Molecular regulations and lineage tracing in early Mouse embryogenesis
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This dissertation research aims to understand the regulations and developmental patterns of mouse early embryogenesis, in order to gain comprehensive knowledge in human early development to further the ultimate goal of designing future novel and effective regenerative therapies. The first part of this research focuses on transcriptional and metabolic regulations that take place in the embryo during the transition from pre- to post-implantation. By utilizing in vitro cell lines established from these two stages (pre-implantation: mESC, and post-implantation, EpiSC/hESC, respectively), we found a dramatic metabolic difference between them. We found that EpiSC/hESC are highly glycolytic, while ESC are bivalent in their energy production, dynamically switching from glycolysis to mitochondrial respiration on demand. Despite having a more developed and expanding mitochondrial content, EpiSC/hESC have low mitochondrial respiratory capacity due to low cytochrome c oxidase (COX) expression. We further show that HIF1α is sufficient to drive ESC to a glycolytic Activin/Nodal-dependent EpiSC like stage. The second part of the research examines patterns of cell lineage development utilizing somatic mutations that inevitably arise with every cell division (a method dubbed "phylogenetic fate mapping"). We cataloged genomic mutations at an average of 110 mutation-prone polyguanine (polyG) tracts for about 100 cells clonally isolated from various corresponding tissues of two sibling littermates of a hypermutable mouse strain. We found that during mouse development, muscle and fat arise from a mixed pool of progenitor cells in the germ layer, but, in contrast, vascular endothelium in brain is derived from a smaller source of progenitor cells. We quantitatively demonstrated that development generally represents a combination of stochastic and deterministic events, as reflected in only partial conservation of cell lineage between individual mice.
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