VILLINSKI, J.V.; DAYAL, S; KIYAMA, T; LIANG, S; KLEIN, W.H.; Univ. Texas, MD Anderson Cancer Center, Houston, TX: Dynamic cis-regulatory evolution in the Spec gene family involves the acquisition of a transcriptional enhancer and evidence of stabilizing selection.

The evolution of genetic regulatory interactions is considered a driving force in generating evolutionary novelty because alterations to the regulatory milieu can lead to new gene expression patterns. Consistent with this view, homologous genes with highly conserved expression patterns can have conserved aspects of regulation, even in cross-species comparisons. The Spec gene family in sea urchins presents an intriguing counterpoint, genes with a highly conserved expression pattern but profound enhancer divergence. Promoter regions are completely dissimilar between the Strongylocentrotus purpuratus Spec2a gene and its homolog in Lytechinus pictus, species which diverged ~40 million years ago. One conspicuous difference is a repeat sequence, termed the RSR enhancer element, which contributes to transcriptional control of at least 3 S. purpuratus Spec genes but is absent in L. pictus, which presumably has the ancestral regulatory control. Here we further dissect the evolutionary history of the Spec regulatory region by determining (i) the phylogenetic expansion of the Spec gene family and (ii) the emergence and proliferation of the RSR element, as inferred by cloning these sequences from phylogenetic intermediates of S. purpuratus and L. pictus. Our results indicate a complicated history of gene family proliferation and RSR functionality, however there is evidence for correlated evolution of Spec orthologs and the RSR regulatory cassette, which first became associated at least ~17 million years ago.