In search of the genetic bases underlying the unique capacities of the mammalian inner ear: an evolutionary study

FRANCISCO PISCIOTTANO; ANA BELÉN ELGOYHEN; LUCÍA F. FRANCHINI

Córdoba

Congreso; II Congreso Argentino de Bioinformática y Biología Computacional; 2011

Sociedad Argentina de Bioinformática y Biología Computacional

During the evolution of mammals, the inner ear went through many important changes that made it different from the hearing organ of other vertebrates. Among these changes we can remark the elongation of the papilla that rendered the characteristic mammalian coiled cochlea, the special and stable distribution of the hair cells all along Corti's Organ and the origin of a unique cellular type, the outer hair cell (OHC). This new kind of cell shows a novel mechanism known as somatic electromotility. This mechanism of mechanic amplification, unique of mammals, depends on OHCs length changes mediated by the motor protein prestin. All together these changes in the inner ear have endowed mammals with unique hearing capacities in the animal kingdom. Our main objective is to study the genetic bases underlying the evolution of the particular functional capacities of the mammalian inner ear. To do that we are following a three-steps evolutionary approach: first we are generating a comprehensive database of proteins that are expressed in the inner ear. Second, using a maximum likelihood method we study the evolution of each protein in vertebrates. Then, we perform a detailed evolutionary analysis of proteins showing signatures of positive selection in the mammalian lineage. Here we present a summary of the results obtained so far. We have analyzed approximately 5 % of inner ear expressing proteins and we have found 22 genes showing signatures of positive selection in the lineage leading to mammals. Among them we have found strong signals of positive selection in mammals in two proteins of the spectrin family. Spectrins are a family of actin binding proteins considered to be central components of the complex that links membrane proteins, membrane lipids and cytosolic factors to the major cytoskeletal filament system of the cell.  In the inner ear it has been recently shown that alphaII-spectrin in association with betaV-spectrin, interacts with prestin, a key player in somatic electromotility. We have previously found that prestin shows strong signatures of positive selection in the mammalian lineage. Our present results suggest that in addition to prestin, other components of the OHC cytoskeleton underwent a differential evolutionary process in mammals that most likely endowed OHC with its novel capacity of somatic electromotility.