Yang Y W, Brown D R, Robcis H L, Rechler M M, de Pablo F
Growth and Development Section, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892.
Regul Pept. 1993 Oct 20;48(1-2):145-55. doi: 10.1016/0167-0115(93)90343-7.
The chick embryo is a useful vertebrate model for studying developmental embryogenesis. Insulin-like growth factor I (IGF-I), a potent mitogen, is thought to contribute to the general growth of the embryo as an endocrine factor, and as a paracrine factor to the development of the early embryo and of specific organs such as the eye. Recent data suggest that a family of at least six IGF binding proteins (IGFBPs) complex IGF-I and modulate its biological actions. In the present study, we examine the expression of IGFBPs in chicken serum and vitreous humor at different stages of embryonic development, and compare it with that of IGF-I. As determined by ligand blotting, the predominant IGFBP in chick serum and vitreous humor between embryonic days 4 and 22 (E4-E22) is a 30 kDa IGFBP. This IGFBP was specifically immunoprecipitated by a polyclonal antiserum raised against rat IGFBP-2, the predominant IGFBP in fetal human and rat serum. Although IGFBP-2 is present in both chick fluids at all times examined, serum IGFBP-2 increased progressively between E10-E22, whereas vitreous IGFBP-2 was highest during eye organogenesis (E4-E8). This suggests that vitreous IGFBP-2 is synthesized locally. Like serum IGFBP-2, levels of immunoreactive IGF-I in serum are higher in the second week of embryogenesis than the first. Despite this correlation, changes in IGFBP-2 do not appear to be regulated by IGF-I: (a) serum IGF-I decreases after day 15, whereas IGFBP-2 levels remain stable until hatching; (b) vitreous IGF-I, like serum IGF-I, is higher in the second week of embryogenesis, whereas vitreous IGFBP-2 is highest in the first week; (c) embryos cultured ex ovo express IGFBP-2 at E15-E19, although they lack the normal mid-embryogenesis surge in IGF-I. We conclude that vitreous IGFBP-2 is synthesized locally in the eye, and that the expression of IGFBP-2 in chick embryos is not directly regulated by IGF-I.
鸡胚是研究发育胚胎学的一种有用的脊椎动物模型。胰岛素样生长因子I（IGF-I）是一种强效促有丝分裂剂，被认为作为一种内分泌因子对胚胎的整体生长有贡献，并且作为旁分泌因子对早期胚胎以及特定器官如眼睛的发育有贡献。最近的数据表明，一个至少由六种IGF结合蛋白（IGFBPs）组成的家族使IGF-I形成复合物并调节其生物学作用。在本研究中，我们检测了胚胎发育不同阶段鸡血清和玻璃体液中IGFBPs的表达，并将其与IGF-I的表达进行比较。通过配体印迹法测定，胚胎第4天至22天（E4-E22）鸡血清和玻璃体液中主要的IGFBP是一种30 kDa的IGFBP。这种IGFBP被针对大鼠IGFBP-2（胎儿人和大鼠血清中的主要IGFBP）产生的多克隆抗血清特异性免疫沉淀。尽管在所有检测时间点IGFBP-2都存在于两种鸡体液中，但血清IGFBP-2在E10-E22之间逐渐增加，而玻璃体液IGFBP-2在眼器官发生期（E4-E8）最高。这表明玻璃体液IGFBP-2是在局部合成的。与血清IGFBP-2一样，胚胎发育第二周血清中免疫反应性IGF-I的水平高于第一周。尽管有这种相关性，但IGFBP-2的变化似乎不受IGF-I调节：（a）第15天后血清IGF-I下降，而IGFBP-2水平在孵化前保持稳定；（b）玻璃体液IGF-I与血清IGF-I一样，在胚胎发育第二周较高，而玻璃体液IGFBP-2在第一周最高；（c）体外培养的胚胎在E15-E19表达IGFBP-2，尽管它们缺乏正常的胚胎中期IGF-I激增。我们得出结论，玻璃体液IGFBP-2是在眼中局部合成的，并且鸡胚胎中IGFBP-2的表达不受IGF-I直接调节。
