Figure 1.

Genome compression in Fugu. (A) Comparison between the murine and pufferfish SCL genes. (B) Three hypothetical ways that compression of the genome could affect regulatory sequence organization: (1) shrinking spacer regions between tissue-specific modules (no simplification) vs. simplification by (2) deletion of selected modules, (3) fusion of modules, or (4) broadening the activity of an upstream regulator for use in different tissues. In both A and B, rectangles above the lines represent genes (exons and introns together), with the gene of interest shown in black. Colored rectangles below the lines show the locations of enhancer modules that drive expression in different tissues. Colored arrows indicate the tissue-specific transcription factors that engage these respective enhancer modules. In B, three hypothetical tissues, and the transcription factors and modules active in each tissue respectively, are coded as orange, blue, and green.