cAMP and spore differentiation in Dictyostelium discoideum.

Abstract

The individual amoebae composing a Dictyostelium aggregate can differentiate into either stalk or spore cells according, it is believed, to the extracellular signals they receive. By inducing the differentiation ofisolated cells we hope to identify these signals. It is shown here that wild-type cells can differentiate into prespore cells in a solution of cAMP plus salts supplemented by conditioned medium. Cell-to-cell contact is not required. More important, isolated cells of various sporogenous mutant strains form spores in similar conditions without needing conditioned medium at all. For these strains at least, cAMP is the sole inducer necessary for spore formation. Earlier work has shown that stalk cells are induced by a combination of cAMP and a low molecular weight factor, differentiation inducing factor (DIF). DIF now appears to be the only pathway-specific inducer involved in the differentiation of sporogenous amoebae and DIF levels in the aggregate may therefore determine whether an amoeba becomes a stalk or a spore cell. In suitable conditions some sporogenous mutants form migrating slugs having an anterior/posterior pattern ofprestalk and prespore cells. This pattern could be generated by the localized activity of DIF. (5) where it serves to induce a later group of gene products (6-9). Differentiation in monolayers of cells that are prevented from undergoing normal morphogenesis by, for instance, a restrictive overlay of cellophane has been reported (10)(11)(12). At high cell density cAMP induces the differentiation of stalk and prespore cells but not of mature spores. However, mutants-termed sporogenous-have been selected in which spores also form and these strains have proved very useful in the current work.It has been repeatedly observed that amoebae can only differentiate into spore or prespore cells if they have been in contact with other cells (9)(10)(11)(13)(14)(15). Recently the resulting belief in a cell contact-dependent inductive process has been challenged by the finding that isolated sporogenous amoebae can form spores-in improved incubation conditions-in the presence of cAMP (16). Nonetheless, spore formation still needed unknown soluble factors released by the cells.After further improvement of the incubation conditions, I show here that wild-type prespore cells can also differentiate without cell-to-cell contact and that cAMP alone is a sufficient inducer of spore formation in various sporogenous strains.MATERIALS AND METHODS Cells. Sporogenous mutants HM18 (tsg-900, acr-900, cob-900, sci-907), HM28 (tsg-901 or tsg-903 or both, cyc-900, whi-900, sci-909), and HM29 (tsg-901 or tsg-903 or both, cyc-900, whi-900, sci-910) derive from the wild-type strain V12M2.

Allorecognition, via TgrB1 and TgrC1, mediates the transition from unicellularity to multicellularity in the social amoebae Dictyostelium discoideum

“…Serafimidis and Kay also reported a dependence of cell differentiation on cell density in NC4-derived strains (Serafimidis and Kay, 2005). However, another wild strain, V12M2, is able to form spores in vitro without cell contact, with added cAMP and media conditioned by starving cells for 18 h (Kay, 1982). These in vitro observations suggest that the development of V12M2 does not depend on TgrB1/TgrC1-mediated allorecognition, though there is no direct data to support this.…”

Modelling cell movement, cell differentiation, cell sorting and proportion regulation in Dictyostelium discoideum aggregations

“…• cAMP is predominantly made by prestalk cells and anterior-like cells and degraded by prespore cells [31,32,33];…”

“…• cAMP signalling induces prespore cell differentiation and blocks prestalk cell differentiation by inhibiting DIF signalling [31,32,33].…”

“…Functions f 1 , g 1 and f 2 , g 2 describe the positive and negative feedback effects of cAMP and DIF on these transitions. Since experimental studies suggested a cAMP and DIF concentrationdependent induction of prestalk and prespore markers [28,30,32], we choose Hill-type forms for these transition functions (for examples of other types of transition functions see Remarks 1 and 2):…”

“…Throughout this article, we use Hill-type functions to describe the saturated effects of DIF and cAMP concentrations on the PSP↔PST transitions. This particular choice for the transition functions was based on experimental studies that calculated the half-maximum concentration of these two chemicals necessary to induce or inhibit cell differentiation [28,30,32]. However, other studies used different types of transition functions.…”