Regulation and functions of Sox17 during endodermal and vascular development

Abstract

The overarching goal of my thesis work is to better understand the transcriptional regulation and functions of Sox17 during early development. To start unveiling the complex molecular mechanisms that modulate Sox17 expression, I identified two evolutionarily conserved regions (CR1 and CR2) as candidates for critical cell type specific cis-regulatory elements of the gene. Phenotypic analysis of CRISPR/Cas9 gene edited mice has indicated that CR1 is important for lymphovasculogenesis via regulating transcription of Sox17 long mRNA, while CR2 is essential for embryonic survival due to its functions not only in regulating Sox17 short mRNA in the endoderm but also in intron processing of the long mRNA forms in the vasculature. By performing biochemical assays and metadata analysis, I have shown that two regions are alternate promoters and are differentially regulated at multiple levels including epigenetics, direct transcription factor bindings and interactions with distal elements. To further examining CR2 function in endodermal organogenesis without intefereing with the vasculature system, additional mouse lines were generated with smaller DNA sequence within CR2 removed or mutated. Initial analysis of these hypomorphic alleles have revealed a concentration-dependent functions of Sox17 in the development of gallbladder and cystic ducts. These findings in mice are consistent with distinct molecular functions of Sox17 suggested from single-cell RNA sequencing data. Predicted Sox17-regulon in endoderm mostly consists of cell cycle genes, while genes in endothelial Sox17-regulon associate with vascular sprouting and angiogenesis. With the single-cell transcriptomic analysis of Sox17-expressing lineages, I also described other insights into the gene expression features of different cell states and cell groups along the developmental trajectories of endothelial-to-hematopoietic transition and hepato-pancreato-biliary formation.