These results are consistent with two models. The chitin filament may act as a sponge. As liquid is drawn into the lumen during development, the sponge-like cable would then expand to uniformly push the epithelial cells outward. Uv, however, favors a second hypothesis in which the filament holds back lumen expansion, much like an anchor; the resultant tension would also force any constrictions to expand. This model implies the existence of a protein complex linking to the apical surface and underlying cytoskeleton.
Tube formation is a fundamental process in many organisms, so analogous mechanisms for shaping tubes may yet be found. “Different organs,” suggests Uv, “will likely use different matrix components to create uniform luminal expansion.”