Figure 7.

A model for Dlx gene regulatory evolution. A summary of the expression of the four P. marinus Dlx genes is shown under “Modern Lampreys.” Comparisons of these expression patterns with those of several gnathostome systems (“Modern Gnathostomes”) and amphioxus (“Euchordate Ancestor”) suggest that several sites of Dlx expression evolved near the time of vertebrate origins (“Vertebrate Ancestor”). These include localized expression in the forebrain, sensory placodes, pharyngeal arches, and the dorsal fin fold. Modern gnathostomes appear to have lost Dlx expression in the somites, but co-opted Dlx function during the origin of limbs and jaws.