When it comes to mouse tissue samples, not all loading control proteins are expressed equally. For example, there are relatively low amounts of β-actin in mouse heart and relatively low amounts of GAPDH in mouse small intestine. Plus, under certain experimental conditions, the protein levels of some loading control proteins can be affected. β-actin mRNA levels, for instance, can change with insulin treatments in some tissues. It is important to do research in advance and determine what the best loading control is for your sample type and experiment.