Santos A, Yusta B, Fernández-Moreno M D, Blázquez E
Department of Biochemistry and Molecular Biology, Faculty of Medicine, Complutense University, Madrid, Spain.
Mol Cell Endocrinol. 1994 May;101(1-2):85-93. doi: 10.1016/0303-7207(94)90222-4.
Insulin-like growth factor-I (IGF-I) is involved in the growth and development of liver and brain during fetal life by acting through specific plasma membrane receptors. In an attempt to determine how the changes in IGF-I receptor number are regulated during development, we have compared [125I]IGF-I binding to membrane fractions with the concentration of IGF-I receptor mRNA in rat liver and brain. IGF-I binding to liver membranes was 4.5 times higher in 20-day-old fetuses than in adult rats. After partial hepatectomy (70%) in adult rats a transient 2-fold increase of IGF-I binding to liver membranes was observed. In fetal and regenerating liver increases similar to those observed for IGF-I binding were observed in IGF-I receptor mRNA concentrations. In brain microsomes IGF-I binding was 3.5 times higher in 20-day-old fetuses than in adults. This difference reflects a similar change in the number of IGF-I receptors without modifications in the affinity of the receptor for the ligand. In contrast to the liver, no significant changes in the concentration of IGF-I receptor mRNA were observed in the developing brain when determined by hybridization solution, Northern blot or RNase protection analysis. These findings suggest that in the liver, the IGF-I receptor gene is regulated at pretranslational level during development and regeneration, while in brain it is preferentially regulated at translational or posttranslational level.
胰岛素样生长因子-I（IGF-I）在胎儿期通过特定的质膜受体发挥作用，参与肝脏和大脑的生长发育。为了确定在发育过程中IGF-I受体数量的变化是如何被调节的，我们比较了大鼠肝脏和大脑中[125I]IGF-I与膜组分的结合情况以及IGF-I受体mRNA的浓度。20日龄胎儿肝脏膜上的IGF-I结合量比成年大鼠高4.5倍。成年大鼠部分肝切除（70%）后，观察到肝脏膜上IGF-I结合量短暂增加2倍。在胎儿肝脏和再生肝脏中，IGF-I受体mRNA浓度的增加与IGF-I结合量的增加相似。在脑微粒体中，20日龄胎儿的IGF-I结合量比成年大鼠高3.5倍。这种差异反映了IGF-I受体数量的类似变化，而受体对配体的亲和力没有改变。与肝脏不同，通过杂交液、Northern印迹或核糖核酸酶保护分析测定时，发育中的大脑中IGF-I受体mRNA浓度没有显著变化。这些发现表明，在肝脏中，IGF-I受体基因在发育和再生过程中在转录前水平受到调节，而在大脑中，它优先在翻译或翻译后水平受到调节。
