Abstract
Abstract: :
Purpose: The generation of retinal cells follows a distinct temporal sequence. Retinal ganglion cells, cone photoreceptors and horizontal cells are born between E11-E14 (early neurogenesis) while the majority of rod photoreceptors, bipolar cells, amacrine cells and Müller glia are generated E18 onward (late neurogenesis). We wanted to study the molecular characteristics of early and late retinal stem cells/progenitor in order to understand mechanisms underlying their distinct proliferative and differentiation potential. Methods: Retinal dissociates from E14 and E18 embryos were cultured for 5 days in the presence of EGF + FGF2 and EGF, respectively. Differentiation was induced by mitogen withdrawal and culturing cells in 1%FBS for another 6 days. Microarray analysis was carried out using cRNA probe on Affimetrix rat U34A chips according to the supplier's instructions. Results: Microarray analysis showed differential expression of genes during proliferation and differentiation of early and late stem cell/retinal progenitors. Following are the percentage of classes of differentially expressed genes represented in the array: cell cycle; 0.31%, transcription factors; 1.02%, cell-signaling; 1.51%, translation and protein trafficking; 1.3%, metabolism; 1.05%. In the cell-signaling class, the modulation of levels of genes representing the components of Notch pathway was particularly interesting. Analysis of their expression levels suggested an increase in Notch signaling during the differentiation of early retinal stem cells/progenitors, presumably to maintain a large pool of uncommitted progenitors. In contrast, Notch signaling appeared to be relatively decreased in late retinal stem cells/progenitors in similar conditions, likely due to the fact that they generate fewer cell types. Conclusion: Our preliminary observations suggest that the early and late retinal stem cells/progenitor populations are distinct in terms of the expression of different classes of genes. Further characterization of these genes will shed light on the maintenance of progenitor populations and help in modulating the fate of these cells towards a particular lineage for therapeutic purposes. Supported by NEI and Nebraska Research Initiative
Keywords: 564 retinal development • 523 proliferation • 417 gene/expression