RESEARCH ARTICLE Molecular Cloning, Functional Characterization, and Evolutionary Analysis of Vitamin D Receptors Isolated from Basal Vertebrates

The vertebrate genome is a result of two rapid and successive rounds of whole genome du-plication, referred to as 1R and 2R. Furthermore, teleost fish have undergone a third whole genome duplication (3R) specific to their lineage, resulting in the retention of multiple gene paralogs. The more recent 3R event in teleosts provides a unique opportunity to gain insight into how genes evolve through specific evolutionary processes. In this study we compare molecular activities of vitamin D receptors (VDR) from basal species that diverged at key points in vertebrate evolution in order to infer derived and ancestral VDR functions of teleost paralogs. Species include the sea lamprey (Petromyzon marinus), a 1R jawless fish; the lit-tle skate (Leucoraja erinacea), a cartilaginous fish that diverged after the 2R event; and the Senegal bichir (Polypterus senegalus), a primitive 2R ray-finned fish. Saturation binding as-says and gel mobility shift assays demonstrate high affinity ligand binding and classic DNA binding characteristics of VDR has been conserved across vertebrate evolution. Concentra-tion response curves in transient transfection assays reveal EC50 values in the low nanomo-lar range, however maximum transactivational efficacy varies significantly betwee