Immunofluorescence microscopy of symplekin on cultured human and Xenopus laevis cell lines, frozen tissue sections, and blood smear preparations of Xenopus, demonstrating dual localization in nuclear and tight junctional forms. (A and B) Human colon carcinoma CaCo2 cells reacted with mAb Sym-TJ-E150 (A) or mAb Sym-Nu (B), showing dual (A) or exclusively nuclear (B) localization. The inset in A shows the distribution of symplekin during mitosis. (C and C′) Cultured X. laevis kidney epithelium XLKE cells, line A6 (C, epifluorescence with mAb Sym-Nu; C′ phase contrast). (D–D") Xenopus skin tissue, showing nuclear immunofluorescence in epidermal keratinocytes (D, epifluorecence with mAb Sym-Nu; D′, nuclear DAPI staining; D", phase contrast). (E and E′) Xenopus heart tissue, including numerous cardiomyocyte nuclei and a blood vessel with positive erythrocyte nuclei (E, epifluorescence with mAb Sym-Nu; E′, DAPI staining). (F) Blood smear preparation, showing the nuclear immunoreaction in the transcriptionally almost fully inactive erythrocyte nuclei. Bars, 20 μm; Inset, 10 μm.