CDNA CLONING AND MESSENGER-RNA EXPRESSION OF THE 6 MOUSE INSULIN-LIKEGROWTH-FACTOR BINDING-PROTEINS

The insulin-like growth factor binding proteins (IGFBPs) comprise a fa mily of six distinct proteins which modulate insulin-like growth facto r action. We have isolated cDNAs encoding the six mouse IGFBPs (mIGFBP s). In addition, we studied the mRNA expression of the six mIGFBPs dur ing development and in various adult tissues. Our results show that ea ch of the six mIGFBPs is highly homologous to their human and rat coun terparts, whereas only the N and C terminal ends are conserved between the six mIGFBPs. Northern blotting revealed that mIGFBP-2, -3, -4 and -5 genes are already expressed at gestational day 11.5, suggesting a role for these mIGFBPs in embryonal development. In liver, a peak of m IGFBP-1 mRNA expression was found around birth, suggesting a function for mIGFBP-1 in the newborn mouse. Finally, tissue-specific expression of the six mouse IGFBP genes was observed in adult tissues suggesting different roles or modes of actions in adult life.