Reduction of endogenous transforming growth factors beta prevents ontogenetic neuron death

We show that following immunoneutralization of endogenous transforming grow th factors beta (TGF-beta) in the chick embryo, ontogenetic neuron death of ciliary, dorsal root and spinal motor neurons was largely prevented, and n euron losses following limb bud ablation were greatly reduced. Likewise, pr eventing TGF-beta signaling by treatment with a T betaR-II fusion protein d uring the period of ontogenetic cell death in the ciliary ganglion rescued all neurons that normally die. TUNEL staining revealed decreased numbers of apoptotic cells following antibody treatment. Exogenous TGF-beta rescued t he TGF-beta -deprived phenotype. We conclude that TGF-beta is critical in r egulating ontogenetic neuron death as well as cell death following neuronal target deprivation.