MOTONEURONS DEPRIVED OF TROPHIC SUPPORT IN-VITRO REQUIRE NEW GENE-EXPRESSION TO UNDERGO PROGRAMMED CELL-DEATH

During normal development, large numbers of neurons die by programmed cell death. This phenomena has been extensively studied in the lateral motor column of chick embryos, where approximately 50% of the motoneu rons that are initially produced, subsequently die due in part to comp etition for a limited supply of target-derived trophic support. Inhibi tors of RNA and protein synthesis block this cell loss in vivo, indica ting a requirement for new gene expression (Oppenheim et al., 1990). P rior to their commitment to death, motoneurons can be isolated as a re latively pure population from chick spinal cord for in vitro study. Ce lls plated with muscle extract, a potent source of target-derived trop hic support, survive, and have large, phase-bright cell bodies and ext ensive neurite outgrowth. In contrast, motoneurons cultured in the abs ence of muscle extract die within 48 h. This death can be blocked by t he RNA synthesis inhibitor actinomycin D, at the time when the cells b ecome committed to die, suggesting that new gene expression is require d for cell death. DNA fragmentation and nuclear condensation indicate that some of these cells die by apoptosis. Therefore, it appears that many aspects of motoneuron development observed in vivo can be reconst ituted in vitro. These cultures can be used as a model system for stud ying neuronal death and may contribute to an understanding of the mole cular mechanisms that mediate programmed cell death during neuronal de velopment. (C) 1994 John Wiley & Sons, Inc.