. "L1 cross linking can activate MAPK cascade components MEK1/2, ERK1/2, as well as Src, Raf-1,and p90rsk. MAP kinase signaling requires endocytosis mediated by Src. ERK2 can phos-phorylate internalized L1 at serine residues 1204 and 1248. This phosphorylation may increase the neurite growth."^^ . . . . .