The evolution of eukaryotic cilia

Thesis

Eukaryotic cilia are complex, highly conserved microtubule-based organelles with a broad phylogenetic distribution. Cilia were present in the last eukaryotic common ancestor and many proteins involved in cilia function have been conserved through eukaryotic diversification. The evolution of these ciliary functions may be inferred from the distribution of the molecular components from which these organelles are composed. By linking protein distribution in 45 diverse eukaryotes with organismal biology, I define an ancestral ciliary inventory. Analysis of these core proteins allows the inference that the cenancestor of the eukaryotes possessed a cilium for motility and sensory function. I show that the centriolar basal body function is ancestral, whereas the centrosome is specific to the Holozoa, and I use this information to predict a number of roles for proteins based on their phylogenetic profile. I also show that while remarkably conserved, significant divergence in ciliary protein composition has occurred in many lineages, such as the unusual centriole of Caenorhabditis elegans and the transitional changes throughout the land plants. I exemplify this divergence through ultrastructural studies of the fern Ceratopteris richardii and the liverwort Marchantia polymorpha both of which have cilia that exhibit a number of distinctive morphological features, the most conspicuous of which is a general breakdown of canonical microtubule arrangements. Cilia have also been lost multiple times in different lineages: at least twice within the land plants. During these evolutionary transitions proteins with ancestral ciliary functions may be lost or co-opted into different functions. I have interrogated genomic data to identify proteins that I predict had an ancestral ciliary role, but which have been maintained in non-ciliated land plants. I demonstrate that several of these proteins have a flagellar localisation in protozoan trypanosomes and I use expression data correlation to predict potential non-ciliary plant roles.

Authors: Hodges, M; Matthew Hodges

• Publication date: 2011
• DOI: 10.5287/ora-zb7k74zzn
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: cilia; basal body; evolution; centriole; flagella
• Subjects: Bioinformatics (life sciences); Plant Sciences; Cell Biology (see also Plant sciences); Biology