Acceleration of early chick embryo morphogenesis by insulin is associated with altered expression of embryonic genes

In the present study, we show that insulin accelerates early morphogenesis in gastrulating chick embryo explants cultured in vitro, whereas antiserum to insulin adversely affects this process. Comparison between length of body axis of control and treated embryos clearly brings out the significant acceleration of development by excess insulin (0.175 to 17.5 nM). In embryos treated with 87.5 and 175 nM insulin, a high occurrence of abnormalities is observed. Treatment of embryos with antiserum to porcine insulin results in a high percentage of abnormalities, particularly in the forming neural tube. In situ hybridization of whole embryos using digoxigenin-labeled riboprobes showed that insulin modifies the expression of crucial developmental genes within 2 hours. While Brachyury, a pan-mesodermal marker gene, ERNI, the earliest known marker for neural induction in chick, and noggin, important in neural tube patterning, are upregulated, expression of goosecoid, necessary for gastrulation movements, does not appear to be significantly altered. During the same time, insulin does not exert any mitogenic effect on chick embryonic cells as assessed by nuclear counts. These findings demonstrate that insulin plays an important role in the early morphogenesis of the chick embryo. The function of insulin appears to be mediated by specific genes which orchestrate pattern formation during early development.