Toshihide Suzuki, Paul J.

The study of mammalian gene expres-sion is often carried out at the level of mRNA. In such analyses, one usually mea-sures the amount of an mRNA of interest un-der different conditions such as stress, growth, development, cell and tissue local-ization or as part of an evaluation of the ef-fects of gene transfection. A variety of tech-niques exist to measure gene expression and most commonly involve Northern hybridiza-tion analysis, ribonuclease protection or RT-PCR. Common to all of these assays is the inclusion of a so-called loading or inter-nal control (i.e., analysis of an mRNA that does not change in relative abundance dur-ing the course of treatments). Here, we dis-cuss the uses and pitfalls of the most popu-lar of these controls, glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and b-actin, with special emphasis on precau-tions associated with the use of GAPDH