UCSF

Multicellular tissues arise from a complex collaboration between the constituent cell types. Proper coordination between cells through signal interactions is crucial for tissue renewal and response to environmental changes such as injury or infection. How do tissues integrate and interpret multiple signals? How does the design of tissues and their lineage structures guide response to perturbations? I investigate these questions in the context of the intestinal epithelium, the single cell layer lining the small intestine. Alongside post-docs in the Altschuler-Wu Lab, Curtis Thorne and Laura Sanman, I developed an enteroid monolayer culture system for high-throughput quantitative profiling of intestinal epithelial cell-type composition. I then employed this system to study how combinations of signals may interact and how lineage structure may guide tissue response in the intestinal epithelial.In Chapter 1, I describe the methods for establishing the enteroid monolayer platform, including the experimental culture methods and image quantification analysis. The approach outlined here forms the foundation for the subsequent investigations into signal feedback and coordination between cell types. In Chapter 2, I dissect the intrinsic roles of two main proliferation regulators, Wnt and BMP, in shaping the intestinal epithelium. We discovered that intrinsic Wnt3a signals from the crypt is important for proper spatial patterning of progenitors. We also found that intrinsic BMP2 secreted by differentiated cells acts as a delayed negative feedback signal for self-regulating increased proliferation in the intestinal epithelium. This finding indicates that external signals can feed into intrinsic signaling circuits, which link distinct cell population compartments. In Chapter 3, I expand the investigation to examine progenitor and differentiated cell types in the intestinal epithelium. We identified an unexpected mutual antagonism interaction between inhibition of the epidermal growth factor receptor and activation with the cytokine IL-4. We also uncovered a general relationship between transit-amplifying cell proliferation and the balance of secretory to absorptive cell types. We proposed a differential amplification model to explain how amplification of fated progenitors can be modulated to control lineage composition. Finally, in Chapter 4, I synthesize the results from these studies and discuss the implications for how the intestinal epithelium integrates and responds to signals. I conclude with potential directions for future research.