Ectopic CGNs in profilin1 mutants. (A) Nissl staining revealed normal cerebellar cortex cytoarchitecture in P8 mutants. Scale bar, 50 μm in A–C. (B) In P12 mutants, layering of the cerebellar cortex was normal, whereas the ML cell density appeared higher. (C) Increased ML cell density, an irregularly shaped PCL (dashed lines) and gaps within the PCL (arrowhead) were noted in P60 mutants. (D) ML cell densities were significantly increased in mutants at P12 (controls: 4,702±222 cells per mm2; mutants: 7,411±206 cells per mm2; n=12 images from 6 mice; P<0.001) and P60 (controls: 1,975±150 cells per mm2; mutants: 3,397±119 cells per mm2; n=16/8; P<0.001), but not at P8 (controls: 5,182±221 cells per mm2; mutants: 6,069±387 cells per mm2; n=6/3; P=0.07). (E) NeuN immunoreactivity (green) and PI counterstaining (magenta) in the ML at P60. Scale bar, 40 μm. Yellow arrowheads indicate PI+/NeuN− cells, whereas blue arrowheads indicate PI+/NeuN+ cells. (F) Although the number of PI+/NeuN− cells was unchanged (controls: 1,971±88 cells per mm2; mutants: 1,789±115 cells per mm2; n=6/3; P=0.242), the number of PI+/NeuN+ cells was increased in the mutant ML (controls: 292±42 cells per mm2; mutants: 1,459±76 cells per mm2; P<0.001). CGN, cerebellar granule neuron; EGL, external granule cell layer; IGL, internal granule cell layer; ML, molecular layer; NeuN, neuron-specific nuclear protein; NS, not significant; P, postnatal day; PCL, Purkinje cell layer; PI, propidium iodide.