A cell cycle alteration precedes apoptosis of granule cell precursors in the weaver mouse cerebellum

A missense mutation in the gene coding for the G-protein-activated inwardly rectifying potassium (GIRK) channel, GIRK2, is responsible for apoptosis i n the external germinal layer (EGL) of the cerebellum and a nonapoptotic de ath of midbrain dopaminergic neurons in the weaver (wv) mouse, Failure of a xonogenesis and migration are considered to be the primary consequences of GIRK2 channel malfunction in the cerebellum, We investigated whether a disr uption of the cell cycle precedes the failure of migration and axonogenesis and leads to massive apoptosis, To this end, immunohistochemistry and immu noblotting for PCNA, Cdk4, cyclin. D, cyclin A, and the Cdk inhibitor p27/k ip1, as well as ill situ end-labeling for apoptotic DNA fragmentation, were applied to cerebella of P7-P21+/+, wv/+, and wv/wv mice, In +/+ and wv/+ m ice, the expression of cell cycle proteins was limited to the outer, premig ratory zone of the EGL, Antibodies to p27, a marker of cell differentiation , gave a reverse staining pattern, Due to migration delay, patches of p27-p ositive cells persisted in the outer EGL in P21 wv/+ mice, On the contrary, marked cell cycle up-regulation and absence of p27 occurred throughout the EGL at all ages in wv/wv mice, indicating an inability to switch off the c ell cycle, Mitotic index evaluation showed that cell cycle activation was u nrelated to proliferative events. Cell cycle proteins were not expressed in the substantia nigra, suggesting that nonapoptotic death of mature dopamin ergic neurons is not preceded by abortive cell cycle reentry, Our data show that abnormalities of the cell cycle in wv/wv cerebellum represent a major and early consequence of GIRK2 channel malfunction and may strongly influe nce the susceptibility of EGL cells to apoptosis,These observations may hel p in understanding the pathogenesis of human neurological channelopathies.