Impaired rostro-caudal polarity in the Mesp quadruple mutant. Rostral expression of tbx18 (A,B) and fgf8 (C,D) is completely absent in the somites of Mesp quadruple mutant embryos at the 11-somite stage (100%, n=20 and 100%, n=13, respectively). In contrast, caudal expression of uncx4.1 (E,F) and myod (G,H) has expanded in the entire somite of the Mesp quadruple mutant embryo at the same stage (100%, n=20 and 100%, n=18, respectively). The absence of tbx18 expression (I,J) and expansion of uncx4.1 expression (K,L) was also observed at the 28-somite stage (100%, n=15 and 100%, n=22, respectively). Expression of tbx18 is increased (M,N) and that of uncx4.1 is reduced (O,P) in the tbx6:ggff; uas:mespba double transgenic embryo at the 11-somite stage. Magnified images are also shown (M′-P′). The black lines indicate the position of somite boundaries. In the Mesp quadruple mutant at 30dpf (R), hemal arches in several vertebral bones have been duplicated (arrowheads in R′′) and neural arches are split (arrows in R′-R′′′) compared with WT (Q). Magnified images are also indicated (Q′-Q′′′,R′-R′′′).
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