O-2A progenitors of the mouse optic nerve exhibit a developmental pattern of antigen expression different from the rat.

In a previous study we demonstrated that differentiation and development of mouse oligodendrocytes is similar to that of the rat after the stage at which O4 is acquired. In this present study we compare directly the early differentiation of oligodendrocytes in the mouse and rat post natal optic nerve and show that the two species differ at the O-2A progenitor and proligodendroblast stages. Mouse progenitors show a variety of morphologies compared to the typical bipolar appearance in the rat. Many murine cells fail to immunolabel with A2B5, GD3, O4, and RmAb, classical markers for rat progenitors, proligodendroblasts, and immature oligodendrocytes. We find that these "unlabeled" cells stain for GAP-43 and that expression of GAP-43 overlaps A2B5 and GD3 in the earlier progenitors and O4, RmAb, and O1 in the later proligodendroblasts and immature oligodendrocytes. Our data suggest that in the development of the mouse O-2A progenitor cells there is a developmental discontinuity between the earlier markers such as A2B5 and GD3 and the later marker O4, which can be filled by GAP-43. We therefore consider that GAP-43 could be used in the mouse, in addition to the classical O-2A markers, for the study of the early oligodendrocyte lineage as it labels an otherwise undetectable O-2A population.