Fig. 6. Phenotypes of the FGFR2-IIIb^-/- embryo. (A) Heterozygous and homozygous littermates at E11.5. Null embryos grow to the same size as heterozygotes at this stage, and are relatively normal, but they lack both fore and hind limbs. (B) Genotyping of embryos by genomic PCR. (C) Alkaline phosphatase (AP)-stained genital ridge and midline preparations are compared in E11.5 embryos. The numbers of ectopic PGCs were drastically reduced in null embryos. (D) Transverse section of AP-stained genital ridges showing a reduction of gonadal germ cells. (E) The targeted FGFR2-IIIb mutation was bred into the OCT4PE:GFP mouse line. The same effect, reduction of ectopic germ cells, was seen in null embryos. (F) Transverse sections of genital ridges shown in E. Sections were stained with OCT3/4 antibody to analyze the density of gonadal germ cells. (G) Sagittal sections of genital ridges were stained for the apoptosis marker cleaved caspase-3 (red). Cleaved caspase-3-positive germ cells are compared in genital ridges at E11.5. (H) BrdU-positive germ cells (arrows) in E11.5 genital ridges of heterozygous and null embryos. (I) The number of ectopic germ cells in heterozygous and null embryos at E11.5. (J) Quantitation of germ cell density in genital rides at E11.5. Because the density of germ cells varied between littermates, the data obtained from null embryos were normalized to the heterozygous littermates. (K) Quantitation of germ cell death in genital ridges at E11.5. (L) Percentage of BrdU-positive germ cells in genital ridges at E11.5. There is no statistically significant difference between the percentage of BrdU-positive germ cells in null gonads and heterozygous gonads. Asterisks in I-K indicate the degree of statistical significance (P<0.05) of increase (^*) and decrease (^**) compared with heterzygotes. Scale bars: 1 mm for A; 200 µm for C,E; 50 µm for D,F,G; 20 µm for H.