Ciliary phosphatidylinositol phosphatase Inpp5e plays positive and negative regulatory roles in Shh signaling

Sonic hedgehog (Shh) signal transduction specifies ventral cell fates in the neural tube and is mediated by the Gli transcription factors that play both activator (GliA) and repressor (GliR) roles. Cilia are essential for Shh signal transduction and the ciliary phosphatidylinositol phosphatase, Inpp5e, is linked to Shh regulation. In the course of a forward genetic screen for recessive mouse mutants, we identified a functional null allele of Inpp5e , ridge top (rdg) , with expanded ventral neural cell fates at E10.5. By E12.5, Inpp5e rdg/rdg embryos displayed normal neural patterning and this correction over time required Gli3, the predominant repressor in neural patterning. Inpp5e rdg function largely depended on the presence of cilia and on Smoothened, the obligate transducer of Shh signaling, indicating Inpp5e functions within the cilium to regulate the pathway. These data indicate that Inpp5e plays a more complicated role in Shh signaling than previously appreciated. We propose that Inpp5e attenuates Shh signaling in the neural tube through regulation of the relative timing of GliA and GliR production, which is important in understanding how duration of Shh signaling regulates neural tube patterning. Summary statement Inpp5e attenuates Sonic hedgehog signal transduction through a combination of positive and negative regulatory roles that likely control the relative timing of Gli processing.