Elucidating the molecular machinery of an evolutionary novelty: Single-cell transcriptomics of Arcella intermedia and characterization of gene expression during shell formation

• Ano de defesa: 2019
• Autor(a) principal: Sousa, Alfredo Leonardo Porfirio de
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Amoebozoa; Arcellinida; Evolutionary novelty; Modelo molecular; Molecular model; Novidade evolutiva; Rab GTPase; Rab GTPases; Tecagênese; Thecagenesis
• Link de acesso: http://www.teses.usp.br/teses/disponiveis/41/41133/tde-07052019-101649/

The present dissertation aims to shed light on the molecular machinery involved in the process of shell formation (thecagenesis) in Arcella (Arcellinida : Amoebozoa). Arcellinida are single-celled testate amoebae organisms, characterized by the presence of an outer shell (test or carapace); it is a monophyletic lineage of Amoebozoa, sister group to a naked amoeboid lineage. No homologous structure to shell is present in the sister group of Arcellinida, thus it is considered an evolutionary novelty. The origin and evolution of the shell in Arcellinida are currently open questions; deciphering its formation process is a key step to address these questions. During each reproductive process by budding division, these organisms build a new shell. In the span of more than a century, several authors have described the thecagenesis process on Arcellinida, primarily focusing on the genus \\textit, based on cyto-morphological evidence. Conversely, the absence of molecular data has impaired advances on describing the molecular aspects of shell formation. In this study, we designed and applied a molecular framework to identify candidate genes and develop a molecular model for the shell formation process in Arcella; we based this framework on single-cell RNA-sequencing, gene expression profiling, Gene Ontology analysis, and comparative analysis of cyto-morphological with newly generated molecular data. We identify and propose a set of 539 genes as the candidate genes for shell formation, based on expression profiling and biological process assignment. We propose a model for the the shell formation process, which describes the mechanistic aspect of this process, hypothetically based on a molecular machinery conserved in Eukaryotes. Additionally, we identified a massive expansion of the Rab GTPase family, a protein likely to be involved on the process of shell formation. In the lights of the present study, we briefly discuss possible evolutionary scenarios involved on the origin and evolution of the shell and present future perspectives; we propose the shell of Arcellinida as a prosperous model to study the origin and evolution of evolutionary novelties, as well as other evolutionary questions