Developing oligodendroglia express mRNA for insulin‐like growth factor‐I, a regulator of oligodendrocyte development

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Abstract
Insulin-like growth factors IGF-I and IGF-II are potent inducers of oligodendrocyte development. Because IGF-I is produced, in some cases, by the same cells that respond to it (autocrine/paracrine action), we examined the possibility that IGF-I is expressed by developing oligodendroglial cells. We employed a sensitive method, reverse transcriptase-polymerase chain reaction (RT-PCR), to detect IGF-I mRNA in purified populations of oligodendroglial cells isolated from rat brain during the period of oligodendrocyte development. Cells were purified by fluorescence activated cell sorting (FACS), using antibodies to the cell surface antigenic markers 04 and galactocerebroside (GC). RNA was isolated from the sorted cells, reverse-transcribed, and PCR-amplified, using a strategy that recognizes IGF-I mRNA but not DNA. The amplified band was identified as IGF-I by size, hybridization to an IGF-I-specific antisense probe, and restriction analysis. IGF-I mRNA was detected in O4-positive/ GC-negative oligodendrocyte precursors and, more weakly, in GC-positive oligodendrocytes. IGF-I mRNA could be detected reproducibly in RNA extracted from 100-cell samples of O4-positive cells, making it unlikely that the mRNA was derived from contaminants in the FACS-sorted cell populations. We conclude that IGF-I is expressed by developing oligodendroglia. Autocrine expression of IGF-I by developing oligodendroglial cells suggests that oligodendrocyte development is, in part, autoregulatory.