[PhD Thesis Presentation_Zoom] - Ivan Mbogo - "The evolution of dual functionality of β-catenin in metazoans"
Presenter: Ivan Mbogo
Supervisor: Professor Hiroshi Watanabe
Unit: Evolutionary Neurobiology Unit
Title: The evolution of dual functionality of β-catenin in metazoans
The evolution of the multicellular body of animals from unicellular organisms is still a significant and long-lasting subject of interest in biology. Acquisition of cell-cell adhesion with cadherin, α- and β-catenin proteins is thought to be tightly coupled with the origin of animal epithelium and consequent evolutionary thrive of animals. Much research has shown, in a wide range of animal lineages such as bilaterians and cnidarians, that β-catenin associates with diverse intracellular proteins involved in gene transcription/translation and plays an essential role in the induction of the signalling centre (organiser) during animal embryogenesis. The pleiotropic and evolutionary conserved functions of β-catenin suggest deep evolutionary roots of the β-catenin complexes and involvement in the emergence of basic animal body plan. Recent progress in genomics has identified genes of the cell-cell adhesion complex and signalling machinery of β-catenin in genomes of early-branching animals, including Porifera (sponges) and Ctenophora (comb jellies). However, due to difficulties in applying molecular and genetic technologies in these non-model animals, the ancestral functions of β-catenin complexes remain largely to be explored.
In this study, I employed structural, proteomic, and functional approaches to understand evolutionarily conserved features of the β-catenin and its associated proteins. Structural analysis suggests a unicellular origin of the basic architecture of β-catenin protein, while amino acid residues critical in adhesive properties are conserved only within animals. To analyze evolutionarily conserved functional characteristics of basal animal β-catenins, I performed transphyletic studies where the basal animal β-catenins are expressed in Xenopus embryos. A series of proteomics analyses of β-catenin-associated proteins provided the first empirical evidence of the deep origin of the cadherin catenin complex. The transphyletic function studies, together with detailed sequence analysis, also revealed the β-catenin’s organiser-inducing function of Cnidaria, Porifera, but not Ctenophora. These data suggest that the primary function of ancestral β-catenin was to play adhesive roles, and its’ signalling properties were equipped later during the evolution of basal animals.