The Journal of Neuroscience, February 1, 2000, 20(3):1056-1065
The Pattern of Avian Intramuscular Nerve Branching Is Determined
by the Innervating Motoneuron and Its Level of Polysialic Acid
Victor F.
Rafuse and
Lynn T.
Landmesser
Department of Neurosciences, Case Western Reserve University,
Cleveland, Ohio 44106
Most skeletal muscles are composed of a heterogeneous population of
fast and slow muscle fibers that are selectively innervated during
development by fast and slow motoneurons, respectively. It is well
recognized that, in both birds and mammals, fast and slow motoneurons
have substantially different intramuscular branching patterns, a
difference critical for proper motor function. However, the cellular
mechanisms regulating these differences in motoneuron branching are
unknown. In a previous study, we showed that the fast and slow pattern
of intramuscular branching, in a chick muscle containing distinct fast
and slow muscle regions, was remarkably similar to normal when formed
by foreign motoneurons. Whether this was attributable to some
property of the innervating "fast" or "slow" motoneurons or to
some property of the developing fast-slow muscle fibers was not
determined. To distinguish between these two possibilities, we
performed chick-quail hindlimb chimeras to force slow chick
plantaris motoneurons to innervate a fast quail plantaris muscle. The
pattern of intramuscular nerve branching in the fast plantaris of these
chimeras closely resembled the slow branching pattern normally observed
in chick slow plantaris muscles. Enzymatic removal of polysialic acid
(PSA) from nerve and muscle during normal quail plantaris development
dramatically changed the normal fast pattern to more closely resemble a
slow pattern. In contrast, removal of PSA from chick plantaris
motoneurons and muscle fibers had little effect on the pattern of nerve
branching. Together, these results indicate that the pattern of
intramuscular nerve branching is determined by the level of PSA on the
innervating motoneurons.
Key words:
muscle; myotubes; NCAM; fast/slow; synaptic transmission
of fast muscle; slow muscle
Copyright © 2000 Society for Neuroscience 0270-6474/00/2031056-10$05.00/0