Temporal expression pattern of insulin-like growth factor mRNA during embryonic development in a teleost, rainbow trout (Onchorynchus mykiss).

The appearance of insulin-like growth factor I (IGFI) and II (IGF-II) mRNA was studied during rainbow trout embryonic development. Reverse transcription-polymerase chain reaction (RT-PCR), followed by Southern blotting and high-stringency hybridization with rainbow trout IGF-I and IGF-II cDNA probes, was used to detect all four forms of IGF-I mRNA and one form of IGF-II mRNA from whole-embryo total RNA isolated from a staged series. IGF-I and IGF-II mRNA were detected in unfertilized eggs. IGF-I and IGF-II mRNA were also detected during cleavage, gastrulation, and organogenesis, at hatching, during yolk absorption, and at feeding. IGF-IEa-1 and Ea-3 mRNA were detected in unfertilized eggs, while IGF-I Ea-4 was first detected at stage 9 when the zygotic genome is believed to become activated in rainbow trout. IGF-IEa-2 was not detected at any stage of embryonic development. IGF mRNA of immunoreactive peptides have been detected durin embryonic development in all vertebrates studied to date. Our results confirm the presence of IGF-I mRNA in teleost embryos. In addition, IGF-II mRNA is also present in teleost embryos. Our results suggest that the role IGF-I and IGF-II play during embryonic development may be conserved in vertebrates.