G

For gene expression analyses, target probes immobilized on the chips are hybridized with labeled mRNA from treated cells or different cell types to assess the expression activity of the genes represented on the chip. Arrays used for this application are classifie as expression arrays.12 Expression arrays measure transcript or protein production relative to a reference control isolated from untreated or normal specimens (Fig. 6-26).

Another application of array technology is comparative genome hybridization (array CGH). This method is used to screen the genome or specific genomic loci for deletions and amplifications.13 For this method, genomic DNA is isolated, fragmented, and labeled for hybridization on the chip (Fig. 6-27). This type of method is analogous to the cytogenetic technique done on metaphase chromosomes. Array CGH can provide higher resolution and more defined genetic information than traditional cytogenetic analysis, but it is limited to the analysis of loci represented on the chip. Genomic arrays can be performed on fixed tissue and limiting samples. Methods have been developed to globally amplify genomic DNA to enhance CGH analysis.14,15 Reading microarrays requires a fluorescent reader and analysis software. After determination of background and normalization with standards included on the array, the software averages the signal intensity from duplicate or triplicate sample data. The results are reported as a relative amount of the reference and test signals. Depending on the program, vari-

Control

Treated

Control

Treated

Control

Treated

Single color fluorescent labeling

Single color fluorescent labeling

Hybridize fluorescent | labeling

^ Hybridize J

Was this article helpful?

0 0

Post a comment