L1 and Growth Cones

Our initial discovery that L1 promoted axon growth lead almost immediately to the observation that different substrates induced amazingly different growth cone morphologies. On L1, retinal ganglion cells have very large growth cones, while on laminin or polylysine they are much smaller. On N-cadherin they are of intermediate size. Not surprisingly, the cytoskeleton is organized differently on different substrate. On L1 the microtubule network extends much farther into the periphery of the growth cone than on laminin, for example. This work was done by Sue Burden-Gullley and Ross Payne

These observations led us to undertake a variety of time-lapse studies. We determined the rates of growth in this way and found that retinal ganglion cell growth cones on L1 grow more slowly than those on laminin but much more quickly than those on poly-lysine. Interestingly growth cones would grow from L1 onto laminin and vice versa so there was not an absolute preference between the two substrate. At the borders there were differences in behavior. When on laminin, they would move on to L1 more quickly than in the opposite direction.

We also did interference reflection studies and found, not surprisingly that different CAMs bound the growth cones more or less closely to the substrate. L1 bound membranes very closely while laminin and merosin substrates showed larger distances between the substrate and the membrane. This might explain why L1 is particularly sensitive to the PSA carbohydrate on NCAM. Movies are available at (link). This work was done by Judy Drazba and Patricia Liljelund.

I have described our studies on L1 recycling on L1 elsewhere in this site. Briefly, these studies show that L1 is internalized at the rear of growth cones and recycled to the front. This provides an economical method to regulate adhesion and probably generates an essential gradient of adhesion that determines to polarity of growth cone movement.

I participated in a study with Teresa Esch and Gary Banker on how substrates contribute to the determination of polarity. The surprising aspect of this study to me was that either L1 or laminin could induce axon formation if only one process of several from a neuron contacted the inducing substrate. It appears that rate of growth is a critical factor in the induction of axonal characteristics.

Related Publications

Lemmon, V., Burden, S.M., Payne, H.R., Elmslie, G.J. and Hlavin, M.L. Neurite growth on different substrates: permissive versus instructive influences and the role of adhesive strength. J. Neuroscience, 12:818-826, 1992

Payne, H.R., Burden, S. and Lemmon, V. Modulation of growth cone morphology by substrate bound cell adhesion molecules. Cell Motility and the Cytoskeleton, 21:65-73, 1992.

Burden-Gulley, S.M., Payne, H.R., Lemmon, V. Growth cones are actively influenced by substrate-bound adhesion molecules. J. Neurosci., 15:4370-4381, 1995.

Burden-Gulley, S.M., Lemmon, V. L1/8D9, N-cadherin and laminin induce distinct distribution patterns of cytoskeletal elements in growth cones, Cell Motility and the Cytoskeleton 35:1-23, 1996.

Drazba, J., Liljelund, P., Smith, C., Payne, R., Lemmon, V. Growth cone interactions with purified cell and substrate adhesion molecules visualized by interference reflection microscopy. Dev. Brain Res. 100:183-197, 1997.

Esch, T., Lemmon, V., Banker, G. Local presentation of substrate molecules directs axon specification by cultured hippocampal neurons. J. Neurosci. 19:6417-6326, 1999.

Kamiguchi, H., Lemmon, V. Recycling of the Cell Adhesion Molecule L1 in Axonal Growth Cones J. Neurosci., 15:3676-3686, 2000.

Esch, T., Lemmon, V., Banker, G. Differential effects of NgCAM and N-cadherin on the development of axons and dendrites by cultured hippocampal neurons. J. Neurocytology 29:215-223, 2000.

Long, K.E. and Lemmon, V. Dynamic regulation of cell adhesion molecules during axon outgrowth. J. Neurobiol. 44:230-245, 2000.

Kamiguchi, H., and Lemmon, V. IgCAMs: Bi-directional signals underlying neurite growth. Current Opinion in Cell Biology, 12:598-605, 2000

A.W. Schaefer, Y. Kamei, H. Kamiguchi, E.V. Wong, I. Rapoport, T. Kirchhausen, C.M. Beach, G. Landreth, S.K. Lemmon, V. Lemmon. L1 endocytosis is controlled by a phosphorylation-dephosphorylation cycle stimulated by outside-in signaling by L1. J. Cell Biology, 157: 1223–1232, 2002

L1 and Growth Cones - the Movies

A wonderful way to study growth cones is to use time lapse video microscopy. It allows observation of behavior that is impossible any other way.

Our first studies were done to accurately measure axon growth rates. (Lemmon et al, 1992).

Next we studied how growth cones behave at borders between different substrates. What was especially interesting was the rapid alterations in growth cone morphologies upon encountering new substrates (Burden-Gulley et al., 1995). See an example of a retinal ganglion cell growth cone crossing from laminin to L1.

We then used interference reflection microscopy to study how growth cone membranes interact with different substrates (Drazba et al., 1997). See examples of retinal ganglion cell growth cones growing on laminin, merosin, poly-lysine, N-cadherin, NgCAM and 8B8 (a NgCAM variant).

We worked with Jerry Silver on two interesting projects. One, done by Diane Snow, was the demonstration that chondritin sulfate inhibits growth cones when presented at borders at appropriate concentrations. The other was done by Perry Brittis, who studied retinal ganglion cell growth cones migrating through retina in the presence and absence of antibodies to different CAMs. His movies can be found at his web site.