Figure 4.

Shorter exposure to Shh signaling causes the loss or anteriorization of posterior skeletal elements. Digit identities were determined by position and counting phalanges. Control forelimbs (A) and hindlimbs (B) treated with carrier are morphologically indistinguishable from wildtype. Treating with cyclopamine at E3 frequently leads to the loss of the ulna and the reduction of the autopod to carpus and two digit-like elements in the forelimb (C), and the loss of the fibula and digit 4 in the hindlimb (D). Digits 1 - 3 have only two phalanges each, meaning that digits 2 and 3 are anteriorized (D). Treating with cyclopamine at E3.5 frequently leads to the loss of digit 4 in the forelimb and hindlimb (E,F), as well as the reduction of digit 3 in the hindlimb to three phalanges (F). Treating with cyclopamine at E4 leads to a partial digit 4 in the forelimb (G), and to a hindlimb digit 4 with only four phalanges (H). All images were acquired at the same magnification and cropped to 1400×700 pixels. Scale bar represent 1 mm, and is approximated from an image of an identically staged limb taken under equivalent magnification.