Isolation and characterization of defective jimpy oligodendrocytes in culture.

This study characterizes jimpy oligodendrocyte-enriched secondary cultures isolated from 10-12 days in vitro primary glial cell cultures derived from 1-2-day-old jimpy mouse brains. Proliferation of defective oligodendrocytes was carefully investigated with regard to the expression of myelin basic protein and proteolipid protein and their respective mRNAs. Less than 5% of contaminating astrocytes (GFAP+ cells) were usually present. The identity of jimpy oligodendrocytes was confirmed using an antibody directed against a peptide from the wild type proteolipid protein C-terminal sequence for immunocytochemistry and an oligonucleotide complementary to mRNA derived from exon 5 of the proteolipid protein gene for in situ hybridization. Both the antibody and the probe recognize only normal oligondedrocytes while jimpy oligodendrocytes always remain unstained. Proteolipid protein in normal and jimpy oligodendrocytes was detected with antibody recognizing normal and mutated forms. Between 80 and 95% of the cells in normal and jimpy cultures at 2 and 4 days in vitro in secondary cultures express myelin basic protein and proteolipid protein and their respective mRNAs. The percentage of oligodendrocytes (PLP+ or MBP+) in S phase of the cell cycle was 7-10% for both normal and jimpy oligodendrocytes. This contrasts with the in vivo situation where the proliferation rate of oligodendrocytes in jimpy brains is higher than in normal brains. In addition, jimpy oligodendrocytes remain unresponsive to basic fibroblast growth factor treatment while a similar treatment stimulates the proliferation of normal oligodendrocytes.