title: Characterization of the execution pathway of developing motoneurons deprived of trophic support.
abstract: Avian spinal motoneurons have been well characterized with regard to developmental programmed cell death (PCD). Approximately 50% of the neurons originally generated undergo cell death as they innervate their target muscles, and target derived trophic support plays an important role in regulating survival of these neurons. To investigate events mediating motoneuron PCD, we have examined the role of Bcl-2 family proteins, cytochrome C, and caspase-9 in this process. We report that while protein levels of Bcl-2, Bcl-xL, and Bax do not change within motoneurons as they become committed to die, a translocation of Bax from the cytosol to organelle membranes and the nucleus occurs coincident with the time when motoneurons become committed to cell death. In addition, cytochrome C is released from mitochondria to the cytosol in dying cells prior to the activation of caspases. Consequently, an enhanced caspase-9-like activity was detected in dying cells, and this activity was upstream and necessary for the appearance of a caspase-3-like activity. These results allow us to further define some of the critical events that mediate the execution phase of motoneuron death following trophic factor deprivation.
authors.affiliation: Department of Neurobiology and Anatomy and Program of Neuroscience, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157, USA.
authors.forename: L
authors.initials: L
authors.lastname: Li
authors.forename: R W
authors.initials: RW
authors.lastname: Oppenheim
authors.forename: C E
authors.initials: CE
authors.lastname: Milligan
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D002454:Cell Differentiation / Q000502:physiology*; D002467:Cell Nucleus / Q000378:metabolism; D002470:Cell Survival / Q000502:physiology*; D002478:Cells, Cultured; D002642:Chick Embryo; D003574:Cytochrome c Group / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism; D009046:Motor Neurons / Q000166:cytology / Q000378:metabolism*; D009414:Nerve Growth Factors / Q000172:deficiency*; D015388:Organelles / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D013116:Spinal Cord / Q000166:cytology / Q000196:embryology* / Q000378:metabolism; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein
chemical_list: D003574:Cytochrome c Group; D009414:Nerve Growth Factors; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D053453:Caspase 9; D020169:Caspases