A large-scale in situ screen provides molecular evidence for the inductionof eye anterior segment structures by the developing lens

The anterior segment of the vertebrate eye includes the cornea, iris, cilia ry body, trabecular meshwork, and lens. Although malformations of these str uctures have been implicated in many human eye diseases, little is known ab out the molecular mechanisms that control their development. To identify ge nes involved in anterior segment formation, we developed a large-scale in s itu hybridization screen and examined the spatial and temporal expression o f over 1000 genes during eye development. This screen identified 62 genes w ith distinct expression patterns in specific eye structures, including seve ral expressed in novel patterns in the anterior segment. Using these genes as developmental markers, we tested for the presence of inductive signals t hat control the differentiation of anterior segment tissues. Organ culture recombination experiments showed that a chick lens is capable of inducing t he expression of markers of the presumptive iris and ciliary body in the de veloping mouse neural retina. The inducing activity from the lens acts only over short ranges and is present at multiple stages of eye development. Th ese studies provide molecular evidence that an evolutionarily conserved sig nal from the lens controls tissue specification in the developing optic cup . (C) 2001 Academic Press.