Morphogenesis of the optic vesicles – The roots of retinogenesis in amniote embryos

Eye number varies dramatically across the animal kingdom. The authors recently discovered a self‐organizing gene network involving the eye master control gene Pax6, which casts new light on eye number regulation. In amniote vertebrates, eye number variation manifests as cyclopia, the formation of a single eye in the centre of the head caused by defects in midline Sonic hedgehog (Shh) signalling. In the developing embryo, the retinas derive from the optic vesicles of the primitive forebrain. The data suggest that optic vesicles may normally grow from paired growth zones within the anterior neural folds of the amniote neural tube. The study hypothesizes that cyclopia occurs following ventral fusion of these growth zones in the absence of midline Shh signalling.