Journal of Neuroscience, Vol 6, 2880-2888, Copyright © 1986 by Society for Neuroscience
Interspecies selective motoneuron projection patterns in chick-quail chimeras
H Tanaka and LT Landmesser
During normal development chick motoneurons have been shown to project
selectively to appropriate muscles by responding to a series of cues, both
specific and nonspecific, within the limb. We tested the ability of
motoneurons from another avian species, the Japanese quail, to respond to
these cues by transplanting chick limb buds onto quail embryos and quail
limb buds onto chick embryos between stages 17 1/2 and 19. Feulgen
staining, which distinguishes chick from quail cells on the basis of
nuclear chromatin, revealed that all limb tissue, including muscle, was of
donor origin, indicating that the migration of somite-derived muscle
precursor cells had been completed by the time of transplantation. Normal
quail motoneuron pools for most muscles were located in the same relative
positions as homologous chick pools. In chick-quail chimeras we found that
the motoneuron pools of one species selectively innervated the homologous
muscles in the limb of opposite species with considerable precision. This
was determined by defining the segmental innervation pattern of the muscles
electrophysiologically and by retrogradely labeling motoneuron pools with
HRP. Selective innervation was confirmed by using the functional activation
patterns of the motoneuron pools as an additional means of identifying
motoneurons. We conclude that any limb-derived cues required by motoneurons
to project to their appropriate muscles must be similar in chick and quail
and that the growth cones of both species must have similar detector
systems for responding to these cues. Only 7 spinal segments were found to
innervate the quail limb (versus 8 for the chick), resulting in an anterior
shift in the spinal segments innervating several posterior quail
muscles.(ABSTRACT TRUNCATED AT 250 WORDS)