BCL-X IS EXPRESSED IN EMBRYONIC AND POSTNATAL NEURAL TISSUES AND FUNCTIONS TO PREVENT NEURONAL CELL-DEATH

Previous studies have implicated the bcl-2 protooncogene as a potential regulator of neuronal survival, However, mice lacking functional bcl-2 exhibited normal development and maintenance of the central nervous system (CNS), Since bcl-2 appears dispensable for neuronal survival, we have examined the expression and function of bcl-x, another member of the bcl-2 family of death regulatory genes, Bcl-2 is expressed in neuronal tissues during embryonic development but is down-regulated in the adult CNS. In contrast, Bcl-x(L) expression is retained in neurons of the adult CNS, Two different forms of bcl-x mRNA and their corresponding products, Bcl-x(L) and Bcl-x(beta), were expressed in embryonic and adult neurons of the CNS, Microinjection of bcl-x(L) and bcl-x(beta) cDNAs into primary sympathetic neurons inhibited their death induced by nerve growth factor withdrawal, Thus, Bcl-x proteins appear to play an important role in the regulation of neuronal survival in the adult CNS.