Exploring the genetic bases of mammalian unique hearing capacities: an evolutionary inner ear database

PISCIOTTANO, FRANCISCO; ELGOYHEN, ANA BELÉN; FRANCHINI, LUCIA FLORENCIA

Rosario - Santa Fe - Argentina

Congreso; 4to Congreso Argentino de Bioinformática y Biología Computacional y 4ta Conferencia Internacional de la Sociedad Iberoamericana de Bioinformática; 2013

Asociación Argentina de Bioinformática y Biología Computacional y Sociedad Iberoamericana de Bioinformática

Mammals possess unique hearing capacities among animals. These capacities are the consequence of an evolutionary process which involves a number of important changes in the inner ear. Among these changes we can remark the coiled cochlea, special and stable distribution of hair cells all along Corti´s Organ and a unique cellular type, the outer hair cell (OHC). This new kind of cell endowed mammals with a novel sound mechanic implification mechanism known as somatic electromotility, crucial for auditory sensitivity and frequency selectivity.Although these features are well studied and most of them are regarded as evolutionary novelties, product of an adaptive process, little is known of the genetic bases underlying the evolution of these features. Only a few inner ear proteins have previously been subject of selection analysis [1,2].Our main objective is to study the evolutionary processes that shaped those genes involved in the evolution of the particular functional capacities of the mammalian inner ear. To do so, we are assembling an inner ear database that comprises genes from different sources. For the construction of this database we aim to concentrate the information generated by seventeen expression libraries that gather 86,744 expressed sequence tags (ESTs). For the evolutionary analysis we perform branch-site specific positive selection test [3] that allow us to recognize those genes that fit the model of adaptive evolution, and the specific sites in the alignment that have evolved under positive selection in the lineage that gave origin to mammals.We present here the results obtained from the analysis of the RIKEN adult mouse inner ear expression library [4]. This is the main rodent library, containing 22,576 ESTs that would represent more than 4,500 genes, and one of the most trustworthy among the inner ear libraries, according toour testing studies. A preliminary test carried out from the first 100 ESTs of this library rendered 84 genes. Although only 34 of them could be analyzed due to the available information, 11 of them showed clues of positive selection (P>0.95), pointing out that there is an important number of inner ear genes that may present signs of adaptation in the mammalian branch. We aim to use this library as a starting point to set our database and then to add the information from other inner earexpression libraries, as well the information gathered from other ources, such as expression analysis.