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Cytoplasmic stress fibers in the developing heart
H Sumida1, R A Ashcraft, R P Thompson
1Department of Anatomy and Cell Biology, Medical University of South Carolina, Charleston.
Insights
This study reveals that filamentous actin in mesenchymal condensations plays a crucial mechanical role during embryonic heart septation in chicks and rats. These findings highlight the importance of actin dynamics in cardiac outflow tract development.
Area of Science:
- Developmental Biology
- Cell Biology
- Cardiovascular Research
Background:
- Cardiac septation is a critical process during embryonic development.
- Understanding the cellular mechanisms underlying septation is essential for identifying congenital heart defects.
Purpose of the Study:
- To investigate the distribution and role of filamentous actin during cardiac septation in embryonic chicks and rats.
- To elucidate the mechanical contribution of mesenchymal cells to the formation of the cardiac outflow tract.
Main Methods:
- Rhodamine-conjugated phalloidin staining to visualize filamentous actin.
- Histochemical and ultrastructural analysis using electron microscopy.
- Comparative study in developing chick and rat embryos.
Main Results:
- Abundant filamentous actin was observed in myocardial and mesenchymal cells within the aorticopulmonary septum of chick embryos.
- Similar actin distribution and mesenchymal condensations were noted in 14-day rat embryos.
- Electron microscopy revealed microfilament bundles in elongated mesenchymal cells and their contacts with myocytes.
Conclusions:
- Mesenchymal condensations, rich in filamentous actin, likely provide a specialized mechanical tensile function during embryonic cardiac septation.
- These findings suggest a novel role for actin-based mechanical forces in shaping the cardiac outflow channels.
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.