EXPRESSION OF IGF-II AND H19 MESSENGER-RNA IN THE NEONATAL RAT DURINGNORMAL MATURATION AND AFTER DEXAMETHASONE ADMINISTRATION

In this study, the expression of IGF-II and H19 was examined in the li ver, skeletal muscle and choroid plexus of the neonatal rat during nor mal maturation and after the administration of dexamethasone. If the t wo genes share common regulatory elements as postulated by an enhancer competition system, their patterns of expression should remain simila r throughout maturation and after treatment with dexamethasone. In the liver, down-regulation of IGF-II and H19 during maturation and after dexamethasone administration was shown. This is consistent with the hy pothesis that IGF-II and H19 are regulated by common enhancers. In the secretory cells of the choroid plexus, expression of IGF-II is known to be IGF-II was expressed in both untreated and dexamethasone-treated animals, regardless of age, whereas H19 expression was not detectable . This is consistent with the postulate that only one from each allele can be engaged by the enhancers. In skeletal muscle, H19 continues to be expressed in the adult after IGF-II is switched off suggesting tha t IGF-II can also be regulated independently of H19.