Identification of genetic innovations in vertebrates

• Main Author: Tuberosa, Joël
• Other Authors: Rodriguez, Ivan
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Université de Genève 2020
• Subjects: info:eu-repo/classification/ddc/590; toothed whales
• Online Access: https://archive-ouverte.unige.ch/unige:156655; https://doi.org/10.13097/archive-ouverte/unige:156655

The evolution of life forms is marked by the emergence of new genes and the transformation of old ones. Thus, genomes possess a reservoir of sequences escaping selective pressures and of fortuitous transcriptional activity, with a potential to encode entirely new functions. In parallel, recycling of genetic material with preexisting function takes place, a process likely more common than the production of genuine original genes. This reconditioning is at the origin of incremental novelties, but also at the origin of spectacular innovations, such as the specialization of oxygen transport or the emergence of chromatic vision. During my thesis, I explored different instances of genetic innovations in neurons. My studies focused, on the one hand, on the evolution of mammalian olfactory chemoreceptors, which constitute a remarkable model to study evolution by gene duplication and acquisition of new expression patterns. Indeed, the gene families encoding for these receptors are characterized by an exceptional rate of gene duplication, diversification and death. On the other hand, my research was initiated by the discovery of an entirely new gene that emerged during vertebrate evolution. The genes encoding for odorant receptors (ORs), one of the olfactory receptor superfamilies, constitute the largest gene family in the mammalian genome. With hundreds of representatives, ORs represent a highly diversified panoply of chemoreceptors that may attend non-olfactory functions when expressed outside of the olfactory system. Ectopic transcription of OR genes was indeed reported multiple times, but the adaptive value of this putative pleiotropy remains unclear. In the first part of this work, we used a comparative genomic approach with the aim to identify ectopic ORs with a non-olfactory role and of evolutionary importance in mammals. For this, we took advantage of the toothed whales evolution, a group which has lost its olfactory system 35 millions of years ago. We found three intact OR coding sequences that were present in ...