Epithelial flow into the optic cup facilitated by suppression of BMP drives eye morphogenesis

The transformation of the oval optic vesicle to a hemispheric bi-layered optic cup involves major morphological changes during early vertebrate eye development. According to the classical view, the lens-averted epithelium differentiates into the retinal pigmented epithelium (RPE), while the lens-facing epithelium forms the neuroretina. We find a 4.7 fold increase of the entire basal surface of the optic cup. Although the area an individual RPC demands at its basal surface declines during optic cup formation, we find a 4.7 fold increase of the entire basal surface of the optic cup. We demonstrate that the lens-averted epithelium functions as reservoir and contributes to the growing neuroretina by epithelial flow around the distal rims of the optic cup. This flow is negatively modulated by BMP, which arrests epithelial flow. This inhibition results in persisting neuroretina in the RPE domain and ultimately in coloboma.