Molecular characterization of Notch1 positive progenitor cells in the developing retina

The oscillatory expression of Notch signaling in neural progenitors suggests that both repressors and activators of neural fate specification are expressed in the same progenitors. Since Notch1 regulates photoreceptor differentiation and contributes (together with Notch3) to ganglion cell fate specification, we hypothesized that genes encoding photoreceptor and ganglion cell fate activators would be highly expressed in Notch1 receptor-bearing (Notch1+) progenitors, directing these cells to differentiate into photoreceptors or into ganglion cells when Notch1 activity is diminished. To identify these genes, we used microarray analysis to study expression profiles of whole retinas and isolated from them Notch1+ cells at embryonic day 14 (E14) and postnatal day 0 (P0). To isolate Notch1+ cells, we utilized immunomagnetic cell separation. RNA from Notch1+ cells and whole retinas at E14 and P0 was extracted and used for microarray analysis. We processed individual samples that each contained 200,000-500,000 Notch1+ cells. A total of three independent biological replicates in the early stage (E14) of retinal development and four independent biological replicates in the late stage (P0) of retinal development were obtained for comparative profiling of Notch1+ cells and whole retinas.