Myelin basic protein isoform expression: A comparison of developing rat brain and myelinating and remyelinating rat brain aggregate cell cultures

Recent evidence suggests myelin basic protein (MBP) exon-2 containing isoforms play a significant role in the onset of myelination as they are more abundant during early development. The pattern of expression of MBP exon-2 containing forms was studied in rat brain aggregate cultures during myelination in order to draw comparisons with the developing brain and upon remyelination following 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 following demyelination with anti-myelin 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) which 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 11 rat brain but no longer by day 15, has been predicted by RT-PCR; however, detection of a corresponding protein with the same developmental pattern and appropriate molecular weight has not been previously reported. The results of this study reinforce the value of the aggregate culture system as a versatile yet accurate model of myelination and remyelination