OlP-1, a novel protein that distinguishes early oligodendrocyte precursors

Oligodendrocyte development may be divided into three distinct stages: I) commitment of neuroectoderm cells to the oligodendrocyte lineage, II) migration of precursors into the surrounding parenchyma concomitant with increased proliferation, and III) cessation of migration and proliferation and initiation of myelination. Stage II of development has remained enigmatic because of the paucity of known molecules that distinguish these immature migratory cells. We describe a novel surface protein, termed OlP-1, which is restricted in expression to this developmental stage in the mouse. Cytofluorographic comparisons with known developmental markers showed OlP-1 to be expressed primarily by stage II precursors in vitro. Histologic analyses supported this conclusion by showing co-localization of OlP-1 with stage II molecules in vivo. Two conclusions were drawn from these results. First, OlP-1 was a novel protein expressed by murine oligodendrocyte precursors at a point in development that suggested a role in migration or proliferation. Second, dispersal of OlP-1-positive cells throughout the developing brain did not correlate with the location of myelination which, observed days later, progressed in a caudal to rostral manner. These data supported the concept that the final steps of maturation and myelin gene expression may be dependent upon extrinsic factors located predominantly within white matter tracts.