Cell Sorting daring Pattern Formation in Dictyostelium

Abstract

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.

Fate and regulation of anterior-like cells in Dictyostelium slugs

“…Sampson's results can be explained if the anterior-like cells progressively lose their ability to form stalk. Such a loss could be due to depletion of the cells' energy reserves under starvation conditions or to a decrease in their sorting ability caused by long and continuous exposure to the sorting inhibitor derived from the anterior cells (Sternfeld and David, 1981a).…”

“…The new pattern is a result of stained anterior-like cells sorting out to form the new anterior region (Sternfeld and David, 1981a). Although the typical anterior-posterior proportions are reestablished, only about 60% (59.1 -t 4.3%; 10 slugs) of the anterior cells are derived from the original stained anterior-like cell population.…”

“…Staining with the vital dyes neutral red (Sigma Chemical Co.) or nile blue A (Hartman-Leddon Co.) was done after the first wash. The cells were resuspended in 2 ml of buffer and 5 drops of a stock solution (0.2 mg/ml; note: Sternfeld and David (1981a) stated an incorrect concentration)…”

“…Additional work indicates that the sorting is probably guided by a differential chemotactic response to cyclic AMP (Matsukuma and Durston, 1979;Sternfeld and David, 1981a). Portions of Dictyostelium slugs also exhibit pattern regeneration (Raper, 1940;Bonner, 1952).…”

“…Portions of Dictyostelium slugs also exhibit pattern regeneration (Raper, 1940;Bonner, 1952). A study of the regeneration of the pattern in isolated posterior tissue has led to the identification of a separate and distinct population of posterior cells (Sternfeld and David, 1981a referred to as anterior-like cells. They are responsible for the rapid pattern regeneration observed in posterior tissue as they sort out from the prespore cells to form the anterior of the regenerated slug.…”