EVALUATING THE EFFECTS OF TISSUE ARCHITECTURE ON DROSOPHILA CHEMOTAXIS USING ADVANCED IMAGING AND ANALYSIS TECHNIQUES

Abstract

Graded concentrations of diffusible signals, such as morphogens and chemoattractants, instruct important developmental processes, like cell specification and cell migration. However, signal distribution in complex tissue geometries in vivo has not been well characterized, which has implications in understanding concentration-dependent signaling effects. Using the border cells, which migrate collectively in the Drosophila egg chamber during oogenesis and are guided by chemoattractants, we can study these important issues in vivo. We find that distinct features in the tissue geometry along the migration route, specifically acellular gaps at multicellular intersections, disrupt local concentrations of secreted chemoattractants to affect directed border cell migration. In live-imaged wild-type egg chambers, we observed declines in posterior speed that occur specifically at intersections; trends that disappear in response to elevated levels of chemoattractant, suggesting that migratory cues differ in these regions, normally. We developed a mathematical model, informed by this data, to predict the migration changes in response to both chemical and architectural inputs. Our model indicates that in silico, border cells slow down in intersections due to local changes in the chemoattractant gradient, which matches our in vivo phenotypes. Importantly, we observed that migration delays in response to modified chemoattractant levels could be rescued by manipulating the tissue geometry, which strongly suggests that chemoattractant concentrations can be buffered by tissue architecture. In characterizing these phenotypes, I updated and improved upon published live-imaging methods to culture egg chambers and visualize border cells over the full course of migration. I also came up with novel mounting strategies that allowed for efficient and reproducible characterization of fluorescently-tagged signals in live egg chambers. These strategies allowed us to visualize the tagged chemoattractant, Platelet-Derived Growth Factor/Vascular Endothelial Growth Factor-Related Factor 1 (PVF1) and characterize its distribution in the border cell migratory domain of live egg chambers for the first time in the field. Finally, we demonstrate that the Heparan Sulfate Proteoglycan (HSPG) and Extracellular Matrix (ECM) component, Perlecan, plays a role in border cell migration, potentially by modulating PVF1 function. Overall, this body of work shows that in vivo tissue architecture can affect the distribution and function of important signaling molecules, with consequences for essential developmental processes, like cell migration. Funding: NSF-IOS 2303857 & NSF-NIGMS 1953423.