Journal of Neuroscience, Vol 6, 2551-2557, Copyright © 1986 by Society for Neuroscience
Survival of motoneurons in the brachial lateral motor column of limbless mutant chick embryos depends on the periphery
ME Lanser, JL Carrington and JF Fallon
Motoneuron survival in the embryonic spinal cord is influenced by the
presence or absence of the developing limb bud. We have recently begun a
reexamination of the relationship between limb absence and motoneuron
survival in a nonsurgical limb deletion model, the limbless mutant chick
embryo. As in surgically limb-deleted normal embryos, only 10% of the
motoneurons that are initially produced in the limbless mutant lateral
motor column (LMC) survive the embryonic period (Lanser and Fallon, 1984).
We now report that, when supplied with a normal periphery (i.e., a normal
limb bud), more than 40% of the motoneurons initially produced in the
limbless LMC survive the embryonic period. Motoneuron cell counts in
one-winged limbless embryos reveal that over 3.5 times as many motoneurons
survive the cell death period in the LMC on the side with the limb than on
the opposite, limbless side. This demonstrates the dependence of embryonic
LMC motoneurons on the developing limb for survival and indicates that the
limbless mutant is an appropriate model for studying the death and survival
of LMC motoneurons during development. Using the limbless mutant to study
LMC motoneuron survival eliminates the complication of possible direct
surgical effects on motoneuron death. In addition, we found that a
substantial effect of the wing on rescuing LMC motoneurons was exerted
prior to the 6th day of embryonic development. Normally, little cell loss
occurs in the brachial LMC during this time. Accordingly, motoneuron death
in the limb-deprived brachial LMC, whether in surgically limb-deleted
normal embryos or in genetically limbless embryos, is accelerated with
respect to cell death in the normal brachial LMC.
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