Figure 2. GeNorm™ analysis. The most stable reference genes were selected from the four most commonly used housekeeping genes (Gapdh, Actb, 18s rRNA, and Hprt1) using the geNorm™ software. They were systematically compared with each other, and the resulting average expression stability plot was used to rank each housekeeping gene in order of expression stability. The genes with the lower average expression level stability (M) values are considered to have more stable expression levels.