Exploring the genetic bases of mammalian unique hearing capacities: an evolutionary approach

FRANCISCO PISCIOTTANO; ANA BELÉN ELGOYHEN; LUCÍA F. FRANCHINI

Bariloche

Congreso; V Congreso Argentino de Bioinformática y Biología Computacional (5CAB2C); 2014

Sociedad Argentina de Bioinformática y Biología Computacional

Mammals possess unique hearing capacities among animals. These capacities are the consequenceof an evolutionary process which involves a number of important changes in the inner ear. Amongthese changes we can remark the the elongation of the papilla that rendered the characteristicmammalian coiled cochlea, the special and stable distribution of hair cells all along Corti's Organand the origin of a unique cellular type, the outer hair cell (OHC). This new kind of cell endowedmammals with a novel sound mechanic amplification mechanism known as somatic electromotility,an active cochlear amplifier process 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 in the mammalian lineage, little is known of the genetic basesunderlying the evolution of these features. Only a few inner ear proteins have previously beensubject of selection analysis [1,2].Our main objective is to study the evolutionary processes that shaped those genes involved in theevolution of the particular functional capacities of the mammalian inner ear. To do so, we areassembling an inner ear database that comprises genes from different sources. For the constructionof this database we aim to concentrate the information generated by seventeen expression librariesthat gather 86,744 expressed sequence tags (ESTs). For the evolutionary analysis we performbranch-site specific positive selection test [3] that allow us to recognize those genes that fit themodel of adaptive evolution, and the specific sites in the alignment that have evolved under positiveselection in the lineage that gave origin to mammals.Among the seventeen publicly available expression libraries, the RIKEN adult mouse inner ear [4]is the main rodent library, containing 22,576 ESTs that would represent more than 4,500 genes, andone of the most trustworthy among the inner ear libraries, according to our testing studies. Apreliminary test carried out from the first 100 ESTs of this library rendered 84 genes. Although only34 of them could be analyzed due to the available information, 11 of them showed signs of positiveselection (P>0.95), pointing out that there is an important number of inner ear genes that may showadaptive evolution along the mammalian branch. We present here the pipeline developed to analyzethe information gathered from the expression libraries and the results obtained from the completeanalysis of the RIKEN library.References1. Franchini LF, Elgoyhen AB: Adaptive evolution in mammalian proteins involved in cochlearouter hair cell electromotility. Mol Phylogenet Evol 2006, 41:622-635.2. Kirwan JD, Bekaert M, Commins JM, Davies KTJ, Rossiter SJ, Teeling EC: A phylomedicineapproach to understanding the evolution of auditory sensory perception and disease inmammals. Evol Appl 2013, 6:412-422.3. Zhang J, Nielsen R, Yang Z: Evaluation of an improved branch-site likelihood method fordetecting positive selection at the molecular level. Mol Biol Evol 2005, 22:2472-2479.4. Okazaki Y, Furuno M, Kasukawa T, Adachi J, Bono H, Kondo S, Nikaido I, Osato N, Saito R,Suzuki H et al.: Analysis of the mouse transcriptome based on functional annotation of 60,770full-length cDNAs. Nature 2002, 420:563-573.