Fig. S1. Transgenic mouse lines used in this study. (A) BATlacZ, in which eight Tcf/Lef binding sites and the Siamosis minimal promoter are cloned upstream of an NLS-lacZ coding sequence (Nakaya et al., 2005). (B) The Catnb^lox(ex3) somatic overexpression allele in which exon 3 and a neo cassette are flanked by loxP sites (triangles) (Harada et al., 1999). (C) Mlr10-Cre transgene contains Cre recombinase coding sequence downstream of 325 bp of murine Cryaa promoter and a Pax6 CBS is inserted into the promoter (stippled box) (Zhao et al., 2004). (D) Pax6^lox, in which exons 4-6 of the mouse Pax6 gene are flanked by loxP sites, including the entire paired domain and the translational start codon (Ashery-Padan et al., 2000).

Fig. S2. Somatic recombination pattern of Pax6^lox/lox;Mlr10;Z/AP lenses. Human alkaline phosphatase (hAP) staining of E13.5 and E14.5 paraffin sections of the Pax6^lox/lox;Mlr10;Z/AP. (A) At E12.5, hAP was detected in some lens fiber cells but only in a few cells in the lens epithelium. (B) At E14.5, most cells of the lens were positive for hAP, in accordance with the loss of Pax6 protein at this stage (see Fig. 2K-P). Scale bars: 100 m.

Fig. S3. Histology of additional developmental stages of Pax6 somatic mutant lenses. H&E-treated paraffin sections of eyes of Pax6^lox/lox controls (A-D) and Pax6^lox/lox;Mlr10 somatic mutants (E-H) at E15.5 (A,E), E16.5 (B,F), P4 (C,G) and adult P30 (D,H), demonstrating lack of new LFC growth. Scale bars: 500 nm.

Fig. S4. αA-crystallin immunostaining in the LE and LFC. Paraffin sections of E14.5 embryonic eyes of Pax6^lox/lox controls (A,B) and Pax6^lox/lox;Mlr10 somatic mutants (C,D), stained with an antibody to αA-crystallin (A,C, red) or secondary antibody only (B,D) and demonstrating the specific expression of αA-crystallin, which is weak in the LE and strong in the LFCs.