UBC Theses and Dissertations
Delineating migratory events in liver and heart development using single-cell transcriptomics Lotto, Jeremy
The cellular complexity and small scale of the mouse embryonic liver and heart valves have constrained analyses probing cell type diversity and differentiation during their development. To address this, we have analyzed 29 single-cell RNA-seq libraries from embryonic day (E)7.5 to E12.5 and have validated the spatiotemporal distribution of identified cell lineages by histology. To assess liver development, we have analyzed 45,334 cells and have detailed the developmental trajectories taken during the early emergence of liver parenchymal and non-parenchymal cell lineages. These analyses describe the development of hepatoblasts, liver endothelium, and mesenchyme from endoderm progenitor specification at E7.5 to liver bud formation at E10.5. Our data detail the divergence of vascular and sinusoidal endothelia, the specification of hepatoblasts, and the emergence of distinct mesothelial cell types. We further identify a novel, hybrid hepatomesenchymal cell type that we hypothesize plays a role in liver bud formation. To delineate atrioventricular (AV) valve development, we have analyzed 48,822 cells from publicly available and newly generated single-cell datasets. These data provide insight into the epithelial-to-mesenchymal transformations from endocardium (EndMT) and epicardium (EpiMT) that contribute to AV mesenchyme during development. During EndMT, we detail the bifurcation of valve mesenchymal and endocardial lineages, which our data suggest involves the sporadic activation of epithelial-mesenchymal plasticity. During EpiMT, scRNA-seq data and histology identify a unique activated epicardial population that emerges at the onset of this process. We further use our transcriptomic data to deconvolve signals that may influence the initiation and progression of EndMT and EpiMT. Lastly, we have assessed the role of AV mesenchymal master regulator SOX9 during EndMT by comparing Sox9 endothelial-specific mutant and wildtype AV canals. Our data show developmental arrest during EndMT without Sox9, including the failure of endocardial transdifferentiation to mesenchyme and the accumulation of endocardium exhibiting epithelial-mesenchymal plasticity. These data reveal surprising diversity during the emergence of liver and AV cell lineages. As a resource, they will serve as comprehensive single-cell atlases of liver and AV lineage establishment for researchers studying the development of these tissues or the reactivation of developmental processes in disease and regenerative contexts.
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