In-vitro fertilization and culture of mouse embryos in vitro significantlyretards the onset of insulin-like growth factor-II expression from the zygotic genome

In this study, the effect of in-vitro fertilization (IVF) and culture of mo use embryos in vitro on the normal expression of insulin-like growth factor -ii (IFG-II) ligand and receptor was examined. The expression of IGF-II inc reased in a linear fashion at least up to the 8-cell stage of development. IGF-II expression in embryos collected fresh from the reproductive tract wa s significantly (P < 0.001) greater than in embryos fertilized in the repro ductive tract and cultured in vitro (in-situ fertilized: ISF), and its expr ession was further reduced (P < 0.001) in IVF embryos at all development st ages tested. The expression of IGF-II was significantly (P < 0.001) lower w hen embryos were cultured individually in 100 mu l drops compared with cult ure in groups of 10 in 10 mu l drops of medium. The addition of platelet ac tivating factor to culture medium partially overcame this density-dependent decline of expression. Culture of ISF and IVF zygotes also caused the onse t of new IGF-II mRNA transcription from the zygotic genome to be significan tly (P < 0.001) retarded, until at least the 8-cell stage of development. T his effect was greater (P < 0.05) for IVF than for ISF embryos. Neither IVF nor culture had any obvious effect on IFG-II/mannose-6-phosphate receptor (IGF-IIr) mRNA expression.