A positional Toll receptor code directs convergent extension in Drosophila

Elongation of the head-to-tail body axis by convergent extension is a conserved developmental process throughout metazoans. In Drosophila , patterns of transcription factor expression provide spatial cues that induce systematically oriented cell movements and promote tissue elongation. However, the mechanisms by which patterned transcriptional inputs control cell polarity and behaviour have long been elusive. We demonstrate that three Toll family receptors, Toll-2, Toll-6 and Toll-8, are expressed in overlapping transverse stripes along the anterior–posterior axis and act in combination to direct planar polarity and polarized cell rearrangements during convergent extension. Simultaneous disruption of all three receptors strongly reduces actomyosin-driven junctional remodelling and axis elongation, and an ectopic stripe of Toll receptor expression is sufficient to induce planar polarized actomyosin contractility. These results demonstrate that tissue-level patterns of Toll receptor expression provide spatial signals that link positional information from the anterior–posterior patterning system to the essential cell behaviours that drive convergent extension. Body axis elongation from head to tail is essential for animal development, however, the spatial cues that direct cell rearrangements relative to the anterior–posterior axis were unknown; this Drosophila study of convergent extension reveals that three Toll family receptors, expressed in overlapping stripes, modulate the contractile properties of cells to generate the polarized cell rearrangements that lead to body axis elongation. Toll receptors in body patterning Body elongation along the head-to-tail axis is essential during animal development. In Drosophila , the spatial cues for elongation are provided by the patterned expression of genes. How the spatial cues direct the cell rearrangements required for elongation has been unknown. This study identifies three cell-surface Toll family receptors, expressed in stripes along the head-to-tail axis, that modulate the contractile properties of cells to generate the polarized rearrangements leading to tissue elongation.