Mena specifically colocalizes with the αII-Spectrin splice variant SH3i. (A, B) Confocal microscopy images of adult mouse heart cryosections stained for Mena (a, green), F-actin (b, red), and total αII-Spectrin (A, image c, blue) or the αII-Spectrin splice variant SH3i (B, image c, blue). (A) Mena, F-actin, and a portion of total αII-Spectrin colocalized at Z-discs (A, merged images d-f, arrowheads) and intercalated discs (A, merged images d-f, arrows. Detailed analyses revealed a doublet appearance of the proteins across the intercalated disc (A, images d-f, insets). Most αII-Spectrin was detected at the lateral plasma membrane (A, image c, asterisks) and colocalization with Mena and F-actin at these sites was minor. (B) SH3i was exclusively detected at Z- and intercalated discs but was absent from the lateral plasma membrane compare image c of A and B). Merged images d-f and magnified views of the indicated areas therein (images g-i) revealed high degree of colocalization of Mena and SH3i at Z-discs (images g-i, arrowheads) and intercalated discs (arrows), the lateral boundaries of the sarcomeres, which are exemplarily highlighted by brackets. Outside Z- and intercalated discs, colocalization of Mena and SH3i with F-actin was minor. Scale bars in images c and f 15 μm, image i 5 μm.