Evolution of size and pattern in the social amoebas.
Bottom Line: The foundation is a recently constructed molecular phylogeny of the Dictyostelia, which was used to examine trends in the evolution of novel forms and in the divergence of genes that shape these forms.The role of cAMP in aggregation arose through co-option of a pathway that originally acted to coordinate fruiting body formation.The genotypic changes that caused this innovation and the role of dynamic cAMP signaling in defining fruiting body size and pattern throughout social amoeba evolution are discussed.
Affiliation: College of Life Sciences, University of Dundee, MSI/WTB/JBC complex, Dow Street, Dundee DD1 5EH, UK. email@example.comShow MeSH
Mentions: Social amoebas also have a trophic amoeboid stage, but they achieve macroscopic dimensions by aggregation.3 This occurs in response to starvation, which triggers regulated secretion of chemoattractant by the amoebas (Fig. 1). Cellular agglomerates are formed, which can consist of up to a million amoebas. Sophisticated cell–cell signalling mechanisms between the amoebas orchestrate the differentiation of up to five different cell types and coordinate an intricate progression of cell movements. In combination with the synthesis of a flexible skin-like matrix, cell differentiation and cellular movement first generate the formation of a motile structure, called the “slug”. The slug responds to chemical gradients and to light and warmth, which cause it to move to the soil's top layer. Here, the slug projects upwards and forms the fruiting body. This again involves highly ordered movement and differentiation and yields a slender column of stalk cells that bears aloft a global mass of spores. Depending on the species, the stalkcan show different patterns of side branches and/or be decorated with disc, root or cup-shaped support structures (Fig. 2). Unlike the ontogeny of sessile organisms like plants and fungi, which depends largely on series of directional cell divisions, the formation of fruiting bodies in social amoebas is more similar to the ontogeny of animal form. Both depend strongly on an intertwined program of cell movement and cell differentiation.
Affiliation: College of Life Sciences, University of Dundee, MSI/WTB/JBC complex, Dow Street, Dundee DD1 5EH, UK. firstname.lastname@example.org