Dictyostelium - Importance

Importance

An important philosophy of experimental biology holds that radically different organisms solve similar problems in similar ways. While a primary goal of a scientist may be to discover what is wrong with the cell recognition systems of human cancer cells, the genetic mechanisms behind the problem may be too complex to unravel. While the human genome is large and highly complex, that of the cellular slime mold D. discoideum, which is presently under study in a great many laboratories in cell biology, is about 100 times smaller than the human genome. Dictyostelium is easy to propagate, and the complete life cycle can be induced in the laboratory. It is a practical matter then, to determine the entire gene sequence for Dictyostelium, and to learn the basics of many cellular processes through genetic engineering and experimentation. The genome was sequenced by 2005.

Most of its life, this haploid social amoeba undergoes a vegetative cycle, preying upon bacteria in the soil, and periodically dividing mitotically. When food is scarce, either the sexual cycle or the social cycle begins. Under the social cycle, amoebae aggregate to cAMP by the thousands, and form a motile slug, which moves towards light. Ultimately the slug forms a fruiting body in which about 20% of the cells die to lift the remaining cells up to a better place for sporulation and dispersal. Under the sexual cycle, amoebae aggregate to cAMP and sex pheromones, and two cells of opposite mating types fuse, and then begin consuming the other attracted cells. Before they are consumed, some of the prey cells form a cellulose wall around the entire group. When cannibalism is complete, the giant diploid cell is a hardy macrocyst which eventually undergoes recombination and meiosis, and hatches hundreds of recombinants.

Professor John Tyler Bonner has spent a lifetime researching the slime molds and created a number of fascinating videos in the 1940s to show the life cycle; he has mostly studied D. discoideum. In the videos, intelligence appears to be observed as the single cells, after separation, regroup into a cellular mass. The time-lapse film captivated audiences; indeed, Bonner when giving conferences has stated that the film “always stole the show”. The video is available on YouTube.

Scientists at the University of Texas at Austin were able to find great similarities between the proteins coded by genes: lvsA, lvsB, lvsC, lvsD, lvsE and lvsF in Dictyostelium and the proteins from the human LYST gene responsible for the Chediak-Higashi syndrome. All of the encoded proteins form part of the poorly understood BEACH family, making Dictyostelium a model organism for investigation. Experiments using mutant versions of these genes found gene lvsB as having an important role in lysosomal trafficking and also showing similar phenotypic characteristics to cells affected by the Chediak-Higashi syndrome. Further investigation on lvsB mutants provided insight for the role of the gene in lysosomal formation. These findings support similarity in LvsB/LYST function.