Biomedical subjects

Emmanuelle Nicolas

Publications and source records attributed to Emmanuelle Nicolas.

7 recordsLinked to original sources

PubMed2007

Assembly of hepatitis delta virus: particle characterization, including the ability to infect primary human hepatocytes.

Efficient assembly of hepatitis delta virus (HDV) was achieved by cotransfection of Huh7 cells with two plasmids: one to provide expression of the large, middle, and small envelope proteins of hepatitis B virus (HBV), the natural helper of HDV, and another to initiate replication of the HDV RNA genome. HDV released into the media was assayed for HDV RNA and HBV envelope proteins and characterized by rate-zonal sedimentation, immunoaffinity purification, electron microscopy, and the ability to infect primary human hepatocytes. Among the novel findings were that (i) immunostaining for delta antigen 6 days after infection with 300 genome equivalents (GE) per cell showed only 1% of cells as infected, but this was increased to 16% when 5% polyethylene glycol was present during infection; (ii) uninfected cells did not differ from infected cells in terms of albumin accumulation or the presence of E-cadherin at cell junctions; and (iii) sensitive quantitative real-time PCR assays detected HDV replication even when the multiplicity of infection was 0.2 GE/cell. In the future, this HDV assembly and infection system can be further developed to better understand the mechanisms shared by HBV and HDV for attachment and entry into host cells.

Antigens, Viral↗

PubMed2007

High-frequency epigenetic repression and silencing of retroviruses can be antagonized by histone deacetylase inhibitors and transcriptional activators, but uniform reactivation in cell clones is restricted by additional mechanisms.

Integrated retroviral DNA is subject to epigenetic gene silencing, but the viral and host cell properties that influence initiation, maintenance, and reactivation are not fully understood. Here we describe rapid and high-frequency epigenetic repression and silencing of integrated avian sarcoma virus (ASV)-based vector DNAs in human HeLa cells. Initial studies utilized a vector carrying the strong human cytomegalovirus (hCMV) immediate-early (IE) promoter to drive expression of a green fluorescent protein (GFP) reporter gene, and cells were sorted into two populations based on GFP expression [GFP(+) and GFP(-)]. Two potent epigenetic effects were observed: (i) a very broad distribution of GFP intensities among cells in the GFP(+) population as well as individual GFP(+) clones and (ii) high-frequency GFP reporter gene silencing in GFP(-) cells. We previously showed that histone deacetylases (HDACs) can associate with ASV DNA soon after infection and may act to repress viral transcription at the level of chromatin. Consistent with this finding, we report here that treatment with the histone deacetylase inhibitor trichostatin A (TSA) induces GFP activation in GFP(-) cells and can also increase GFP expression in GFP(+) cells. In the case of the GFP(-) populations, we found that after removal of TSA, GFP silencing was reestablished in a subset of cells. We used that finding to enrich for stable GFP(-) cell populations in which viral GFP reporter expression could be reactivated by TSA; furthermore, we found that the ability to isolate such populations was independent of the promoter driving the GFP gene. In such enriched cultures, hCMV IE-driven, but not the viral long terminal repeat-driven, silent GFP reporter expression could be reactivated by the transcriptional activator prostratin. Microscopy-based studies using synchronized cells revealed variegated reactivation in cell clones, indicating that secondary epigenetic effects can restrict reactivation from silencing. Furthermore we found that entry into S phase was not required for reactivation. We conclude that HDACs can act rapidly to initiate and maintain promoter-independent retroviral epigenetic repression and silencing but that reactivation can be restricted by additional mechanisms.

Clone Cells↗

PubMed2005

Drosophila central brain formation requires Robo proteins.

The Robo proteins have been extensively studied in the Drosophila embryonic ventral nerve cord, in which their expression level controls the midline crossing and optic lobe formation, but nothing is known about their activities during adult central brain formation. We have analyzed how Robo guidance cues influence central complex (CX) and mushroom body (MB) formation. Mutations of robo2 and robo3 confer a series of strong MB and CX defects. We found that the Robo2 and Robo3 proteins are expressed in two structures of the developing CX, the fan-shaped body (FB) and the noduli (NO), and by fibers across the central neuropile. We conclude that the Robo2 and Robo3 receptors play postembryonic roles during central brain formation.

Animals↗

PubMed2005

The zinc finger transcription factor Th-POK regulates CD4 versus CD8 T-cell lineage commitment.

Development of immature T-cell precursors (thymocytes) to either the CD4 helper or CD8 killer T-cell lineages correlates precisely with their T-cell receptor specificity for major histocompatibility complex class II or class I molecules, respectively, indicating that the process is carefully regulated. Although intensively studied owing to its importance in determining the composition of the mature T-cell compartment and as a general model of binary lineage decisions, the underlying molecular pathways remain obscure. We have previously reported a spontaneous mouse mutant (HD (helper deficient) mice) in which lineage commitment is specifically perturbed without affecting positive selection. Here we show that a point mutation in the zinc finger transcription factor Th-POK (T-helper-inducing POZ/Krüppel-like factor) is responsible for redirection of class-II-restricted thymocytes to the CD8 lineage in HD mice. Furthermore, we demonstrate that constitutive expression of this factor during thymic development leads to redirection of class-I-restricted thymocytes to the CD4 lineage, indicating that Th-POK is a master regulator of lineage commitment.

Amino Acid Sequence↗

PubMed2005

Enzymatic mutation detection technologies.

Mutation is as necessary for life as fidelity is in DNA replication. The study of mutations reveals the normal functions of genes, messages, proteins, the causes of many diseases, and the variability of responses among individuals. Indeed, recent mutations that have not yet become polymorphisms are often deleterious and pertinent to the disease history of afflicted individuals. This review discusses the principles behind a variety of methods for the detection of mutations and factors that should be considered in future methods design. One enzymatic approach in particular using orthologs of the CEL I nuclease that show high specificity for all mismatches, appears to be easy and robust. Further developments of this and other methods will allow mutation detection to become an integral component of individualized medicine.

Base Pair Mismatch↗

PubMed2004

Altered gene expression in phenotypically normal renal cells from carriers of tumor suppressor gene mutations.

BACKGROUND: The inherently complex signaling networks of tumors result from genetic and epigenetic alterations that occur during cancer initiation and progression. METHODS: In an attempt to identify early molecular changes associated with dominantly inherited predisposition to "two-hit" renal tumors, the expression profiles of primary cultures of phenotypically normal renal epithelial cells from individuals bearing a germline mutation in either the von Hippel-Lindau (VHL) or the tuberous sclerosis complex (TSC) gene were compared to that of renal epithelial cells from control nonmutation carriers by microarray analysis. RESULTS: Reliability of the microarray data from pooled samples was confirmed by real-time RT-PCR. Principal Component Analysis revealed substantial differences in the gene expression profiles of the renal epithelial cells from VHL and TSC mutation carriers. In several instances, the microarray data confirm our present knowledge of the cellular pathways affected by biallelic VHL and TSC mutations. CONCLUSIONS: These findings demonstrate that heterozygosity for a mutant tumor suppressor gene may alter the expression profiles of phenotypically normal epithelial cells in a gene-specific manner. Detectable effects of "one-hit" represent early molecular changes in tumorigenesis that may serve as targets for chemopreventive intervention.

Biomarkers, Tumor↗

PubMed2004

miR-122, a mammalian liver-specific microRNA, is processed from hcr mRNA and may downregulate the high affinity cationic amino acid transporter CAT-1.

These studies show that miR-122, a 22-nucleotide microRNA, is derived from a liver-specific noncoding polyadenylated RNA transcribed from the gene hcr. The exact sequence of miR-122 as well as the adjacent secondary structure within the hcr mRNA are conserved from mammalian species back to fish. Levels of miR-122 in the mouse liver increase to half maximal values around day 17 of embryogenesis, and reach near maximal levels of 50,000 copies per average cell before birth. Lewis et al. (2003) predicted the cationic amino acid transporter (CAT-1 or SLC7A1) as a miR-122 target. CAT-1 protein and its mRNA are expressed in all mammalian tissues but with lower levels in adult liver. Furthermore, during mouse liver development CAT-1 mRNA decreases in an almost inverse correlation with miR-122. Eight potential miR-122 target sites were predicted within the human CAT-1 mRNA, with six in the 3'-untranslated region. Using a reporter construct it was found that just three of the predicted sites, linked in a 400-nucleotide sequence from human CAT-1, acted with synergy and were sufficient to strongly inhibit protein synthesis and reduce mRNA levels. In summary, these studies followed the accumulation during development of miR-122 from its mRNA precursor, hcr, through to identification of what may be a specific mRNA target, CAT-1.

Animals↗