Expression of the transcription factor Olig2 in proliferating cells in the adult zebrafish telencephalon.

The telencephalon of the adult zebrafish is highly proliferative: Dividing cells are found along the entire ventricular zone and in the parenchyma. Here, we investigated the relation of proliferating cells in the telencephalic parenchyma to the oligodendrocyte lineage. We find at least three different cell types of the oligodendrocyte lineage (olig2-and sox10-positive) in the parenchyma of the telencephalon: Proliferating progenitors (PCNA-positive), including a subpopulation of slowly dividing progenitors (long term label-retaining), as well as mature oligodendrocytes (Mbp-positive) and presumptive quiescent OPCs (neither Mbp-positive nor proliferating). Furthermore, in the ventricular zone (in and ventral to the RMS), two different subpopulations of olig2-positive cell populations are present. Since these ventricular olig2-positive cells do not express the oligodendrocyte marker sox10, it is not clear whether these cells indeed belong to the oligodendrocyte lineage. Taken together, we detected at least five different classes of olig2-positive cells in the telencephalon of the adult zebrafish.