![]() ![]() ![]() In younger fish, these spatial shifts in enhancer activity are less pronounced. ![]() In older fish, the two alleles drive partially overlapping expression in both mesenchyme and epithelium of developing teeth, but the freshwater enhancer drives a reduced mesenchymal domain and a larger epithelial domain relative to the marine enhancer. Here, we use a bicistronic reporter construct containing a genetic insulator and a pair of reciprocal two-color transgenic reporter lines to compare enhancer activity of marine and freshwater alleles of this enhancer. Previous work identified a series of polymorphisms within an intronic enhancer of the Bone morphogenetic protein 6 ( Bmp6) gene that are associated with evolved tooth gain, a derived increase in freshwater tooth number that arises late in development. ![]() Threespine sticklebacks ( Gasterosteus aculeatus) are a robust system for studying enhancer evolution due to abundant natural genetic variation, a diversity of evolved phenotypes between ancestral marine and derived freshwater forms, and the tractability of transgenic techniques. Mutations in enhancers have been shown to often underlie natural variation but the evolved differences in enhancer activity can be difficult to identify in vivo. ![]()
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