Which statement best reflects the involvement of ZO-1 and ZO-3 in actin binding?

• A. ZO-2 mediate actin binding
• B. ZO-1 and ZO-3 mediate actin binding
• C. ZO-1 suppress tumor growth
• D. ZO-3 degrade basement membrane

Answer: (B)

Tight junctions anchor to the actin cytoskeleton through scaffold proteins that bind both the junctional complex and F-actin. ZO-1 and ZO-3 act as the main bridge, connecting transmembrane tight junction proteins like occludin and claudins to the actin filaments that lie just beneath the membrane. This linkage stabilizes the junction and helps regulate paracellular permeability. While ZO-2 can associate with these structures in some contexts, the strongest and most direct actin-binding role is described for ZO-1 and ZO-3, making that option the best reflection of how actin binding is mediated at tight junctions. The other statements describe features not characteristic of these proteins.