Schmidtea mediterranea genome sequencing project. Schmidtea mediterranea s2f2

Alejandro Sánchez Alvarado Laboratory University of Utah Salt Lake City, UT Planarians are free-living representatives of the phylum Platyhelminthes, a group of some 50,000 species of flatworms. Flatworms are among the simplest animals with similar right and left sides: they have no body cavity, yet they possess derivatives of all three germ layers organized into complex organ systems. Thus, Platyhelminthes have been thought to occupy an important position in Metazoan evolution. Planarians are best known for their capacity to regenerate complete individuals from minuscule body parts, as well as for their ability to 'de-grow' when starved. Such extraordinary plasticity in the adult is in direct contrast to the rigidity displayed by currently used invertebrate models such as Caenorhabditis elegans and Drosophila melanogaster. The difference lies in a population of adult somatic (body) stem cells, called neoblasts, which are distributed throughout the planarian body. Neoblasts are the only cells that divide in planarians, and their division progeny generate the 30-40 different cell types found in these organisms. In intact planarians, these stem cells replace cells lost to normal turnover; whereas, in amputated animals, they give rise to the regeneration blastema, the structure in which missing tissues are regenerated. The successful introduction of cell, molecular, and RNAi techniques in planarians, along with heightened interest in stem-cell biology and the plasticity of the differentiated state, has re-kindled interest in these fascinating organisms. Sequencing the 4.8x108 bp genome of the sexual, diploid planarian S. mediterranea will provide a vital resource for the development of a unique model to study metazoan evolution, regeneration, and the regulation of the ability to differentiate into several types of cells. Insights into these basic biological problems will have deep and obvious implications for the improvement of human health.