3.1. Expression Array
The major application of DNA microarrays has been for the measurement of gene expression levels. RNA is extracted from cells, directly fluorescently labeled, and converted to labeled cDNA. The labeled cDNA is hybridized to the microarray, the array is washed, and the signal is detected by measuring fluorescence at each spot. The intensity of the signal on each spot is taken as a measure of the expression level of the corresponding gene [9,15].
Multiple studies have successfully used these techniques to evaluate gene expression levels in human diseases, including cancers. Shim et al. [16] performed an expression profile of genes associated with human cervical cancer using cDNA expression arrays. Rhee et al. [17] showed molecular evidence of the qualitative and quantitative high heterogeneity in gene expression among three human glioblastoma cell lines using cDNA expression arrays.