Ancient Roles of Non-coding RNAs in Eukaryotic Evolution Contributions from Social Amoebae and Other Protists

RNAs not coding for proteins, non-coding RNAs (ncRNAs) have many important roles in all kingdoms of life. Especially in eukaryotes, the regulatory functions of ncRNAs have been suggested as a major force in the evolution of complex traits. Cellular processes that are regulated by ncRNAs include for example cell differentiation, organ development and defense against viruses and transposable elements. This is achieved through a number of mechanisms like RNA destabilization and modification, transcriptional and translational control and chromatin modifications. Dictyostelium discoideum is a social amoeba and the best studied organism representing Amoebozoa, one of the eukaryotic supergroups. It has for long served as an excellent model for many basic cellular events like chemotaxis, differentiation and development and recently also for infection. The ncRNA population in D. discoideum is in many ways typical of eukaryotes but also harbors particularities. In this thesis I have studied spliceosomal RNAs as well as the RNA interference and microRNA pathways, which probably were present in the last eukaryotic common ancestor. I have also characterized Class I RNAs which seems to be specific to social amoebae. In addition, we have described the signal recognition particle RNA in several protists and also the involvement of a ncRNA during host interaction and stress in Giardia lamblia. Combining the well established molecular tools and knowledge about various pathways in D. discoideum, with the growing understanding of ncRNA, could in the future give important information about the function of ncRNAs as well as their ancient roles and evolution.