Showing papers by "Pauline Schaap published in 2009"

Activated cAMP receptors switch encystation into sporulation

Abstract: Metazoan embryogenesis is controlled by a limited number of signaling modules that are used repetitively at successive developmental stages. The development of social amoebas shows similar reiterated use of cAMP-mediated signaling. In the model Dictyostelium discoideum, secreted cAMP acting on 4 cAMP receptors (cARs1-4) coordinates cell movement during aggregation and fruiting body formation, and induces the expression of aggregation and sporulation genes at consecutive developmental stages. To identify hierarchy in the multiple roles of cAMP, we investigated cAR heterogeneity and function across the social amoeba phylogeny. The gene duplications that yielded cARs 2-4 occurred late in evolution. Many species have only a cAR1 ortholog that duplicated independently in the Polysphondylids and Acytostelids. Disruption of both cAR genes of Polysphondylium pallidum (Ppal) did not affect aggregation, but caused complete collapse of fruiting body morphogenesis. The stunted structures contained disorganized stalk cells, which supported a mass of cysts instead of spores; cAMP triggered spore gene expression in Ppal, but not in the cAR null mutant, explaining its sporulation defect. Encystation is the survival strategy of solitary amoebas, and lower taxa, like Ppal, can still encyst as single cells. Recent findings showed that intracellular cAMP accumulation suffices to trigger encystation, whereas it is a complementary requirement for sporulation. Combined, the data suggest that cAMP signaling in social amoebas evolved from cAMP-mediated encystation in solitary amoebas; cAMP secretion in aggregates prompted the starving cells to form spores and not cysts, and additionally organized fruiting body morphogenesis. cAMP-mediated aggregation was the most recent innovation.

The Evolution of Morphogenetic Signalling in Social Amoebae

Abstract: Multicellular organisms have evolved several times from unicellular protists giving rise to the familiar forms of animals, plants and fungi. An important question in biology is how such transitions occurred. Multicellular life is typically dependent on complex communication between cells, whereas unicellular organisms respond mainly to environmental signals. Social amoebae are eminently suited to study the evolution of multicellularity, since they still combine a unicellular feeding stage with a stage where thousands of cells aggregate to form motile slugs and fruiting structures. In this chapter we summarize the signalling mechanisms that coordinate multicellular development in social amoebae and we discuss how these signalling mechanisms evolved from a response to environmental stress in solitary amoebae.