A A: suitable, B: applicable, C: not applicable. 1 Time-course assay is suitable for extra-cellular reporters compared to intra-cellular reporters. 2 An in vivo imaging system is needed to detect luciferase and GFP. 3 A tissue specific transgenic mouse is needed to detect specific tissue expression of extra-cellular reporters. 4 Chemiluminescence is more sensitive than fluorescence. CAT: Chloramphenicol acetyltransferase; β-Gal: β-Galactosidase; GFP: green fluorescent protein; SEAP: secreted alkaline phosphatase; MetLuc: Metridia longa luciferase; HTS: high throughput screening; CCD: charge-coupled device.