The Organism
Dictyostelium discoideum, a soil-living amoeba, is an excellent organism for the study of the molecular mechanisms of cell motility, signal transduction, cell-type differentiation and developmental processes. Genes involved in any of these processes can be knocked-out rapidly by targeted homologous recombination. Since Dictyostelium is haploid, mutants are readily isolated and the REMI (restriction enzyme mediated integration) technique of insertional mutagenesis allows the facile cloning of disrupted genes. The determination of the entire information content of the Dictyostelium genome will be of great value to those working with this organism directly, as well as to those who would like to determine the functions of homologous genes from other species.

The Genome
The hereditary information is carried on 6 chromosomes with sizes ranging from 4 to 7 Mb resulting in a total of about 34 Mb of DNA, a multicopy 90 kb extrachromosomal element that harbours the rRNA genes, and the 55 kb mitochondrial genome. The number of genes in the genome is about 12,000 and many of the known genes show a high degree of sequence similarity to homologues in vertebrate species.

The developmental cycle
from the vegetative form to the stalk with fruiting body offers a rich field to study developmental processes.

Figure 1: The stages of Dictyostelium life cycle [Copyright, M.J. Grimson & R.L. Blanton]

During development the cells in the slug differentiate partly. Some become prespore cells, others become prestalk cells, but apparently a few become cells with innate immune-like functions. They are called sentinel cells.