Sternfeld, John; David, Charles N.
Cell Sorting daring Pattern Formation in Dictyostelium.
In: Differentiation, Vol. 20: pp. 10-21
Formation of the prestalk-prespore pattern in Dictyostelium was investigated in slugs and submerged clumps of cells. Prestalk and prespore cells were identified by staining with vital dyes, which are shown to be stable cell markers. Dissociated slug cells reaggregate and form slugs that contain a prestalk-prespore pattern indistinguishable from the original pattern. The pattern forms by sorting out of stained prestalk cells from unstained prespore cells. Sorting also occurs in clumps of dissociated slug cells submerged in liquid or agar. A pattern arises in 2 h in which a central core of stained cells is surrounded by a periphery of unstained cells. Sorting appears to be due to differential chemotaxis of stained and unstained cells to cAMP since exogenous cAMP (>10−7 M) reverses the normal direction of sorting-out such that stained cells sort to the periphery of the clumps.
Isolated portions of slugs regenerate a new prestalk-prespore pattern. Posterior isolates regenerate a pattern within 2 h due to sorting of a population of vitally stained ‘anterior-like’ cells present in posteriors. Anterior-like cells do not sort in intact slugs due to the influence of a diffusible inhibitor secreted by the anterior region. During posterior regeneration this signal is absent and anterior-like cells rapidly acquire the ability to sort. Anterior isolates regenerate a staining pattern more slowly than posterior isolates by a process that requires conversion of stained prestalk cells to unstained prespore cells.
The results suggest that pattern formation in Dictyostelium consists of two processes: establishment of appropriate proportions of two cell types and establishment of the pattern itself by a mechanism of sorting-out.