IGFBP-3 Function In Zebrafish Embryos

Insulin-like growth factor binding protein (IGFBP)-3 is the major IGF carrierprotein in the bloodstream. The IGFBP-3 / IGF complex prolongs the half-life of IGFs incirculation and prevents the potential hypoglycemic effect of IGFs. IGFBP-3 is alsoexpressed in many peripheral tissues in fetal and adult stages. In vitro studies usingcultured cells suggest that IGFBP-3 can inhibit / potentiate IGF actions, and evenpossesses IGF-independent activities, suggesting that local IGFBP-3 may also act in aparacrine / autocrine fashion. The in vivo function of IGFBP-3, however, is unknown. Inthis study, we have explored the developmental role of IGFBP-3 using the zebrafishmodel. RNA hybridization analyses revealed that IGFBP-3 mRNA expression began at14 hour post fertilization (hpf) in the migrating cranial neural crest cells. It was latertransiently expressed in pharyngeal arches, and in pectoral fin buds. IGFBP-3 mRNA ispredominantly and persistently expressed in the developing otic vesicle. IGFBP-3 is alsoexpressed in optic stalk, retina, pineal gland, tegmentum in midbrain, anterior pituitaryand midline floor of hypothalamus. To determine the developmental role of IGFBP-3, weablated the IGFBP-3 gene product by injecting morpholino-modified antisenseoligonucleotides (MOs). The IGFBP-3 knocked-down morphants had delayed pharyngealskeleton morphogenesis and greatly reduced pharyngeal cartilage differentiation.Knockdown of IGFBP-3 also significantly reduced sizes of otic vesicle, optic primordia,pectoral fin bud, and disrupted the differentiations of hair cell and optic stalk, as well asthe formations of semicircular canal and pineal gland. Furthermore, re-introduction of aMO-resistant form of IGFBP-3 "rescued" the MO-induced defects. This findings are thefirst to provide in vivo evidences for IGFBP-3 playing an important role in regulatingdevelopment and growth of pharyngeal cartilage and otic vesicle, differentiations of opticand motor neuron, as well as its involving in the development of eye, pineal gland andpectoral fin bud in zebrafish.