ALTERED GENE-EXPRESSION IN NEURONS DURING PROGRAMMED CELL-DEATH - IDENTIFICATION OF C-JUN AS NECESSARY FOR NEURONAL APOPTOSIS

We have examined the hypothesis that neuronal programmed cell death re quires a genetic program; we used a model wherein rat sympathetic neur ons maintained in vitro are deprived of NGF and subsequently undergo a poptosis. To evaluate gene expression potentially necessary for this p rocess, we used a PCR-based technique and in situ hybridization; patte rns of general gene repression and selective gene induction were ident ified in NGF-deprived neurons. A temporal cascade of induced genes inc luded ''immediate early genes,'' which were remarkable in that their i nduction occurred hours after the initial stimulus of NGF removal and the synthesis of some required ongoing protein synthesis. The cascade also included the cell cycle gene c-myb and the genes encoding the ext racellular matrix proteases transin and collagenase. Concurrent in sit u hybridization and nuclear staining revealed that while c-jun was ind uced in most neurons, c-fos induction was restricted to neurons underg oing chromatin condensation, a hallmark of apoptosis. To evaluate the functional role of the proteins encoded by these genes, neutralizing a ntibodies were injected into neurons. Antibodies specific for either c Jun or the Fos family (c-Fos, Fos B, Fra-1, and Fra-2) protected NGF-d eprived neurons from apoptosis, whereas antibodies specific for Jun B, Jun D, or three nonimmune antibody preparations had no protective eff ect. Because these induced genes encode proteins ranging from a transc ription factor necessary for death to proteases likely involved in tis sue remodeling concurrent with death, these data may outline a genetic program responsible for neuronal programmed cell death.