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Fig. 6. Developmental history of the aorta in relationship with endothelial
remodeling and smooth muscle formation. (A) Before fusion of the
aortae, aortic ECs (red) derive from the splanchnopleura. The dorsolateral
quadrant of the somite displays a population of ECs (yellow). (B)
Immediately before fusion, the initial roof of splanchnopleural origin (red)
has been replaced by ECs from the somite (yellow). (C) After fusion,
the roof is of somite origin, the sides and floor remain of splanchnopleural
origin. (D) During early hematopoiesis, the floor begins to loose
endothelial markers and acquires of hematopoietic traits
(Jaffredo et al., 1998).
(E) At the hematopoietic clusters stage, clusters are budding into the
lumen, whereas some HCs ingress into the mesentery. At the same time, somitic
ECs replace the initial floor, whereas numerous somitic ECs are found in the
floor either underneath the clusters. At this time, cells of somite origin
reach the aorta (gray). When these cells reach the aorta, they begin to
express
SMA (green). (F) Completion of hematopoiesis. The aortic
floor has disappeared and is replaced by somitic ECs. Aortic ECs are entirely
of somite origin. Somite cells in abluminal position now express
SMA
(green).