Another important consideration in developing in situ hybridization technology involves the preservation of the cells or chromosomes. It is important to preserve the morphology (shape) and geographical site in the cell or chromosome where the target DNA or mRNA is located. Investigators may choose to use frozen sections, or they may treat cells or tissues with fixatives that cross-link proteins and stabilize cell structure. This prevents destruction during the hybridization and washing protocols.
Preserving DNA is easy because it is a highly stable molecule. However, preserving RNA is much more difficult because of a very stable enzyme called RNase, which may be found on glassware, in lab solutions, or on the hands of the cytochemist. RNase will quickly destroy any RNA in the cell or the RNA probe itself. Thus, investigators that work with RNA must use sterile techniques, gloves, and solutions to prevent RNase from contaminating and destroying the probe or tissue RNA.
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