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At least 109 records · Page 6Linked to original sources
PubMed2006

Extrinsic cues orient the cell division axis in Drosophila embryonic neuroblasts.

Cell polarity must be integrated with tissue polarity for proper development. The Drosophila embryonic central nervous system (CNS) is a highly polarized tissue; neuroblasts occupy the most apical layer of cells within the CNS, and lie just basal to the neural epithelium. Neuroblasts are the CNS progenitor cells and undergo multiple rounds of asymmetric cell division, ;budding off' smaller daughter cells (GMCs) from the side opposite the epithelium, thereby positioning neuronal/glial progeny towards the embryo interior. It is unknown whether this highly stereotypical orientation of neuroblast divisions is controlled by an intrinsic cue (e.g. cortical mark) or an extrinsic cue (e.g. cell-cell signal). Using live imaging and in vitro culture, we find that neuroblasts in contact with epithelial cells always ;bud off' GMCs in the same direction, opposite from the epithelia-neuroblast contact site, identical to what is observed in vivo. By contrast, isolated neuroblasts 'bud off' GMCs at random positions. Imaging of centrosome/spindle dynamics and cortical polarity shows that in neuroblasts contacting epithelial cells, centrosomes remained anchored and cortical polarity proteins localize at the same epithelia-neuroblast contact site over subsequent cell cycles. In isolated neuroblasts, centrosomes drifted between cell cycles and cortical polarity proteins showed a delay in polarization and random positioning. We conclude that embryonic neuroblasts require an extrinsic signal from the overlying epithelium to anchor the centrosome/centrosome pair at the site of epithelial-neuroblast contact and for proper temporal and spatial localization of cortical Par proteins. This ensures the proper coordination between neuroblast cell polarity and CNS tissue polarity.

Animals↗
PubMed1999

Opioids modulate cell division in the germinal zone of the late embryonic neocortex.

Opioid effects on cell division in the embryonic cerebral cortex were examined using two experimental approaches: (i) the presence of opioid receptors in the embryonic day 16 mouse neocortex was tested using immunohistochemical techniques; (ii) the values of the indices of [3H]thymidine pulse labelled cells and mitotic indices were estimated in the ventricular zone of the embryonic day 16 mouse neocortex 2.5, 4.5 and 8.5 h after administration to pregnant females of selected opioid receptor agonists or the opioid antagonist naloxone. The immunohistochemical study demonstrated that distinct subpopulations of the ventricular zone cells express mu, delta or kappa opioid receptors. Acute exposure of mouse embryos to mu, delta and kappa opioid receptor agonists or naloxone differentially affects the indices of [3H] thymidine pulse labelled cells and mitotic indices indicating changes in the cell cycle composition. Treatment with the mu opioid receptor agonist D-Ala2-MePhe4, Gly-ol5-enkephalin (DAGO), or the partially selective kappa opioid receptor agonist bremazocine, increased the [3H]thymidine labelling and mitotic indices. In contrast, the delta receptor agonist (D-Ser8)-leucine enkephalin-Thr (DSLET) produced a decrease in the labelled cell indices and mitotic indices. Naloxone provided a biphasic effect: a decrease in the values of labelled cell indices 2.5 h after naloxone administration, followed by an increase in the values of the indices at 4.5 and 8.5 h. These results suggest that the endogenous embryonic/maternal opioid systems are involved in the regulation of cell division in the ventricular zone of the late embryonic cortex.

Animals↗
PubMed2002

The Caenorhabditis elegans histone hairpin-binding protein is required for core histone gene expression and is essential for embryonic and postembryonic cell division.

As in all metazoans, the replication-dependent histone genes of Caenorhabditis elegans lack introns and contain a short hairpin structure in the 3' untranslated region. This hairpin structure is a key element for post-transcriptional regulation of histone gene expression and determines mRNA 3' end formation, nuclear export, translation and mRNA decay. All these steps contribute to the S-phase-specific expression of the replication-dependent histone genes. The hairpin structure is the binding site for histone hairpin-binding protein that is required for hairpin-dependent regulation. Here, we demonstrate that the C. elegans histone hairpin-binding protein gene is transcribed in dividing cells during embryogenesis and postembryonic development. Depletion of histone hairpin-binding protein (HBP) function in early embryos using RNA-mediated interference leads to an embryonic-lethal phenotype brought about by defects in chromosome condensation. A similar phenotype was obtained by depleting histones H3 and H4 in early embryos, indicating that the defects in hairpin-binding protein-depleted embryos are caused by reduced histone biosynthesis. We have confirmed this by showing that HBP depletion reduces histone gene expression. Depletion of HBP during postembryonic development also results in defects in cell division during late larval development. In addition, we have observed defects in the specification of vulval cell fate in animals depleted for histone H3 and H4, which indicates that histone proteins are required for cell fate regulation during vulval development.

3' Untranslated Regions↗
PubMed1993

Modulation of preimplantation embryonic development by antisense oligonucleotides to major histocompatibility complex genes.

The Ped (preimplantation embryo development) gene, which controls the rate of mouse preimplantation embryonic cleavage division and subsequent survival of the embryo, maps to the Q region of the MHC (major histocompatibility complex). Mouse embryos were treated with antisense oligonucleotides to mRNA for the Q region genes Q7/Q9, each of which encodes the Qa-2 antigen. The reverse transcription polymerase chain reaction (RT-PCR) was used to show that antisense treatment, but not sense treatment, decreased the level of mRNA for Qa-2 antigen in preimplantation embryos. Furthermore, both the expression of Qa-2 protein and the rate of embryonic cleavage division were decreased by treatment with antisense but not sense oligonucleotides. These results provide direct evidence that the Ped gene phenotype is at least partially encoded by the Q7/Q9 genes. It is likely that the mouse Ped gene has a human homolog, perhaps within HLA-F. Identification of genes--such as the Ped gene--that affect survival of the embryo may be vitally important for the enhancement of animal and human reproductive success.

Animals↗
PubMed1986

Effects of a very low dose rate of chronic ionizing radiation on the division potential of human embryonic lung fibroblasts in vitro.

Among the various parameters that are supposed to play a role in aging at the cellular level, the "free radical theory" involves biochemical modifications that can be induced by radiation. Human embryonic lung fibroblasts were serially subcultivated at low density under chronic low dose rate irradiation (40 mrad/day) and in a normal environment. Irradiation increases cell attachment and the population doubling/day throughout their entire in vitro lifespan. Consequently, the doubling potential reached by irradiated cells was higher than that of control cultures. Finally, the total number of cells produced under chronic irradiation was 8-14 times higher than in a normal environment. These results are discussed with respect to the increased enzymatic activities (superoxidismutase, catalase, glutathion-reductase, G6PD) found in some irradiated organisms.

Cell Adhesion↗
PubMed1982

Abnormal differentiation of selected nuclear centers in the brain of a duck embryo associated with partial duplication of the primitive streak.

In a control set of duck embryos, an abnormal duck embryo of 16 days incubation was found which had two beaks as the only outward sign of duplication. The beaks were of equal size, each with upper and lower bills. Bill-clapping movements were absent. The embryo had two normal eyes placed one on either side of the head, and the rest of the body was normal in external appearance. Sections through the head revealed further duplication of the fore-, mid-, and hindbrain divisions. The medial half of each of the embryonic brain divisions, however, was greatly reduced. Two additional optic primordia were also noticed in sections, each of which was reduced to a mass of tissue representing a lens and a much-folded pigment epithelium. The orbital tissues associated with the rudimentary eyes were greatly disorganized. Abnormal differentiation associated with duplication of the brain divisions was determined by cell counts in selected nuclear centers. Cell numbers in each case appeared to be remarkably proportional to the size of the innervation field. Our data, based on cell counts in the nuclear centers chosen for this study in the abnormal embryo and normal control embryos of the same age, are consistent with the hypothesis that cell survival in related parts of the nervous system may be regulated by their peripheral field of innervation.

Animals↗
PubMed2002

Miranda, a protein involved in neuroblast asymmetric division, is associated with embryonic centrosomes of Drosophila melanogaster.

Miranda, a highly coiled-coil protein, has been shown to be one of the key components necessary for the differential segregation of fate-determining factors during neurogenesis in Drosophila embryos. The multidomain protein Miranda, by segregating the transcription factor Prospero, guarantees the generation of cell diversity during the formation of the embryonic nervous system. While looking for new molecular components of the centrosome in Drosophila embryos, we have isolated a short isoform of Miranda. An antibody was raised directed against the central coiled-coil region of Miranda. and the pattern of expression of the protein was studied in details throughout Drosophila development. Here, we show that Miranda has a broad pattern of expression and is a rather ubiquitous molecule. Immunofluorescence on syncytial Drosophila embryos shows that Miranda has a dynamic redistribution and is associated with centrosomes. Electron microscopy on purified syncytial centrosomes shows that Miranda is located on the pericentriolar material along with gamma-tubulin. Taken all together, our data indicate for the first time that Miranda belongs to a growing class of proteins that concentrate at the centrosome in a cell-cycle and stage-specific manner. The observations that Miranda has a broad range of expression, as well as a dynamic and cell-cycle dependent subcellular localization, suggest that it may have alternative functions outside the embryonic nervous system. These potential new functions are discussed in this paper.

Animals↗
PubMed2002

Cell division cycle control in embryonal and alveolar rhabdomyosarcomas.

In this study, we investigated the mRNA level of several genes involved in cell cycle regulation in alveolar (ARMS) and embryonal rhabdomyosarcomas (ERMS). p21(Cip1), Cyclin D1, Cyclin D2, Cyclin D3, CDK2, and CDK4 were evaluated by RT-PCR. All (13 out of 13) ERMS expressed the p21(Cip1) gene compared with only 40% (4 out of 10) of the ARMS. Moreover, the amount of p21(Cip1) mRNA was noticeably higher in the ERMS samples than in the positive ARMS specimens. p27(Kip1) protein were analysed by immunohistochemical and immunoblotting. A noticeable difference was observed, in that ERMS had higher amounts of the cell cycle inhibitor compared with the ARMS. Finally, treatment of two rhabdomyosarcoma cell lines, RH-30 and RD, with butyrate, resulted in complete growth inhibition and in the upregulation of the p21(Cip1) and p27(Kip1) levels. Our results demonstrate that ERMS have a much higher level of p27(Kip1) and p21(Cip1) than the alveolar types, explaining, at least in part, the distinct features and outcomes (i.e. a poor prognosis of the alveolar type) of the two forms of this childhood solid cancer. Moreover, the data on butyrate-treated cell lines suggest that the two genes are potential novel therapeutic targets for the treatment of rhabdomyosarcomas.

CDC2-CDC28 Kinases↗
PubMed1996

Repression of gene expression in the embryonic germ lineage of C. elegans.

The distinction between soma and germline was recognized more than a century ago: somatic cells form the body of an organism, whereas germ cells serve to produce future generations. In Caenorhabditis elegans, the separation of some and germline occurs through a series of asymmetrical divisions, in which embryonic germline blastomeres divide unequally to produce one somatic daughter and one germline daughter. Here we show that after each asymmetrical division, embryonically transcribed RNAs are detected in somatic, but not germline, blastomeres. This asymmetry depends on the activity of the germline specific factor, PIE-1. In the absence of PIE-1, embryonically transcribed RNAs are detected in both somatic and germline blastomeres. Furthermore, ectopic expression of PIE-1 in somatic blastomeres can significantly reduce the accumulation of new transcripts in these cells. Taken together, these results suggest that germ-cell fate depends on an inhibitory mechanism that blocks new gene expression in the early embryonic germ lineage.

Animals↗
PubMed2001

Vanadocenes as potent anti-proliferative agents disrupting mitotic spindle formation in cancer cells.

We present experimental data which establish the organometallic compounds vanadocene dichloride (VDC) and vanadocene acetylacetonate (VDacac) as potent anti-proliferative agents. We first examined the effects of VDC and VDacac on the rapid embryonic cell division and development of Zebrafish. Both compounds were capable of causing cell division block at the 8-16 cell stage of embryonic development followed by total cell fusion and developmental arrest. We next examined the effect of VDC and VDacac on proliferation of human breast cancer and glioblastoma cell lines using MTT assays. VDC inhibited the proliferation of the breast cancer cell line BT-20 as well as the glioblastoma cell line U373 in a concentration-dependent fashion with IC50 values of 11.0, 14.9 and 18.6 microM, respectively. VDacac inhibited cellular proliferation with IC50 values of 9.1, 26.9 and 35.5 microM, respectively. Whereas in vehicle-treated control cancer cells mitotic spindles were organized as a bipolar microtubule array and the DNA was organized on a metaphase plate, vanadocene-treated cancer cells had aberrant monopolar mitotic structures where microtubules were detected only on one side of the chromosomes and the chromosomes were arranged in a circular pattern. In contrast to control cells which showed a single focus of gamma-tubulin at each pole of the bipolar mitotic spindle, VDC- or VDacac-treated cells had two foci of gamma-tubulin on the same side of the chromosomes resulting in a broad centrosome at one pole. All monopolar spindles examined had two foci of gamma-tubulin labeling consistent with a mechanism in which the centrosomes duplicate but do not separate properly to form a bipolar spindle. These results provide unprecedented evidence that organometallic compounds can block cell division in human cancer cells by disrupting bipolar spindle formation. In accordance with these results vanadocene treatment caused an arrest at the G2/M phase of the cell cycle. This unique mechanism of anti-mitotic function warrants further development of vanadocene complexes as anti-cancer drugs.

Animals↗
PubMed1987

Nerve growth factor stimulation of mouse embryonal carcinoma cell migration.

Embryonal carcinoma cells localize to a specific array of target tissues including the male submaxillary gland following intracardiac injection. These target tissues or conditioned medium derived from them have been shown to stimulate the in vitro migration of embryonal carcinoma cells. Here we show that in vitro migration of mouse embryonal carcinoma cells is induced by the simultaneous presence of two different components. One of these is a specific requirement for a fibronectin substrate. The other component is present in male submaxillary conditioned medium and may be nerve growth factor (NGF). Migration of embryonal carcinoma cells on a fibronectin substrate could be induced by purified NGF, but not epidermal growth factor, and submaxillary conditioned medium contained very high levels of nerve outgrowth activity which could be blocked by anti-NGF antibody. Only the high molecular weight 7S NGF complex was active in inducing migration, while the low molecular weight 2.5S NGF inhibited migration. Neither type of NGF or submaxillary conditioned medium stimulated the in vitro growth of embryonal carcinoma cells. 7S NGF thus differentially affects murine embryonal carcinoma cells by inducing cell motility but not cell division. That embryonal carcinoma cells require 7S NGF for their migration in vitro raises the interesting possibility that these cells may respond similarly in vivo, and be stimulated by tissue-specific high molecular weight NGF molecules to migrate or extravasate into the parenchyma of target organs.

Animals↗
PubMed2001

The cell cycle machinery and asymmetric cell division of neural progenitors in the Drosophila embryonic central nervous system.

Asymmetric cell divisions can be mediated by the preferential segregation of intrinsic cell fate determinants into one of two sibling daughters. In dividing Drosophila neural progenitors the apical-basal orientation of the mitotic spindle, the basal cortical localization of the cell fate determinants Numb and/or Prospero as well as the coordination of these events are mediated by several proteins which include Bazooka (Baz), Inscuteable (Insc) and Partner of Inscuteable (Pins) which localize as an apical cortical complex starting at interphase. Here I will summarize data which suggest that the formation of this apical complex involves two distinct steps: (1) during the initiation of apical complex formation in interphase neuroblasts, there appears to be a hierarchical relation amongst these components where Baz recruits Insc and Baz/Insc in turn recruit Pins to the apical cortex/stalk; (2) while in delaminated mitotic neuroblasts the maintenance of the apical cortical localization of these proteins is dependent on the presence of all three components. Moreover, we show that the maintenance of this apical protein complex is essential for the correct execution of asymmetric division. Finally, the localization of the various asymmetrically localized proteins shows cell cycle dependence; however, the involvement of the cell cycle regulator in asymmetric cell divisions has not been previously shown. Here we present evidence from ongoing experiments which suggest a requirement for the key cell cycle regulator cdc2 in asymmetric cell divisions.

Animals↗
PubMed1992

The role of interleukin-6 in development.

Interleukin-6 is a member of a class of hormone-like molecules termed cytokines. The actions of IL-6 are highly pleiotropic. In adults IL-6 functions as a major mediator of inflammatory responses as well as inducing the synthesis of acute phase proteins by the liver following infection or injury. Based on in vitro and in vivo studies IL-6 also has important functions in regulating the development of multiple lineages of hemopoietic cells. It may also be an inflammatory mediator in the central nervous system. Although IL-6 has been found in early mouse embryos, its function has not yet been determined. Its expression by placental trophoblasts and maternal decidua suggests that it has some role in fetal-maternal interactions. Finally, the response of fetal hemopoietic progenitor cells to IL-6 suggests that IL-6 may have a broader action on the expansion and maturation of fetal precursors. New approaches such as those involving the disruption of the IL-6 gene in mice will be needed for a more complete understanding of IL-6's role in embryonic development.

Animals↗
PubMed1995

The ncl-1 gene and genetic mosaics of Caenorhabditis elegans.

A ncl-1 mutation results in enlarged nucleoli, which can be detected in nearly all cells of living animals by Nomarski microscopy. Spontaneous mitotic loss of a ncl-1(+)-containing free duplication in an otherwise homozygous ncl-1 mutant animal results in mosaicism for ncl-1 expression, and the patterns of mosaicism lead us to conclude that ncl-1 acts cell autonomously. The probability of mitotic loss of the duplication sDp3 is approximately constant over many cell divisions. About 60% of the losses of sDp3 at the first embryonic cell division involve nondisjunction. Frequencies of mitotic loss of different ncl-1(+)-bearing free duplications varied over a 200-fold range. The frequencies of mitotic loss were enhanced by a chromosomal him-10 mutation. We have used ncl-1 as a cell autonomous marker in the mosaic analysis of dpy-1 and lin-37. The focus of action of dpy-1 is in hypodermis. A mutation in lin-37 combined with a mutation in another gene results in a synthetic multivulva phenotype. We show that lin-37 acts cell nonautonomously and propose that it plays a role, along with the previously studied gene lin-15, in the generation of an intercellular signal by hyp7 that represses vulval development.

Alleles↗
PubMed2006

The turnip mutant of Arabidopsis reveals that LEAFY COTYLEDON1 expression mediates the effects of auxin and sugars to promote embryonic cell identity.

The transition from embryonic to vegetative growth marks an important developmental stage in the plant life cycle. The turnip (tnp) mutant was identified in a screen for modifiers of POLARIS expression, a gene required for normal root growth. Mapping and molecular characterization of tnp shows that it represents a gain-of-function mutant of LEAFY COTYLEDON1 (LEC1), due to a promoter mutation. This results in the ectopic expression of LEC1, but not of other LEC genes, in vegetative tissues. The LEC class of genes are known regulators of embryogenesis, involved in the control of embryonic cell identity by currently unknown mechanisms. Activation of the LEC-dependent pathway in tnp leads to the loss of hypocotyl epidermal cell marker expression and loss of SCARECROW expression in the endodermis, the ectopic accumulation of starch and lipids, and the up-regulation of early and late embryonic genes. tnp also shows partial deetiolation during dark growth. Penetrance of the mutant phenotype is strongly enhanced in the presence of exogenous auxin and sugars, but not by gibberellin or abscisic acid, and is antagonized by cytokinin. We propose that the role of LEC1 in embryonic cell fate control requires auxin and sucrose to promote cell division and embryonic differentiation.

1-Phosphatidylinositol 4-Kinase↗
PubMedDate not supplied

The molecular mechanism of fetal alcohol syndrome (FAS). I. Ethanol-induced growth suppression.

Of the birth defects associated with alcohol consumption during pregnancy, in situ growth retardation resulting in neonates that are small for gestational age is the most common observation in both humans and animal models. A variety of alcohol-induced alterations in maternal, placental and/or fetal physiology have been proposed as the basis for this retarded fetal growth. The molecular mechanism(s) of this retardation, however, is obscure; and it remains to be determined whether the growth suppression is the result of the action of ethanol or its metabolites on embryonic, maternal or placental tissue. Using the embryonic chick as a model which circumvents changes in maternal and placental function, we have measured ethanol-induced growth suppression as a function of embryonic age and ethanol dosage. The data suggest that ethanol per se suppresses the rate of cell division in embryonic tissue resulting in fewer cells/embryo for a given time of gestation. The suppression of cell division is proportional to the ethanol dose and appears to be related to ethanol-induced changes in the metabolism of the prostaglandin hormones and resulting changes in the cyclic-AMP levels of the developing embryos.

Alcohol Dehydrogenase↗