Msx-2 and p21 mediate the pro-apoptotic but not the anti-proliferative effects of BMP4 on cultured sympathetic neuroblasts

The differentiation, survival, and proliferation of developing sympathetic neuroblasts are all coordinately promoted by neurotrophins. In this study, we demonstrate that bone morphogenetic protein 4 (BMP4), a factor known to be necessary for the differentiation of sympathetic neurons (Schneider et a l., 1999), conversely reduces both survival and proliferation of cultured E 14 sympathetic neuroblasts. The anti-proliferative effects of BMP4 occur mo re rapidly than the pro-apoptotic actions and appear to involve different i ntracellular mechanisms. BMP4 treatment induces expression of the transcrip tion factor Msx-2 and the cyclin-dependent kinase inhibitor p21(CIP1/WAF1) (p21). Treatment of cells with oligonucleotides antisense to either of thes e genes prevents cell death after BMP4 treatment but does not significantly alter the anti-proliferative effects. Thus Msx-2 and p21 are necessary for BMP4-mediated cell death but not for promotion of exit from cell cycle. Al though treatment of cultured E14 sympathetic neuroblasts with neurotrophins alone did not alter cell numbers, BMP4-induced cell death was prevented by co-treatment with either neurotrophin-3 (NT-3) or nerve growth factor (NGF ). This suggests that BMP4 may also induce dependence of the cells on neuro trophins for survival. Thus, sympathetic neuron numbers may be determined i n part by factors that inhibit the proliferation and survival of neuroblast s and make them dependent upon exogenous factors for survival. (C) 2001 Aca demic Press.