Heterogeneity Among Neuroepithelial Cells in the Chick Retina Revealed by Immunostaining with Monoclonal Antibody PM1

Neuroepithelial cells appear as a homogeneous population of cells in the cell cycle that seem to behave as pluripotent neural precursors. The study of the intrinsic heterogeneity and subtle developmental changes among neuroepithelial cells has been hindered by the lack of specific markers. To address that study, a panel of monoclonal antibodies was produced against early developing chick retina. The monoclonal antibody precursor marker 1 (PM1) labels most, if not all, of the early neuroepithelial cells in embryonic day 4 retinal sections. This pattern is transient since the labelling becomes restricted to the peripheral retina as development proceeds and eventually disappears from the neuroepithelial cells. However, apparently in parallel, the differentiating retinal ganglion cells become PM1-positive. The expression of the PM1 antigen, a 73 × 10³ M _r protein, as shown by western blotting, also decreases with development. In addition, a chick retina dissociated-cell culture system, where retinal neuroepithelial cells actively proliferate and undergo differentiation under defined conditions, in combination with monoclonal antibody PM1, allowed us to characterize and quantify the proliferating and differentiating neuroepithelial cells. Interestingly, the fraction of total neuroepithelial cells that are stained with PM1 sharply decreases as retinal development proceeds, in correlation with the staining pattern in sections from matched stages. These data thus reveal that the pluripotent neural precursors in the chick retina already represent an intrinsically heterogeneous population, and that this population changes with development.