Fig. 7. A model for E-cadherin signaling during tube fusion. E-cadherin signals via ß-catenin (Arm) to initiate track assembly. An unknown factor (X) associated with the juxtamembrane domain is required to assemble or stabilize track-associated microtubules. Microtubules are required for track maturation. Maturation events involve the subsequent reinforcement of initial F-actin/Shot assembly or the disassembly of apical cytoskeletal structures and the track itself prior to fusion. Shot functions to stabilize F-actin and microtubules associated with the track. The track components together stabilize the new E-cadherin contact and coordinate apical surface movements and remodeling.