REGULATORY BIOLOGY

Reprogramming of individual cells

The Physarum polycephalum plasmodium is a macroscopic multinucleate single cell with a naturally synchronous population of nuclei which provides unique experimental options for systems-oriented analyses of reprogramming at the single cell level:

One can take multiple samples from the same plasmodial cell for biochemical analyses (e.g. 10-20 mg fresh weight per sample). As the cell is not destroyed or disturbed by sampling, the samples can be taken at different time points after differentiation has been experimentally triggered.

By fusion of the plasmodial cells of different mutants of arbitrary relative size one can perform gene dosage titration or time-resolved somatic complementation and analyse the relaxation kinetics that occur in response to the perturbation of the regulatory network.

By systematic genetic screening and by characterisation of the obtained differentiation control mutants with various quantitative techniques we reconstruct the regulatory network that controls cellular reprogramming and analyse its functional dynamics. These studies are preformed at the single cell level, as identically treated cells from a clonal population take alternative pathways to differentiate.

Physarum polycephalum

With its relatives Dictyostelium discoideum and Entamoeba histolytica, Physarum polycephalum belongs to the Amoebozoa group of eukaryotes. Physarum has a rich cell biology with many animal cell-like features. This is also reflected at the molecular level e.g. through orthologs of STAT-like transcription factors or germ cell regulators like Piwi and Pumilio that are differentially regulated during Physarum development.

During its developmental cycle, Physarum can differentiate into seven distinct types of cells, each with a specific morphology, function and gene expression pattern. Differentiation is under the control of environmental signals. Unlike in multicellular organisms, these cell types occur in temporal order instead of developing in parallel to build a body

We focus on the question of how the plasmodium, a multinucleate single cell, loses its unlimited replicative potential and is irreversibly committed to sporulation, taking one of alternative developmental pathways. Differentiation can be experimentally triggered by a brief pulse of far-red light.