DEVELOPMENTAL APPEARANCE, ANTIGENIC PROFILE, AND PROLIFERATION OF GLIAL-CELLS OF THE HUMAN EMBRYONIC SPINAL-CORD - AN IMMUNOCYTOCHEMICAL STUDY USING DISSOCIATED CULTURED-CELLS

We have investigated the time of appearance of the earliest differenti ating glial cell types of human spinal cord using a panel of antigenic markers to identify them in cultures from 6- to 9-week-old human embr yos. Immunolabeling performed at 14 h in vitro with the O4 mAb, an ear ly oligodendrocyte marker, showed the presence of oligodendrocytes dur ing the 7th week of age. At 8 weeks only a few of the O4+ cells expres sed galactocerebroside (GalC), a marker of more differentiated oligode ndrocytes. All the O4+ and GalC+ cells were vimentin+ and some of the GalC+ cells were A2B5+, GD3+ and SSEA-1+. During the first week in vit ro many of the O4+ cells exhibiting a more immature, bi- or tri-polar morphology incorporated [H-3]thymidine into their nuclei. Cells expres sing the astrocyte-specific marker GFAP could be first observed at 8 w eeks; almost all of these GFAP+ cells, which should correspond to radi al glia on the basis of the current literature, were vimentin+, A2B5+, GD3+, and SSEA-1+. At 2 days in vitro incorporation of [H-3]thymidine could be shown in a small fraction of these cells. The finding that r adial glia and oligodendrocytes expressed similar antigenic features a nd the additional observation that a small, but consistent fraction of the cells were simultaneously labeled by O4 and anti-GFAP antibodies support the hypothesis that, in the human spinal cord, radial glial ce lls can give rise to both oligodendrocytes and astrocytes; in this res pect, radial glial cells may be similar to the A2B5+, GD3+, vimentinbipotential glial progenitors previously identified in cultures from d eveloping rat CNS, which also express A2B5, GD3. and vimentin.