Cytoplasmic stress fibers in the developing heart

Authors

  • Hiroshi Sumida,

    Corresponding author
    1. Department of Anatomy and Cell Biology, Medical University of South Carolina, Charleston, South Carolina
    • Department of Geneticopathology, Research Institute for Nuclear Medicine and Biology, Hiroshima University, Hiroshima 734, Japan
    Search for more papers by this author
  • Robert A. Ashcraft Jr,

    1. Department of Anatomy and Cell Biology, Medical University of South Carolina, Charleston, South Carolina
    Search for more papers by this author
  • Robert P. Thompson

    1. Department of Anatomy and Cell Biology, Medical University of South Carolina, Charleston, South Carolina
    Search for more papers by this author

Abstract

Rhodamine-conjugated phalloidin staining was used to study the distribution of filamentous actin in the developing heart of embryonic chicks and rats during the morphogenetic period of cardiac septation. In the chick, intense fluorescence indicative of abundant filamentous actin was observed along the myocardium and in the mesenchymal condensations that formed within the aorticopulmonary septum at day 5. Such cellular condensations and concentration of filamentous actin were not seen in the atrioventricular cushions nor in the preseptation outflow tract. Similar results were found in the 14-day rat embryo. In electron micrographs, microfilament bundles with irregular dense bodies were seen in elongated mesenchymal cells between the valve sites of both species. Cell-cell contacts were observed between such elongated cells and myocyte processes protruding from the nearby myocardial sheath. These histochemical and ultrastructural observations suggest that such mesenchymal condensations serve a specialized mechanical tensile role during embryonic septation of cardiac outflow channels.

Ancillary