Expression of the basic helix–loop–factor Olig2 in the developing retina: Olig2 as a new marker for retinal progenitors and late-born cells

In this study, we examined the spatiotemporal expression patterns of Olig2, a basic helix–loop–helix transcription factor, in the developing mouse retina. Expression of Olig2 was initially detected on embryonic day 12.5 (E12.5). The majority of Olig2-positive cells were identified as retinal progenitor cells throughout embryogenesis. During later embryonic stages, the number of Olig2-positive retinal progenitor cells increased, and Olig2-positive cells were confined only to the neuroblast layer (NBL). Olig2 expression was not observed in the ganglion cell layer (GCL) nor in the inner nuclear layer (INL) that contain the differentiated retinal cell types, indicating that Olig2 is not expressed in differentiated cells in prenatal retina. In later postnatal stages, Olig2 expression was retained in mature neurons and glial cells, namely retinal ganglion cells (RGCs), amacrine cells (ACs), horizontal cells, bipolar cells and Müller glial cells. Thus, Olig2 is an marker both for retinal progenitor cells during embryonic stages, and also for differentiated retinal subpopulations within the GCL and INL during postnatal stages.