Origin of the Retinal Oligodendrocyte in the Chicken Embryo

Seo, Je Hoon; Cho, Sa Sun

Abstract

Unlike other retinal cells, oligodendrocytes originate from the ventral midline of the third ventricle, and migrate to the retina at embryonic day 10 (E10) through the optic chiasm and the optic nerve in the bird. Recent studies have demonstrated that sonic hedgehog (shh), a differentiation factor for oligodendrocytes, was secreted by ganglion cells in the developing retina, indicating that microenvironment of the retina is sufficient for the generation of oligo-dendrocytes. Furthermore, it was revealed that uncommitted progenitors could differentiate into all cell types in the murine retina. On the basis of these reports, we proposed that a subpopulation of oligodendrocytes might generate in the retina in situ of the chick embryo. In order to verify our hypothesis, we injected the intraretinal space of chick embryos with a replication-defective retroviral vector (LZ12), and identified oligodendrocytes among LZ12-incorporated cells. Plp/dm-20 and pdgfr-alpha, oligodendrocyte specific transcripts were already expressed in the E5 retina. The expression of shh transcripts was also detected in the same stage. Analysis of the retina with intraretinal space injection demonstrated many clones consisting of various cell types arranged vertically through the retina. In addition, we found a few clones that had O4 +/-oligodendrocytes. In case of third ventricle injection, we found that LZ12-incorporated cells occurred in rows, the typical shape of interfascicular oligodendrocytes in the optic nerve, and were located in the nerve fiber layer adjacent to the ganglion cells in the retina. These cells were also labeled with TfBP antibody. These results indicate that retinal oligodendrocytes of birds are differentiated from retinal precursor cells, together with undifferentiated cells adjacent to the third ventricle.