Non-invasive imaging of reporter gene expression offers a powerful tool for monitoring spatial and temporal expression in live animals (or people). One limitation of such techniques is the low expression of genes driven by tissue-specific promoters. In the December 4 Proceedings of the National Academy of Sciences, Iyer et al. describe using a two-step transcriptional amplification (TSTA) approach to amplify the signal for non-invasive detection (Proc Natl Acad Sci USA 2001, 98:14595-14600).

They designed a system in which the prostate-specific antigen (PSA) promoter drives the expression of GAL4-VP16 fusion proteins with strong transactivating properties. In the second step, GAL4-VP16 controls the expression of a marker gene, such as firefly luciferase, placed downstream of GAL4-response elements. They tested the system in LNCaP prostate cancer cells and could demonstrate tissue-specific, androgen-responsive marker gene regulation.

Iyer et al. also showed that the system could be used to detect...