osr1 knockdown causes expansion of endoderm. (A-F) Expression of endoderm marker sox17 in control (A-C) and osr1 morphants (D-F) at the shield stage. (A,D) Dorsal views; (B,E) side views with dorsal facing; (C,F) magnified views of boxed regions in B,E, respectively. The number of tiers of sox17-expressing cells was significantly increased in osr1 morphants at the blastoderm margin (bar in E,F) and in the ventral region of the embryo (arrowhead, D) when compared with control (A,C; bar in B). (G-L) Expression of mesendoderm marker, foxa2 in control (G-I) and osr1 morphants (J-L) at the shield stage. (G,J) Dorsal views; (H,K) side views with dorsal facing; (I,L) magnified views of boxed regions in H,K, respectively. The number of tiers of foxa2-expressing cells were significantly increased in osr1 morphants with more layers of foxa2-expressing cells at the blastoderm margin (bar in K,L) and enhanced expression in the ventral region of the embryo (arrowhead, J) when compared with control (G,I; bar in H). (M-O) Expression of foxa2 at 18 somites in control (M), osr1 morphants (N) and sox32 (cas) morphants (O). Development of foxa2-positive pharyngeal endoderm was enhanced in osr1 morphants (arrowheads, N) when compared with control embryos (arrowheads, M) and was completely blocked by sox32 knockdown (arrowheads, O).
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