<i>Atoh1^trhl/trhl</i>mutant compared to wild-typecontrol cerebellum morphology.

<p>Cerebellar abnormalities in H&E-stainedand cresyl violet-counterstained sections through the cerebellum of a representative wild-type control (left panels) and a <i>Atoh1^trhl/trhl</i>(right panels) mouse shown under increasing magnification from 5X to 63X (n = 3 per group).Cerebella from each genotype were examined. The cerebellum in wild type is well developed and foliated(<b>A</b>), but it is smooth(<b>B</b>) in <i>Atoh1^trhl/trhl</i>mice.The external granule layer (EGL)is indicated by the arrow in both middle panels. In (<b>D</b>) the EGL of the<i>Atoh1^trhl/trhl</i>mice is significantly underdeveloped as compared to (<b>C</b>).Under high magnification, the Purkinje cell layer (PCL), indicated by the star in both (<b>E</b>) and (<b>F</b>), appears disorganized in the mutant, with some Purkinje cells (asterisk in <b>F</b>) located deep in the cerebellum,where they are not normally found.