IN-SITU LABELING OF GRANULE CELLS FOR APOPTOSIS-ASSOCIATED DNA FRAGMENTATION REVEALS DIFFERENT MECHANISMS OF CELL LOSS IN DEVELOPING CEREBELLUM

We have examined the role apoptosis plays during postnatal development of the mouse cerebellum by a new method utilizing T7 DNA polymerase f or the in situ detection of DNA fragmentation associated with cell dea th. Granule cell loss between the third and fifth postnatal weeks, hyp othesized to affect the granule cell to Purkinje cell stoichiometry, i s not associated with DNA fragmentation. However, cerebellar granule c ells undergo extensive nuclear DNA fragmentation between postnatal day s 5 and 9. Cell death prior to synaptogenesis may help regulate granul e cell number. Our results suggest that different mechanisms of cell d eath within the same neuronal cell population occur during development .