Lens Induction

AbstractLens tissue develops from the embryonic head ectoderm through its interaction with the retinal primordium, the optic vesicle. This developmental mechanism has served as a paradigm of embryonic tissues induction. The application of modern techniques for gene manipulation and monitoring gene activities in developing embryonic tissues have revealed the two optic vesicle‐dependent mechanisms that underlie the lens induction process: local activation of the cooperative transcription factorsSOX2(SRY‐related‐HMG‐box 2) andPAX6(paired box 6) in the head ectoderm; and elimination of the influence of the cephalic neural crest, which is otherwise inhibitory to lens development. Lens induction reciprocally influences the development of the optic vesicle and organizes the lens‐centered optic cup. The action ofSOX2andPAX6is also common to other lens‐generating processes, including during lens regeneration from the dorsal iris in the newt eye, and lens transdifferentiation from the pituitary primordium as occurs in certain mutant embryos.Key concepts:Tissue induction is the process of deriving new cell types from a tissue through interaction with another tissue.Transcription factors are proteins that regulate gene transcription by binding to the gene regulatory regions of DNA.Signalling molecules, which are often proteins, are secreted from a group of cells, bound by receptors on another group of cells, and cause changes in the cells that bind the molecules.