A dynamic cell recruitment process drives growth of the Drosophila wing by overscaling the Vestigial expression pattern

Abstract

Organs mainly attain their size by cell growth and proliferation, but sometimes also grow through recruitment of undifferentiated cells. Here we investigate the participation of cell recruitment in establishing the pattern of Vestigial (Vg), the product of the wing selector gene in Drosophila. We find that the Vg pattern overscales along the dorsal-ventral (DV) axis of the wing imaginal disc, i.e., it expands faster than the DV length of the pouch. This overscaling cannot be explained by differential proliferation or apoptosis, nor correlates with the dynamics of the Wingless gradient, which orchestrates patterning along the DV axis. We show that Vg overscaling is recapitulated by a mathematical model that explicitly considers cell recruitment. Experimentally, when cell recruitment is genetically impaired, the Vg pattern almost perfectly scales and adult wings are 20% smaller, demonstrating that cell recruitment contributes to organ growth. Furthermore, using lineage-tracing tools, we find that cell recruitment takes place in a specific time during normal development. Altogether, our work quantitatively shows when, how, and by how much cell recruitment shapes the Vg pattern and drives growth of the Drosophila wing. Summary statement Cell recruitment enhances growth of the developing Drosophila wing by expanding the expression of the wing selector gene, vestigial.