title: Somatomedin-C/insulin-like growth factor-I and insulin-like growth factor-II mRNAs in rat fetal and adult tissues.
abstract: Somatomedin-C or insulin-like growth factor I (Sm-C/IGF-I) and insulin-like growth factor II (IGF-II) have been implicated in the regulation of fetal growth and development. In the present study 32P-labeled complementary DNA probes encoding human and mouse Sm-C/IGF-I and human IGF-II were used in Northern blot hybridizations to analyse rat Sm-C/IGF-I and IGF-II mRNAs in poly(A+) RNAs from intestine, liver, lung, and brain of adult rats and fetal rats between day 14 and 17 of gestation. In fetal rats, all four tissues contained a major mRNA of 1.7 kilobases (kb) that hybridized with the human Sm-C/IGF-I cDNA and mRNAs of 7.5, 4.7, 1.7, and 1.2 kb that hybridized with the mouse Sm-C/IGF-I cDNA. Adult rat intestine, liver, and lung also contained these mRNAs but Sm-C/IGF-I mRNAs were not detected in adult rat brain. These findings provide direct support for prior observations that multiple tissues in the fetus synthesize immunoreactive Sm-C/IGF-I and imply a role for Sm-C/IGF-I in fetal development as well as postnatally. The abundance of a 7.5-kb Sm-C/IGF-I mRNA in poly(A+) RNAs from adult rat liver was 10-50-fold higher than in other adult rat tissues which provides further evidence that in the adult rat the liver is a major site of Sm-C/IGF-I synthesis and source of circulating Sm-C/IGF-I. Multiple IGF-II mRNAs of estimated sizes 4.7, 3.9, 2.2, 1.75, and 1.2 kb were observed in fetal rat intestine, liver, lung, and brain. The 4.7- and 3.9-kb mRNAs were the major hybridizing IGF-II mRNAs in all fetal tissues. Higher abundance of IGF-II mRNAs in rat fetal tissues compared with adult tissues supports prior hypotheses, based on serum IGF-II concentrations, that IGF-II is predominantly a fetal somatomedin. IGF-II mRNAs are present, however, in some poly(A+) RNAs from adult rat tissues. The brain was the only tissue in the adult rat where the 4.7- and 3.9-kb IGF-II mRNAs were consistently detected. Some samples of adult rat intestine contained the 4.7- and 3.9-kb IGF-II mRNAs and some samples of adult liver and lung contained the 4.7-kb mRNA. These findings suggest that a role for IGF-II in the adult rat, particularly in the central nervous system, cannot be excluded.
mesh_terms: D000818:Animals; D001921:Brain / Q000196:embryology / Q000378:metabolism; D003001:Cloning, Molecular; D004247:DNA / Q000378:metabolism; D005260:Female; D005333:Fetus / Q000378:metabolism*; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000235:genetics*; D007335:Insulin-Like Growth Factor II / Q000235:genetics*; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000196:embryology; D008099:Liver / Q000196:embryology / Q000378:metabolism; D008168:Lung / Q000196:embryology / Q000378:metabolism; D008297:Male; D051379:Mice; D008970:Molecular Weight; D011247:Pregnancy; D012333:RNA, Messenger / Q000235:genetics* / Q000302:isolation & purification; D051381:Rats; D013002:Somatomedins / Q000235:genetics*
chemical_list: D012333:RNA, Messenger; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D004247:DNA