Reduced numbers and mispositioning of <i>Tnc</i>⁺ BG cells in the EGL of the <i>Fgfr2</i> cKO CbA.

<p>(<b>A–J</b>) Representative sagittal brightfield views of E16.5 (A–D, n = 4 embryos/genotype), E17.5 (E–H, n = 1 embryo/genotype) and E18.5 (I,J, n = 3 embryos/genotype) control (A,C,E,G,I) and <i>Fgfr2</i> cKO (B,D,F,H,J) cerebella hybridized with radioactive <i>Tnc</i> (A–F,I,J) and <i>Fgfr2</i> (G,H) riboprobes. (C,D) are higher magnifications of the boxed areas in (A,B). (E–H) are higher magnifications of the anterior CbA in adjacent sections from control or mutant embryos. Red arrowheads in (D,F) point at ectopically positioned <i>Tnc</i>⁺ BG cells in the mutant EGL. Note the complete absence of the <i>Fgfr2</i> ISH signal correlating with less <i>Tnc</i>⁺ and intensely Nissl-stained cells in the CbA of the <i>Fgfr2</i> cKO embryo shown in (F,H), although some <i>Fgfr2</i>⁺ cells are detected in the (non-neural) mesenchyme overlying the mutant EGL. Red dotted line in (A,I) delimits the anterior area used for quantification. (<b>K,L</b>) High magnification views of the EGL and PCL on adjacent sections from an E18.5 control (wild-type) embryo, hybridized with a radioactive riboprobe for <i>Fgfr2</i> (red in K) or <i>Tnc</i> (black in L). Black arrowheads point at intensely Nissl-stained cells showing an ISH signal for <i>Fgfr2</i> (K) or <i>Tnc</i> (L). Empty arrowheads point at larger, weakly Nissl-stained cells devoid of <i>Fgfr2</i> (K) or <i>Tnc</i> (L) ISH signals. (<b>M,N</b>) Quantification of <i>Tnc</i>⁺ cells in the anterior CbA (M) and EGL (N) of control (grey bars) and mutant (white bars) embryos at E16.5 and E18.5 (<i>Tnc</i>⁺ cells/µm² (M): E16.5: control, 6.49×10⁻⁴±2.5×10⁻⁵ (n = 4 embryos); <i>Fgfr2</i> cKO, 4.43×10⁻⁴±2.4×10⁻⁵ (n = 4 embryos); E18.5: control, 9.41×10⁻⁴±5.9×10⁻⁵ (n = 3 embryos); <i>Fgfr2</i> cKO, 6.25×10⁻⁴±5.6×10⁻⁵ (n = 3 embryos); <i>Tnc</i>⁺ cells in anterior EGL (N): E16.5: control, 3.00±0.41 (n = 4 embryos); <i>Fgfr2</i> cKO, 17.00±1.29 (n = 4 embryos); E18.5: control, 5.67±0.88 (n = 3 embryos); <i>Fgfr2</i> cKO, 13.33±2.33 (n = 3 embryos); Student's <i>t</i>-test). EGL, external granular layer; PCL, Purkinje cell layer; VZ, cerebellar ventricular zone. Scale bars: 100 µm (B); 50 µm (D,H); 30 µm (L).