Fig. 3.

Different cell types are constituents of the subepicardial blood islands (a–j). a, b, c, d Confocal microscopy images of sections from a 13 dpc heart stained with anti-CD41 (green) (b), anti-NP1 (white) (c) antibodies and the merged picture stained additionally with Hoechst (blue) (a, d). The blood island shown in the white box of panel a is enlarged on panels b–d. Endothelial cells of blood island express NP1 (red arrows) (c, d), whereas CD41⁺ cells (green) (b, d) are present inside of the blood island. Scale bars 50 µm. e, f, g, h, i, j Electron microscopic pictures of blood islands. Cells with the ultrastructural features of endothelium positioned at the periphery of blood islands are indicated by red arrows. The interior of blood islands is represented by the following hematopoietic lineages: erythroblastic (E) (e–j) and megakaryoblastic (Me) (g, h, j); proplatelets occur adjacent to some Me (white arrow in g,) and other Me are devoid of proplatelets (j). Platelets (black arrows) (e, f) are numerous components of blood islands, whereas mesenchymal-like cells (M) are rarely found (i)