mRNA may be derived from any species, including bacteria, fungi, plants or animals. The messenger RNA molecules (mRNA) contain between 400 to 10,000 or more nucleotides, the sequence of which serves to indicate the corresponding amino acid sequence of a protein.
Tissue Banks. The establishment of suitable tissue banks is a logical adjunct to any in-depth RNA analysis of human tissue; repositories must address issues of appropriate collection and storage and also ensure that the samples are accompanied by appropriate patient information, including treatment, outcome and epidemiological and family history data.
Microdissection. Diseased tissue contains a mixture of normal tissue, inflammatory cells, necrotic tissue and, in cancer samples, areas of different stages. All of these elements can combine to produce a complex RNA expression profile. Microdissection capability is thus critical for microarray studies involving tissues [33].Current protocols for fluorescent labeling of RNA demand large quantities of RNA. To obtain a pure material, laser-based microdis­section [34] has often been used.
Cell Lines. The process of obtaining large amounts of RNA from a homogeneous cell population is greatly simplified when using continuous cell lines. It is important to remember that most microarray analyses do not measure absolute levels of RNA but rather compare RNA levels between two samples.