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Liv 12 Lil Boosie - Facetime Feat. Mystikal - Murda, Prodigy, Illaghee, Pharrell Hello 11 Lil Wayne Feat. Created on. Jason Scott Archivist. Sketch the Cow Archivist. To determine whether differential expression of PSA on fast and slow motoneurons determines the pattern of intramuscular nerve branching in developing chick and quail plantaris muscles, Endo-N was injected into the hindlimbs of St.
As shown in the St. Unlike the high degree of defasciculation, transverse pattern of axon growth, and reductive branching normally observed in St. All these patterns of growth are characteristics of a slow pattern. As a control, removal of PSA from slow chick plantaris muscles did not alter the basic branching pattern, which remained slow in nature Fig. However, the number of secondary branches that emerged from the main nerve trunks was clearly reduced compared with control.
This is not unexpected because PSA is still present on slow nerve branches, although at lower levels than fast. This observation is also consistent with an earlier study that found a reduction in the secondary branches in the slow IFIB muscle after complete removal of PSA with Endo-N Landmesser et al.
The intramuscular slow nerve branching pattern is determined by the level of PSA on the innervating motoneurons. A , Intramuscular nerve branching in late St. B , Enzymatic removal of PSA from normal quail plantaris nerves and muscles during the period of initial muscle innervation dramatically alters the pattern of innervation such that the nerves become highly fasciculated with the major intramuscular nerve growing parallel to the myotubes.
C , Intramuscular nerve branching pattern in a late St. D , Enzymatic removal of PSA from normal chick plantaris nerve and muscle during the period of initial innervation does not dramatically alter the branching pattern, although there is some reduction in the number of secondary branches that emerge from the main nerve trucks.
Together, these results strongly indicate that the intramuscular nerve branching pattern is determined by the degree of polysialylation of the innervating fast and slow motoneurons. Neurons innervating avian fast and slow muscles, or muscle regions, have dramatically different intramuscular branching patterns, which in turn determine the different patterns of synapse formation observed on fast and slow myotubes Dahm et al.
The results presented here extend our previous studies, which showed that the pattern of branching in slow and fast muscle was strongly modulated by PSA Landmessser et al. Here, we show that the characteristic reductive branching pattern of fast motor axons is caused by a high level of PSA expression on the innervating neurons, whereas slow axons exhibit the more fasciculated slow pattern attributable to low PSA expression.
Furthermore, the present study makes the novel finding that neither the architectural structure of developing myotubes nor the distinct molecular make-up of developing fast and slow muscle fibers regulates intramuscular branching patterns. Thus, slow chick plantaris motoneurons innervating fast quail plantaris muscles in chick—quail hindlimb chimeras displayed a characteristic slow branching pattern. This indicates that the pattern is regulated by some property of the motor axons and is not a result of some structural or molecular property of the fast fibers being innervated.
In addition, enzymatic removal of PSA from fast motoneurons altered the normal reductive branching pattern to a highly fasciculated slow axon branching pattern, indicating that the level of PSA on the innervating axon plays a major role in regulating intramuscular axon branching. The first generation of muscle fibers to develop are primary myotubes, which differentiate into distinct fast and slow phenotypes by a nerve-independent process.
Secondary myotubes begin to develop alongside the primary myotubes, in what is thought to be a nerve-dependent process, only after the muscle has been innervated by all of its motoneurons Butler et al.
The basic fast—slow intramuscular nerve branching patterns are established before the onset of secondary myogenesis Dahm and Landmesser, at a time when few synapses have formed and the muscle is only beginning to be activated Dahm and Landmesser, In previous studies, we proposed that intramuscular nerve branching patterns were regulated by the relative strength of axon—axon versus axon—myotube adhesion Landmesser et al.
According to this model, increasing axon—axon adhesion would promote axon fasculation, resulting in a slow branching pattern such that the main intramuscular branches grow parallel to the muscle fibers. Decreasing axon—axon adhesion, while simultaneously increasing axon—myotube adhesion, would promote a fast pattern of axon branching such that the axons grow transverse to the myotubes and undergo a reductive branching pattern.
Enzymatic removal of PSA from both axons and myotubes, at the time when the IFIB muscle is first being innervated, dramatically alters the normal branching pattern such that the axons innervating the fast region now grow with a slow branching pattern Landmesser et al. These results raised the possibility that intramuscular branching patterns are regulated by the level of PSA expressed by innervating neurons. However, developing myotubes also express PSA in a developmentally regulated manner Fredette et al.
In addition, we demonstrated that developing fast muscles express higher levels of PSA than slow muscle Fig. Consequently, our previous study could not determine whether it was PSA levels on motoneurons or muscle fibers that influenced the intramuscular branching pattern. By forcing slow chick neurons to innervate a fast quail muscle in chick—quail hindlimb chimeras, we are now able to demonstrate that the intramuscular branching pattern is regulated by the level of PSA being expressed by the innervating neurons.
In addition, enzymatic removal of PSA during early plantaris nerve innervation dramatically altered the fast nerve branching pattern such that it more closely resembled a slow pattern. Removal of PSA from developing slow chick plantaris muscles produced only moderate changes in the branching pattern. Together, these results indicate that the intramuscular branching pattern is regulated by the level of PSA expressed by the innervating neurons and is independent of the type of muscle fiber being innervated.
Previous studies have shown that muscle fibers can change their phenotype late in development i. Consequently, we cannot rule out the possibility that conversion of muscle fiber properties later in development might have modified late stages of the intramuscular branching pattern.
However, such activity-dependent conversion of fiber types cannot have influenced the initial branching patterns that we characterized, because these patterns would have been formed before synapse formation and the electrical activation of most of the muscle fibers Dahm and Landmesser, PSA expression is regulated on developing axons and myotubes in complex spatial and temporal patterns Rutishauser and Landmesser, Contact with muscle targets results in a decrease in PSA levels and polysialyltransferase activity in ciliary ganglion neurons Bruses et al.
Electrical activity has also been shown to regulate PSA expression on chick motor axons and myotubes. Blocking muscle fiber electrical activity, both in vivo Fredette et al. Similarly, increasing muscle fiber activity increases PSA on developing myotubes in culture Rafuse and Landmesser, Additionally, it has been found recently that in vivo application of the neuromuscular blocking agent d -tubocurare, which was previously shown to increase PSA expression on motor axons Landmesser et al.
Thus, in both nerve and muscle, PSA expression may require electrical activity. How might activity be coupled to PSA expression? We have shown here that PSA on motor axons regulates the fast—slow pattern of intramuscular nerve branching, and previous studies have shown that fast and slow motor axons have different levels of PSA.
Is electrical activity only permissive for PSA expression, or could different patterns of electrical activity in fast and slow motor axons explain their differential PSA expression? Developing chick flexor and extensor motoneurons have been shown to be spontaneously active early in development several days before nerve—muscle contact and to have different patterns of activity Milner and Landmesser, A fundamental rule in motor control is that motor units defined as the motoneuron and all of the muscle fibers it innervates are recruited from the least forceful to the most forceful during muscle contraction Henneman and Olson, This orderly recruitment according to size allows for a smooth gradation of muscle force as additional units are activated Henneman and Mendell, One reason why larger units which tend to be fast generate more force than smaller units which tend to be slow is because they branch and innervate more muscle fibers Bodine et al.
Whether differences in the level of PSA expression by fast and slow mammalian motoneurons regulates their degree of intramuscular axon branching is unknown.
However, this hypothesis is currently being tested in the muscles of NCAM null and thus PSA null mice, which, if the hypothesis is true, would be expected to exhibit a reduction in the range in motor unit force, because the larger motoneurons would branch less.
In summary, by using chick—quail hindlimb chimeras to force slow axons to innervate a fast muscle, we have shown that the distinct patterns of intramuscular nerve branching are determined by the type of innervating motor axon and not by the molecular properties or structure of the type of muscle fiber.
Together with the results of PSA removal, this study supports the model that the pattern of intramuscular axon branching is determined by the relative amount of axon—axon versus axon—myotube adhesion and that this is regulated by the level of PSA being expressed by the developing motoneurons.
We thank Shilpi Banerjee and Marianne Usiak for their helpful comments on this manuscript. In addition, we thank U. Rutishauser for supplying the endoneurominadase-N, D. Fambrough for the 5D2 monoclonal antibody, and F. Stockdale for the S58 antibody. Correspondence should be addressed to Dr. E-mail: ude. Read article at publisher's site DOI : Free to read at www. Nat Commun , 11 1 , 09 Oct PLoS One , 9 3 :e, 13 Mar Invest Ophthalmol Vis Sci , 53 13 , 13 Dec Neurorehabil Neural Repair , 27 3 , 16 Oct Cited by: 8 articles PMID: Dev Biol , 2 , 22 Aug Cited by: 37 articles PMID: To arrive at the top five similar articles we use a word-weighted algorithm to compare words from the Title and Abstract of each citation.
Anat Embryol Berl , 2 , 01 Jan Cited by: 6 articles PMID: J Neurosci , 16 21 , 01 Nov Tanaka H , Landmesser LT. J Neurosci , 6 10 , 01 Oct Landmesser L. J Neurobiol , 23 9 , 01 Nov Cited by: 39 articles PMID: Kuno M.
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