Wang, D.; Jia, X.; Zhang, Q.; Xu, K.; Zheng, Y.; Zhang, Q.; Liu, N.; Wang, H.; Yu, L.

Membrane tethers, thin tubular extensions of the plasma membrane, form during cell migration, adhesion, and signaling. Various types exist, though their maintenance mechanisms are not fully understood. This study employs live cell imaging, in vitro reconstitution, and in situ cryo-EM analysis to show that Tspan7, typically a freely diffusing transmembrane protein, forms long cylindrical polymers in right-handed helical formations on retraction fibers. These polymers assemble into spiral tubule structures, acting as a \"transmembrane skeleton\", enriching Tspan7 on retraction fibers and promoting their formation. Our findings reveal a novel assembly strategy for transmembrane proteins and a mechanism for maintaining membrane tethers.