Dynamics of the pluripotent stem cell system

A steady stream of progenitor cells originating from continuous pluripotent stem cell divisions provide the raw material for sculpting the planarian body plan. Understanding morphogenesis in planarians therefore also necessitates understanding the interplay between the stem cell system and the patterning pathways. Questions we are particularly interested in include the mechanistic control of the different activity states of the stem cell system, the maintenance of the dynamic steady state between stem cell divisions and the removal of differentiated cells or the location-dependent orchestration of lineage choices. In parallel with investigations at the cellular level, we have also developed tools to quantify shape and growth dynamics at the organismal level. In close collaboration with the Jülicher group at the MPI-PKS, we aim to obtain a multi-scale understanding of planarian growth and degrowth.

Left: Planarians contain large numbers of pluripotent stem cells (red) within their mesenchyme. The image on top shows stem-cell specific expression of piwi-1, the cartoon below a sagittal cross-section at the level of the pharynx. Centre: Cartoon representation of the planarian dynamic steady state. A single type of pluripotent stem cells continuously divides to give rise to all types of differentiated cells. The energy to maintain system dynamics comes from either dying differentiated cells or from ingested food. Right: Quantification and analysis of the ratios between cross-sectional area (y-axis) and body length (x-axis) in a population of planarians. Image courtesy of Steffen Werner, Juelicher group.