Cell-autonomous involvement of Mab21l1 is essential for lens placode development

The mab-21 gene was first identified because of its requirement for ray identity specification in Caenorhabditis elegans. It is now known to constitute a family of genes that are highly conserved from vertebrates to invertebrates, and two homologs, Mab21l1 and Mab21l2, have been identified in many species. We describe the generation of Mab21l1-deficient mice with defects in eye and preputial gland formation. The mutant mouse eye has a rudimentary lens resulting from insufficient invagination of the lens placode caused by deficient proliferation. Chimera analyses suggest that the lens placode is affected in a cell-autonomous manner, although Mab21l1 is expressed in both the lens placode and the optic vesicle. The defects in lens placode development correlate with delayed and insufficient expression of Foxe3, which is also required for lens development, while Maf, Sox2, Six3 and PAX6 levels are not significantly affected. Significant reduction of Mab21l1 expression in the optic vesicle and overlying surface ectoderm in Sey homozygotes indicates that Mab21l1 expression in the developing eye is dependent upon the functions of Pax6 gene products. We conclude that Mab21l1 expression dependent on PAX6 is essential for lens placode growth and for formation of the lens vesicle; lack of Mab21l1 expression causes reduced expression of Foxe3 in a cell-autonomous manner.