Extracellular cues control developmental processes in a concentration‐dependent manner. Different amounts of morphogens elicit distinct cell fate decisions, and cells travel up chemoattractant gradients by assessing cue availability. Such signals must be tightly controlled to assure proper function. The concentration of signals in space and time depends on the parameters that govern the signal's release, diffusion, uptake, and decay rates. Chemical cues are often modeled as diffusing into open domains, but the structure of adjacent tissue could influence local signal availability, and thus cellular responses. The relatively simple tissue architecture of the Drosophila egg chamber, in which large germline cells are surrounded by a follicular epithelium, makes an ideal context to study how tissue contours influence extracellular signaling. In mid‐oogenesis, two anterior follicle cells secrete Unpaired (Upd) to activate the conserved factor Signal Transducer and Activator of Transcription (STAT) in nearby cells, and high STAT activity instructs a subset of those cells to become motile. Our genetic analysis identified specific vesicle trafficking components that modulate the secretion rate of Upd. While all cells near the source of Upd are responsive, we found that STAT activation and the resulting arrangements of motile cells often arose in unexpected, asymmetric patterns. We developed a mathematical model of the spatio‐temporal distribution of Upd in three‐dimensions to characterize signaling activity in the extracellular domain. Simulation results and genetic analysis of mutant phenotypes support the idea that irregular tissue domains result in asymmetric distributions of the Upd signal, consistent with outcomes in vivo. Additionally, modeling results suggest that the concentrations of chemoattractant signals that guide the motile cells can be spatially impacted by tissue structure. We conclude that the interstitial space generated by adjacent tissues creates complex distributions of signaling molecules, which impacts responding cells. This work illustrates novel aspects of how tissue topography alters signaling, and sheds light on cell motility during animal development.Support or Funding InformationNational Science Foundation IOS‐1656550This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.