Focus formation assay illustrating the oncogenic potential of

GSH2. Monolayer of cells overexpressing wild-typeGSH2 (A,B: 2 different frames of the same dish), indicating a high number (> 200 foci/10 cm dish) of relatively small foci, compared with the monolayer of cells transduced with the empty MSCV vector (C). In the latter case, spontanous foci (0-10 foci/10 cm dish) were observed. Typically, these foci were relatively larger than the foci observed with GSH2 overexpression (compare panels A and B with D). The N-terminal deletion mutant and homeobox deletion mutant of GSH2 induced only a low number of foci, similar to the empty vector. The monolayers observed with these construct are shown in panels E and F. (A-F: scale bar = 2 mm). The morphology and size of the foci observed for these constructs were similar to the foci observed for the empty vector. Although the cells overexpressingGSH2 generated relatively small foci, higher-magnification pictures (G,H) clearly show the presence of transformed cells growing on top of the monolayer.