Astrocyte proliferation during development of the human retinal vasculature

Wholemounts of human fetal retinas were labeled with antibodies to Ki67 or proliferating cell nuclear antigen, to map the distribution of proliferatin g cells in the developing primary vasculature and neural retina. Double lab eling was used to determine the relative proportions of endothelial cells ( CD34), astrocytes (glial fibrillary acidic protein - GFAP) and microglia (m ajor histocompatability complex class II) associated with the developing ve ssels. The differentiated region of neural retina (cold spot) was 3.5 mm(2) at 15 weeks gestation (WG), centred on the incipient fovea, and increased in size with age to 80.5 mm(2) by 23-24 WG. Ki67 immunoreactive cells were distributed throughout the developing vasculature at all ages. The mean den sity of dividing cells in the neural retina increased with gestational age from 146 mm(-2) at 15 WG, to 624 mm(-2) at 23-24 WG. By 20 WG proliferation in the vasculature overlapped the margins of the cord spot, which was almo st completely vascularized by 23-24 WG, except for a narrow strip on the ho rizontal meridian, which included the incipient fovea. Counts of CD34/Ki67 immunoreactive cells indicated that 15-52 % of proliferations in the develo ping vasculature at 18 WG are endothelial cells. In contrast, in the fellow retina 65-85% cells were Ki67/GFAP immunoreactive, indicating proliferatio n of astrocytes in situ. No dividing microglia were observed. The findings suggest that large numbers of proliferating astrocytes accompany the develo ping vessels as they migrate across the primate retina. (C) 1999 Academic P ress.