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

Abstract

A digital image analysis system for extracting motion information from timevarying 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 a t approx. 1.2 pm s-l. 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.

Cell Movements and Mechanical Force Distribution During the Migration of Dictyostelium Slugs

“…Waves of movement exist in the longer 2D slugs analyzed. Our estimates of average wave speed and periodicity (i.e., 56 ± 10 µm/minute and 5.2 ± 1.2 minutes, respectively) are similar to previous measurements in 3D slugs using various methods [4,6,31], (iii) We occasionally observed spiral motion in a plane perpendicular to slug migration at the tip of a large 2D slug (not shown). This slug was certainly thicker than the others as we sometimes lost partially focus during the cell rotation.…”

“…It is unlikely that traction and resistive forces (see below) compensate exactly each other. We believe the absence of force is rather due to the vertical raising of the tip may as found in 3D slugs [4,5]. The fact that forces exist in the tip of flat 2D slugs ( Figure 6) supports also this conclusion.…”

“…The peaks in the cross-correlation represent the phase differences between the velocity oscillations of the two cells. We analyzed the relation between the phase of the oscillations and the cell coordinates as previously done by Breen and Williams for 3D slugs [4]. In Figure 2c, we have plotted the positions of the first four peaks as a function of the cell-cell distance along the slug's antero-posterior axis.…”

“…Although molecular details are still unknown, it is assumed that chemotactic waves organize the aggregation of free living single amoebae and the cell movements in multicellular aggregates including slugs [2]. There is a characteristic pattern of cell movement in Dictyostelium slugs: cells in the anterior prestalk zone show vigorous rotational movement around the central core of the tip, while cells in the prespore zone move straight forward in the direction of slug migration in a periodic fashion along the slug axis [3][4][5]. Periodic motion and optical waves with the same period have been observed in slugs of many Dictyostelium strains [6].…”

Migration of Dictyostelium slugs: Anterior‐like cells may provide the motive force for the prespore zone

“…Slugs move at a constant speed proportional to slug length [Rieu et al, 2004]. There is a characteristic pattern of movements in slugs: cells in the anterior prestalk zone show vigorous lateral movement which is often helical around the central core of the aerial portion of the tip [Siegert and Weijer, 1992], while cells in the central prespore zone move straight forward in the direction of slug migration in a generally periodic fashion [Breen and Williams, 1994;Dormann et al, 1996]. Siegert and Weijer [Siegert and Weijer, 1992] proposed that the prestalk cell movement is organized by a rotating scroll wave of cAMP, which serves as pacemaker for the formation of planar cAMP waves, which in turn direct periodic forward movement of prespore cells.…”