Molecular signatures of selection on the human GLI3 associated central nervous system specific enhancers.

The zinc finger-containing transcription factor Gli3 is a key mediator of Hedgehog (Hh) signaling pathway. In vertebrates, Gli3 has widespread expression pattern during early embryonic development. Along the anteroposterior axes of the central nervous system (CNS), dorsoventral neural pattern elaboration is achieved through Hh mediated spatio-temporal deployment of Gli3 transcripts. Previously, we and others uncovered a set of enhancers that mediate many of the known aspects of Gli3 expression during neurogenesis. However, the potential role of Gli3 associated enhancers in trait evolution has not yet received any significant attention. Here, we investigate the evolutionary patterns of Gli3 associated CNS-specific enhancers that have been reported so far. A subset of these enhancers has undergone an accelerated rate of molecular evolution in the human lineage in comparison to other primates/mammals. These fast-evolving enhancers have acquired human-specific changes in transcription factor binding sites (TFBSs). These human-unique changes within subset of Gli3 associated CNS-specific enhancers were further validated as single nucleotide polymorphisms through 1000 Genome Project Phase 3 data. This work not only infers the molecular evolutionary patterns of Gli3 associated enhancers but also provides clues for putative genetic basis of the population-specificity of gene expression regulation.