Fig. 7. Cultured embryonic chick cardiomyocytes double-stained for (A,E) -actinin and (B,F) filamin. Composite images (C,G) show both -actinin staining in red and filamin staining in green. (D,H) The multiplied products of the red and green channels emphasize regions containing both filamin and -actinin fluorescence intensity. (A-D) Large regions of premyofibrils are characterized by punctate -actinin staining along the cell preiphery (asterisks); filamin staining exhibits a more diffuse, mesh-like appearance in these regions. More centrally located mature myofibrils exhibit broad periodic striations of filamin staining that co-localize with the -actinin staining in Z-lines (arrowheads). (E-H) Some myofibril precursors are characterized by near continuous -actinin and filamin staining (arrows). As sarcomeres mature and -actinin spacing increases, filamin staining is still observed between the newly formed Z-lines (arrowheads). In fully mature regions, filamin staining is restricted to the Z-lines (asterisks).