Figure 7

Model for the evolution of syndecans in fish and tetrapods. The upper panel of the model shows the hypothesized ancestral genomic context of a single syndecan gene, originating in an ancestral chordate (chordate 2) subsequent to the divergence of the Urochordate lineage. The model assumes that four-fold paralogy was then set up in an ancestral vertebrate as a result of two rounds of whole-genome duplication. This process also sets up pairing within each set of paralogues. The lower right hand panel represents how the initial complete paralogy has degenerated through gene rearrangements in modern tetrapods. Fish underwent an additional round of genome duplication that would have generated additional paralogous pairs [58]. The lower left-hand panel represents the situation in two modern fish, in which only the two matrilin-3 paralogues have been retained from FSGD. The syndecan-1 locus appears to have been lost early in the fish lineage. Other gene rearrangements or losses appear specific to the zebrafish or pufferfish lineages.