Oligodendrocyte origin and development in the zebrafish visual system

Oligodendrocytes are the myelinating cells in the central nervous system (CNS). Their developmental origin and specification are well known in birds and mammals but remains unclear in fish. To fulfill this gap, we have studied their early progression during zebrafish visual morphogenesis using the transgenic line Olig2:GFP. We have tracked the Olig2+ cells in the visual system from 48 hours post fertilization (hpf) until 11 days post fertilization (dpf). We have also analyzed the differential expression of the Sox2 and Sox10 transcription factors in this cellular line. Oligodendrocyte progenitor cells (OPCs) originate at 48hpf in regions close to the preoptic area, near to the ventral hypothalamus. Then, at 5 dpf, they migrate to the optic chiasm, where they invade the optic nerve, extending towards the retina. While OPCs in the retina also express Sox2, in the the optic tectum they express Sox10. Within the optic nerve tract, they express both. We have also observed that these Olig2:GFP line do not colocalize with the expression of Mbpa, a myelin marker, but are intimately intertwined. Our data matches with other animal models, where OPCs are specified in the preoptic area and migrate to the optic nerve through the optic chiasm. We revealed that oligodendrocyte is a complex population of cells expressing different transcription factors.