SUMMARY Hedgehog (Hh) proteins regulate important developmental processes including cell proliferation and differentiation. While Patched acts as the main Hh receptor, in Drosophila, Hh signaling absolutely requires the additional Hh-binding proteins Ihog and Boi. Here we show that, unexpectedly, cerebellar granule neuron progenitors (CGNPs) lacking Boc and Cdon, the vertebrate orthologs of Ihog and Boi, still proliferate in response to Hh. This is because in their absence, Gas1, a Hh-binding protein not present in Drosophila, mediates Hh signaling. Consistently, only CGNPs lacking all three molecules Boc, Cdon, and Gas1 have a complete loss of Hh-dependent proliferation. In a complementary manner, we find that a mutated Hh ligand which binds Patched1 but neither Boc, Cdon, nor Gas1 cannot activate Hh signaling. Together, this demonstrates an absolute requirement for Boc, Cdon, and Gas1 in Hh signaling and reveals a distinct requirement for ligand-binding components that distinguishes the vertebrate and invertebrate Hh receptor systems.

Polynitrogen compounds have been actively pursued driven by their potential as ultra-high-performing propellants or explosives. Despite remarkable breakthroughs over the past two decades, the two figures of merit for a compelling material, namely a large fraction of nitrogen by weight and a bulk stability under ambient conditions, have not yet been achieved. We report the synthesis of a lithium pentazolate solid by compressing and laser-heating lithium embedded in molecular N around 45 GPa along with its recovery under ambient conditions. The observation by Raman spectroscopy of vibrational modes unique to the cyclo-N anion is the signature of the formation of LiN. Mass spectroscopy experiments confirm the presence of the pentazolate anion in the recovered compound. A monoclinic lattice is obtained from X-ray diffraction measurements and the volume of the LiN compound under pressure is in good agreement with the theoretical calculations.

Studies of polynitrogen phases are of great interest for fundamental science and for the design of novel high energy density materials. Laser heating of pure nitrogen at 140 GPa in a diamond anvil cell led to the synthesis of a polymeric nitrogen allotrope with the black phosphorus structure, bp-N. The structure was identified in situ using synchrotron single-crystal x-ray diffraction and further studied by Raman spectroscopy and density functional theory calculations. The discovery of bp-N brings nitrogen in line with heavier pnictogen elements, resolves incongruities regarding polymeric nitrogen phases and provides insights into polynitrogen arrangements at extreme densities.