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

Abstract

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, Inpp5erdg/rdg embryos displayed normal neural patterning and this correction over time required Gli3, the predominant repressor in neural patterning. Inpp5erdg 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.

Down-Regulation of Inpp5e Associated With Abnormal Ciliogenesis During Embryonic Neurodevelopment Under Inositol Deficiency

“…Cranial NTDs have occurred in mice embryos lacking Inpp5e ( 6 ). A null allele of Inpp5e caused abnormal Shh response during the developing neural tube at E 10.5 ( 7 ). Using a mouse model of NTDs with folate metabolic disturbance, we observed a gradual decline in the Inpp5e expression along a normal embryonic development course at E 11.5, E 13.5, E 15.5, but not in NTDs embryos; and that Inpp5e expression was significantly lower in NTDs embryos than controls at E 11.5 ( 8 ).…”

“…Knockout of the Inpp5e gene ( Inpp5e −/− ) in mice resulted in embryonic and early postnatal death with a phenotype that recapitulates JBTS, containing NTDs, polycystic kidneys and polydactyly ( 6 ). A null allele of Inpp5e caused abnormal Shh response, which played a critical role in the intermediate region along the dorso-ventral (D-V) axis of the developing neural tube at E 10.5 ( 7 ). In a previous study, we found that the expression of Inpp5e decreased during a normal course of embryonic development, but no obvious trend was observed in methotrexate (MTX)-induced NTDs mice embryos, and that the expression levels of Inpp5e in NTDs embryos was significantly lower than the controls at E 11.5 ( 8 ).…”

Defective INPP5E distribution in NPHP1‐related Senior–Loken syndrome

“…Interestingly, nephronophthisis and Joubert syndrome are two types of ciliopathies with overlapping clinical manifestations, including cystic kidney disease and retinal degeneration. Previous publications showed that NPHP1 and INPP5E mutations are responsible for Joubert syndrome (Constable et al, 2020; Jacoby et al, 2009). Our study shows that NPHP1 deletion results in the abnormal expression of INPP5E, which supports the hypothesis that Joubert syndrome and nephronophthisis represent the same biological disorder but with different versions of clinical manifestations.…”

Smoothened and ARL13B are critical in mouse for superior cerebellar peduncle targeting

“…Timed matings of mice were performed to generate somite-matched embryos at embryonic day 10.5 (E10.5). Embryos were dissected in cold PBS and processed for immunofluorescence staining as previously described (Constable et al 2020). Primary antibodies used were: mouse anti-Shh (5E1, 1:10), mouse anti-Pax6 (PAX6, 1:100) (Developmental Studies Hybridoma Bank), and rabbit anti-Olig2 (AB9610, 1:500, Millipore Sigma).…”