Limb Development.
Different species display characteristic digit patterning alongthe anterior-posterior axis. The forelimbs of bats are modifiedsuch that the posterior digits are elongated and maintain theirwebbing (to make the functional bat wing). Researchers observedthat in addition to the normally timed expression of Sonic hedgehog(Shh) in the bat ZPA, there is a second phase of both Fgf8 and Shhexpression in the developing forelimb in the interdigitaltissue.
How does the second phase of Fgf8 and Shh contribute to both theelongation of the forelimb digits and to the maintenance of thewebbing between the digits?
