Muller cells express the neuronal progenitor cell marker nestin in both differentiated and undifferentiated human foetal retina

Tritiated thymidine studies suggest that Muller cells are the last cells born in the retina, although several authors describe Muller cells throughout the retina from very early ages. In this study immunohistochemistry was used to identify progenitor and Muller cells in human foetal retina. Antibodies to nestin (an intermediate filament protein expressed by neural progenitor cells), vimentin, cellular retinaldehyde binding protein (CRALBP) and glutamate and aspartate transporter (GLAST), which are each expressed by Muller cells, were used in combination with anti-Ki67 to identify proliferating cells. By definition, Ki67-positive proliferating cells were present in undifferentiated retina, but not in differentiated retina. Nestin-immunoreactive (IR) cells colocalized with vimentin throughout the retina. CRALBP-IR was detected in differentiated retina and in some proliferating cells. GLAST-IR cells were present only within the differentiated region. Nestin, vimentin and CRALBP each colocalized with mitotic Ki67-IR cells, suggesting that in foetal retina Muller cells and retinal progenitor cells are overlapping populations and that Muller cells are end-stage progenitor cells.