Mapping Chemoattractant Gradients in Live Tissues.

Chemoattractant gradients guide cell migration in immunity, tissue repair, and development, yet their spatial and temporal distribution remains difficult to measure. In this review, we discuss how the field is moving beyond static source maps and indirect cellular proxies toward direct visualization of extracellular guidance cues. We outline the strengths and limitations of classical approaches for inferring chemoattractant gradients and highlight new strategies provided by genetically encoded chemoattractant indicators (GECHIs). Emerging PBP- and GPCR-based biosensors enable continuous visualization and localization of extracellular ligands in living tissues using fluorescence intensity- or lifetime-based readouts. Although the current toolbox is limited to a small number of chemoattractants, ongoing sensor development is likely to expand ligand coverage and enable multiplexed measurements with spectrally distinct sensors in the near future.