Presenter(s): Joshua Braunstein – Biology
Faculty Mentor(s): Kryn Stankunas, Scott Stewart
Poster 83
Research Area: Developmental Biology
Funding: ESPRIT
IMB Summer Scholarship Award
Alden Award
Zebrafish remarkably regenerate severed fins, perfectly restoring their original size and branched skeletal pattern. Sonic hedgehog a (Shha)-expressing epidermal cells mediate ray branching during regeneration by guiding localization of the pre-osteoblasts (pObs) while migrating and splitting into two populations. However, mechanisms of shha induction, the splitting of shha+ epidermal cells, and the mechanisms underlying epidermal to pObs interactions remain unresolved. Towards answering these questions, we explored if Hh/Smo signaling and epidermal dynamics also underlie developmental ray branching. We found that shha is expressed initially in basal epidermal cells along the entire length of forming fin bones in juvenile fish. As bones progressively mature, shha becomes distally restricted to epidermal cells neighboring Runx2+ pObs. We used TgBAC(ptch2:Kaede) fish and photoconversion to show Hh/Smo signaling is restricted to these pObs and immediately adjacent epidermal cells. shha+ epidermal cells split into two groups immediately preceding ray branching. By live imaging, we found these basal epidermal cells migrate distally over the pObs, cease Hh/Smo signaling, and are then shed. Small molecule inhibition of Hh/Smo using BMS-833923 increased epidermal migration speed, suggesting Hh/Smo signaling typically restricts the rate of migration by adhering epidermal cells to the pObs. Additional small molecule trials show the pathway is largely dedicated to ray branching during fin development. We conclude that instructive shha+ epidermal movements and Shh/Smo-promoted adhesion between epidermal cells and pObs direct branching morphogenesis to pattern the fin skeleton during both development and regeneration.