Date of Award
Doctor of Philosophy (PhD)
Differentiating cells express subsets of genes to build the cellular machinery necessary to perform their specific function as they acquire their mature fate. These subsets of genes are regulated by networks of transcription factors as cells progress through their developmental program. In secretory tissue, highly-specialized cells establish a complex secretory apparatus and scale up their cellular architecture to facilitate the production and secretion of large amounts of protein. Here, we identify a network of transcription factors responsible for the development of this cellular machinery in these professional secretory cells, and develop new tools to better study the molecular networks that control the differentiation of secretory cell lineages.
We present that the expression of Xbp1, a transcription factor responsible for establishing and maintaining the ER in gastric zymogenic (chief) cells (ZCs), is enhanced by HNF4α. HNF4α directly binds the Xbp1 promoter and is sufficient to enhance its expression in gastric epithelial cells. We observe that loss of HNF4α disrupts normal differentiation in the gastric epithelium, and causes morphological changes similar to the loss of XBP1, suggesting it acts through Xbp1 to maintain homeostasis in the mouse stomach.
To facilitate the characterization of the molecular underpinnings of ZC differentiation, we sought to develop a technique to isolate pure ZC populations from the gastric mucosa. Using a microarray-based screen, we identified ANPEP as a surface marker of mature ZCs that enabled us to sort homogenous ZC populations using flow cytometry. We found that ANPEP is rapidly lost as ZCs dedifferentiate in response to damage or disease in both mouse and human models, and our improved method allowed us to use flow cytometry to quantify these molecular changes to the ZC surface.
While we found that HNF4α is required for maintenance of the gastric epithelium, it has already been well-established that HNF4α plays a critical role in pancreatic beta-cell function. Mutations in HNF4α cause a prevalent subset of inheritable diabetes, MODYI. However, the mechanism through which mutated HNF4α causes beta-cell dysfunction has not yet been established. Our data shows that HNF4α is required for expression of both Xbp1, and downstream targets of Xbp1, and that loss of HNF4α leads to diminished ER morphology in mouse beta-cells. We show data suggesting that the loss of glucose-stimulated insulin secretion in MODYI may be due to impaired calcium signaling from the ER, and that restoring Xbp1 expression is sufficient to rescue insulin secretion in HNF4α-null beta-cells.
Taken together, the data presented below characterizes an important new transcriptional relationship in both the stomach and endocrine pancreas, and establishes new tools for the study of secretory cells. These results illustrate how the study of a basic transcriptional relationship can have broad implications in the development and treatment of prevalent human diseases.
Chair and Committee
Fumihiko Urano, David Rudnick, Joseph Corbo, Rodney Newberry
Moore, Benjamin David, "Transcriptional Regulation of the Endoplasmic Reticulum in Dedicated Secretory Cells" (2015). Arts & Sciences Electronic Theses and Dissertations. 668.