Sandrine Imbeaud

Deciphering cellular states of innate tumor drug responses.

BackgroundThe molecular mechanisms underlying innate tumor drug resistance, a major obstacle to successful cancer therapy, remain poorly understood. In colorectal cancer (CRC), molecular studies have focused on drug-selected tumor cell lines or individual candidate genes using samples derived from patients already treated with drugs, so that very little data are available prior to drug treatment.ResultsTranscriptional profiles of clinical samples collected from CRC patients prior to their exposure to a combined chemotherapy of folinic acid, 5-fluorouracil and irinotecan were established using microarrays. Vigilant experimental design, power simulations and robust statistics were used to restrain the rates of false negative and false positive hybridizations, allowing successful discrimination between drug resistance and sensitivity states with restricted sampling. A list of 679 genes was established that intrinsically differentiates, for the first time prior to drug exposure, subsequently diagnosed chemo-sensitive and resistant patients. Independent biological validation performed through quantitative PCR confirmed the expression pattern on two additional patients. Careful annotation of interconnected functional networks provided a unique representation of the cellular states underlying drug responses.ConclusionMolecular interaction networks are described that provide a solid foundation on which to anchor working hypotheses about mechanisms underlying in vivo innate tumor drug responses. These broad-spectrum cellular signatures represent a starting point from which by-pass chemotherapy schemes, targeting simultaneously several of the molecular mechanisms involved, may be developed for critical therapeutic intervention in CRC patients. The demonstrated power of this research strategy makes it generally applicable to other physiological and pathological situations.

‘The 39 steps’ in gene expression profiling: critical issues and proposed best practices for microarray experiments

Gene expression microarrays have been used widely to address increasingly complex biological questions and to produce an unprecedented amount of data, but have yet to realize their full potential. The interpretation of microarray data remains a major challenge because of the complexity of the underlying biological networks. To gather meaningful expression data, it is crucial to develop standardized approaches for vigilant study design, controlled annotation of resources, careful quality control of experiments, robust statistics, and data registration and storage. This article reviews the steps needed in the design and execution of valid microarray experiments so that global gene expression data can play a major role in the pursuit of future biological discoveries that will impact drug development.

SMARCA2 and other genome-wide supported schizophrenia-associated genes: regulation by REST/NRSF, network organization and primate-specific evolution

The SMARCA2 gene, which encodes BRM in the SWI/SNF chromatin-remodeling complex, was recently identified as being associated with schizophrenia (SZ) in a genome-wide approach. Polymorphisms in SMARCA2, associated with the disease, produce changes in the expression of the gene and/or in the encoded amino acid sequence. We show here that an SWI/SNF-centered network including the Smarca2 gene is modified by the down-regulation of REST/NRSF in a mouse neuronal cell line. REST/NRSF down-regulation also modifies the levels of Smarce1, Smarcd3 and SWI/SNF interactors (Hdac1, RcoR1 and Mecp2). Smarca2 down-regulation generates an abnormal dendritic spine morphology that is an intermediate phenotype of SZ. We further found that 8 (CSF2RA, HIST1H2BJ, NOTCH4, NRGN, SHOX, SMARCA2, TCF4 and ZNF804A) out of 10 genome-wide supported SZ-associated genes are part of an interacting network (including SMARCA2), 5 members of which encode transcription regulators. The expression of 3 (TCF4, SMARCA2 and CSF2RA) of the 10 genome-wide supported SZ-associated genes is modified when the REST/NRSF-SWI/SNF chromatin-remodeling complex is experimentally manipulated in mouse cell lines and in transgenic mouse models. The REST/NRSF-SWI/SNF deregulation also results in the differential expression of genes that are clustered in chromosomes suggesting the induction of genome-wide epigenetic changes. Finally, we found that SMARCA2 interactors and the genome-wide supported SZ-associated genes are considerably enriched in genes displaying positive selection in primates and in the human lineage which suggests the occurrence of novel protein interactions in primates. Altogether, these data identify the SWI/SNF chromatin-remodeling complex as a key component of the genetic architecture of SZ.

Response of human renal tubular cells to cyclosporine and sirolimus : A toxicogenomic study

The molecular mechanisms involved in the potentially nephrotoxic response of tubular cells to immunosuppressive drugs remain poorly understood. Transcriptional profiles of human proximal tubular cells exposed to cyclosporine A (CsA), sirolimus (SRL) or their combination, were established using oligonucleotide microarrays. Hierarchical clustering of genes implicated in fibrotic processes showed a clear distinction between expression profiles with CsA and CsA+SRL treatments on the one hand and SRL treatment on the other. Functional analysis found that CsA and CsA+SRL treatments preferentially alter biological processes located at the cell membrane, such as ion transport or signal transduction, whereas SRL modifies biological processes within the nucleus and related to transcriptional activity. Genome wide expression analysis suggested that CsA may induce an endoplasmic reticulum (ER) stress in tubular cells in vitro. Moreover we found that CsA exposure in vivo is associated with the upregulation of the ER stress marker BIP in kidney transplant biopsies. In conclusion, this toxicogenomic study highlights the molecular interaction networks that may contribute to the tubular response to CsA and SRL. These results may also offer a new working hypothesis for future research in the field of CsA nephrotoxicity. Further studies are needed to evaluate if ER stress detection in tubular cells in human biopsies can predict CsA nephrotoxicity.

Genome-wide gene expression profiling of fertilization competent mycelium in opposite mating types in the heterothallic fungus Podospora anserina.

Background Mating-type loci in yeasts and ascomycotan filamentous fungi (Pezizomycotina) encode master transcriptional factors that play a critical role in sexual development. Genome-wide analyses of mating-type-specification circuits and mating-type target genes are available in Saccharomyces cerevisiae and Schizosaccharomyces pombe; however, no such analyses have been performed in heterothallic (self-incompatible) Pezizomycotina. The heterothallic fungus Podospora anserina serves as a model for understanding the basic features of mating-type control. Its mat+ and mat− mating types are determined by dissimilar allelic sequences. The mat− sequence contains three genes, designated FMR1, SMR1 and SMR2, while the mat+ sequence contains one gene, FPR1. FMR1 and FPR1 are the major regulators of fertilization, and this study presents a genome-wide view of their target genes and analyzes their target gene regulation. Methodology/Principal Findings The transcriptomic profiles of the mat+ and mat− strains revealed 157 differentially transcribed genes, and transcriptomic analysis of fmr1− and fpr1− mutant strains was used to determine the regulatory actions exerted by FMR1 and FPR1 on these differentially transcribed genes. All possible combinations of transcription repression and/or activation by FMR1 and/or FPR1 were observed. Furthermore, 10 additional mating-type target genes were identified that were up- or down-regulated to the same level in mat+ and mat− strains. Of the 167 genes identified, 32 genes were selected for deletion, which resulted in the identification of two genes essential for the sexual cycle. Interspecies comparisons of mating-type target genes revealed significant numbers of orthologous pairs, although transcriptional profiles were not conserved between species. Conclusions/Significance This study represents the first comprehensive genome-wide analysis of mating-type direct and indirect target genes in a heterothallic filamentous fungus. Mating-type transcription factors have many more target genes than are found in yeasts and exert a much greater diversity of regulatory actions on target genes, most of which are not directly related to mating.

Self–organized living systems: conjunction of a stable organization with chaotic fluctuations in biological space–time

Living systems have paradoxical thermodynamic stability, the intrinsic property of self–organization, fluctuation and adaptation to their changing environment. Knowledge accumulated in the analytical reductionist framework has provided useful systematic descriptions of biological systems which appear to be insufficient to gain deep understanding of their behaviour in physiologic conditions and diseases. A state–of–the–art functional genomics study in yeast points to the current inability to appraise ‘biological noise’, leading to focus on few genes, transcripts and proteins subject to major detectable changes, while currently inaccessible small fluctuations may be major determinants of the behaviour of biological systems. We conjecture that biological systems self–organize because they operate as a conjunction between the relatively variable part of a stable organization and the relatively stable part of a chaotic network of fluctuations, and in a space with a changing number of dimensions: biological space–time. We propose to complement the precepts of the analytical reductionist framework with those of the biosystemic paradigm, in order to explore these conjectures for systems biology, combining in an iterative mode systemic modelling of biological systems, to generate hypotheses, with a high level of standardization of high–throughput experimental platforms, enabling detection of small changes of low–intensity signals, to test them.

The Human Anatomic Gene Expression Library (H-ANGEL), the H-Inv integrative display of human gene expression across disparate technologies and platforms

The Human Anatomic Gene Expression Library (H-ANGEL) is a resource for information concerning the anatomical distribution and expression of human gene transcripts. The tool contains protein expression data from multiple platforms that has been associated with both manually annotated full-length cDNAs from H-InvDB and RefSeq sequences. Of the H-Inv predicted genes, 18u2009897 have associated expression data generated by at least one platform. H-ANGEL utilizes categorized mRNA expression data from both publicly available and proprietary sources. It incorporates data generated by three types of methods from seven different platforms. The data are provided to the user in the form of a web-based viewer with numerous query options. H-ANGEL is updated with each new release of cDNA and genome sequence build. In future editions, we will incorporate the capability for expression data updates from existing and new platforms. H-ANGEL is accessible at http://www.jbirc.aist.go.jp/hinv/h-angel/.

A Functional and Regulatory Network Associated with PIP Expression in Human Breast Cancer

Background The PIP (prolactin-inducible protein) gene has been shown to be expressed in breast cancers, with contradictory results concerning its implication. As both the physiological role and the molecular pathways in which PIP is involved are poorly understood, we conducted combined gene expression profiling and network analysis studies on selected breast cancer cell lines presenting distinct PIP expression levels and hormonal receptor status, to explore the functional and regulatory network of PIP co-modulated genes. Principal Findings Microarray analysis allowed identification of genes co-modulated with PIP independently of modulations resulting from hormonal treatment or cell line heterogeneity. Relevant clusters of genes that can discriminate between [PIP+] and [PIP−] cells were identified. Functional and regulatory network analyses based on a knowledge database revealed a master network of PIP co-modulated genes, including many interconnecting oncogenes and tumor suppressor genes, half of which were detected as differentially expressed through high-precision measurements. The network identified appears associated with an inhibition of proliferation coupled with an increase of apoptosis and an enhancement of cell adhesion in breast cancer cell lines, and contains many genes with a STAT5 regulatory motif in their promoters. Conclusions Our global exploratory approach identified biological pathways modulated along with PIP expression, providing further support for its good prognostic value of disease-free survival in breast cancer. Moreover, our data pointed to the importance of a regulatory subnetwork associated with PIP expression in which STAT5 appears as a potential transcriptional regulator.

A general framework for optimization of probes for gene expression microarray and its application to the fungus Podospora anserina

BackgroundThe development of new microarray technologies makes custom long oligonucleotide arrays affordable for many experimental applications, notably gene expression analyses. Reliable results depend on probe design quality and selection. Probe design strategy should cope with the limited accuracy of de novo gene prediction programs, and annotation up-dating. We present a novel in silico procedure which addresses these issues and includes experimental screening, as an empirical approach is the best strategy to identify optimal probes in the in silico outcome.FindingsWe used four criteria for in silico probe selection: cross-hybridization, hairpin stability, probe location relative to coding sequence end and intron position. This latter criterion is critical when exon-intron gene structure predictions for intron-rich genes are inaccurate. For each coding sequence (CDS), we selected a sub-set of four probes. These probes were included in a test microarray, which was used to evaluate the hybridization behavior of each probe. The best probe for each CDS was selected according to three experimental criteria: signal-to-noise ratio, signal reproducibility, and representative signal intensities. This procedure was applied for the development of a gene expression Agilent platform for the filamentous fungus Podospora anserina and the selection of a single 60-mer probe for each of the 10,556 P. anserina CDS.ConclusionsA reliable gene expression microarray version based on the Agilent 44K platform was developed with four spot replicates of each probe to increase statistical significance of analysis.

Mutations in the Saccharomyces cerevisiae Kinase Cbk1p Lead to a Fertility Defect That Can Be Suppressed by the Absence of Brr1p or Mpt5p (Puf5p), Proteins Involved in RNA Metabolism

In Saccharomyces cerevisiae the protein kinase Cbk1p is a member of the regulation of Ace2p and cellular morphogenesis (RAM) network that is involved in cell separation after cytokinesis, cell integrity, and cell polarity. In cell separation, the RAM network promotes the daughter cell-specific localization of the transcription factor Ace2p, resulting in the asymmetric transcription of genes whose products are necessary to digest the septum joining the mother and the daughter cell. RAM and SSD1 play a role in the maintenance of cell integrity. In the presence of a wild-type SSD1 gene, deletion of any RAM component causes cell lysis. We show here that some mutations of CBK1 also lead to a reduced fertility and a reduced expression of some of the mating type-specific genes. As polarized growth is an integral part of the mating process, we have isolated suppressors of the fertility defect. Among these, mutations in BRR1 or MPT5 lead to a restoration of fertility and a more-or-less pronounced restoration of polarity; they also show genetic interactions with SSD1. Our experiments reveal a multilayered system controlling aspects of cell separation, cell integrity, mating, and polarized growth.