Myelin basic protein isoforms in myelinating and remyelinating rat brain aggregate cultures.

Recent evidence suggests that myelin basic protein (MBP) exon-2-containing isoforms play a significant role in the onset of myelination because they are more abundant during early development. The pattern of expression of MBP exon-2-containing isoforms was studied in rat brain aggregate cultures during myelination to draw comparisons with the developing brain and at remyelination after demyelinative treatment. The pattern of MBP isoform expression in the aggregate cultures was found to be similar to that of the brain and was recapitulated after demyelination with antimyelin antibodies. Macrophage enrichment, resulting in increased accumulation of total MBP in the cultures, did not alter the isoform distribution. Both control and enriched cultures expressed a 16-kDa protein (26+/-9.8% of total MBP for control samples) that reacted with MBP antisera at the onset of myelination (day in vitro 14) but was barely detectable by day in vitro 21. The expression of this protein, also present in postnatal day 6 rat brain but no longer by day 11, has been predicted by reverse transcription polymerase chain reaction in embryonic mouse brain. The results of the present study reinforce the value of the aggregate culture system as a versatile yet accurate model of myelination and remyelination.