Fig. 9. Cultured embryonic chick cardiomyocytes double-stained for -actinin (red) and Krp1 (green). (A) Krp1 staining is diffuse during early stages of myofibril assembly. (B-D) In more mature cells, Krp1 often outlines the periphery of longitudinally oriented myofibrils (arrows). The boxed area in (D) is shown at higher magnification in (E), and (F) shows the multiplied product of the red and green channels, which emphasizes regions containing both -actinin and Krp1 fluorescence intensity. (E,F) Krp1 staining is often punctate and periodic, exhibiting spacings from 0.5 to 1.0 µm (arrowheads). This example also shows Krp1 localized near narrow myofibrils that appear to be fusing laterally with more mature striations (arrows), but no Krp1 staining in a region of the same myofibril that appears to have already undergone this fusion process (asterisk).

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