Abstract

Planarians are remarkable animals. They can regenerate from tiny tissue pieces, maintain continuous cell turn over via abundant pluripotent stem cells and continuously grow or literally shrink their bodies in a food-supply dependent manner. Such astonishing adult size plasticity is accompanied by the size dependence of multiple aspects of planarian physiology, including the organismal growth and de-growth rates, levels of metabolic energy stores or the formation of the reproductive system at a precise size threshold. This implies the existence of mechanisms that sense system size and elicit size-dependent physiological changes, the elucidation of which is a long-standing goal of my laboratory. My talk will present recent findings, including direct size-dependencies in planarian gene expression, their upstream control via a size dependent hormone and downstream functional consequences. Our results thus far suggest the existence of magnigens, the levels of which encode system size and that, via dose-dependent effects on target gene expression, tune physiology to the momentary size of the animal.