Lens regeneration in mammals: a review.

Lens regeneration occurs in New Zealand albino rabbits after endocapsular lens extraction, if the anterior and posterior capsules remain relatively intact. Research beginning in the 19th century showed that regeneration of the lens begins as early as 2 weeks postoperatively, depends on the size of the capsulotomy and how it has scarred, and is faster in younger animals. More recently, implantation of embryonic ectoderm at the time of lens removal has been shown to improve the growth and quality of the regenerated lenses. Lens fiber differentiation follows a process similar to embryological development with proliferation of epithelial cells along the anterior and posterior capsule, elongation of the posterior epithelial cells, and differentiation into lens fibers. Signals required for lens fiber differentiation include FGF, IGF-1, and TGF-beta. Identifying other signals, and providing these factors to the regenerating lens, could speed up lens regeneration and improve normality of the resulting structure. The regenerated lenses contain the same proteins as normal lenses, including all the major crystallins (alpha, beta, and gamma). However, regenerated lenses have typically been irregular in shape due to lack of lens growth at the site of the anterior capsulotomy and its adhesion to the posterior capsule. Sealing the capsulotomy and refilling the bag to maintain its shape seem to allow for more normal lens regeneration. Lens regeneration is a potential approach to restoring normal vision after cataract surgery. Importantly, lenses have been shown to regenerate after removal of cataracts in several mammals, and primate lenses do have regenerative capability.