[Characteristics of the cell proliferation in the developing human retina]

The retinal primordia were studied in human embryos at developmental weeks 5-8 to examine the expression of proliferation-associated proteins (Ki67 and PCNA), the number of nucleoli in the nuclei of neuroepithelial cells (in respect to their distance to the apical surface) and the distribution of DNA-synthesizing cells after a short-term (20 min) incubation in vitro in serum-free medium containing BrdU. In 5-week embryos, retinal primordium contains the neuroepithelium with a typical structure. BrdU-positive nuclei and nuclei with small number of nucleoli were found in the basal portion of the ventricular zone. However, this organization was disturbed in the initial period of the formation of inner nuclear layer (week 6). At this stage DNA-synthesizing cells were seen even at the apical surface. In retinal primordia of embryos at weeks 6-7 there appeared an additional area of cell proliferation in the Chievitz layer and in the inner nuclear layer. In embryos at week 8 the dividing cells were concentrated in the outer nuclear layer, which has regained the organization, typical for a neuroepithelium.