Fig. 4.

Effect of WNK4 on structure of tight junctions. (a-d) Transmission EM of WNK4-Q562E cells. Monolayers were grown in the presence and absence of doxycyline, and were subjected to transmission EM. The depth of tight junctions is unaffected by WNK4-Q562E induction. Similar results were seen for WT-WNK4 (data not shown). ZA, zonula adherens; TJ, tight junctions (zonula occludens). (e and f) Freeze-fracture EM of WNK4-Q562E cells. Monolayers were treated as above and subjected to freeze-fracture EM as described in Methods. The number and complexity of tight-junction strands (indicated by arrows) are unchanged by induction of WNK4-Q562E. Similar results were seen for WT-WNK4 (data not shown). WNK4 does not impart its effect on paracellular permeability by eliciting gross structural changes on the tight-junction complex.