REARRANGEMENT OF INTERCELLULAR-JUNCTIONS AND CYTOSKELETAL PROTEINS DURING RABBIT MYOCARDIUM DEVELOPMENT

A direct and close association between desmosomes and intermediate-siz ed filaments of the keratin type exists in embryonic and in adult epit helial tissues. Cardiomyocytes are interconnected by spot-desmosomes, which are found in the intercalated disks and can be immunocytochemica lly detected by antibodies to desmoplakins. In this study at the light microscopical level, me describe an interaction of keratin filaments with desmoplakins during rabbit myocardiogenesis. In the early stages (0-1 somites), desmoplakins are more abundant in the heart anlagen tha n in the adjacent intra- and extraembryonic mesoderm. During developme nt of the myocardium, desmoplakin expression gradually rearranges from an apicolateral into an intercalated disk localization in later stage s. Keratin expression in the developing myocardium of the rabbit heart decreases with the age of the embryo. Keratin filaments are gradually lost via dot-like aggregates which colocalize with desmoplakin-positi ve clusters. Our results suggest a role for keratins in the developmen tal rearrangement of desmoplakins into the intercalated disks. A direc t relation of desmin and titin reorganization to desmoplakin rearrange ment, which was examined because of the dominant role of these protein s in cardiogenesis, was not found.