Expression of insulin-like growth factor-binding protein messenger RNAs in developing rat oligodendrocytes and astrocytes.

Insulin-like growth factors, IGF-I and IGF-II, are potent regulators of oligodendrocyte development. Most of the IGF present in vivo is bound to members of a family of six high-affinity IGF-binding proteins (IGFBPs), which can either potentiate or inhibit IGF action, depending on other conditions. Additionally, serum contains a structurally unrelated protein, acid-labile sub-unit (ALS), which forms a ternary complex with IGF and IGFBP3. In this study, we used reverse-transcriptase polymerase chain reaction (RT-PCR) to examine the expression of mRNAs for IGFBP 1-6 and ALS in purified populations of oligodendroglial cells and astrocytes. We found that astrocytes express all six IGFBPs. A2B5+/O4- oligodendrocyte precursors, O4+/O1- intermediate precursors, and O1+ oligodendrocytes express IGFBP3, 5, and 6, while IGFBP4 is expressed in oligodendrocyte precursors but not at more mature stages. We were unable to detect ALS mRNA in whole brain or in cultured oligodendroglial cells. The presence of differentially expressed IGFBPs in developing oligodendrocytes and astrocytes could significantly affect the biological activity of IGF-I and IGF-II in the central nervous system and the IGF-responsiveness of the IGFBP-expressing cells.