Dictyostelium discoideum

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A protoctist that has the ability to alternate between unicellular and multicellular life-styles. Individual Dictyostelium amoebas live in forest soil and eat bacteria and yeasts. However, when challenged by adverse conditions, such as starvation, groups of up to 100,000 cells signal each other by secreting acrasin (q.v.). This chemical attractant causes the amoebas to aggregate, forming a motile slug that is surrounded by a slimy extracellular matrix. At the apex of the mound, a fruiting body that produces spores differentiates. Dictyostelids are placed in the phylum Acrasiomycota (q.v.) and go by common names such as slime molds, social amoebas, or amoebozoans. They represent one of the earliest branches from the last common ancestor of all eukaryotes. Slime molds diverged after the split between the plants and opisthokonts (q.v.), but before the split of the fungi and animals. Therefore the slime molds, fungi, and metazoa are sister groups. D. discoidium has a genome size of 34 mb of DNA distributed among six chromosomes. The number of genes is about 12,500, and many of these have orthologs among the genes of opisthokonts. For example, there are 64 genes that are orthologs of human disease genes, such as Tay-Sachs, G6PD deficiency, and cystic fibrosis. The Dictyostelium genome contains genes that encode cell adhesion and signaling molecules (normally exclusive to animals) and genes that encode proteins controlling cellulose deposition and metabolism (normally exclusive to plants). See Chronology, 2005, Eichinger et al.

Subjects: Genetics and Genomics — Chemistry.

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