Figure 6

Summary of evolutionary insights provided in this study. The constructed molecular phylogenetic trees for Fas, FADD and Casp8 colored with green, red and blue lines, respectively, are shown together. Gene rearrangements and the appearance of divergent genes, domains, or domain architectures are indicated by an arrow at the appropriate evolutionary timepoint. Death receptors including Fas appear to be unique to vertebrates because no orthologs of death receptors have been identified in the decoded genomes of non-vertebrates [41,42,53,54]. Gene rearrangements of the segment including the fadd gene were detected by comparative gene mapping in the present study. In addition, the extended C-terminal portion of FADD, which is phosphorylated for the regulation of mitosis [43,44], is uniquely detected in mammals. Early during vertebrate evolution, the casp8 and related genes arose from tandem duplication events of an ancestral casp8 gene as described [34]. Based on our computational analysis, it was hypothesized that the card-casp8 gene was originally generated in the fish lineage by local duplication.