INSULIN-II GENE-EXPRESSION IN RAT CENTRAL-NERVOUS-SYSTEM

Controversy persists concerning the origin of insulin in the central n ervous system. While there has been convincing evidence in vitro to de monstrate the presence of neuronal insulin mRNA, conventional assays h ave failed to detect the same in whole brain preparations. Here we emp loyed RNAse-protection and sensitive reverse transcription-polymerase chain reaction (RT-PCR) assays in attempts to detect insulin I and II mRNAs in rat brains obtained from different developmental stages. The RNAse-protection assay did not detect insulin I or insulin II transcri pts in fetal (13 to 21 day gestation) or adult brains. RT-PCR, while d etecting low amounts of insulin I transcripts in other extrapancreatic tissues such as the rat yolk sac and fetal liver previously shown to express insulin II, failed to detect insulin I in brain at any age exa mined. Insulin II mRNA was detected by RT-PCR in fetal, neonatal and a dult rat brains, just as in yolk sac, fetal and adult livers. We concl ude that while the duplicated insulin I gene is not expressed, the anc estral insulin II gene is expressed in fetal, neonatal and adult rat b rains. Our observations support the concept of de novo brain insulin I I synthesis beyond the pre-pancreatic stage of embryonic development.