IGF-binding proteins prolong the half-life of the IGFs and have been shown to either inhibit or stimulate the growth promoting effects of the IGFs on cell culture. They alter the interaction of IGFs with their cell surface receptors. Interacts equally well with igf1 and igf2. In embryos at 24 hpf, initially expressed in the lens and cranial region, and at 48 and 72 hpf in the brain boundary vasculature. Expression in these regions persists throughout the hatching period and by 96 hpf expression is most abundant in the liver. In both male and female adults, highest expression is in the liver with modest expression in the brain. In male but not females adults, expressed at a low level in muscle and gonad. Also expressed in the adult intestine. Not expressed until 10 hpf. Expression gradually increases from 10 to 36 hpf and is maintained at high levels thereafter. Expression increases in response to prolonged fasting but decreases in response to growth hormone (GH).