The lac-z reporter gene: A tool for in vitro studies of malignant glioma cell invasion

A reporter gene (lac-z) was introduced into rat (BT4C) and human (D-54 MG) proliferating glioma cell lines by means of liposomal transfection. Lac-z-transfected glioma cells were first cultured as multicellular spheroids and then confronted with fetal brain aggregates. After various intervals the lac-z reporter gene product, bacterial β-galactosidase, was histochemically detected in the cocultures. β-Galactosidase was only detected in the glioma cells which showed an intense blue staining, which made them easily distinguishable from fetal tissue. Both glioma cell lines showed a clear pattern of migration and increasing invasion with time as the tumor cells infiltrated and destroyed the brain aggregates. Spheroid growth curves showed no significant differences between transfected and nontransfected cell lines. Likewise, flow cytometry measurements revealed no significant changes in ploidy between transfected and nontransfected rat glioma cells. In comparison, a shift in ploidy was observed in the human glioma cells after lac-z transfection. Stable integration of the lac-z gene into tumor cells was verified by Southern blot analysis. The results indicate that transfection of the lac-z reporter gene into glioma cells lines does not affect their growth or invasion potential in vitro. The lac-z reporter gene can thus be exploited to facilitate visualization of single migrating tumor cells and quantification of tumor invasion in in vitro coculture systems.