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Presenting Author(s) Geffrey Stopper
Abstract Title Hedgehog Function in the Patterning of Urodele Limbs and other Osteichthyan Paired Appendages.
Full author List Geffrey F. Stopper, Jean M. P. Joss, Günter P. Wagner
Text of abstract Sonic hedgehog (shh) is known, from many lines of evidence, to play an important role in the patterning of the anterior-posterior axis of amniote limbs. Although studies have revealed some data on shh in amphibian limbs, these studies are few and largely describe data on only expression patterns, or functional data in regeneration. We have used short periods of ubiquitous exposure to cyclopamine, a steroidal alkaloid that appears to interact with Smoothened (a transducer of the hedgehog signal), to down-regulate the function of Shh during five different stages of limb development in the urodele, Ambystoma mexicanum. The exposures resulted in a range of digit loss, with posterior digits lost first, including single-digited phenotypes with no identifiable anterior-posterior differentiation in skeletal elements resulting from the earliest exposures. These results are consistent with those from experiments reducing limb bud cell proliferation and with natural variation in urodeles with reduced digit numbers. The single digit phenotype is extremely similar in morphology to limbs of mice and chicks lacking functional Shh in limbs. These experiments reveal a broad conservation of the function of Shh between amniotes and urodeles, in that its action is necessary to permit development of the normal number of digits. They suggest that the specification of digit number occurs very early in urodele development, and over a relatively short period of time. Similar experiments in the Australian Lungfish, Neoceratodus forsteri, result in a reduction of elements in both the proximal-distal and anterior-posterior axes.
Which session is your work most relevant to: Limb evolution