Motoneuron survival factors: biological roles and therapeutic potential.

The existence of factors that promote motoneuron survival in the spinal cord at critical stages of development was first deduced 50 yr ago. The large amount of work that has been put into characterizing such factors reflects both their biological importance and the hope that such molecules may be used therapeutically to slow motoneuron death in pathologies such as the spinal muscular atrophies and amyotrophic lateral sclerosis. Since 1990, several factors have been shown to have in vitro and/or in vivo activities that suggest they play a role in regulating motoneuron survival. Their physiological functions during motoneuron development are probably different and complementary. Several of them seem reasonable candidates for preclinical development, but many crucial experiments remain to be done.