UCSF

Organogenesis requires the complex interactions of multiple cell lineages that coordinate their expansion, differentiation, and maturation over time. In Chapters 2 and 3, we utilize a combination of single-cell RNA-sequencing, immunofluorescence, in situ hybridization, and genetic lineage tracing, to profile the cell types within the epithelial and mesenchymal compartments of the murine pancreas across developmental time. We find a previously undescribed endocrine progenitor population, as well as an analogous population in both human fetal tissue and human embryonic stem cells differentiating towards a pancreatic beta cell fate. Further, we identify candidate transcriptional regulators along the differentiation trajectory of this population towards the alpha or beta cell lineages. Within the mesenchyme, we identify previously underappreciated cellular heterogeneity and reconstruct potential lineage relationships among the pancreatic mesothelium and mesenchymal cell types. In Chapter 4, we further characterize the pancreatic mesothelium, identifying novel markers and secreted factors expressed within this population. Knockout of the secreted factor specifically expressed by the mesothelium, Fgf9, reveals a hypoplastic pancreas by late gestation. We find a disrupted ratio of epithelial and mesenchymal cells that suggests Fgf9 regulates the epithelial-mesenchymal interactions critical for pancreatic development. In Chapter 5, we extend our single-cell RNA-sequencing approach to adult pancreatic homeostasis and disease, describing multiple subtypes of mesenchymal and mesothelial populations in both conditions. Comparison of diseased and healthy pancreata reveal shifts in mesenchymal cell types, highlighting populations and transcriptional targets that may regulate the development of disease. In summary, this work reveals transcriptional and cellular heterogeneity of the developing, adult, and diseased pancreas, and identifies lineage relationships among novel populations within both the epithelial and mesenchymal compartments.