The actin cytoskeleton is disorganized at junction breakage sites in claudin/JAM-A KO cells. The actomyosin organization at the junction breakage sites was observed by STED microscopy. (A–E) F-actin organization at junction breakage sites. The F-actin bundles were loosened at junction breakage sites (arrows), but coalesced and became attached to the cell junctions where ZO-1 localization persisted (arrowheads). (F–J) Myosin IIA localization at junction breakage sites. The myosin IIA bundles were loosened at large junction breakage sites (F–H, arrows). The myosin IIA localization was fragmented at small ZO-1 fragmentation sites (I and J, arrows). Remnant myosin IIA staining was observed at the sites where ZO-1 localization persisted (J, arrowheads). (K–O) Myosin IIB localization at junction breakage sites. The myosin IIB bundles were loosened at large junction breakage sites (K–M, arrows). The myosin IIB localization was fragmented at small ZO-1 fragmentation sites (N and O, arrows). Remnant myosin IIB staining was observed at the sites where ZO-1 localization persisted (O, arrowheads). Scale bar: 10 μm.