Lack of correct data format and comparability limits future integrative microarray research.
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Data Collection↗
Biomedical subjects
Rickard Sandberg
Publications and source records attributed to Rickard Sandberg.
Comparative microarray analysis.
Microarrays enable high-throughput parallel gene expression analysis, and their use has grown exponentially during the past decade. We are now in a position where individual experiments could benefit from using the swelling public data repositories to allow microarrays to progress from being a hypothesis-generating tool to a powerful resource that can be used to test hypothesis about biology. Comparative microarray analysis could better distinguish phenotypes from associated phenotypes; identify valid differentially expressed genes by combining many studies; test new hypothesis; and discover fundamental patterns of gene regulation. This review aims to describe the additional methodology needed for such comparative microarray analysis, and we identify and discuss a number of problems such as loss of published data, lack of annotations, and variable array quality, which need to be solved before comparative microarray analysis can be used in a more systematic and powerful manner.
Animals↗
The molecular portrait of in vitro growth by meta-analysis of gene-expression profiles.
BACKGROUND: Cell lines as model systems of tumors and tissues are essential in molecular biology, although they only approximate the properties of in vivo cells in tissues. Cell lines have been selected under in vitro conditions for a long period of time, affecting many specific cellular pathways and processes. RESULTS: To identify the transcriptional changes caused by long term in vitro selection, we performed a gene-expression meta-analysis and compared 60 tumor cell lines (of nine tissue origins) to 135 human tissue and 176 tumor tissue samples. Using significance analysis of microarrays we demonstrated that cell lines showed statistically significant differential expression of approximately 30% of the approximately 7,000 genes investigated compared to the tissues. Most of the differences were associated with the higher proliferation rate and the disrupted tissue organization in vitro. Thus, genes involved in cell-cycle progression, macromolecule processing and turnover, and energy metabolism were upregulated in cell lines, whereas cell adhesion molecules and membrane signaling proteins were downregulated. CONCLUSION: Detailed molecular understanding of how cells adapt to the in vitro environment is important, as it will both increase our understanding of tissue organization and result in a refined molecular portrait of proliferation. It will further indicate when to use immortalized cell lines, or when it is necessary to instead use three-dimensional cultures, primary cell cultures or tissue biopsies.
Cell Adhesion↗
Assessment of tumor characteristic gene expression in cell lines using a tissue similarity index (TSI).
The gene expression profiles of 60 cell lines, derived from nine different tissues, were compared with their corresponding in vivo tumors and tissues. Cell lines expressed few tissue-specific (2%) or tumor-specific (5%) genes when analyzed group-wise. A tissue similarity index (TSI) was designed based upon singular value decomposition that measured in vivo tumor characteristic gene expression in each cell line independently. Only 34 of the 60 cell lines received the highest TSI toward its tumor of origin. In addition, we identified the most appropriate cell lines to be used as model systems for different in vivo tumors. Seven cell lines were identified as being of another origin than the originally presumed one. The proposed TSI will likely become an important tool for the selection of the most appropriate cell lines in pharmaceutical screening programs and experimental and biomedical research.
Cell Line, Tumor↗
Gene expression perturbation in vitro--a growing case for three-dimensional (3D) culture systems.
Cells grown in vitro are dramatically perturbed by their new microenvironment. Analyses of genome-wide gene expression levels offer a first glance at which genes and pathways are affected in cell lines as compared to their tissues of origins. We have summarized available gene expression data and review how cell lines adapt to in vitro environments, to what degree they express markers of their tissues of origins and discuss how cells grown in three-dimensional (3D) cultures may have more physiological interactions with neighbouring cells and extracellular matrix. We will also discuss the interplay between malignant cells and stroma present in tumours but lacking in cell lines and how these differences might affect gene expression comparisons of cell lines to tumours. A model simulating impact of stromal cells on gene expression profiles is presented. Understanding the transcriptomes of cells grown in 2D and 3D cultures and how they compare to those of in vivo cells are important for improving cell line model systems and for the reconstituting of tissues in vitro.
Cell Adhesion↗
Quantifying the species-specificity in genomic signatures, synonymous codon choice, amino acid usage and G+C content.
Each prokaryote has a unique genomic signature as evidenced by a set of species-specific frequencies of short oligonucleotides. With respect to genomic signatures a bacterial genome is homogenous and the variation within a genome is smaller than the variations between genomes of different species. This study quantifies the species-specificity of genomic signatures in the complete genomes of 57 prokaryotes. The species-specificity in the genomic signature was related to the quantification of other sequence biases, such as G+C content, synonymous codon choice and amino acid usage. The results confirm that the genomic signature is genome-wide with high species-specificity in both coding and non-coding regions. In coding regions the species-specific bias in synonymous codon choice was comparable to the genomic signature, while the bias in amino acid usage only captured about 50% of the species-specific bias in the genomic signature. A correlation between the species-specificity in synonymous codon choice and amino acid usage was identified, in which proteins with species-specific amino acid usage were also coded with species-specific synonymous codon choice. However, we demonstrated that the G+C content captures only approximately 40% of the species-specificity in the genomic signature, and is insufficient to explain the species specificity in the non-coding regions. Thus, the species-specific bias in non-coding regions remains largely unknown. Further, we compared the genomic signature in relation to phylogenetic distance. This was performed in order to illustrate the feasibility of a hierarchical classification scheme in future applications of the described classification methodology in screening for horizontal gene transfer and biodiversity studies.
Amino Acids↗
Systems biology is taking off.
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Animals↗
Antisense PNA effects in Escherichia coli are limited by the outer-membrane LPS layer.
Antisense peptide nucleic acids (PNAs) can inhibit Escherichia coli gene expression and cell growth through sequence-specific RNA binding, and this opens possibilities for novel anti-infective agents and tools for microbial functional genomics. However, the cellular effects of PNAs are limited relative to effects in cell extracts, presumably because of cell barrier components such as the outer-membrane lipopolysaccharide (LPS) layer or drug efflux pumps, both of which function to exclude antibiotics and other foreign molecules. To evaluate the importance of such cellular factors on PNA effects, the authors developed a positive assay for antisense inhibition by targeting the lac operon repressor and compared PNA susceptibilities in mutant and wild-type E. coli by assessing lacZ induction. Strains with defective LPS (AS19 and D22) were more permeable to the antibiotic nitrocefin and more susceptible to PNA than the wild-type. Also, PNA potency was improved in wild-type cells grown in the presence of certain cell-wall-permeabilizing agents. In contrast, the activities of the Acr and Emr drug efflux pumps were not found to affect PNA susceptibility. The results show that the LPS layer is a major barrier against cell entry, but PNAs that can enter E. coli are likely to remain active inside cells.
Bacterial Proteins↗