Differential Display to Define Molecular Markers and Genes That Mediate Malignancy

Differential display is a powerful way to identify alterations in gene expressron that can be contrasted by different states or treatments in side-by-side comparisons (1 ). An inherent strength of the polymerase chain reaction (PCR)-based differential-display approach is that only a very modest amount of starting material is needed. For example, DNAs from untreated and treated matched preparations are run side-by-side so that bands that have been induced are absent in the untreated preparation and displayed prominently in the treated lane, while repressed gene bands are noted by their absence in the treated lane. As few as 2 μg of total RNA is theoretically sufficient for displaying all genes induced by any single treatment. Signals selected from differential-display gels are then used to screen an expression library for the full-length cDNA Thus, the differential-display approach has the potential for Identifying individual genes that correspond to different biological states or respond to different treatments. These identifications are then followed by efforts to determine if the full-length cDNAs that are displayed will introduce the correct responses when transfected to appropriate test cells. This approach has been used to successfully identify:

1.	Genes expressed in human breast carcmoma vs mammary epithellal cells (2 );
2.	A candidate tumor suppressor gene in human mammary eplthelial cells (3 ),
3.	The gene for the M2 subumt of ribonucleotide reductase in premalignant breast epithellal lessons (4 ),
4.	A downstream target gene in the ras signaling pathway (5 );
5.	Genes drfferentlally expressed in human ovanan carcinoma (6 );
6.	Genes expressed in the later stages of liver regeneration, including the ribosomal protein S24 (7 ),
7.	Genes for the histocompatibility antigen (HLA-DR), laminin B2, melanoma inhibitory activity, and tissue inhibitor metalloproteinase-3 (8 ),
8.	Homeobox genes in tobacco (9 ); and
9.	The cytokeratin endo A gene and the α subunit of mitochondrial F1 , adenosine triphosphate (ATP) synthase in mouse preimplantation development (10 )