Bimodal distribution of motility and cell fate in Dictyostelium discoideum

Abstract

Pre-starvation amoebae of Dictyostelium discoideum exhibit random movements. Starved cells aggregate by directed movements (chemotaxis) towards cyclic AMP and differentiate into live spores or dead stalk cells. Many differences between presumptive spore and stalk cells precede differentiation. We have examined whether cell motility-related factors are also among them. Cell speeds and localisation of motility-related signalling molecules were monitored by live cell imaging and immunostaining (a) in nutrient medium during growth, (b) immediately following transfer to starvation medium and (c) in nutrient medium that was re-introduced after a brief period of starvation. Cells moved randomly under all three conditions but mean speeds increased following transfer from nutrient medium to starvation medium; the transition occurred within 15 min. The distribution of speeds in starvation medium was bimodal: about 20% of the cells moved significantly faster than the remaining 80%. The motility-related molecules F-actin, PTEN and PI3 kinase were distributed differently in slow and fast cells. Among starved cells, the calcium content of slower cells was lower than that of the faster cells. All differences reverted within 15 min after restoration of the nutrient medium. The slow/fast distinction was missing in Polysphondylium pallidum, a cellular slime mould that lacks the presumptive stalk and spore cell classes, and in the trishanku (triA -) mutant of D. discoideum, in which the classes exist but are unstable. The transition from growth to starvation triggers a spontaneous and reversible switch in the distribution of D. discoideum cell speeds. Cells whose calcium content is relatively low (known to be presumptive spore cells) move slower than those whose calcium levels are higher (known to be presumptive stalk cells). Slow and fast cells show different distributions of motility-related proteins. The switch is indicative of a bistable mechanism underlying cell motility.

RasG signaling is important for optimal folate chemotaxis in Dictyostelium

“…There are also effects on cell motility. First, bacterially grown cells move faster than axenic cells in random motility assays [28-30]. Indeed, our own measurements show that bacterially grown JH10 and rasG-/rasC- cells migrate at higher velocities than their axenically grown counterparts during folate chemotaxis (Additional file 1: Figure S1).…”

Evolution of Reproductive Division of Labor – Lessons Learned From the Social Amoeba Dictyostelium discoideum During Its Multicellular Development

“…Concisely, several workers have proven that when cells grown at two different nutritional conditions, are reconstituted and finally allowed to enter the developmental cycle, there appears a clear distinction in the spatial distribution of these cells in the morphogenetic structures. For instance, when cells grown in glucose fortified medium were mixed with those cells grown in the medium lacking glucose and allowed forming fruiting bodies; chiefly, those cells grown in glucose fortified medium occupied the spore mass, whereas the stalk was made from those cells grown in medium lacking glucose (Leach et al, 1973;Thompson and Kay, 2000;Sistla et al, 2012). Based on this observation, we speculated a difference in glucose reserves between the haploids and diploids, as the diploids are double the size of haploids.…”

Social Conflicts in <em>Dictyostelium discoideum</em> : A Matter of Scales

“…Both calcium concentration (Azhar, Manogaran, et al, 1996) and pH (Van Duijn and Inouye, 1991) differences, moreover, can result in heterogeneity in cell motility, which is also known to vary with the phase of the cell cycle (Walmod et al, 2004). Analysis of a handful of trajectories suggests that, corresponding to bimodality in calcium concentration at the onset of development (Azhar, Manogaran, et al, 1996), also cell motility could be bimodally distributed (Goury-Sistla et al, 2012). Already in 1957 John Tyler Bonner suggested that faster cells would position themselves to the front of the slug, thus becoming stalk with a higher probability (Bonner, 1957).…”