Physical Chemistry Seminar
7 April

Size scaling from cells to organisms

Le 7 April - 11h-12h

Appropriate size of the body and its parts is crucial for organismal function. For example, small discrepancies in limb length severely obstruct motility, and overgrowth of cardiac muscle is a prevalent cause of heart failure. Faithful development must therefore involve mechanisms that ensure correct body size, and that coordinate the growth of different cells and organs.
We combine theory and quantitative experiments with C. elegans to identify mechanisms ensuring size homeostasis. We show that the pharynx of C. elegans increases by a constant absolute volume per larval stage that is independent of its size at larval stage entry, leading to volume convergence during development. Moreover, pharyngeal size proportions are robust to tissue-specific experimental perturbation of growth signaling in the pharynx and in other tissues, suggesting a mechanism involving reciprocal tissue-to-tissue communication. A fundamentally different mechanism prevents the divergence of total body size among individuals, which involves the dynamic coupling of the growth rate with the frequency of an oscillatory developmental clock to produce a constant volume fold change per larval stage. By experimental modulation of the oscillatory frequency, we uncouple growth from development to predictably alter the adult body volume. 
Our research highlights a hierarchy of growth and size control with distinct mechanisms across size scales and demonstrates how models of multi-cellular growth can guide the rational modulation of body and organ size.

At Amphi Curie and on TEAMS

University of Bern, Institute for Cell Biology, Bern, Switzerland
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