Fig. 7.

Lumens enlarge and fuse during single lumen formation. (A) During single lumen formation, vhnf1 drives lumen enlargement through Cldn15 and Na⁺/K⁺ ATPase regulated fluid accumulation. Next, smoothened regulates remodeling through Rab11a-mediated trafficking to facilitate lumen fusion. Red indicates the luminal surface. (B) During the fusion process, Rab11 traffics apical proteins (red) to the luminal surface and recycles basolateral proteins (green) from bridge contacts to lateral membranes. As the lumens expand, the bridge contacts between the lumens shrink and split, and the lumens fuse.