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G Keller

Publications and source records attributed to G Keller.

At least 109 records · Page 6Linked to original sources
PubMed1993

Effects of CCK8 and of the CCKB-selective agonist BC264 on extracellular dopamine content in the anterior and posterior nucleus accumbens: a microdialysis study in freely moving rats.

The effects of the local administration of cholecystokinin octapeptide (CCK8) in the posterior nucleus accumbens (N. Acc.) and of BC264 (a selective CCKB agonist) in the anterior N. Acc. on dopamine (DA) neurotransmission were studied in awake rats. Microdialysis was used to quantify the extracellular contents of DA and its two metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). In the posterior N. Acc., a perfusion of 10(-5) M CCK8 for 40 min (i.e. 25 pmol) increased the extracellular levels of DA, DOPAC and HVA. In contrast, 10(-4) M BC264 perfused for 40 min (i.e. 350 pmol) into the anterior N. Acc. reduced extracellular DA but did not modify DOPAC and HVA levels. These findings suggest that the CCK-DA interactions are different in various regions of the N. Acc. and emphasize the functional heterogeneity of the N. Acc., issuing in part from its particular DA innervation (mixed CCK-DA terminals only in the posterior region) but also from the distribution of the CCK fibers and binding sites in this nucleus. This microdialysis study, using perfusions of CCK compounds in the N. Acc. of freely moving rats, shows that the CCK system might play an important regulatory role in limbic DA function.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1993

Expression of a gene encoding a unique protein-tyrosine kinase within specific fetal- and adult-derived hematopoietic lineages.

A gene encoding a unique protein-tyrosine kinase was isolated by PCR from undifferentiated embryonic stem (ES) cells. The gene, Emsk (embryonic stem cell kinase), is expressed in a number of different lymphoid and myeloid hematopoietic lineages and has been shown to be identical to the recently isolated focal adhesion-associated kinase gene (Fadk). Within the nonlymphoid lineages analyzed, Emsk/Fadk was found to be expressed in primitive and definitive erythroid cells but not in mast cells or macrophages. All CD5+ (B-1a) B cells tested, as well as freshly isolated conventional (B-2) B cells, expressed readily detectable levels of Emsk/Fadk. Within the T-cell lineage, Emsk/Fadk was expressed in V gamma 5 gamma/delta cells as well as in immature alpha/beta cells found within the thymus. As the alpha/beta T-cell population matures and exits the thymus, expression of Emsk/Fadk appears to be down regulated. The expression pattern outlined here suggests a role for Emsk/Fadk in multiple stages of hematopoietic development and raises the possibility that the kinase encoded by this gene has a broader spectrum of activities than was initially suggested.

Amino Acid Sequence↗
PubMed1993

Nuclear type II estradiol binding sites and type I estrogen receptors in human endometrial cancer: a 5-year follow-up study.

Type II nuclear-estrogen binding sites (type II EBS) have been postulated to play a crucial regulatory role in estrogen-stimulated uterine growth. The pathogenesis of endometrial cancer is known to be connected to estrogens. However, there are no data on type II EBS in human endometrial cancer. Therefore, we investigated the presence of nuclear type II EBS and nuclear type I estrogen receptors (ER) by radioligand-binding assays in endometrial tumorous tissues (n = 135). Determination of cytoplasmic ER and progesterone receptor (PR) concentrations were also included in the study. Estradiol (E2) and progesterone (P) hormone levels in sera of patients were determined by RIAs. In addition, all data were analyzed on 5-year survival rates. Saturation analyses of 3H-E2 binding in crude nuclear pellets (n = 5) showed two types of estradiol binding: type I ER having high affinity and low capacity and type II EBS binding estradiol with lower affinity and high capacity in a positive cooperative fashion. The nuclear type II EBS and type I ER concentrations were significantly higher in cancers of increasing grade. In contrast, a significant decrease of cytoplasmic 3H-E2 binding was detected. Cytoplasmic PR binding capacities were high in G1 and G2, but low in G3 tumors. The 5-year survival data showed nuclear type I ER to have the best correlation for prognostic value (cut-off, 0.5 pmol/mg DNA), while type II EBS had no significant impact on it. Serum E2 concentrations decreased with tumors of higher grade, but were generally still higher than the control values. The serum P levels did not alter. None of the parameters investigated here differed from control values in adenoacanthoma (n = 6), suggesting a separate pathomechanism. As type II EBS are known to be stimulated by E2 under conditions that cause uterine hyperplasia, we concluded that the higher "runaway" nuclear type II EBS levels, in contrast with the lower serum estradiol concentrations, might be connected with the strong proliferative and invasive character of higher grade endometrial adenocarcinomas. This is the first demonstration of the presence of nuclear type II EBS and their possible pathological role in human endometrial cancer, and of the high prognostic significance of nuclear type I ER to identify a subgroup having a fatal form of the disease in a 5-year survival study.

Aged↗
PubMed1993

Human relaxin decreases collagen accumulation in vivo in two rodent models of fibrosis.

The reproductive hormone, relaxin, inhibits collagen synthesis in vitro by normal human dermal fibroblast. In the present study, recombinant human relaxin is shown to modulate collagen accumulation and organization by mesenchymal cells in vivo in two rodent models of fibrosis: 1) fibrotic infiltration of polyvinyl alcohol sponge implants in rats, and 2) capsule formation around implanted osmotic pumps in mice. In the sponge, relaxin inhibits collagen accumulation, a measured by hydroxyproline content, in a dose-responsive manner by up to 25-29% in animals receiving 30 ng/ml relaxin, a finding supported by a decrease in collagen-specific trichrome staining in sections of sponges from relaxin-treated animals. In mice, the capsules surrounding relaxin-containing pumps are thinner and less dense than are capsules from control pumps. Ultrastructurally, control capsules are composed of densely packed parallel arrays of collagen fibrils, whereas fibrils more frequently are not packed in parallel arrays and are less abundant in treated capsules.

Animals↗
PubMed1993

Hematopoietic commitment during embryonic stem cell differentiation in culture.

We report that embryonic stem cells efficiently undergo differentiation in vitro to mesoderm and hematopoietic cells and that this in vitro system recapitulates days 6.5 to 7.5 of mouse hematopoietic development. Embryonic stem cells differentiated as embryoid bodies (EBs) develop erythroid precursors by day 4 of differentiation, and by day 6, more than 85% of EBs contain such cells. A comparative reverse transcriptase-mediated polymerase chain reaction profile of marker genes for primitive endoderm (collagen alpha IV) and mesoderm (Brachyury) indicates that both cell types are present in the developing EBs as well in normal embryos prior to the onset of hematopoiesis. GATA-1, GATA-3, and vav are expressed in both the EBs and embryos just prior to and/or during the early onset of hematopoiesis, indicating that they could play a role in the early stages of hematopoietic development both in vivo and in vitro. The initial stages of hematopoietic development within the EBs occur in the absence of added growth factors and are not significantly influenced by the addition of a broad spectrum of factors, including interleukin-3 (IL-3), IL-1, IL-6, IL-11, erythropoietin, and Kit ligand. At days 10 and 14 of differentiation, EB hematopoiesis is significantly enhanced by the addition of both Kit ligand and IL-11 to the cultures. Kinetic analysis indicates that hematopoietic precursors develop within the EBs in an ordered pattern. Precursors of the primitive erythroid lineage appear first, approximately 24 h before precursors of the macrophage and definitive erythroid lineages. Bipotential neutrophil/macrophage and multilineage precursors appear next, and precursors of the mast cell lineage develop last. The kinetics of precursor development, as well as the growth factor responsiveness of these early cells, is similar to that found in the yolk sac and early fetal liver, indicating that the onset of hematopoiesis within the EBs parallels that found in the embryo.

Animals↗
PubMed1992

Factor-dependent erythroid cell lines derived from mice transplanted with hematopoietic cells expressing the v-src oncogene.

Transplantation of spleen cells from primary reconstituted mice expressing the v-src oncogene to secondary and tertiary irradiated recipients resulted in the emergence of erythroid precursors with a transformed phenotype. When cultured in methyl cellulose, these precursors generated colonies of undifferentiated cells that could be expanded into continuously growing factor-dependent cell lines in liquid culture. All lines tested had a similar phenotype and expressed the v-src oncogene. In addition they responded to factors that regulate normal erythroid development, namely erythropoietin (Epo), interleukin-3 (IL-3), and mast cell growth factor (MGF), the ligand to the c-kit encoded receptor. When cells from one of the lines were maintained in the absence of factor, a "factor independent" subpopulation emerged that appeared to grow in an autocrine fashion. Conditioned medium from these cells stimulated their own growth as well as the growth of broad spectrum of normal precursors. Studies with neutralizing antibodies indicated that the predominant colony-stimulating factor produced by these cells is IL-3.

Animals↗
PubMed1992

Experimental changes in mineral content of juvenile mouse femora.

Juvenile laboratory mice were exposed to hypergravity (8 g), burrowing exercise, swimming to exhaustion, an anabolic steroid, and swimming and an anabolic steroid for 30 days to determine the variability of skeletal mineralization during growth. Changes in mineralization were correlated with changes in bending strength. Experimental mouse femora were loaded to failure in a cantilever beam configuration to determine bending strength, and ashed to determine total mineral content. Between experimental groups, mineral content ranged from 66.0 to 71.2% with the greatest change from the control being a 4.7% decrease in mineralization in the male swimming exercise group (P less than 0.001). Within two age-matched experiments, the first showed that the group with the greatest decrease in mineralization also had the greatest reduction in bending strength (P less than 0.001). The second age-matched experiment showed that the group with the greatest reduction in mineralization had bending strength greatly reduced (P less than 0.001). However, in this experiment, the weakest femora were in the anabolic steroid group that did not have the mineral content reduced. We conclude that (1) mineralization of juvenile mouse femora is extremely variable given varied conditions of exercise or loading; (2) mineralization of normal bone is decreased more often and to a greater extent than increased from normal exercise controls; (3) the decrease in mineralization seen here can decrease bending strength; and (4) the decrease in mineralization seen was not caused by a decrease in a mechanical loading but was probably due to a corticosterone-mediated psychological stress response.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1992

Hematopoietic stem cells.

Recent studies indicate that hematopoietic stem cells that provide long-term reconstitution can be separated from more mature hematopoietic cells that provide radioprotection and short-term repopulation. With these findings it is now possible to design assays that will specifically measure long-term repopulating stem cells, as well as to develop culture systems that can be used to analyze the effects of known and putative novel cytokines on their growth and differentiation.

Animals↗
PubMed1992

Influence of metabolic inhibitors on the degradation of tight junctions in HT29 cells.

The human colon adenocarcinoma cell line HT 29 grows in culture without tight junctions (TJ). Tight junction strands of the fascia occludens type can be induced by treatment with proteases and are subsequently degraded during a period of about 3 h. Experiments using a variety of metabolic inhibitors such as 2-deoxyglucose, 2,4-dinitrophenol, and CCCP show that the degradation of TJ is retarded under conditions of ATP depletion. Thus it appears that the removal of TJ from the cell surface is an energy-dependent process. Moreover, DNP can specifically inhibit the degradation of TJ even in the absence of ATP depletion. The possible involvement of a proton gradient in the mechanism of TJ degradation is discussed.

2,4-Dinitrophenol↗
PubMed1992

Rescue of erythroid development in gene targeted GATA-1- mouse embryonic stem cells.

Development of definitive (fetal liver-derived) red cells is blocked by a targeted mutation in the gene encoding the transcription factor GATA-1. We used in vitro differentiation of GATA-1- mouse embryonic stem (ES) cells to reveal a requirement for GATA-1 during primitive (yolk sac-derived) erythropoiesis and to establish a rescue assay. We show that the block to development includes primitive, as well as definitive, erythroid cells and is complete at the level of globin RNA expression; that the introduction of a normal GATA-1 gene restores developmental potential both in vivo and in vitro; and that efficient rescue is dependent on a putative autoregulatory GATA-motif in the distal promoter. Use of in vitro differentiated ES cells bridges a gap between conventional approaches to gene function in cell lines and analysis of loss of function mutations in the whole animal.

Animals↗
PubMed1991

Fractionation of mouse bone marrow by adherence separates primitive hematopoietic stem cells from in vitro colony-forming cells and spleen colony-forming cells.

Fractionation of mouse bone marrow by adherence to tissue culture plastic was used to characterize the adhesive properties of hematopoietic stem (HS) cells capable of long-term reconstitution. The adherent fraction that represents approximately 13% of the total marrow population was virtually devoid of in vitro colony-forming cells and spleen colony-forming cells but did contain approximately 30% of the total HS cells recovered from the procedure. These cells could be detected by both the competitive repopulation assay and by repopulation of W/Wv recipients. In approximately 60% of the recipients from the competitive repopulation experiments, the contribution of the adherent marrow cells was relatively low early (8 to 10 weeks) after transplantation. With time, however, the hematopoietic contribution from these cells increased, reaching a stable level 20 to 30 weeks posttransplantation. In the remaining recipients (40%), the contribution from adherent cells was already significant within 8 to 10 weeks of transplantation and did not change dramatically throughout the course of the experiment. Adherent bone marrow containing significant numbers of HS cells was unable to protect mice from radiation death, indicating that these early cells in the absence of later-stage progenitors are unable to provide this function.

Alleles↗
PubMed1991

Multiple hematopoietic lineages develop from embryonic stem (ES) cells in culture.

When embryonic stem cells are cultured directly in semisolid media (methyl cellulose), they proliferate and differentiate to generate colonies known as embryoid bodies (EBs). These EBs consist of differentiated cells from a number of lineages including those of the hematopoietic system. Following 10 days of culture in the presence of 10% fetal calf serum, more than 40% of all EBs from three different ES cell lines, CCEG2, D3 and SQ1.2S8 contained visible erythropoietic cells (i.e. red with hemoglobin). Beta H1 (z globin) mRNA is detectable in EBs within 5 days of differentiation, whilst beta(maj)-globin RNA appears by day 6. In the presence of erythropoietin (Epo), the frequency of EBs with erythropoietic activity increases to greater than 60%; Epo also prolongs this erythropoietic activity. Interleukin-3 (IL-3) does not significantly increase the frequency of EBs that contain erythroid cells, but increases slightly the number of erythropoietic cells associated with them. In the presence of IL-3, in addition to cells of the erythroid lineage, macrophages, mast cells and in some instances neutrophils are found within differentiating EBs. The development of macrophages is significantly enhanced by the addition of IL-3 alone or in combination with IL-1 and M-CSF or GM-CSF. When well-differentiated EBs are allowed to attach onto tissue-culture plates and grown in the presence of IL-3, a long-term output of cells from the mast cell lineage is observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Initial experience with placental protein 4 (PP-4) as tumor marker in cervical and endometrial cancer.

PP-4, a recently characterized glycoprotein from human placenta was studied using a specific double-antibody radioimmunoassay in sera of 130 volunteers, 74 cervical cancer patients and 43 endometrial cancer patients. Elevated levels (greater than 3 micrograms/l) were found in 35 (47.3%) cervical cancer patients and in 18 (41.9%) endometrial cancer patients. Degree of elevation were not correlated with clinical stage, histology, and histological degree of differentiation. 36 patients with cervical cancer and 20 patients with endometrial cancer were monitored on two to seven occasions during four to 50 weeks. Rising, remaining unchanged of falling levels of PP-4 correlated with progression, stabilization or regression of disease 55.5% in patients with cervical and 65.0% in patients with endometrial cancer. During and some months after external telecobalt irradiation therapy wide range of PP-4 levels were observed in some patients. The study suggest that PP-4 can be regarded as a tumor associated protein which most likely can serve as tumor marker in cervical and endometrial cancer.

Annexin A5↗
PubMed1990

Life span of multipotential hematopoietic stem cells in vivo.

The findings reported in this study highlight several important features of the development of hematopoietic stem cells after transplantation into irradiated recipients. First, they demonstrate the existence of a class of primitive multipotential stem cells that can function for a significant portion of the lifetime of a mouse (15 mo). In addition, they clearly show that these primitive stem cells can be infected with recombinant retroviruses and thus would be appropriate targets for gene therapy in somatic tissues. Second, our data indicate that the progeny of some, but not all, of the primitive stem cells have fully expanded into the various hematopoietic lineages by 2 mo after reconstitution. Finally, our analysis of the secondary recipients provides strong evidence suggesting that the primitive stem cell population can actually clonally expand. Our current experiments are aimed at determining the extent to which this expansion can occur and whether or not this expansion can be influenced by exogenous factors.

Animals↗
PubMed1990

Cell-type control of membrane biogenesis induced by HMG-CoA reductase.

Quantitative increases in HMG-CoA reductase, the rate-limiting enzyme in sterol biosynthesis, induce membrane biogenesis in both yeast and mammalian cells. The subcellular organization of the resulting membrane differs in the two cell types: mammalian cells generate crystalloid endoplasmic reticulum whereas yeast cells assemble karmellae. We examined the consequences of heterologous expression of HMG-CoA reductase to distinguish features of this response that were cell-type specific from those that were isozyme-specific. This analysis demonstrated that membrane proliferation was induced in both mammalian and yeast cells by HMG-CoA reductase from either organism. However, the morphology of the induced membranes was determined by the cell type rather than the particular isozyme. Thus, both yeast and mammalian HMG-CoA reductase contained functional signals for membrane proliferation that were operational in either cell type, but the qualitative response to those signals was cell-type specific.

Animals↗