High-sensitivity detection methods for low-abundance RNA species: applications for functional genomics research

Gene expression analysis has facilitated a more complete understanding of the molecular biology of cellular processes and how variations of RNA expression are useful for the classification of various diseases. Furthermore, recent analysis of a variety of noncoding RNAs, such as microRNAs, has demonstrated that these RNAs play an important role in many cellular events, including cell differentiation and death, and may also serve as biological markers for disease. Besides helping in the understanding of diseases, RNA analysis is used in drug discovery, patient prognosis and treatment evaluation. One obstacle left to overcome is the amount of material required for the analysis, particularly when trying to extract information from precious, limited, clinical samples. Here we review the many approaches scientists take to either amplify the amount of RNA or amplify the signal generated from small amounts of RNA.