Menglan Xiang

Date of Award

8-2019

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical Sciences

First Advisor

Ke Zhang

Second Advisor

Linglin Xie

Abstract

The cardiac outflow tract (OFT) is a transient conduit that connects the embryonic heart chambers to the vascular network. Transcription factor Osr1 promotes the proliferation and cell cycle progression of second heart field (SHF), an essential cell population that contribute to the developing OFT. In this study, we investigated the role of Osr1 in OFT development on cellular and molecular levels using a systems biology approach. We observed OFT rotation and elongation defects, as well as double-outlet right ventricle and overriding aorta as a result of SHF-specific deletion of Osr1. Using genetic inducible fate mapping, we showed that Osr1-expressing SHF cells migrate to the pulmonary trunk, however the cell lineage is ectopically distributed in the aorta, in addition to the pulmonary trunk, in Osr1 knockout embryos. To understand the molecular mechanism that leads to the aberrant localization of the Osr1 cell lineage, we performed transcriptional profiling of the isolated Osr1+ SHF population which showed Osr1-dependent expression of genes involved in tight junctions, cell adhesions, tissue connectivity and movement. Using in vivo and in vitro transcription factor binding assays, qRT-PCR as well as immunohistochemistry, we demonstrated that cell surface receptor Pdgfrb is a novel transcription target of Osr1. Furthermore, we showed that the Drosophila Pdgfrb homolog Pvr is required for the alignment and organization of Odd-expressing pericardial cells in the Drosophila larvae, demonstrating that the Osr1-Pdgfrb function is evolutionarily conserved.

The heart is derived from two progenitor pools: first heart field (FHF) and second heart field (SHF). The SHF is a heterogeneous population and consists of subregions anterior SHF (aSHF) and posterior SHF (pSHF). Although being adjacent to each other and of similar cell types, their cell fates significantly differ. In this study, we investigated how epigenetic mechanisms shape the transcriptional profiles of the cardiac progenitor populations. Using Assay for Transposase Accessible Chromatin with high-throughput sequencing, we found that tissue-specific accessible regions are enriched with corresponding cardiac transcription factor binding motifs. Using whole-genome bisulfite sequencing, we showed that hypermethylation correlates with inhibited gene expression for tissue-specific markers. Thus this study addressed a multi-tier regulatory mechanism for cardiac progenitor cells.

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