CLDN3 and melanoma: To study the association between claudin-3 and melanoma metastasis, we used claudin-3−/− mice and control claudin-3+/+ mice to establish a popliteal lymph node metastasis model by injecting 5 × 105 mCherry-labeled melanoma cell line B16F10 subcutaneously into the footpad (Fig. 1a).