Fig. 3. Early markers of the prospective forelimb mesenchyme are absent in Tbx5^lox/lox;Prx1Cre embryos. (A-F) Expression analysis by whole-mount RNA in situ hybridisation. (A) Expression of Fgf10 in the forelimb (arrowed) of a control embryo E9.5. (B) Fgf10 is not expressed in the forelimb region of a Tbx5^lox/lox;Prx1Cre embryo at E9.5. (C) Dorsal view of the embryo shown in A. Fgf10 expression in the forelimb buds is indicated by an asterisk. (D) Dorsal view of the embryo shown in B. No Fgf10 expression is detected in the forelimb-forming region. (E) Expression of Pea3 in the forelimb (black arrow) and intermediate mesoderm (red arrow) of a control embryo at E9.5. (D) Pea3 is expressed in the intermediate mesoderm (red arrow) but not the forelimb region of Tbx5^lox/lox;Prx1Cre embryos at E9.5 (black arrow). (G-J) Analysis of cell death in the limb. G) Whole-mount TUNEL staining of the forelimb region of a control embryo at E9.5. (H) Whole-mount TUNEL staining of the forelimb region of a Tbx5^lox/lox;Prx1Cre embryo at E9.5. A zone of increased apoptotic cell death is present at the site where the forelimb would normally form (arrowed). (I) Whole-mount TUNEL staining of the forelimb region of a control embryo at E10.5. Some cell death is observed in the limb and foci of apoptotic cells are observed in the somites (arrowed). (J) Whole-mount TUNEL staining of the forelimb region of a Tbx5^lox/lox;Prx1Cre embryo at E10.5. A region of increased cell death is present in the forelimb-forming region (bracketed). Foci of apoptotic cells are also observed in the somites in a similar pattern to the control embryo (arrowed).