Heatmap of log2 arbitrary expression values. Relative expression indexes (REI) were calculated for the dataset. For each gene, a mean expression level was calculated from the four samples, and the REI corresponds to the ratio between the expression level measured for a given sample and the mean reference. Log2 transformed data were subjected to MeV software for visualization. Each gene is represented by a row of colored boxes (corresponding to REI values) and a single column represents each stage