Mechanisms of pancreatic islet morphogenesis

This proposal aims to increase our understanding of the control of pancreatic islet formation. Recent studies have shown that the majority of insulin-producing beta cells in vertebrates arise from progenitors located in pancreatic duct epithelium. However, the molecular mechanisms underlying the subsequent delamination, migration, and assembly of these cells remain poorly understood due to the inaccessibility of the pancreas in most vertebrate model organisms. In this project, we will apply microscopy techniques recently developed in our lab that enable high resolution in vivo visualization of islet morphogenesis in zebrafish embryos, which is not possible in any other model system. Live imaging approaches will be combined with genetic manipulations, pharmacological treatments and newly available technology for automated chemical screening, in order to identify signaling pathways and cellular mechanisms critical for endocrine cell formation and islet assembly. Insight gained from these studies can lead to improved methods for enhancing islet formation for treatment of diabetes, either from progenitors growing as cultured cells or from endogenous progenitors in patients. Furthermore, these studies will contribute to our understanding of cell migration in general, which is a critical first step for developing new therapies for the pathological migratory processes seen in inflammatory diseases and cancer invasion.

In the pancreas, the beta cells of the islet maintain blood sugar by producing insulin that is released into the bloodstream. Diabetes, a common disease in which the islets are lost or don`t function properly, is often treated by supplying insulin. Scientists hope in the future to treat diabetes by producing new islets in the laboratory that can be transplanted into patients. Our work aims to better understand how islets form during development in order to better recreate this process in the lab. During development, single cells come together to form islets. How these cells find each other and form clusters is not well understood because it is difficult to view the pancreas as it grows and matures deep inside mammals such as mouse and man. To learn about islet formation, we use the model organism zebrafish, which is a vertebrate like man, but which develops outside the mother and is nearly transparent. The zebrafish is especially useful for studying the islets of the pancreas, because islet formation can be sped up and observed through the microscope in living animals. For this project, we used fish that make glowing fluorescent proteins in the cells of the pancreas, which lets us observe, with fine detail, shape and movement of cells. By taking close-up movies of cells as they form islets, we discovered that the separated cells actively reach out with long finger-like projections to contact other islet cells. These fine connections develop into bridges that seem to guide cells towards each other during cluster formation. We then tested what molecules might be important for making these projections and bringing the islet cells together. We found that if we blocked a group of proteins called G-protein-coupled receptors (GPCRs) from sending messages into the cells, the cells made fewer protrusions and could not properly form islets. Giving chemicals that interfered with the molecule Phosphoinosotide-3- Kinase (PI3K) had similar effects. PI3K acts inside cells to bring proteins to new locations, to cause cells to change shape, or to turn on and off production of other proteins. The goal of our continuing work is to better understand how the cell movements are controlled, how islet cells recognize each other, and the forces that bring them together.