Visualization and identification of cytoskeletal filaments in embryonic chick heart by the quick-freeze deep-etch method combined with immunocytochemistry.

Cytoskeletal filaments in myocardial cells of chick embryo (stage 18-20, day 3) were studied by immunocytochemical and rapid-freeze deep-etch methods. A three-dimensional network of cytoplasmic filaments surrounding nascent myofibrils was visualized in saponin-treated myocardial cells. The major part of the network was composed of 12 to 14 nm filaments in platinum replicas. To identify the filaments, the myocardial cells were permeabilized with Triton X-100 and treated with myosin subfragment-1 (S1) for actin or immunogold-labeled antibody for desmin. A large number of filaments in myofibrils and a few cytoplasmic filaments were decorated with S1. A loose network surrounding the myofibrils was not decorated with S1 but with gold particles. This finding means that the majority of filaments occupying the interfibrillar space were desmin-containing filaments.