Figure 4. Embryonic Nf1 inactivation is required for optic glioma formation.

(A) The timing of Nf1 inactivation by Cre-mediated excision is shown for each strain. (B) X-gal staining reveals GFAP-Cre transgene expression in the lv-SVZ and TVZ beginning at E15.5. Whereas lv-SVZ cells are Ki67⁺ from E15.5 through PN8, scant numbers of Ki67⁺ or nestin⁺ cells are detected in the TVZ by PN2. (C) Cre expression and Nf1 gene recombination (Nf1^Rec) is detected by E13.5 in the anterior forebrain/lv-SVZ (“forebrain”) and by E16.5 in the hypothalamus/TVZ (“hypothalamus”) of GFAP-Cre* mice. (D) Cre-mediated Nf1 gene recombination (PCR) in Nf1^+/−GFAP mice and in tamoxifen-treated Nf1^flox/flox; GFAP-Cre^ER and Nf1^flox/mut; GFAP-Cre^ER mice was seen. Wild-type (WT) C57BL/6 mouse brain was used as a negative control, whereas Ad5Cre-infected (Cre) and Ad5LacZ-infected (LacZ) Nf1^flox/flox astrocytes served as positive and WT controls, respectively. Cre-ER fusion protein (~70 KDa) expression was detected in GFAP-Cre^ER (ER), but not in WT, mouse brains. EGFP was expressed in tamoxifen-treated ROSA-GREEN; GFAP-Cre^ER mouse brains and optic nerves at 1 month of age, but not in a WT mouse optic nerve (ON-WT). HP: hippocampus, Th: thalamus, Ch: chiasm, ON: optic nerve. (E) Whereas optic gliomas develop in Nf1^+/-GFAP and Nf1^+/-GFAP* mice, no gliomas formed in Nf1^flox/flox or Nf1^flox/mut; GFAP-Cre^ER treated with tamoxifen (+Tam) beginning at PN1 or PN14. Increased Ki67⁺ cells were found in the prechiasmatic and chiasmal regions (square) of Nf1^+/−GFAP and Nf1^+/−GFAP* mice. In contrast, the number of Ki67⁺ cells in Nf1^flox/mut; GFAP-Cre^ER postnatally-treated with tamoxifen is indistinguishable from control Nf1^flox/flox mice. Values denote the mean ± SEM. See also Figure S3.