부산대학교 도서관

The evolution of multicellularity allowed complex organisms to develop with specialised cell types. The social amoeba, Dictyostelium discoideum, is a model for the uni- to multicellularity transition, and while the multicellular stage of most Dictyostelids comprises two cell types, D. discoideum contains at least two more, thereby showing the evolution of complexity within the Dictyostelia lineage. Here I investigate components of the signalling pathways that regulate somatic cell differentiation and transcription factors essential to development. In the first part of this thesis, I validated the expression pattern of putative cell-type-specific genes by X-gal staining of cell lines containing promoter-lacZ constructs. I then investigated the signals regulating the expression of some specifically expressed genes and showed c-di-GMP is a regulator of stalk genes, but not cup genes. The effects of DIF-1 on gene expression was less apparent. In the second part of this thesis, I investigated the conservation and change of transcription factors and small GTPases across Dictyostelia to reveal the evolution of signal transduction genes. While many transcription factors and GTPases were well conserved throughout Dictyostelia, others were specific to certain species. More transcription factors were upregulated during development and encystation than GTPases, but a higher percentage of GTPases were enriched to cup cells than the transcription factors. Focussing on the transcription factors, I selected genes to knock out based on their regulation and conservation and revealed 4 genes essential to development. Possible roles are proposed, but further experiments are required. This project showed that analysing transcriptional regulation and gene conservation effectively identified genes with roles in development. Therefore, we can target unknown genes using this bioinformatic approach, rather than performing genome-wide mutagenesis screens or consecutively investigating genes based on prior knowledge from orthologs.