Abstract
The cell adhesion glycoproteins, TgrB1 and TgrC1, are essential for Dictyostelium development and allorecognition, but it has been impossible to determine whether their pleiotropic roles are due to one common function or to distinct functions in separate pathways. Mutations in the respective genes, tgrB1 and tgrC1, abrogate both development and allorecognition and the defects cannot be suppressed by activation of the cyclic AMP dependent protein kinase PKA, a central regulator of Dictyostelium development. Here we report that mutations in genes outside the known PKA pathway partially suppress the tgrC1-null developmental defect. We separated the pleiotropic roles of tgrC1 by testing the effects of a suppression mutation, stcinsA under different conditions. stcAins modified only the developmental defect of tgrC1– but not the allorecognition defect, suggesting that the two functions are separable. The suppressor mutant phenotype also revealed that tgrC1 regulates stalk differentiation in a cell-autonomous manner and spore differentiation in a non-cell-autonomous manner. Moreover, stcAins did not modify the developmental defect of tgrB1–, but the less robust phenotype of tgrB1– obscures the possible role of stcA relative to tgrB1.
Highlights
The social soil amoeba Dictyostelium discoideum is used as a model system for the study of development, cell type differentiation and the evolution of multicellularity
We propose that TgrC1 participates in a critical control point in Dictyostelium development, allowing the cells to integrate inputs from both differentiation signals and from self recognition signals and to mount the proper responses
Suppressor mutations partially rescue the developmental defect of tgrC1
Summary
The social soil amoeba Dictyostelium discoideum is used as a model system for the study of development, cell type differentiation and the evolution of multicellularity. Upon starvation, they stop dividing, aggregate into multicellular structures that contain thousands of cells and develop into fruiting bodies composed of two cell types, the reproductive spores and the somatic stalks. In the first quarter of development, the cells entrain each other using extracellular cAMP They begin to aggregate and after 8–10 hours they form mounds, while starting to differentiate into the two major cell types. At 16 hours, the mound is transformed into a slug, in which the different cell types have sorted out into designated regions along the long axis of the slug – prestalk cells mostly in the front and prespore cells in the back. The slug erects itself and the prestalk cells descend through the prespore cell mass as both cell types undergo terminal differentiation into stalks and spores
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