Fig. 5. Delayed generation of autopod progenitors in Fgfr2^AER-KO forelimbs. (A-T) Whole-mount in situ hybridization assays for Hoxa13, Hoxd13 and Sox9 expression. (A-L) Generation and expansion of autopod progenitors as indicated by Hoxa13 expression. Hoxa13 expression was delayed by 2 s stages in the mutant. The outline of mutant limb buds changed between the 45 s (H) and 47 s (J) stages, coinciding with the onset of autopod condensation (S,T). (M-P) Hoxd13 expression in the distal autopod. Asterisk in N,P indicates residual Hoxd13 expression in mutant limb buds. The proximal domain of Hoxd13 expression (arrowheads) was present in control (M) and mutant limb buds (N) at the 47 s stage. (Q-T) Skeletal progenitors at the 40 s and 46 s stages as marked by Sox9 expression. Skeletal condensation of the autopod, yet to start at the 40 s stage (Q,R), occurred by the 46 s stage as indicated by primitive limb elements (S). (U,U') Quantification of the area of Hoxa13-expression domain during autopod development. Values in parentheses at each data point are the numbers of control and mutant samples examined, and the percentage of the area of Hoxa13-expression domain in the mutant compared with that in the control. Values are the mean±s.d. for each data point in U,U'. Scale bars: 200 µm. Abbreviations: an, anterior; Au, autopod; di, distal; po, posterior; pr, proximal; s, somite; St, stylopod; Ze, zeugopod.