In vivo mRNA expression of human housekeeping genes GAPDH and β-actin in biopsies of normal brain (NB), low-grade astrocytoma and glioblastoma. (A). Semiquantitative RT-PCR screening of tissue lysates from three normal brain, 11 astrocytoma and 11 glioblastoma samples. GAPDH and β-actin mRNA is homogenously expressed in all analysed samples. + = positive control, - = negative control using water as template. (B) Expression intensities of the PCR-bands were densitometrically evaluated. The bar graphs show GAPDH expression after normalization to the corresponding expression of β-actin. GAPDH was not regulated by the severely hypoxic tumor environment typical of glioblastoma.