Optical flow analysis of the ventral cellular layer of the migrating Dictyostelium discoideum slug

A digital image analysis system for extracting motion information from time-varying digital light microscopy images is presented. This system is then used to map out the movement profile of the surface layer of cells in contact with the substratum through the extracellular matrix (ECM) of the migrating Dictyostelium discoideum slug. From digital high magnification light microscopy images, the morphology of moving cells within the tail region of a young migrating wild-type WS380B slug is described, and compared with the morphology of streaming D. discoideum cells. It is shown that: (i) when the migrating tip of the slug touches the agar substrate, cells in the anterior ventral surface layer of the tip region slow dramatically; (ii) overall cell movement in the ventral surface layer of the migrating D. discoideum slug is slower than the movement of the slug as a whole; and (iii) in less than 10% of cases a wave of movement (groups of cells synchronously slowing down and then accelerating forward) propagates down the slug axis at approx. 1.2 microns s-1. The time interval between waves may be related to the time interval between tip-to-substratum contact that is periodically re-established during normal WS380B slug migration after each aerial projection of the tip.