['lizbeth]

Transcriptomics is more than just another brilliant technical innovation. It promises to take us to a new level in the hunt for the genes that cause illness: using microarray technology we can discover the chemical basis for particular afflictions by studying the differences between healthy and diseases tissue as a function of gene expression. The logic is simple. We carry out microarray gene expression analysis on both normal and cancerous tissue, and spot the difference between the two, the genes being expressed in one and not the other. Once we can identify which genes are malfunctioning – either over- or underexpressing themselves in the cancerous tissue, for instance – we may be able to establish a target that can be attacked with pinpoint molecular therapies as opposed to broadly toxic radio-and chemotherapies that destroy health as well as diseased cells . . .

At Cold Spring Harbor Laboratory, Michael Wigler is using the method in yet another way: rather than adding RNA to a microarray and looking for gene expression, he is adding DNA from cancer cells to create a profile of the genetic diversity present in tumors. Many cancers are caused by chromosomal rearrangements – such as might occur when segments of a chromosome are inadvertently duplicated, leading to an excess in the number of genes that code for growth-promoting proteins. Other cancers arise due to the loss of genes coding for proteins that repress cell growth. Applying Wigler’s technique, clinicians biopsy cancerous and healthy tissues from the same person. DNA from the cancerous tissue is chemically tag with red dye white the DNA from the normal tissue is tagged green. Genes amplified in cancer cells are marked by red spots (because there are many more red-tagged molecules binding to that spot than green-tagged ones) while genes deleted in cancer cells show up as green spots on the microarray (because there is no red-tagged molecule to bind there). Such experiments already greatly expanded the list of genes know to contribute to breast cancer.