Fig. 4. Limb outgrowth is disrupted following misexpression of dominant-negative Tbx5 in the chick wing bud. Scanning electron micrographs of (A) control and (B) dominant-negative Tbx5 (Tbx5) injected limb buds at stage 20 show a dramatic reduction in limb size after Tbx5 misexpression. A, anterior; P, posterior. Sections through (C) contralateral control and (D) dominant-negative Tbx5 (Tbx5) injected limb buds at stage 20 stained with an antibody against phosphohistone H3 to identify cells undergoing mitosis (pink). Sections through (E) contralateral control and (F) dominant-negative Tbx5 (Tbx5) injected limb buds at stage 20 stained with TUNEL reagents to identify cells undergoing apoptotic cell death (green). (G) Schematic representation of the Tbx5 full-length, truncated and En/VP16-fusion retroviral constructs (see Materials and Methods for details). (H) Transverse section in situ hybridisation analysis of chick Grg4 expression in the chick limb at stage 22.

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