Hoyt E C, Van Wyk J J, Lund P K
Department of Pediatrics, University of North Carolina School of Medicine, Chapel Hill 27514.
Mol Endocrinol. 1988 Nov;2(11):1077-86. doi: 10.1210/mend-2-11-1077.
To obtain information about the functional significance of the structural heterogeneity that has been described for rat insulin-like growth factor I (IGF-I) cDNAs, we hybridized polyadenylated RNAs from rat tissues at different developmental stages with probes specific for two variant 5'-sequences (designated here as type 1 and type 2), with a probe specific for IB type E domain coding sequences and with a probe for E domain sequences common to IA and IB type IGF-I cDNAs. Northern blot analyses revealed that previously reported rat liver IGF-I mRNAs of estimated size 7.5-7.0, 1.9-1.5, and 1.2-0.9 kilobases each are comprised of multiple closely migrating IGF-I mRNA species containing either of two 5'-sequences and either IA or IB type E domain coding sequences. In liver, each of these detected IGF-I mRNA species showed postnatal increases in abundance. The mRNAs detected with the probe for type 2 5'-sequences were detected exclusively in postnatal liver and also showed a different pattern of postnatal increase in abundance than other IGF-I mRNA types. IGF-I mRNAs detected with the probe for IB type E domain coding sequences likewise were highly liver specific and were undetectable or barely detectable in other fetal or adult rat tissues. In contrast, IGF-I mRNAs that hybridized with probes for type 1 5'-sequences or for E domain coding sequences common to IA and IB type IGF-I mRNAs were detected in all fetal and adult rat tissues tested. These findings suggest development and tissue specific regulation of the expression of different rat IGF-I mRNA types, and also suggest a possible role of different precursor sequences encoded by the various mRNAs in targeting of IGF-I to a local site of action.
为了获取有关已报道的大鼠胰岛素样生长因子I（IGF-I）cDNA结构异质性的功能意义的信息，我们用针对两种变体5'-序列（在此称为1型和2型）的特异性探针、针对IB型E结构域编码序列的特异性探针以及针对IA和IB型IGF-I cDNA共有的E结构域序列的探针，与来自不同发育阶段大鼠组织的聚腺苷酸化RNA进行杂交。Northern印迹分析显示，先前报道的估计大小为7.5 - 7.0、1.9 - 1.5和1.2 - 0.9千碱基的大鼠肝脏IGF-I mRNA，各自由多个紧密迁移的IGF-I mRNA种类组成，这些种类包含两种5'-序列之一以及IA或IB型E结构域编码序列。在肝脏中，这些检测到的IGF-I mRNA种类中的每一种在出生后丰度都增加。用2型5'-序列探针检测到的mRNA仅在出生后的肝脏中被检测到，并且其出生后丰度增加的模式也与其他IGF-I mRNA类型不同。用IB型E结构域编码序列探针检测到的IGF-I mRNA同样具有高度肝脏特异性，在其他胎儿或成年大鼠组织中未检测到或几乎检测不到。相比之下，与1型5'-序列探针或与IA和IB型IGF-I mRNA共有的E结构域编码序列探针杂交的IGF-I mRNA在所有测试的胎儿和成年大鼠组织中都被检测到。这些发现表明不同大鼠IGF-I mRNA类型的表达存在发育和组织特异性调控，并且还表明各种mRNA编码的不同前体序列在将IGF-I靶向局部作用位点方面可能发挥的作用。
