expression in normal and malignant rat and human prostate tissues. BMP-6 was detected in both rat normal prostate and in Dunning rat-prostate adenocarcinoma sublines. The levels of BMP-6 mRNA and protein were similar for normal and malignant rat prostate, regardless of the metastatic potential. Moreover, castration had no apparent effect on BMP-6 production in rat normal ventral prostate, suggesting an androgen-independent gene regulation of this protein. BMP-6 mRNA and protein were also produced by normal and neoplastic human prostate cancer (radical prostatectomy specimens and human carcinoma cell lines DU145 and PC3). BMP-6 mRNA and protein expression, however, was higher in prostate cancer as compared with adjacent normal prostate, with higher-grade tumors (Gleason score of 6 or more) having greater BMP-6 immunostaining than the lower-grade tumors (Gleason score of 4 or less). Taken together, these results suggest that BMP-6 protein expression may serve as a potential marker for prostate cancer but not as a metastatic marker. Moreover, BMP-6 may contribute to prostate neoplastic behavior even in the absence of androgens.

Androgens↗
PubMed1985

Developmental control of transduced dopa decarboxylase genes in D. melanogaster.

Seventeen new euchromatic integration sites of the dopa-decarboxylase gene (Ddc) have been generated using p-mediated transduction. The developmental expression of the integrated genes was examined by monitoring the embryonic induction of dopa decarboxylase enzyme activity (DDC) and by monitoring the developmental pattern of DDC activity from late third instar to eclosion. The majority of inserts are regulated correctly within about 30% of controls. Several cases of multiple insertion events were recovered and these show correspondingly elevated levels of activity and are regulated normally. The pattern of expression of one insert (15C) falls outside the normal range. Multiple copies of transduced Ddc genes are used to test for effects of elevated gene dose on levels of expression. One insert on the X chromosome shows little or no dosage compensation. Possible reasons for the differences between the regulation of transduced genes in Drosophila and the regulation of transformed genes in mammalian systems are discussed.

Animals↗
PubMed1989

Angular homeostasis: III. The formalism of discrete orbits in ontogeny.

The formal properties of orbits in a plane are explored by elementary topology. The notions developed from first principles include: convex and polygonal orbits; convexity; orientation, winding number and interior; convex and star-shaped regions. It is shown that an orbit that is convex with respect to each of its interior points bounds a convex region. Also, an orbit that is convex with respect to a fixed point bounds a star-shaped region. Biological considerations that directed interest to these patterns are indicated, and the implications of the prospect of higher orders of star-shapedness mentioned.

Cell Communication↗
PubMed1988

Renal epithelial development in organotypic culture.

An in vitro model system for the experimental study of renal epithelial differentiation is described. Fetal murine metanephric tissue consisting of nephrogenic blastema and branched ureteric bud is isolated following 24-36 h of natural embryonic inductive interaction (13 +/- 0.4 days gestation) and cultured as an intact organ in a Trowell-type assembly. During 120 h of organ culture incubation in completely defined serum-free medium, advanced organotypic proximal tubular and glomerular epithelial differentiation proceed in the absence of vascularization, perfusion, and urine production. The system thus experimentally separates the processes of three-dimensional organ growth and post-induction renal epithelial differentiation from glomerular filtration, flow-related phenomena, endothelial or mesangial cell interactions, and the effects of growth factors or transport substrates present in mammalian serum or urine. Studies to date in the model system have defined the growth factor requirements of epithelial growth and differentiation and have demonstrated that specific hormonally induced alterations in tubular epithelial cell metabolism and function may lead to specific patterns of tubular maldevelopment. Whole organ metanephric organ culture is thus a valuable in vitro model system for future investigations into the complex processes of normal and abnormal renal epithelial differentiation.

Animals↗
PubMed1976

Cytochemical evidence for stage-specific changes of nuclear RNA and nonhistone protein content during early development of Triturus vulgaris.

During early embryogenesis of Triturus vulgaris, RNA and nonhistone protein contents of neuroectoderm nuclei change with stage specifically. Maximum values were found in the late gastrula after embryonic induction, and in the late neurula with the formation of the neural tube. The stage-specific increases of RNA and nonhistone protein are correlated with a preceding increase of Feulgen-DNA content.

Animals↗
PubMed2000

NKX2 gene expression in neuroectoderm but not in mesendodermally derived structures depends on sonic hedgehog in mouse embryos.

NKX2 genes in vertebrates encode a sub- family of homeodomain-containing transcription factors which regulate morphogenetic events and cell differentiation during embryogenesis. In mouse embryos several NKX2 genes are expressed in the ventral midline domains of the neuroectoderm, while other NKX2 genes are primarily expressed in the mesendoderm and mesendodermally derived organs, such as heart and gut. Within several patterning centers for tissue organization sonic hedgehog (Shh) is an important signal in the formation of ventral midline structures in vertebrate embryos. Here, we investigated the role of Shh in the embryonic expression of six different but closely related NKX2 genes in Shh null mutant mice. We found that expression of NKX2.1, NKX2.2, and NKX2.9 in neural domains requires Shh signaling, whereas NKX2.3, NKX2.5 and NKX2.6 expression in endoderm and mesoderm is independent of Shh.

Animals↗
PubMed1984

Ontogenetic expression of cell adhesion molecules: L-CAM is found in epithelia derived from the three primary germ layers.

Immunofluorescence techniques using specific antibodies against the liver cell adhesion molecule, L-CAM, were used to explore the appearance of L-CAM during early embryogenesis and organogenesis, as well as in adult tissue. Immunoblots of L-CAM from embryonic and adult organs indicated that molecules detected in each tissue were L-CAM, and that the antibodies were not simply detecting cross-reacting molecules. L-CAM was found in low levels on pregastrulation embryos. During gastrulation, the molecule remained present on ectoderm but was not detected on mesodermal and definitive endodermal cells. During neurulation, L-CAM disappeared from the neural ectoderm, in which staining for the neural cell adhesion molecule, N-CAM, had previously been shown to increase markedly. During organogenesis, L-CAM appeared in all endodermal structures, in ectoderm other than neural derivatives, in placodes, in extraembryonic ectoderm and endoderm, and in some mesodermal structures such as Wolffian ducts, oviduct, and kidney epithelium. Other mesodermal derivatives were not stained and the molecule was not detected in hemangioblastic areas of the lateral plate mesoderm nor in splanchnopleural derivatives such as spleen, adrenal glands, and gonads. During embryonic induction, for example, neurulation and in early kidney development, changes in L-CAM distribution were correlated with both locations and times of induction events. Analysis of distribution in the adult revealed that L-CAM was present in the stratum germinativum of the skin, in endodermally derived epithelia, in the female reproductive tract, and in the kidneys. In several fully differentiated glandular organs, L-CAM staining was restricted to basal or apical parts of the cell surface. When correlated with previous results obtained for N-CAM, these findings support the idea that local cell surface modulation of a small number of cell adhesion molecules may regulate other primary processes of development to yield specific patterns, both in early development and in organogenesis. Reflections of these patterns remain in adult life.

Animals↗
PubMed1991

Larsen's syndrome with novel congenital anomalies.

A full-term female infant with the rare Larsen's syndrome who died after 2 days is presented. The infant exhibited several of the anomalies characteristically reported with this syndrome. These include multiple joint deformities, a flattened facies, hydrocephalus, cardiac defects, and tracheal stenosis. We now report two additional congenital malformations that have not been previously reported with this syndrome: complete agenesis of the anus, with the distal colon ending in a cul-de-sac, and the presence of a bifid uterus. These novel congenital anomalies further support the etiology of Larsen's syndrome as a generalized mesenchymal disorder, since they arise from a defective process of embryonal induction involving mesenchymal tissue.

Abnormalities, Multiple↗
PubMed1991

An hypothesis: phosphorylation fields as the source of positional information and cell differentiation--(cAMP, ATP) as the universal morphogenetic Turing couple.

It is hypothesized that (cAMP, ATP) is the elusive, universal Turing morphogenetic couple, which defies the second law of thermodynamics, i.e. the inexorable march towards homogeneity. cAMP and ATP can be distributed nonhomogeneously because the whole of the intermediary metabolism is so organized that they mutually satisfy the Turing bifurcation conditions upon nonlocalized application of an extracellular ligand, in particular a soluble peptide growth factor, which is nature's distinguished universal bifurcation parameter, acting homogeneously in space and removing the substrate inhibition from adenylate cyclase and thus triggering embryonic induction by triggering the (cAMP, ATP) Turing system. The hypothesis predicts that although the extracellular signal, the growth factor, is applied homogeneously, an organized "dissipative structure" will emerge spontaneously in the responding tissue; this "symmetry breaking" in a reaction-diffusion system occurs precisely in the manner envisaged by Turing, where (cAMP, ATP) constitutes the "reaction-diffusion system". This Turing bifurcation explicates the recent experiments where a differentiated embryoid emerges from the mere immersion of frog animal caps in an homogeneous growth factor solution, and similar experiments on chicks. The "metabolic" patterns found by Child and colleagues also reflect dissipative structures arising in a (cAMP, ATP) reaction-diffusion system when interpreted in the light of modern biochemistry: in particular, the localized glycogen depletion reflects localized cAMP; localized redox, respiratory or susceptibility activity reflects localized ATP. The dramatic collapse of organized structure found by Child and colleagues, for example, when Planaria or a section of it is exposed to an homogeneous environment of a narcotic solution, and the reemergence of structure upon return to water, are explained on the basis of the violation or satisfaction of the Turing bifurcation conditions with respect to (cAMP, ATP), respectively. cAMP is the "activator", ATP is the "inhibitor", and together they mutually satisfy the four activator-inhibitor inequalities, including the all-important autocatalytic cAMP production, as well as the lateral inhibition condition. The functional significance of gap junctions is to generate a multicellular purely reaction-diffusion system for (cAMP, ATP) as envisaged by Turing. It is emphasized that localization and pattern formation occur intracellularly in gap junction-coupled cells and not, as often suggested, extracellularly, the latter localization being too fragile to be maintained for long enough, and soon succumbing to the mixing effect of convection and movement. The activator-inhibitor property of (cAMP, ATP) means that the spatial distribution of cAMP and ATP could be not only nonhomogeneous but also of the same shape.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Triphosphate↗
PubMed1988

Role of laminin A chain in the development of epithelial cell polarity.

Kidney organ culture was used to study the conversion of embryonic mesenchymal cells into a polarized, differentiated kidney epithelium. We examined the expression of laminin, a basement membrane glycoprotein, during this conversion. The B chains of laminin were constitutively expressed, whereas the appearance of the A chain of laminin was dependent on embryonic induction and coincided with the onset of cell polarization. Antisera against the carboxy-terminal end of laminin inhibited polarization but did not affect the developmental events that precede polarization. Antisera against N-terminal parts of laminin failed to inhibit morphogenesis. Since the fragments at the carboxy-terminal end contain parts of the A chain, we suggest that the appearance of this chain is fundamental for initiation of cell polarity.

Animals↗