Lens Induction


Lens 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 factors SOX2 (SRY‐related‐HMG‐box 2) and PAX6 (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 of SOX2 and PAX6 is 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.

Keywords: lens; head ectoderm; optic vesicle; Sox2; Pax6; crystallin

Figure 1.

Crystallin expression in the lens. A histological section through the eye of a 3‐day‐old chicken embryo stained with anti‐δ‐crystallin antibodies. Lens epithelium (LE) and lens fibres (LF) are indicated.

Figure 2.

Schematic representation of experiments utilizing ablation of the retina rudiment (optic vesicle) as initially described by Spemann .

Figure 3.

The temporal order of the expression (broken arrows) and activity (solid arrows) of transcription factors active during the early stages of lens development. Histological sections of chicken embryo at the developmental stages indicated at the top of each panel are used as a template for illustrations, but the scheme also applies to a wide range of vertebrate species. Crystallin expression in the chicken lens is also indicated as a reference.



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Further Reading

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Okada TS (1991) Transdifferentiation. New York: Oxford University Press.

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Kondoh, Hisato(Apr 2010) Lens Induction. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001142.pub2]