Fig. 7. MSX and EN1 act in separate pathways to promote AER formation and DV patterning, respectively. (A-D) Msx1 misexpression does not disrupt DV patterning. Alternate sections from a stage 19 limb bud detected for (A) Fgf8 RNA, (B) Wnt7a RNA, (C) EN1 immunolocalization (bracket) and (D) virus with anti-GAG antibody. GAG staining in the mesenchyme reflects expression in blood vessels. Wnt7a is downregulated only in regions of ectopic Fgf8 expression (arrows in B and A, respectively) as Wnt7a is normally not detected in the AER. (E-H) En1 misexpression does not alter Msx expression, except in cases of AER loss, where Msx expression, which marks the AER, is lost. Msx1 expression in stage 23 uninfected (E) and En1-infected (F) limbs. Msx2 expression in stage 24 uninfected (G) and En1-infected (H) limbs. (I,J) Fgf8 expression in uninfected (I) and En1- infected (J) limbs. In J, arrows indicate faint Fgf8 staining, asterisk indicates dorsal displacement of the Fgf8-positive AER. Note that the dorsally displaced AER fragments are often still connected to the midline AER by a line of Fgf8 expression.
