Fig. 2. Absence of a forelimb bud in Tbx5^lox/lox;Prx1Cre embryos. Scanning electron micrographs of (A) a control embryo and (B,C) Tbx5^lox/lox;Prx1Cre embryos at E10.5. In B, no morphological limb bud or AER is present in the forelimb region (arrowed). In C, a small outgrowth of tissue from the flank is present (arrowed). (D-G) Expression analysis of limb bud markers by whole-mount RNA in situ hybridisation. (D) Fgf8 expression in the AER of the forelimb (arrowed) and hindlimb of a control embryo at E9.5. (E) Fgf8 expression in the hindlimb AER but absence in the forelimb region of a Tbx5^lox/lox;Prx1Cre embryo. (F) Shh expression in the ZPA of the forelimb (arrowed) and hindlimb of a control embryo at E10.5. (G) Shh expression in the hindlimb ZPA but absence in the forelimb region of a Tbx5^lox/lox;Prx1Cre embryo. (H-K) Hindlimb markers are not upregulated in Tbx5^lox/lox;Prx1Cre embryos. (H) Tbx4 expression in the hindlimb but not the forelimb (arrowed) of a control embryo at E10.5. (I) Tbx4 is expressed normally in the hindlimb and is not upregulated in the forelimb region of an E10.5 Tbx5^lox/lox;Prx1Cre embryo. (J) Pitx1 expression in the hindlimb but not the forelimb (arrowed) of a control embryo at E10.5. (K) Pitx1 is expressed normally in the hindlimb but is not upregulated in the forelimb region of an E10.5 Tbx5^lox/lox;Prx1Cre embryo. FL, forelimb; HL, hindlimb.