One of the best characteristics for the functional state of a given cell is its gene expression pattern. Cells belonging to different tissues, cells in different developmental or metabolic stages, cells under the influence of specific compounds, or cells within a carcinogenic process differ in their gene expression patterns and therefore in their mRNA pools. Currently, the most important technique for accurate quantification of gene expression is real-time fluorescent quantitative RT-PCR (Muller et al., 2002a). Reverse transcription (RT) followed by polymerase chain reaction (PCR) is the technique of choice to analyze mRNA expression derived from various sources. Real-time RT-PCR is highly sensitive and allows quantification of rare transcripts and small changes in gene expression. It is easy to perform, provides the necessary precision and produces reliable and rapid quantification results (Pfaffl, 2001). Many of the key proteins (e.g. cytokines and transcription factors) are found in such low abundance that real-time RT-PCR quantification of their mRNAs represents the only technique sensitive enough to reliably measure their expression in vivo, low copy number targets of interest for which alternative tests do not exist or do not have the required sensitivity, (Huggett et al., 2005a) RNA cannot serve as a template for PCR, the first step in a test RT-PCR is the reverse transcription of the RNA template into complementary DNA and followed by its exponential amplification in a PCR reaction. Typically, this involves the use of dedicated RNA and DNA-dependent DNA polymerases, either in separate (“two-enzyme/two-tube”) reactions or in single (“two-enzyme/one-tube”) reactions, since the use of dedicated enzymes with several correct...... middle of paper......polymerase chain reaction assays transcription rse." Journal of molecular endocrinology 25.2 (2000b): 169-193. (article provided)3 Huggett, J., et al. Real-time RT-PCR normalization; strategies and considerations." Genes and immunity 6.4 (2005a): 279-284.4. Huggett, J., et al. "Real-time RT-PCR normalization; strategies and considerations." Genes and immunity 6.4 (2005b): 279-284.5. Muller, Patrick Y., et al. "A Brief Technical Report on the Processing of Gene Expression Data Generated by Quantitative Real-Time RT-PCR." Biotechniques 32.6 (2002a): 1372-1379.6. “Brief technical report on the processing of gene expression data generated by quantitative RT-PCR.” new mathematical model for relative quantification in real-time RT-PCR research 29.9 (2001): e45-e45.