Figure 11.

Model of Crygd/e/f regulation during lens development. The retinoic acid receptors (interacting with the RARE element), Prox1 and Sox1 are activators, while Pax6 and Six3 are inhibitors of the Crygd/e/f promoters. The retinoic acid receptors, Pax6 (E8.0) and Six3 (E6.5) are expressed before eye development. Prox1 (E9.5, interacting with the PRORE element) is apparent even before lens development. Crygd/e/f are not expressed during early lens development due to the repressor Six3 (interacting with the SIRE). During lens fibre cell differentiation an additional activator, Sox1, is expressed. The repressor Six3 disappears. Therefore, Cryg expression begins in the fibre cells. In lens epithelium cells γ-crystallins cannot be observed during lens development because of the presence of Six3 (until E18.0).