| Description |
Sonic hedgehog (Shh) is a critical morphogen used for the generation and patterning of many diverse animal tissues. A morphogen gradient of Shh ligand generates patterned cell specification, but how cells decode and respond to exact doses of Shh ligand is poorly understood. Here, we identify a previously unknown component of Shh signaling, intracellular calcium release through Ryanodine Receptors (RyRs) and Inositol Triphosphate Receptors (ITPRs). In zebrafish, when RyRs are knocked down genetically or inhibited pharmacologically, Shh-dependent cells fail to form, Shh-dependent tissues are mispatterned, Shh-dependent gene expression is reduced, and the precursors of Shh-dependent cells adopt an alternate fate. When RyRs are stimulated with channel agonists, Shh-dependent gene expression and patterning are expanded. The requirement for RyR function resides in the Shh ligand receiving cell within the signal transduction pathway. Additionally, in zebrafish and mammalian cells, when both RyRs and ITPRs are inhibited, Shh-dependent gene expression is completely abrogated, suggesting that calcium release from intracellular stores is an evolutionarily conserved intrinsic requirement for Shh activation. Therefore, modulating intracellular calcium release modifies the level of response to Shh ligand within the ligand receiving cell. Furthermore, intracellular calcium release is required for the Shh ligand-dependent accumulation of Smoothened (Smo) within the primary cilium. This work expands our understanding of how ligand receiving cells tune their response to particular doses of Shh ligand. |
