Changes in the cerebellar cortex of hairless Rhino-J mice (hr-rh-j)

A mutation in the hr gene is responsible for typical epithelium phenotype in hairless mice. As this gene is expressed at high levels not only in the skin but also in the brain, the aim of the study was to clarify its role in the central nervous system. We have analyzed by morphological and immunocytochemical methods (calbindin D-28k, phosphorylated and 200 kDa neurofilament protein) the cerebellum of a mutated mouse strain, the hairless (hr-rh-j) type carrying the homozygous hr gene rhino mutation. The cerebellar cortex was studied in young (3 months) and adult (9 months) wild type and mutated mice. No major structural change was found in any of the groups and neuronal density or neuronal arrangement were similar in mutated animals to their age-matched controls. Nevertheless there were changes in shape and size of the Purkinje neurons in the old mutated animals respect to their normal littermates, while the molecular and the granule cell layers were apparently invariable. Calbindin (CB) immunohistochemistry revealed a significant decrease in the expression of this protein in the Purkinje cells of the aged mutated mice. Immunohistochemistry for a neurofilament protein (NFP) showed a reduction of staining in all the cerebellar cortex layers in the older animals, which was much more evident in the (hr-rh-j) mutated mice. These results suggest that hr gene is involved in the structural maintenance of the mature cerebellar cortex, rather than in the development. Our findings may also be consistent with an accelerated aging of the central nervous system in rh-rh-j mice.