Diversified Sex Characteristics Developments in Teleost Fishes: Implication for Evolution of Androgen Receptor (AR) Gene Function

Abstract

Gene duplication is a dominant driving force of evolution. The steroid hormone receptor (SR) gene family is thought to have arisen from gene duplication. However, the molecular events which produce new protein functions after genome duplication have not been fully understood. Teleost fishes present an excellent model to investigate an accurate evolutionary history of protein function after whole genome duplication (WGD), because the teleost-specific WGD (TSGD) 350 million years ago (Ma) resulted in a variety of duplicated genes that exist in modern fishes. We focused on the androgen receptor (AR) gene, since two different subtype genes, ARα and ARβ, were generated in the TSGD. It was previously shown that ARβ has retained the ancestral function, whereas ARα has evolved as a hyperactive form of AR in the teleost lineage. Such evolutionary novelty of protein function in AR genes might facilitate the emergence of divergent sex characteristics in the teleost lineage. Results of the combined functional and 3D analyses of medaka ARs identified the substitutions that led to changes in protein structure and function between medaka ARα and ARβ. By tracing evolutionary changes in protein function of ARs in teleost lineage, we recently revealed that the substitutions generating a new functionality of teleost ARα were fixed in the teleost genome after the divergence of the Elopomorpha lineage. Such findings would provide an historical explanation for the retention of the duplicated AR copies in the euteleost genome. We also highlighted the molecular mechanisms of secondary sex characteristics development in teleost fishes, using Western mosquitofish and medaka as models.