Stem Cells in Turbellaria

The functional requirements of self-renewal and totipotency of stem cells in Platyhelminthes make them a suitable tool for studying cell differentiation and stem cell (neoblast) properties. We attempt to characterize the stem cell system of Macrostomum ana a planarian species applying ultrastructural and immuno-cytochemical approaches in combination with microinjection and the isolation of neoblasts-specific genes. In previous studies we have applied Bromodeoxyuridine labeling to show the distribution, migration, and differentiation of S-phase neoblasts in this species. An ultimate proof for totipotency was not possible yet. Here we propose to further characterize the stem cell system of the microturbellarian Macrostomum by (1) assessing the differentiation potential (totipotency?) of neoblasts (2) generating molecular markers for neoblasts and (3) identifying and tracing the fate of individual redetectable neoblasts. Macrostomum has many avantages for this task: (1) BrdU labeling is extremely easy to perform, (2) its small size (only 25.000 cells) allows us to follow individual neoblast clusters in differentiation, and differentiating tissues can be surveyed easily; (3) DiI labeled neoblasts can be followed in vivo. From previous projects the organization of the nervous-, muscle-, and neoblast system is particularly well described. In addition we have selected one planarian species with an extremely high percentage of neoblasts for comparison, because most data from such experiments have been accumulated for this taxon. Only crude extracts of neoblasts have been examined so far, however, without testing the nature of the injected cell suspension with TEM. In this project we plan to specify the nature of injcected cells by light- and electron microscopical methods. Microinjection of fluorescent tracers, purification and labeling of neoblasts together with molecular and cytological approaches will lead to a better understanding of the platyhelminth stem cell system. Because of the conserved nature of signaling pathways and the regulation of cell differentiation, the results will have an impact on the knowledge of stem cells of higher organisms as well, including the human stem cell systems. The collaborations with 5 labs we have established should increase research with Marcostomum which we hope will become a model organism among lower Metazoa.

In this project we have studied the stem cell system of free-living Platyhelminthes. The stem cells of these animals - also called neoblasts - have the capability to differentiate into all cell types including germ cells (totipotency). This unique potential is usually characteristic for embryonic stem cells. However, in the species studied here (Macrostomum lignano, Convoluta - now Isodiametra - pulchra, Convolutriloba, Dugesia tahitiensis, Schmidtea polychroa) totipotent stem cells are also present in adult animals. Therefore these species - especially Macrostomum lignano - are highly suitable to study stem cell biology during development, growth, and regeneration. Studies on stem cell proliferation, migration and differentiation were made. Neoblasts were characterised in histological and ultrastructural terms. Macrostomum lignano was described as a new species and a detailed analysis of the embryonic development was published. With the production of DNA libraries, the sequencing of thousands of genes and the adaptation of molecular techniques a significant molecular basis is available for Macrostomum lignano and Isodiametra pulchra. Because of the key position in evolution these groups have attracted many researchers for phylogenetic studies. The gene sequences obtained in this project provide significant data for comparative phylogenetic analyses that are currently carried out. Macrostomum lignano is an appropriate species to address questions related to reproductive biology. The small size (1 mm), its transparency, the fact that it is a hermaphrodite and several methodological aspects allowed us to examine and publish on various aspects of reproduction. The research carried out was performed by intensifying existing cooperations (Lukas Schärer, presently Univ. Innsbruck, Prof. Volker Hartenstein, UCLA, USA; Prof. Seth Tyler, University of Maine, USA) and by establishing new cooperations (Prof. Kiyokazu Agata, RIKEN, Kobe, Japan; Dr. Tom Artois, University Diepenbeek, Belgium) during the project runtime.