Fig. 6. Cre-mediated recombination leads to enlarged optic nerves. X-gal staining of the proximal optic nerve immediately adjacent to the retina (A) and distal optic nerve near the chiasm (asterisk) (B). Optic nerves were dissected from 2-month-old mice with the genotype of hGFAP-cre+; Rosa26-lacZ/+ (n=3). (C,D) Adjacent sections to A,B were subjected to double-labeling immunofluorescence with anti-lacZ (red) and anti-GFAP (green). Most of the lacZ-positive cells are GFAP-expressing astrocytes. (E) hGFAP-cre-mediated recombination in the optic nerve was revealed by PCR analysis. Upper panel: a PCR assay identifying the floxed NF1 allele (x1) and recombined floxed allele () indicated that a significant number of the floxed NF1 alleles in the optic nerve (ON), cerebral cortex (Ctx) and hippocampus (Hp) of the Nf1^flox/+;hGFAP-cre+ mice transformed into the recombined alleles. Bottom panel: a PCR assay that identifies the wild type (+) and the floxed (x1) NF1 allele confirmed the genotype of the tissues analyzed. (F) A representative of control (left) and mutant (right) eyes with the optic nerves and chiasm (arrowheads). High-magnification of view of control (G) and mutant (H) optic nerves with chiasms (asterisk). The mutant nerve has a conspicuous enlargement (indicated by broken lines and arrowheads). Scale bars: 100 µm in A-D; 1 mm in F-H.