What function is described for ZO-3?

• A. Antibody production
• B. Bind DNA
• C. Mediate actin binding
• D. Gatekeeper of ion channels

Answer: (C)

ZO-3 serves as a cytoplasmic scaffold at tight junctions, anchoring transmembrane components such as occludin and claudins to the actin cytoskeleton. This actin linkage via ZO-3 helps organize and stabilize the junctional plaque, supporting the seal between neighboring epithelial cells and allowing dynamic remodeling as needed. In the MAGUK family, ZO-3 brings together junctional proteins and cytoskeletal elements through its interaction domains, enabling proper barrier function and signaling at the junction.

Antibody production is not a function of ZO-3, as this protein is not involved in immune antibody synthesis. It does not bind DNA as part of transcriptional regulation. While tight junctions influence paracellular permeability, ZO-3 itself is not a gatekeeper of ion channels; its role is organizing and linking junctional proteins to the actin network to maintain the barrier.