Negative regulation of Shh levels by Kras and Fgfr2 during hair follicle development

► Hair shaft defects result from ectodermal activation of Kras in mice. ► Shh is a RAS-responsive target gene. ► Shh levels acutely respond to FGF stimulation or MAPK/PI3K inhibition. ► Shh RNA has a short half-life and its levels are dependent on transcription. ► Ectodermal Fgfr2 regulates Shh levels in vivo.