Fig 6. Model of neurite regulation by the HNK-1 epitope on tenascin-C and contactin-1.

In E16 mouse brains, the HNK-1 epitope is expressed on both TNC and CNTN, inducing maximal neurite outgrowth, which could promote brain development and/or neuronal circuit formation (left panel). As development progresses, the HNK-1 epitope on TNC is nearly lost completely in the P7 mouse brain, whereas the epitope is expressed by CNTN. However, TNC is still expressed in the brain, and exhibits neurite-promoting activity, which might induce efficient neurite outgrowth via HNK-1-expressing CNTN in early development (middle panel). However, in the P14 mouse brain, TNC expression is almost abolished, resulting in weak neurite promotion (right panel).