Figure 2. Four dimensional tomographic imaging of gene expression patterns and Principal Component Analysis of images. (A) For each of the 254 embryo samples (120 genes) in the EPIC database and each of the 210 time steps, we conducted tomographic imaging with the virtual embryo along each of the 3 body axes. (B) The genes showed the dynamically changing expression patterns during embryogenesis. The central section images of the pha-4 gene, for instance, was upregulated at the later stage of time step 137 to begin with the processes of pharynx and intestine organogenesis. (C) Principal Component Analysis of the images identified the tissue regions where gene expression levels varied most significantly, as highlighted in bright yellow colors. The leading Principal Component images were presented for each of the 3-body axis.