UCSF

Precise regulation of both the timing and dosage of gene expression is critical for thedevelopment of the early embryo and the extraembryonic tissues that support it. These signals enable molecular communication within and between tissues, thereby allowing cells to differentiate to the correct identity and migrate to the correct location for patterned organ systems to emerge. Some of the genes active during early development orchestrate morphogenesis in a dose-dependent manner, whereby reduced expression fulfills some of the gene’s functions, but is insufficient to drive normal patterning. How gene dosage informs morphogenesis is not well understood. This dissertation focuses on how varying expression levels of two transcription factors with dose-dependent phenotypes, TBXT and CDX2, influence the patterning and kinetics of the embryonic and extraembryonic mesoderm populations during gastrulation. By utilizing in vitro models of early human gastrulation and mesoderm development, I demonstrate that TBXT dosage directly influences the temporal progression of the epithelial-to-mesenchymal transition (EMT) in the nascent mesoderm and hypothesize that this influences the temporal and spatial migration kinetics surrounding primitive streak morphogenesis. I additionally show that CDX2 dosage influences the gene regulatory network (GRN) underlying extraembryonic mesoderm development despite heterozygous expression being sufficient to maintain a wild-type-like chromatin accessibility profile. This work suggests that the regulation of downstream gene expression is not solely dependent on chromatin remodeling and implies that proper regulation of this GRN is potentially critical for the development of extraembryonic structures such as the allantois. These findings clarify how varying dosages of specific transcription factors can influence the gene regulatory networks underlying early gastrulation, thereby contributing to our understanding of both dose-dependent gene regulation and early human development.