The insulin-like growth factors, isolated from plasma, are structurally and functionally related to insulin but have a much higher growth-promoting activity. Promotes head development by inhibiting Wnt signaling during embryogenesis (PubMed:11709186, PubMed:11944947). Acts as a ligand for IGF1R. Binds to the alpha subunit of IGF1R, leading to the activation of the intrinsic tyrosine kinase activity which autophosphorylates tyrosine residues in the beta subunit thus initiatiating a cascade of down-stream signaling events leading to activation of the PI3K-AKT/PKB and the Ras-MAPK pathways. Binds to integrins. Its binding to integrins and subsequent ternary complex formation with integrins and IGFR1 are essential for IGF1 signaling (By similarity). Expressed in adult liver, lung, heart, kidney and peritoneal fat. Expressed both maternally and zygotically after the midblastula transition. Present both dorsally and ventrally at the beginning of neurulation. Expression is restricted to the developing heart at the tailbud stage. Belongs to the insulin family.