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Fig. 9 osr1 knockdown does not affect specification of pronephric and angioblast mesoderm, but does affect their subsequent maintenance. (A,B) Expression of pax2a and myoD in control (A) and osr1 morphants (B) is similar at five somites (arrowheads in A and B). myoD is used as a internal somite staging control. (C,D) Expression of pax2a in a 14-somite control (C) and osr1 morphants (D) reveals a substantial reduction in the number of pax2a-positive cells in the anterior IM (arrowheads, C,D). (E,F) Expression of pax2a in 24 hpf control (E) and osr1 morphants (F) shows a complete loss of pax2a-positive cells in the proximal pronephros (arrowheads, E,F). (G,H) Expression of scl in osr1 morphants (H) is similar to that of control embryos at 8 somites (G). (I,J) However, by the 14-somite stage, the number of scl-expressing cells is significantly upregulated in the anterior lateral plate mesoderm of osr1 morphants (arrowhead, J) when compared with control embryos at the same stage (arrowhead, I).