Peng Liang & Arthur B. Pardee 
Differential Display Methods and Protocols 

Of the estimated 80, 000 individual genes encoded by the human genome, approximately 10-20% are expressed by the average cell. This subset is a major determinant of a cell’s properties. In addition to the control of cellular phenotype and the normal physiological processes of an organism, an alt- ation in gene expression (either induction or repression) underlies the etiology of numerous, diverse pathological processes. Therefore understanding the mechanisms of these normal and pathological processes requires identifi- tion, isolation, and characterization of differentially expressed genes. This requirement has led to the development of a variety of techniques capable of identifying small quantities of proteins or m RNAs that are key to a multitude of diverse pathological processes. Differential display (DD) is an emerging "fingerprinting" technology that facilitates the identification of m RNAs in a cell or tissue, in particular those with altered expression resulting from diff- ences in transcription or m RNA degradation. In contrast to conventional te- niques, DD can be used to compare m RNA expressions in many samples created under multiple experimental conditions. DD was conceived because of the inadequacy of two-dimensional p- tein display. The latter method was used in this laboratory during the 1980s in an attempt to identify the restriction point protein, proposed from cell biology as a key molecule controlling cell proliferation.