Elastic extracellular matrix of the embryonic chick heart: An immunohistological study using laser confocal microscopy

Abstract

The "elastic matrix" constitutes a specialized component of the extracellular matrix which confers resiliency to tissues and organs subjected to repeated deformations. The role of the elastic matrix in living organisms appears to be of key importance since diseases characterized by expression of defective inherited genes which encode components of the elastic matrix lead to premature death. While the elastic matrix of adult organs has received a great deal of attention, little is known about when it first appears in embryonic tissues or its possible role in developing organs. In the present study we have performed an immunohistochemical study of the distribution of elastin and three additional components often associated with elastic matrices in adult tissues (i.e., fibrillin, emilin, and type VI collagen) during the development of the chicken embryonic heart. The threedimensional arrangement of these components was established through the observation of wholemount specimens with scanning laser confocal microscopy. Our results revealed three different periods of heart development regarding the composition of the elastic matrix. Prior to stage 21 the embryonic heart lacks elastin but exhibits a matrix scaffold of fibrillin and emilin associated with the endocardium and the developing cardiac jelly. Between stages 22 and 29 the heart shows a transient elastic scaffold in the outflow tract which contains elastin, fibrillin, and emilin. Elastin-positive fibrillar material is also observed during these stages in the base of the atrioventricular cushion adjacent to the myocardial wall. In addition, emilin-positive material appears to be associated with the zones of formation of ventricular trabeculae. Collagen type VI was not detected during these early stages. From stage 30 to stage 40 a progressive modification of the pattern of distribution of elastin, fibrillin, emilin, and collagen type VI is observed in association with the formation of the definitive four-chambered heart. The distribution of the elastic scaffold in the outflow tract appears to be rearranged and becomes restricted to the roots of the main arteries. Each of the components studied here is also deposited at increasing levels in the developing valvular appa-ratus including the valve leaflets and the chordae tendinea. The components are also present in the subendocardial space where they form aligned fibrillar tracts, an arrangement suggestive of a role in ventricular contractile function. The epicardium constitutes an additional region of elastic matrix deposition during these later stages and contains elastic, fibrillin, and collagen type VI. Finally, during the later stages the intramyocardial matrix (''myocardial interstitium") is formed and characterized by an abundance of collagen type VI, emilin, and fibrillin but lacks elastin-positive material. This study suggests that during cardiac development there is not a fixed composition of the so-called "elastic matrix.'' Rather, combinations of the different components of the elastic matrice...

Spatial and Temporal Analysis of Extracellular Matrix Proteins in the Developing Murine Heart: A Blueprint for Regeneration

“…ELN was previously identified in the E12 myocardium and E14 epicardium, subendocardium, and blood vessels of the embryonic chick heart, while we did not detect ELN during these stages. 72 In assessing our results, perhaps, the increase in ELN at E16.5 is necessary for providing the elasticity for heart recoil as the heart is required to exert more ejection force with an increasing size of the heart and fetal circulation. Soon after birth, the relative decrease in ELN may be the result of, or the stimulus for, complete maturation of cardiomyocytes and corresponding maturation of functional sarcomeres.…”

The epicardium and epicardially derived cells (EPDCs) as cardiac stem cells

“…This subepicardium is a hydrated ECM, rich in proteins, including collagens I, IV, V, and VI and fibronectin (Tidball, 1992;Hurlé et al, 1994;Ká lmá n et al, 1995;Bouchey et al, 1996;Kim et al, 1999), flectin (Tsuda et al, 1998), fibulin-2 (Tsuda et al, 2001), GP68 (Morita et al, 1998), laminin and proteoglycans (Ká lmá n et al, 1995), vitronectin, fibrillin-2, elastin (Bouchey et al, 1996), and tenascin-X (Burch et al, 1995). It has been shown that both the epicardium and myocardium contribute proteins to this matrix (Bouchey et al, 1996).…”

Expression patterns of laminin receptor splice variants α6Aβ1 and α6Bβ1 suggest different roles in mouse development

“…Furthermore, fibronectin has been implied in the migration of endocardial cushion tissue cells (Mjaatvedt et al, 1987;ffrench-Constant and Hynes, 1988;Icardo et al, 19921, and molecules such as fibrillin, emilin (Hurle et al, 1994) and other, yet uncharacterized, extracellular matrix components (Mjaatvedt et al, 1991) could also be involved.…”