Scale and proportion during planarian regeneration

Our group is fascinated by tissue formation. What determines shape, size and proportions of developing tissues?  How is the balance set between addition of new cells and removal of old ones? Or during regeneration, how can the remaining tissue rebuild exactly the body parts that have been lost due to injury?

We are addressing these questions in a fascinating new model system with a long lab history, planarian flatworms. Planarians contain large numbers of pluripotent adult stem cells that continuously divide. The production of new cells is balanced by the death of old cells in a dynamic steady state, such that the entire animal continuously rebuilds itself. Feeding shifts the balance towards addition of new cells by causing a brief burst of increased stem cell divisions. Starvation shifts the balance towards a net loss of cells, thus literally shrinking the animals (“de-growth”). Even though the size of a worm can therefore fluctuate dramatically over time, the animals manage to scale their external and internal proportions within a 40-fold range in body length. And as if this weren’t feat enough, planarians regenerate in their entirety even when chopped into tiny pieces.

Taking full advantage of the interdisciplinary research environment in Dresden, we use cell biology, genomics and physics to understand the interplay between molecules, cells and tissues. One current focus is the molecular coordinate system that defines and maintains shape and proportions of the planarian body plan. A second line of projects examines regulatory dynamics and lineage choices of the pluripotent adult stem cell system. Third, we have established a live collection of planarian species from around the globe, allowing us to address also evolutionary aspects of regeneration, tissue turn-over rates or body shape.