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Distribution of collagens and fibronectin in the subepicardium during avian cardiac development
1Department of Kinesiology, University of California, Los Angeles 90024.
Insights
The subepicardium, a connective tissue layer in developing chick hearts, changes composition and organization. Its fibronectin and collagen content influences cardiac mechanics from embryonic development through adulthood.
Area of Science:
- Developmental biology
- Cardiac morphogenesis
- Connective tissue biology
Background:
- The subepicardium is a crucial connective tissue layer between the ventricular epicardium and myocardium.
- Its developmental role in cardiac mechanics is not fully understood.
Purpose of the Study:
- To investigate the developmental timeline and composition of the chick heart subepicardium.
- To understand the contribution of subepicardial connective tissue to cardiac mechanics.
Main Methods:
- Electron microscopy
- Light microscopy
- Immunohistochemical techniques
Main Results:
- Subepicardial volume rapidly increases from embryonic day 6 to 11 (E6-E11) due to mesenchymal cell invasion.
- Fibronectin is an early prominent constituent, with collagen type III appearing at E8 and collagen type I at E10.
- Collagen types I and III, along with fibronectin, are concentrated in the subepicardium during later development and in adult hearts.
Conclusions:
- The subepicardium's composition and organization evolve significantly during chick heart development.
- Subepicardial connective tissue likely plays a vital role in cardiac mechanics from mid-embryogenesis to adulthood.
Abstract:
The development of the layer of connective tissue between ventricular epicardium and myocardium was studied during chick morphogenesis using electron microscopy, light microscopy and immunohistochemical techniques. This layer, called the subepicardium, increases rapidly in volume from embryonic day 6 to 11 (E6-E11) during mesenchymal cell invasion. Fibrous, matrix components are initially apparent at E11 to E16, and as fibrous connective tissue structures accumulate, subepicardial volume decreases. Antibody labeling shows that fibronectin is an early, prominent constituent of the subepicardium, and by E8, the subepicardium is the cardiac site most enriched in fibronectin. Collagen type III is present in circumferentially-oriented fibers at E8. During subsequent cardiac growth, collagen type III fibers become broadly distributed in the subepicardium, with some fibers appearing to attach myocardium to epicardium. Collagen type I fibers are not apparent until E10. At E12 collagen type I fibers are distributed circumferentially around the heart in bundles crimped into waves of low amplitude. Other collagen type I fibers are oriented radially in the subepicardium. During late cardiac morphogenesis and in fully-differentiated hearts, fibronectin and collagen types I and III are more concentrated in the subepicardium than within the myocardium. These observations suggest that the composition and organization of the subepicardial connective tissue may make important contributions to cardiac mechanics from the latter half of embryonic development through adulthood.