Heat-shock-mediated conditional regulation of hedgehog/gli signaling in zebrafish.

Background: Hedgehog (Hh) signaling is required for embryogenesis and continues to play key roles postembryonically in many tissues, influencing growth, stem cell proliferation, and tumorigenesis. Systems for conditional regulation of Hh signaling facilitate the study of these postembryonic Hh functions.

Results: We used the hsp70l promoter to generated three heat-shock-inducible transgenic lines that activate Hh signaling and one line that represses Hh signaling. Heat-shock activation of these transgenes appropriately recapitulates early embryonic loss or gain of Hh function phenotypes. Hh signaling remains activated 24 hr after heat shock in the Tg(hsp70l:shha-EGFP) and Tg(hsp70l:dnPKA-BGFP) lines, while a single heat shock of the Tg(hsp70l:gli1-EGFP) or Tg(hsp70l:gli2aDR-EGFP) lines results in a 6- to 12-hr pulse of Hh signal activation or inactivation, respectively. Using both in situ hybridization and quantitative polymerase chain reaction, we show that these lines can be used to manipulate Hh signaling through larval and juvenile stages. A ptch2 promoter element was used to generate new reporter lines that allow clear visualization of Hh responding cells throughout the life cycle, including graded Hh responses in the embryonic central nervous system.

Conclusions: These zebrafish transgenic lines provide important new experimental tools to study the embryonic and postembryonic roles of Hh signaling.