The study of lens development provides a useful experimental system for investigating fundamental processes in developmental biology. The vertebrate lens develops from a series of interactions between the surface ectoderm, the optic vesicle, and the surrounding mesoderm, and these interactions involve successive steps of bias, competence, specification, and differentiation (see chap. 2 of this volume; see also McAvoy et al., 1999; Hirsch and Grainger, 2000). In recent years, these cellular and morphogenetic processes have been subject to investigation focusing on the molecular events underlying them (Weaver and Hogan, 2001). In particular, important insights were gained through genetic studies performed on the development of the eye in Drosophila (Treisman, 1999) and by comparisons of gene expression and function between the eyes of invertebrate and vertebrate species (Hill et al., 1991; Quiring et al., 1994; reviewed in Wawersik and Maas, 2000; Wawersik et al., 2000). These studies have led to the identification of conserved regulatory pathways mediating eye formation in both the fly and vertebrates.
Additional insight into these molecular events has been provided by the evaluation of mouse or human syndromes in which morphogenesis is defective (Freund et al., 1996; Graw, 2000). The eye is frequently affected by inherited eye disorders: roughly one—quarter of the phenotypes listed in Mendelian Inheritance in Man involve the eye (Boyadijiev and Jabs, 2000), and several candidate genes implicated in these phenotypes have so far been identified.