Expressive genomic hybridisation: gene expression profiling at the cytogenetic level.

Aims: To describe a cytogenetic technique suitable for the rapid assessment of global gene expression that is based on comparative genomic hybridisation (CGH), and to use it to understand the relation between genetic amplifications and gene expression.

Methods: Whereas traditional CGH uses DNA as test and reference in hybridisations, expressive genomic hybridisation (EGH) uses globally amplified mRNA as test and normal DNA as reference. EGH is a rapid and powerful tool for localising and studying global gene expression profiles and correlating them with loci of genetic amplifications using traditional CGH.

Results: EGH was used to correlate genetic amplifications detected by CGH with the expression profile of two independent cell lines-Colo320 and T47D. Although many amplifications resulted in overexpression, other amplifications were partially or completely silenced at the cytogenetic level.

Conclusion: This technique will assist in the analysis of overexpressed genes within amplicons and could resolve a controversial issue in cancer cytogenetics; namely, the relation between genetic amplifications and overexpression.