Modulation of Shh signaling by microRNAs

Abstract

Sonic hedgehog (Shh) exhibits a dynamic expression sequence in the head. First, Shh is detected in the forebrain and then Shh is induced in the facial ectoderm where it forms a signaling center, the Frontonasal Ectodermal Zone (FEZ) that regulates morphogenesis of the upper jaw. Induction of Shh in the FEZ is regulated by SHH from the brain, but the mechanisms underlying this induction pattern is unknown. Here, we examine the extent to which the SHH pathway is regulated by miRNAs. Microarray analysis revealed that miR199b was expressed at lower levels in the FEZ at HH18 compared to HH22, and was up‐regulated in response to exogenous SHH. In situ hybridization at HH18 revealed that miR199b was expressed broadly in the future Shh domain of the FEZ, and by HH21 became restricted to the edge of the Shh domain in the FEZ. A similar complementary expression pattern between Shh and miR199b was found in the floorplate of the neural tube. Over‐expressing mir199b in embryos caused narrowing of the face that was associated with decreased Shh expression. There was no obvious increase in apoptosis, but we observed reduced cell proliferation in the mesenchyme. To assess how miR199b affects SHH signaling, we determined that infection of RCAS::mir199b in DF‐1 cells inhibited SHH signal activation and cell proliferation. Taken together, these results suggest that miR199b acts a negative regulator of SHH signaling in embryos and cultured cells.Grant Funding Source : This work was funded by grant from the National Institutes of Health (5R01‐DE018234 to R.M.).MicroRNA array was supported from the Sandler Asthma Basic Research (SABRE) Center Functional Genomics Core Facility.