Figure 2. Role of the sub-aortic mesenchyme in aortic hematopoiesis.

(A) Experimental scheme and further development. The cut separates somite and future kidney from the lateral plate. (upper scheme) preventing the splanchnopleural mesoderm to contribute to the aortic region (lower scheme). Ectoderm: white; endoderm: green, somites: dark pink and lateral plate: light pink.

(B) Schematic reprentation of normal and operated embryos 48h after the slit. Mid-trunk level.

Left hand scheme: normal embryo. Somite-derived structures are in dark pink. The aorta (red, median circle) has two rows of hematopoietic cells. The gut endoderm (green) is surrounded by the mesenchyme (light pink) are appended into the coelomic cavity.

Right hand scheme: operated embryo. Symmetry is not affected except in the ventral part of the embryo. Aortic hematopoiesis pattern is affected. Coelom on the operated side is lacking and gut is opened. Endoderm and ectoderm have fused

(C–F) Aortic region at 24h (C, D) and 48h (E, F) after the slit. In situ hybridization with runx1 (C, E) and ve-cadherin (D, F)

(C) Runx1 expression is present on the control side (left) but absent on the operated side (right).

(D) Ve-cadherin pattern is normal suggesting that no major modification of EC identity has occurred. Bar=130μm.

(E) Runx1⁺ HC clusters are visible on the control side (black arrow) but are lacking on the operated side. Note the presence of a loose ventral tissue on the operated side compared to the control side.

(F) Ve-cadherin expression is normal. Note the decrease of ve-cadherin expression mRNA in the HC clusters as reported (Jaffredo et al., 2005). Bar=150μm.

C, coelom, CV, cardinal vein.

See also Figure S2.