Journal of Neuroscience, Vol 4, 2043-2050, Copyright © 1984 by Society for Neuroscience
Development of the lateral motor column in the limbless mutant chick embryo
ME Lanser and JF Fallon
This is a report on the development of the lateral motor column (LMC) in
the limbless mutant chick embryo. The limbless mutant was used to study the
effects of the absence of a periphery on the developing nervous system. The
limbless mutant provides a unique opportunity to compare the effects on the
LMC of deletion of a limb caused by the genotype with those seen following
surgical removal of the limb primordium. Cell counts of the total number of
motoneurons in the LMC at both the brachial and lumbar levels were done in
a large series of limbless embryos and on their normal siblings. In normal
embryos, a substantial loss of LMC motoneurons was observed during the
course of normal development. At the brachial level, 54% of the initial LMC
cell population was lost between day 6 and day 18. At the lumbar level, 40%
of the initial population was lost between the 6th and 12th days of
development with no further loss through day 18. An even more massive cell
loss was observed in the limbless mutant LMC at both brachial and lumbar
spinal cord levels between day 5 and day 12. This resulted in the
elimination of at least 85% of the motoneurons that were initially present
in the limbless LMC. Our data demonstrate that the effects of peripheral
deprivation on LMC development in the limbless mutant are similar to those
seen following surgical removal of the periphery. The initial production of
motoneurons and assembly of the LMC did not appear to be significantly
affected by the mutation, while the subsequent degeneration of LMC
motoneurons is greatly accelerated and increased in comparison to the
normal.
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