Further Development 15.16: Mechanisms of Cell-to-Cell Adhesion

Neural Crest Cells and Axonal Specificity

The most common cell-to-cell railway for pathfinding axons are on the backs of previously laid axons. The process of one axon adhering to and using another axon for growth is called fasciculation (see Figure 15.25A). For example, motor neurons may be intrinsically locked into the location of their final targets (see Figure 15.25B–D), but sensory neurons actually need the axons of motor neurons to find their appropriate connections (Hamburger 1929; Landmesser et al. 1983; Honig et al. 1986). It appears that the subtypes of motor neurons produce specific compounds (such as Ephs) that cause the sensory neurons to adhere to the motor axons and tract along them (Huettl et al. 2011; Wang et al. 2011).

Once fasciculated to an axon bundle, how might a pathfinding growth cone detach and navigate off in a different direction? The spinal nerve pathfinding illustrates this decision best. The axons of the spinal nerve use NCAM to fasciculate together during their shared outgrowth; the dorsal divergence of axons to innervate the epaxial (back) musculature, however, requires the modification of NCAM with polysialic acid (PSA). Modification with PSA transiently breaks the homophilic NCAM interactions, which facilitates defasciculation and the exploration of different pathways in response to such cues as FGFs, mentioned above (Tang et al. 1992; Allan and Greer 1998).

These are examples of local contact-mediated guidance cues (Ephs/NCAMs) that regulate a close adhesive connection between motor neurons and their associated sensory neurons (see Figure 15.26).

Literature Cited

Allan, D. W. and J. J. Greer. 1998. Polysialylated NCAM expression during motor axon outgrowth and myogenesis in the fetal rat. J. Comp. Neurol. 391: 275–292.
PubMed Link

Hamburger, V. 1929. Experimentelle Beiträge zur Entwicklungsphysiologie der Nervenbahnen in der Froschextremität. Roux's Arch. Dev. Biol. 119: 47–99. doi:10.1007/BF02111182

Huettl, R.-E., H. Soellner, E. Bianchi, B. G. Novitch and A. B. Huber. 2011. Npn-1 contributes to axon-axon interactions that differentially control sensory and motor innervation of the limb. PLoS Biol. 9(2): e1001020.
PubMed Link

Landmesser, L. T., M. J. O’Donovan and M. Honig. 1983. The response of avian hindlimb motor and sensory neurons to an altered periphery. In Limb Development and Regeneration (J. F. Fallon and A. I. Caplan, eds.), pp. 207–216. Alan R. Liss, New York.

Tang, J., L. Landmesser, and U. Rutishauser. 1992. Polysialic acid influences specific pathfinding by avian motoneurons. Neuron 8: 1031–1044.
PubMed Link

Wang, L., R. Klein, B. Zheng and T. Marquardt. 2011. Anatomical coupling of sensory and motor nerve trajectory via axon tracking. Neuron 71: 263–277.
PubMed Link

All the material on this website is protected by copyright. It may not be reproduced in any form without permission from the copyright holder.