Expression of the homeobox genes PAX6, OTX2, and OTX1 in the early human fetal retina.

We studied the spatial and temporal expression of the homeobox genes PAX6, OTX2, and OTX1 using a developmental series of human fetal eyes aged from 6 to 10 weeks post-conception. Previous animal studies have shown that PAX6 may regulate progenitor cell proliferation, timing of differentiation and neural retina cell fate determination. OTX2 may play a role in development of the retinal pigment epithelium and photoreceptor differentiation, whereas OTX1 may be important in ciliary body development. In this study, we demonstrate the presence of the mRNAs and proteins for these genes within human fetal retinas of different stages. By in situ hybridization and immunohistochemistry, we show that PAX6 was primarily localized to nuclei of the neural retina, OTX2 was localized to the nuclei of retinal pigment epithelium and OTX1 expression was confined to anterior retina. Expression peaks for PAX6 occur at days 51-60 and for OTX2 occur around fetal days 48-54. We conclude that the human expression patterns correspond spatially with the patterns observed in the rat retina. Further, the expressions occur during similar fetal stages as described in the developing rat retina.