EXPRESSION OF CYCLIN-A DECREASES DURING NEURONAL APOPTOSIS IN CULTURED RAT CEREBELLAR GRANULE NEURONS

Cultured cerebellar granule neurons died in an apoptotic manner when t he K+ concentration in culture medium was lowered to the normal level (5 mM) after maturation of cells with a high concentration of K+ (26 m M). The changes in expression Df 14 cell cycle-related genes in this C NS apoptosis model were analyzed by quantitative RT-PCR. Most of the g enes analyzed were stable during apoptosis. The expression of cyclin A mRNA, however, transiently decreased 1 h after the induction of apopt osis, and recovered within 3 h to above the basal level. In this syste m, the level of cyclin D1, which has been reported to be up-regulated in apoptosis of NGF-deprived cultured sympathetic neurons, did not cha nge. These results suggest that the molecular mechanisms in these two apoptosis models are different. To determine cyclin A protein level, w e used an immunostaining method, The number of cyclin A-positive neuro ns decreased during apoptosis. Moreover, the numbers of MAP2- and cdk2 -positive neurons also decreased in a similar manner, Taken together, these results suggest that there is a relationship between apoptosis a nd cell cycle, and that morphological changes during apoptosis result from cytoskeletal structure degradation.