SURGICAL REMOVAL OF LIMB BUD SONIC HEDGEHOG RESULTS IN POSTERIOR SKELETAL DEFECTS

Using Sonic Hedgehog (Shh) as a marker for polarizing region cells we have repeated the experiments of MacCabe ct al. (1973) and Fallen and Crosby (1975) in an attempt to reexamine the question of a continuous role for the polarizing region during limb development. We report that the earlier experiments probably left Shh-expressing cells after surg ery. Our results show that Shh-expressing cells do not regenerate and complete removal of the polarizing region results in truncations along the anteroposterior (A-P) axis; further, A-P patterning cannot be res tored when a bead soaked in FGF is implanted in the limb bud mesenchym e to maintain outgrowth after extirpation of the polarizing region. Ho wever, in order to reproducibly remove all Shh-positive cells, it is p ossible that cells with posterior limb skeletal fate also must be remo ved. Therefore, microsurgical approaches do not permit an unequivocal answer to the question raised in this and the earlier papers and it re mains a reasonable possibility that at least up to stage 20-21 the pol arizing region plays a continuous role in patterning of the limb bud d uring its development. (C) 1996 Academic Press, Inc.