Motor neuron degeneration is attenuated in bax-deficient neurons in vitro

Apoptosis plays a major role in motor neuron survival during developmental cell death, after axotomy, and in motor neuron diseases. Bar is the first m ember of the bcl-2 family shown to promote apoptosis, In the present study, we used the bax-deficient mouse model to determine the role of bar in moto r neuron survival in vitro by using dissociated spinal cord cultures. This system enables the maturation of individual motor neurons in a controlled i n vitro environment. Motor neurons were identified by using the antineurofi lament antibody SMI-32 and the antitranscription factor antibody Islet1, Bo th antibodies labeled large motor neurons in wild-type and bar-null culture s. Differentiated wild-type cultures exhibited a reduction in long-term cul tures of two- and fivefold in the number of SMI-32- and Islet1-positive cel ls, respectively, The reduction in the number of motor neurons was attenuat ed in bar -/- cultures. Bar deficiency also attenuated serum withdrawal- an d kainate-induced apoptosis in motor neurons. For comparison, necrotic cell death led to significant motor neuron cell death in both wild-type and bar -/- cultures. In addition, bar deficiency did not induce proliferation of motor neuron precursors in vitro. This study indicates for the first time t hat bar has a dominant role in the survival of long-term cultured motor neu rons. (C) 1999 Wiley-Liss, Inc.