Figure 1

Figure 1

The zebrafish arterial valve is anatomically similar to other vertebrate arterial valves. (A) Overview of the orientation of the heart in adult zebrafish, with planes of imaging for C-N. (B) Haematoxylin and eosin–stained long-axis sections of excised adult zebrafish heart (female, 9 months old) (n = 4). (C) 3D reconstruction of the arterial pole, viewed ventrally, reconstructed from (B). The arterial valve leaflets (green, red) are hinged in the ventricular myocardium and span the myocardial (grey)-arterial (pink) boundary and are not in continuity with the atrioventricular valve (blue). The arterial valve leaflets are aligned along the anterior-posterior axis of the zebrafish and are defined by their position within the adult: dextral (green) and sinistral (red) with their coaptation region spanning the myocardial-arterial boundary. (D and E) Haematoxylin and eosin–stained short-axis sections of excised adult zebrafish heart (male, 9 months old) at the level of distal (D) and proximal myocardium (E) showing two leaflets of the arterial valve, with sinuses (asterisks) between the leaflets and the wall (n = 4). (F) Masson’s trichrome-stained short-axis section of excised adult zebrafish heart (female, 14 months) at the commissures of arterial leaflets in the bulbus arteriosus. Collagen (blue) is present in the bulbus arteriosus, enriched in the commissures and largely absent from the leaflets. (G) Same heart as (F) at the proximal myocardium. Collagen is present in the lumen facing portion of the leaflets (arrowheads), the wall of the sinus (asterisks) but is excluded from the leaflet interstitium. (H) Masson’s trichrome-stained long-axis section of excised adult zebrafish heart (female, 12 months old) showing the sinistral leaflet. Collagen is present on the luminal surface (arrowhead) of the leaflet, the root, and the bulbus arteriosus. (I) Alcian blue–stained sections, same heart shown in (F) and (G). Proteoglycans (blue) are abundant in the bulbus arteriosus and leaflets but absent from the commissures (asterisks). (J) Same heart as (I) at the proximal myocardium. Proteoglycans are present throughout the interstitium of the leaflets, with very weak signal in the sinus wall (asterisk). (K) Alcian blue–stained section, same heart shown in (H), showing the bulbus arteriosus and leaflets are rich in proteoglycans. (L) Miller’s elastin-stained sections, same heart shown in (F), (G), (I), and (J). Elastin (purple) is abundant in the bulbus arteriosus, absent from the tips of the leaflets and commissures (asterisks). (M) Same heart as (L) at the proximal myocardium. Elastin is present throughout the leaflet, but is enriched on the luminal surface of the leaflets and the sinus wall (arrowheads). (N) Miller’s elastin-stained section, same heart shown in (H) and (K). Elastin is present in the bulbus arteriosus, enriched in the lumen facing aspect of the arterial leaflets, and present in the root of the valve (for F, G, I, J, L, and M: n = 5; for H, K, and N: n = 4). (O) Masson’s trichrome-stained short-axis section of postnatal day (P) 90 mouse aortic valve. The aorta and commissures (asterisks) are rich in collagen, whilst there is enrichment on the sinus facing aspect of the leaflets (arrowhead). (P and Q) Masson’s trichrome-stained long-axis section P90 mouse aortic valve, showing left (P) and non-coronary leaflets (Q). Collagen is present in the aortic root, hinge, and wall. In the leaflets, collagen is mainly localized to the arterial aspect and absent from the luminal surface (P and Q, arrowheads). (R) Alcian blue–stained section of same heart shown in (O). Proteoglycans are present in the leaflets and commissures (asterisks) but absent from the aorta. (S and T) Alcian blue–stained section, same heart shown in (P) and (Q). Sulfated proteoglycans are present in the aortic root and hinge, but largely absent for the wall of the aorta. (U) Miller’s elastin-stained section, same heart shown in (O) and (R). Elastin fibres are present in the aorta and absent from the commissures (asterisks) and valve leaflets. (V and W) Miller’s elastin-stained section, same heart shown in (P), (Q), (S), and (T). Mature elastin fibres are present in the wall of the aorta, with diffuse staining in the hinge. There are no clear fibres of elastin in the leaflets. (B), (H), (K), (N), (P), (Q), (S), (T), (V), and (W): anterior: up, left: right. (D)–(G),( I), (J), (L), and (M): dorsal: up, left: right. V, ventricle; BA, bulbus arteriosus; A, atrium; SV, sinus venosus; LV, left ventricle; Ao, aorta; H, hinge; L, lumen; RΔNC, right/non-coronary commissure; NCΔL, non-coronary/left commissure; LΔR, left/right commissure. Scale bars: (B) and (D)–(N): 20 μm; (O)–(W): 50 μm.