Role of Notch signaling in cell-fate determination of human mammary stem/progenitor cells

INTRODUCTION: Notch signaling has been implicated in the regulation of cell-fate decisions such as self-renewal of adult stem cells and differentiation of progenitor cells along a particular lineage. Moreover, depending on the cellular and developmental context, the Notch pathway acts as a regulator of cell survival and cell proliferation. Abnormal expression of Notch receptors has been found in different types of epithelial metaplastic lesions and neoplastic lesions, suggesting that Notch may act as a proto-oncogene. The vertebrate Notch1 and Notch4 homologs are involved in normal development of the mammary gland, and mutated forms of these genes are associated with development of mouse mammary tumors. METHODS: In order to determine the role of Notch signaling in mammary cell-fate determination, we have utilized a newly described in vitro system in which mammary stem/progenitor cells can be cultured in suspension as nonadherent 'mammospheres'. Notch signaling was activated using exogenous ligands, or was inhibited using previously characterized Notch signaling antagonists. RESULTS: Utilizing this system, we demonstrate that Notch signaling can act on mammary stem cells to promote self-renewal and on early progenitor cells to promote their proliferation, as demonstrated by a 10-fold increase in secondary mammosphere formation upon addition of a Notch-activating DSL peptide. In addition to acting on stem cells, Notch signaling is also able to act on multipotent progenitor cells, facilitating myoepithelial lineage-specific commitment and proliferation. Stimulation of this pathway also promotes branching morphogenesis in three-dimensional Matrigel cultures. These effects are completely inhibited by a Notch4 blocking antibody or a gamma secretase inhibitor that blocks Notch processing. In contrast to the effects of Notch signaling on mammary stem/progenitor cells, modulation of this pathway has no discernable effect on fully committed, differentiated, mammary epithelial cells. CONCLUSION: These studies suggest that Notch signaling plays a critical role in normal human mammary development by acting on both stem cells and progenitor cells, affecting self-renewal and lineage-specific differentiation. Based on these findings we propose that abnormal Notch signaling may contribute to mammary carcinogenesis by deregulating the self-renewal of normal mammary stem cells

Structure-Function Analysis of STRUBBELIG, an Arabidopsis Atypical Receptor-Like Kinase Involved in Tissue Morphogenesis

Tissue morphogenesis in plants requires the coordination of cellular behavior across clonally distinct histogenic layers. The underlying signaling mechanisms are presently being unraveled and are known to include the cell surface leucine-rich repeat receptor-like kinase STRUBBELIG in Arabidopsis. To understand better its mode of action an extensive structure-function analysis of STRUBBELIG was performed. The phenotypes of 20 EMS and T-DNA-induced strubbelig alleles were assessed and homology modeling was applied to rationalize their possible effects on STRUBBELIG protein structure. The analysis was complemented by phenotypic, cell biological, and pharmacological investigations of a strubbelig null allele carrying genomic rescue constructs encoding fusions between various mutated STRUBBELIG proteins and GFP. The results indicate that STRUBBELIG accepts quite some sequence variation, reveal the biological importance for the STRUBBELIG N-capping domain, and reinforce the notion that kinase activity is not essential for its function in vivo. Furthermore, individual protein domains of STRUBBELIG cannot be related to specific STRUBBELIG-dependent biological processes suggesting that process specificity is mediated by factors acting together with or downstream of STRUBBELIG. In addition, the evidence indicates that biogenesis of a functional STRUBBELIG receptor is subject to endoplasmic reticulum-mediated quality control, and that an MG132-sensitive process regulates its stability. Finally, STRUBBELIG and the receptor-like kinase gene ERECTA interact synergistically in the control of internode length. The data provide genetic and molecular insight into how STRUBBELIG regulates intercellular communication in tissue morphogenesis

Oxidation kinetics of n-nonane: Measurements and modeling of ignition delay times and product concentrations

International audienceOxidation of n-nonane (n-C9H20) under conditions of high dilution (>97% inert) has been studied over a broad range of temperature (530 < T (K) < 1591) and equivalence ratio (0.5, 1.0, 2.0) at pressures near 1 and 10 atm using shock-tube and jet-stirred reactor facilities. Excited-state hydroxyl radical (OH*) time histories were measured using emission spectroscopy of OH behind reflected shock waves from which ignition delay and peak formation times were extracted. Temperature-dependent species concentrations were measured using gas chromatography, FTIR, TCD, and FID of jet-stirred reactor combustion products. Ignition delay times show a strong dependence on equivalence ratio, increasing by a factor of nearly 5 at both 1 and 10.4 atm. An overall ignition delay time correlation was constructed, revealing a pressure dependence of P^^0.48. Experimental data from both facilities were utilized to develop and validate a chemical kinetics mechanism for n-nonane oxidation. Kinetic model predictions of ignitiondelay time compare well, particularly for the lean and stoichiometric mixtures. Jet-stirred reactor data show excellent overall agreement with major species, as well as alkanes and alkenes present in the combustion products. Alkenes up to C9 were produced from n-nonane oxidation and ethylene, a dominant product of n-nonane thermal decomposition, is identified as the most abundant among them. The present studyprovides an extensive series of fundamental measurements on n-nonane oxidation, resulting in the formulation of a mechanism used to describe and predict associated reaction kinetics

Kinetics of Oxidation of a Reformulated Jet Fuel (1-Hexanol/Jet A-1) in a Jet-Stirred Reactor: Experimental and Modeling Study

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Tropospheric multiphase chemistry of 2,5- and 2,6-dimethylphenols: determination of the mass accommodation coefficients and the Henry's law constants.

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Experimental Study of the Oxidation of N -Tetradecane in a Jet-Stirred Reactor (JSR) and Detailed Chemical Kinetic Modeling

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Oxidation of commercial and surrogate bio-Diesel fuels (B30) in a jet-stirred reactor at elevated pressure: Experimental and modeling kinetic study

International audienceThe oxidation of a commercial B30 (30% FAME by vol.) bio-Diesel fuel and a B30 bio-Diesel surrogate fuel (49% n-decane, CAS 124-18-5; 21% 1-methylnaphthalene, CAS 90-12-0; 30% methyl octanoate, CAS 111-11-5, in mole) was performed using a pressurized fused-silica jet-stirred reactor under the same initial experimental conditions (560–1030 K, 6 and 10 atm, equivalence ratios of 0.25–1.5, 10,300 ppm of carbon). The results of this series of experiments consisted of concentration profiles of reactants, stable intermediates and products measured as a function of temperature by low-pressure probe sampling followed by Fourier transform infrared absorption spectrometry and gas chromatography analyses. The results obtained with the commercial and surrogate B30 mixtures were compared with each other, showing that the mixture n-decane/1-methylnaphthalene/methyl octanoate 49/21/30% in mole is an excellent simple B30 Diesel fuel surrogate. A detailed chemical kinetic reaction mechanism consisting of 7748 reactions involving 1964 species was proposed based on previous chemical kinetic reaction mechanisms for the oxidation of n-decane, methyl octanoate, and 1-methylnaphthalene under similar conditions. The kinetic modeling showed reasonable agreement between the present data and computations over the entire range of conditions considered in this study

A wide-ranging kinetic modeling study of methyl butanoate combustion

International audienceA detailed chemical kinetic model has been used to study methyl butanoate (a model compound for biodiesel fuels) oxidation over a wide range of conditions. New experimental results obtained in a jet stirred reactor (JSR) at 0.101 MPa, Φ = 1.13 and 800 < T (K) < 1350 were obtained and used to test and modify an earlier model. In addition, new experimental data generated in an opposed-flow diffusion flame at 0.101 MPa and in the Princeton variable pressure flow reactor (VPFR) at 1.266 MPa, 0.35 < Φ < 1.5 and 500 < T (K) < 900 are presented and compared against the revised model. The numerical model consists of 295 chemical species and 1498 chemical reactions and gives a good description of the data. Experimentally, the oxidation of methyl butanoate shows very little low temperature and negative temperature coefficient behaviour, with hot ignition occurring at about 800 K. Modeling results show similar diminished low temperature oxidation character, but reasonably reproduce hot ignition behaviour found in the VPFR. At higher temperature conditions, the model well describes the intermediate species found in the jet stirred reactor and in opposed flow diffusion flame experiments