Mouse mutants for eye development

Teleost lens development and degeneration

The transparent properties of the lens and its ability to focus light onto the retina are critical for normal vision. Optical clarity of the lens is achieved and maintained by a unique, highly regulated integration of lens cell proliferation and differentiation that persists throughout life. Zebrafish is a powerful genetic model for studying vertebrate lens differentiation and growth because the structural organization of the lens and gene functions are largely conserved with mammals, including humans. However, some features of zebrafish lens developmental morphology and gene expression are different from those of mammals and other terrestrial vertebrates. For example, the presumptive zebrafish lens delaminates from the surface ectoderm to form a solid mass of cells, in which the primary fibers differentiate by elongating in circular fashion. Both mutational and candidate gene analyses have identified and characterized developmental gene functions of the lens in zebrafish. This chapter presents the recent morphological analysis of zebrafish lens formation. In addition, the roles of Pitx3, Foxe3, and the lens-specific protein Lengsin (LENS Glutamine SYNthetase-like) in lens development are analyzed. Selected zebrafish lens mutants defective in early developmental processes and the maintenance of lens transparency are also discussed.

Arrested differentiation and epithelial cell degeneration in zebrafish lens mutants

In a chemical mutagenesis screen, we identified two zebrafish mutants that possessed small pupils. Genetic complementation revealed these two lines are due to mutations in different genes. The phenotypes of the two mutants were characterized using histologic, immunohistochemical, and tissue transplantation techniques. The arrested lens (arl) mutant exhibits a small eye and pupil phenotype at 48 hr postfertilization (hpf) and lacks any histologically identifiable lens structures by 5 days postfertilization (dpf). In contrast, the disrupted lens (dsl) mutants are phenotypically normal until 5 dpf, and then undergo lens disorganization and cell degeneration that is apparent by 7 dpf. Histology reveals the arl mutant terminates lens cell differentiation by 48 hpf, whereas the dsl lens exhibits a defective lens epithelial cell population at 5 dpf. Lens transplantation experiments demonstrate both mutations are autonomous to the lens tissue. Immunohistochemistry reveals the retinal cells may suffer subtle effects, possibly due to the lens abnormalities.