32 research outputs found
Visible photodissociation spectroscopy of PAH cations and derivatives in the PIRENEA experiment
The electronic spectra of gas-phase cationic polycyclic aromatic hydrocarbons
(PAHs), trapped in the Fourier Transform Ion Cyclotron Resonance cell of the
PIRENEA experiment, have been measured by multiphoton dissociation spectroscopy
in the 430-480 nm spectral range using the radiation of a mid-band optical
parametric oscillator laser. We present here the spectra recorded for different
species of increasing size, namely the pyrene cation (C16H10+), the
1-methylpyrene cation (CH3-C16H9+), the coronene cation (C24H12+), and its
dehydrogenated derivative C24H10+. The experimental results are interpreted
with the help of time-dependent density functional theory calculations and
analysed using spectral information on the same species obtained from matrix
isolation spectroscopy data. A kinetic Monte Carlo code has also been used, in
the case of pyrene and coronene cations, to estimate the absorption
cross-sections of the measured electronic transitions. Gas-phase spectra of
highly reactive species such as dehydrogenated PAH cations are reported for the
first time
Quantitative Comparison of Constitutive Promoters in Human ES cells
BACKGROUND: Constitutive promoters that ensure sustained and high level gene expression are basic research tools that have a wide range of applications, including studies of human embryology and drug discovery in human embryonic stem cells (hESCs). Numerous cellular/viral promoters that ensure sustained gene expression in various cell types have been identified but systematic comparison of their activities in hESCs is still lacking. METHODOLOGY/PRINCIPAL FINDINGS: We have quantitatively compared promoter activities of five commonly used constitutive promoters, including the human β-actin promoter (ACTB), cytomegalovirus (CMV), elongation factor-1α, (EF1α), phosphoglycerate kinase (PGK) and ubiquitinC (UbC) in hESCs. Lentiviral gene transfer was used to ensure stable integration of promoter-eGFP constructs into the hESCs genome. Promoter activities were quantitatively compared in long term culture of undifferentiated hESCs and in their differentiated progenies. CONCLUSION/SIGNIFICANCE: The ACTB, EF1α and PGK promoters showed stable activities during long term culture of undifferentiated hESCs. The ACTB promoter was superior by maintaining expression in 75-80% of the cells after 50 days in culture. During embryoid body (EB) differentiation, promoter activities of all five promoters decreased. Although the EF1α promoter was downregulated in approximately 50% of the cells, it was the most stable promoter during differentiation. Gene expression analysis of differentiated eGFP+ and eGFP- cells indicate that promoter activities might be restricted to specific cell lineages, suggesting the need to carefully select optimal promoters for constitutive gene expression in differentiated hESCs
Pre-microRNA and Mature microRNA in Human Mitochondria
Chantier qualité GAInternational audienceBACKGROUND: Because of the central functions of the mitochondria in providing metabolic energy and initiating apoptosis on one hand and the role that microRNA (miRNA) play in gene expression, we hypothesized that some miRNA could be present in the mitochondria for post-transcriptomic regulation by RNA interference. We intend to identify miRNA localized in the mitochondria isolated from human skeletal primary muscular cells. METHODOLOGY/PRINCIPAL FINDINGS: To investigate the potential origin of mitochondrial miRNA, we in-silico searched for microRNA candidates in the mtDNA. Twenty five human pre-miRNA and 33 miRNA aligments (E-value35) for the smallest RNA input concentration and 204 miRNA for the maximum RNA input concentration. In silico analysis predicted 80 putative miRNA target sites in the mitochondrial genome (E-value<0.05). CONCLUSIONS/SIGNIFICANCE: The present study experimentally demonstrated for the first time the presence of pre-miRNA and miRNA in the human mitochondria isolated from skeletal muscular cells. A set of miRNA were significantly detected in mitochondria fraction. The origin of these pre-miRNA and miRNA should be further investigate to determine if they are imported from the cytosol and/or if they are partially processed in the mitochondria
a New Approach to Investigate PAH Derived Cations as DIB Carriers
International audiencePolycyclic aromatic hydrocarbons (PAHs) and their cations are considered as attractive candidates for the Diffuse Interstellar Bands, some discrete absorption features observed throughout the visible and near-infrared spectral range whose origin is still investigated. So far, not a single PAH species has been identified on the basis of a spectral agreement. This indicates either that the molecular diversity is very large or that the candidates that have been considered are not the correct ones. In particular, small/medium-sized PAHs are submitted to photodissociation under UV photons from stars. It is therefore of interest to characterize the spectroscopy of key breakdown products. These spectroscopic studies should be performed in conditions that mimic those found in interstellar space, that leads to additional experimental difficulties. We will describe the approach we are developing with the PIRENEA set-up and present results on 1-methylpyrene cation and derived species. Experimental measurements are guided by calculations based on density functional theory and its time-dependent implementation. F. Useli-Bacchitta, A. Bonnamy, G. Malloci, G. Mulas, D. Toublanc, and C. Joblin, Chem. Phys. 371 (2010), 16-23. Joint ANR project GASPARIM, ANR-10-BLAN-50