Abstract

The cardiovascular system is generated by mesodermal progenitors that give rise to endothelial, hematopoietic and muscle (smooth muscle and cardiomyocyte) lineages. Although vascular endothelial growth factor (VEGF), its receptor, FLK1/KDR and the transcription factor ETV2 are critically required for hemangiogenic specification, Flk1 and Etv2 expression has been observed in other mesodermal derivatives. During gastrulation, mesodermal progenitors are specified to contribute to the cardiovascular system; however, the early divergence of hemangiogenic and muscle progenitors, and their shared marker expression, complicates identification of common mesoderm progenitor populations contributing to both lineages. In this dissertation, I demonstrate how Flk1+ and Etv2+ lineage relationships contribute to endothelial, hematopoietic, smooth muscle and cardiomyocyte cell types, and define the molecular mechanisms engaged by ETV2 to specify hemangiogenic fate. A dual lineage tracing approach using mouse embryos demonstrates that dual Flk1+ and Etv2+ mesodermal progenitors contribute mainly to endothelial, hematopoietic and cardiac valve lineages, and partially to smooth muscle cells and cardiomyocytes. Transcriptomic profiling of in vitro-derived PDGFRalpha+FLK1+ (double-positive, DP) and PDGFRalpha-FLK1+ (single-positive, SP) mesodermal progenitors revealed modular Flk1+ gene programs distinguishing hemangiogenic and muscle fate. Integrating these data with single-cell RNA-seq analyses show that Etv2+ SP progenitors share transcriptional features of hematoendothelial progenitors and endothelium, while Etv2+ DP and Etv2- SP share features similar to embryonic mesenchyme, which appear competent to generate either cardiomyocytes or smooth muscle lineages. To determine the molecular mechanisms enabling ETV2 function, chromatin accessibility profiling by ATAC-seq, and chromatin immunoprecipitation (ChIP) assays were performed using in vitro-derived mesodermal progenitors. Mass spectrometry identified BRG1/BRM-associated factor (BAF) chromatin remodeling complex subunits BAF155 and BAF57, as an interacting partners of ETV2. Baf155 deletion in embryonic stem (ES) cells impaired ETV2 binding at target loci, reduced hemangiogenic gene expression, and hematopoietic colony-forming potential. Baf155 deletion in Etv2+ and Flk1+ lineages is consistent with embryonic lethality due to yolk sac hematopoietic defects and suggests an essential molecular cooperation between ETV2 and the BAF complex subunit, BAF155 during hemangiogenic lineage specification. Altogether, this work demonstrates how FLK1+ mesoderm is allocated during cardiovascular development to contribute to hemangiogenic and muscle lineages and uncovers a molecular mechanism engaged by ETV2 to establish hemangiogenic lineage identity. These findings will have implications of regenerative medicine and congenital disease modeling.

Committee Chair

Kyunghee Choi

Committee Members

Amber Stratman; David Ornitz; Kory Lavine; Kristen Kroll; Ting Wang

Degree

Doctor of Philosophy (PhD)

Author's Department

Biology & Biomedical Sciences (Developmental, Regenerative, & Stem Cell Biology)

Author's School

Graduate School of Arts and Sciences

Document Type

Dissertation

Date of Award

3-30-2026

Language

English (en)

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