The Dynamics of Sonic hedgehog Function in Frog Limb Development

Students: Samantha Balestrieri*, Abigail Sollars, Mary Garside and Allison Riggs
Mentor: Geffrey Stopper
Major: Biology

Sonic hedgehog (Shh) is a diffusible morphogen that is expressed in the posterior of tetrapod limbs and patterns the anterior-posterior axis of the limb. In most tetrapods, absence of Shh or blocking of its function causes severe reduction of development across the anterior-posterior axis, but has very little effect on outgrowth along the proximal-distal axis. Our previous research in one species of frog, Xenopus tropicalis, showed a complete loss of outgrowth in many limbs in response to the blocking of Shh signaling with the chemical cyclopamine. This role of Shh in limb outgrowth has never been observed in any other tetrapod species, and phylogenetic comparisons of the species in which Shh function has been studied suggest that this is a novel role for Shh in frogs. But it remains unclear to what extent this applies very narrowly to X. tropicalis, if it applies to all frogs, or it applies to some clade of intermediate size. Here we use cyclopamine to investigate the effects of blocking Shh in another species of frog, X. laevis, in hopes of better understanding whether this role of maintaining limb bud outgrowth is unique to X. tropicalis or if it applies to other frogs in the family Pipidae. Additionally, we investigate the temporal dynamics of Shh function in X. laevis limb development by performing cyclopamine exposures at varying stages of limb development.

*Honors Senior