MULTIPLE FUNCTIONS FOR PAX6 IN MOUSE EYE AND NASAL DEVELOPMENT

Mouse embryos, homozygous for the small eye (Sey) mutation die soon af ter birth with severe facial abnormalities that result from the failur e of the eyes and nasal cavities to develop. Mutations in the Pax6 gen e are responsible for the Sey phenotype. As a general disruption of ey e and nasal development occurs in the homozygous Sey embryos, it is un clear, from the mutant phenotype alone, which tissues require function al Pax6. To examine the roles for Pax6 in eye and nasal development we produced chimeric mouse embryos composed of wild-type and Sey mutant cells. In these embryos we found that mutant cells were excluded from both the lens and nasal epithelium. Both of these tissues were smaller , and in some cases absent, in chimeras with high proportions of mutan t cells. The morphology of the optic cup was also severely affected in these chimeras; mutant cells were excluded from the retinal pigmented epithelium and did not intermix with wild-type cells in other regions . The evidence shows that Pax6 has distinct roles in the nasal epithel ium and the principal tissue components of the embryonic eye, acting d irectly and cell autonomously in the optic cup and lens. We suggest th at Pax6 may promote cell surface changes in the optic cup and control the fate of the ectoderm from which the lens and nasal epithelia are d erived.