Fig. 3. Retroviral misexpression of T in prospective hindlimb causes anterior extension of the AER and early changes in Fgf10 expression. All panels show dorsal side of embryos except B, which is viewed from the top (craniad) down and D, which shows a ventral view. The anteroposterior (a-p) or dorsoventral (d-v) orientations are indicated to left. (A-C) Fgf8 expression in infected embryos harvested at stages 20 (A), 22 (B), and 24 (C). The embryo in C was also hybridized with a Shh probe. Broadening of the anterior limb bud on the infected (inf.) side compared to the contralateral control (con.) side was always accompanied by anterior extension of Fgf8 expression in AER (arrows). No ectopic Shh expression was seen in the context of AER extension (C). (D) Fgf4 expression in infected embryo at stage 21 showing expression has extended anteriorly in the AER on the infected side (arrows). (E) Fgf10 expression in infected embryos at stage 20 was stronger and more extensive in the distal subridge mesoderm on the infected side. Color development times for Fgf10 probe were kept very short to visualize mainly the distal mesoderm and prevent signal saturation. (F) Wnt5a expression was only slightly increased by stage 23 on the infected side (arrows), but showed no expression difference at earlier stages following infection (data not shown).

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