Type 1 insulin-like growth factor receptor (IGF1R) is a receptor tyrosine kinase that regulates cell growth and proliferation, and can be activated by IGF1, IGF2, and insulin. Here, we report the cryo-EM structure of full-length IGF1R–IGF1 complex in the active state. This structure reveals that only one IGF1 molecule binds the Γ-shaped asymmetric IGF1R dimer. The IGF1-binding site is formed by the L1 and CR domains of one IGF1R protomer and the α-CT and FnIII-1 domains of the other. The liganded α-CT forms a rigid beam-like structure with the unliganded α-CT, which hinders the conformational change of the unliganded α-CT required for binding of a second IGF1 molecule. We further identify an L1–FnIII-2 interaction that mediates the dimerization of membrane-proximal domains of IGF1R. This interaction is required for optimal receptor activation. Our study identifies a source of the negative cooperativity in IGF1 binding to IGF1R and reveals the structural basis of IGF1R activation.

RET is a receptor tyrosine kinase (RTK) that plays essential roles in development and has been implicated in several human diseases. Different from most of RTKs, RET requires not only its cognate ligands but also co-receptors for activation, the mechanisms of which remain unclear due to lack of high-resolution structures of the ligand/co-receptor/receptor complexes. Here, we report cryo-EM structures of the extracellular region ternary complexes of GDF15/GFRAL/RET, GDNF/GFRα1/RET, NRTN/GFRα2/RET and ARTN/GFRα3/RET. These structures reveal that all the four ligand/co-receptor pairs, while using different atomic interactions, induce a specific dimerization mode of RET that is poised to bring the two kinase domains into close proximity for cross-phosphorylation. The NRTN/GFRα2/RET dimeric complex further pack into a tetrameric assembly, which is shown by our cell-based assays to regulate the endocytosis of RET. Our analyses therefore reveal both the common mechanism and diversification in the activation of RET by different ligands.

Key Points Tmod3 deletion leads to reduced erythroid progenitors and impaired erythroblast survival, cell-cycle exit, and enucleation. Erythroblast-macrophage islands are reduced in the absence of Tmod3, which is required in both cell types for island formation.

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The present study investigated the effect of transplanting endothelial progenitor cells (EPCs) transfected with the vascular endothelial growth factor gene (VEGF165) into the corpora cavernosa of rats with diabetic erectile dysfunction (ED). A rat model of diabetic ED was constructed via intraperitoneal injection of streptozotocin. After streptozotocin treatment, pre-treated EPCs from each of three groups of rats were transplanted into their corpora cavernosa. Our results, following intracavernosal pressure (ICP) monitoring, showed that ICP increased significantly among rats in the trial group when compared to the results from rats in the blank-plasmid and control groups during basal conditions and electrical stimulation (P<0.01 for both comparisons). Histological examination revealed extensive neovascularisation in the corpora cavernosa of rats in the trial group. Fluorescence microscopy indicated that many of the transplanted EPCs in the trial group survived, differentiated into endothelial cells and integrated into the sites of neovascularisation. Based on the results of this study, we conclude that transplantation of VEGF165-transfected EPCs into the corpora cavernosa of rats with diabetic ED restores erectile function.