NOVEL STAGE IN THE OLIGODENDROCYTE LINEAGE DEFINED BY REACTIVITY OF PROGENITORS WITH R-MAB PRIOR TO O1 ANTI-GALACTOCEREBROSIDE

The developmentally regulated appearance of surface immuno-reactivity of proligodendroblasts [oligodendrocyte progenitors reacting with monoclonal antibodies A007 and O4, but not anti-galactocerebroside (GalC), i.e., A007/O4+GalC-] to monoclonal antibodies R-mAb and O1 was studied both in culture and in vivo. In both cases staining with R-mAb shortly preceded that with O1; that is, a transient population of R-mAb+O1- cells was observed. R-mAb-O1+ cells were not detected. Differential staining with R-mAb and O1 was also noted at the subcellular level. In younger cultures in which R-mAb+ cells were first acquiring O1 immunoreactivity, many of these cells were stained by O1 only on the cell bodies and proximal portions of the processes, whereas in contrast R-mAb stained the whole cell, including the distal portions of the processes. Only in older, more mature R-mAb+ cells did O1 also stain the distal portions of processes. The expression of reactivity to R-mAb and O1 was compared to the proliferative capacity of the cells. Proliferation [assessed by bromodeoxyuridine (BrdU) incorporation] of both R-mAb+ and O1+ cells was negligible both in culture and in vivo. However, treatment of cells in culture with 10 ng/ml basic fibroblast growth factor resulted in an enhancement of proliferation of the R-mAb+ cells. Within the proliferating R-mAb+ BrdU+ population, 80% of the cells were O1- (i.e., anti-galactocerebroside negative). These events occur during a critical period of development when A007/O4+ proligodendroblasts begin to become post-mitotic and express surface galactocerebroside. The data demonstrate that the use of R-mAb as an "anti-GalC" must be interpreted with caution, and indicate the utility of dual staining with R-mAb and O1 to (1) further subdivide the oligodendrocyte lineage, thus identifying an additional, GalC- developmental compartment, and (2) observe the distribution of R-mAb and O1 immunoreactivity at a subcellular level.