Location-dependent intracellular particle tracking using a cell-based coordinate system

Intracellular structure and active processes have been studied by particle tracking using the motion of internalised probes. Intracellular particle motion is driven by a complex combination of active and thermal processes within heterogeneous and dynamically changing micro-environments. Regions in the cells may react differently to environmental changes or following treatment, exhibiting location-dependent responses. Hence, to reveal such responses, we introduce cell-specific polar coordinate systems. The coordinates are defined for each cell by its nucleus location and orientation, providing relative particle locations in the cytoplasm. The utility of our approach is demonstrated by comparing Adenosine Triphosphate (ATP)-depleted and control cells. In both cells, we observe differences in particle transport with the distance from the nucleus. Following ATP depletion, basic particle motion analysis shows an expected reduction in activity driving particle transport. However, it is our location-dependent approach which reveals that while morphology changes primarily at the cortex, the cell response is actually nearly uniform across the cytoplasm.