Neural adhesion molecule L1 as a member of the immunoglobulin superfamily with binding domains similar to fibronectin

Diverse glycoproteins of cell surfaces and extracellular matrices operationally termed 'adhesion molecules' are important in the specification of cell interactions during development, maintenance and regeneration of the nervous system^1,2. These adhesion molecules have distinct functions involving different cells at different developmental stages, but may cooperate when expressed together^3-6. Families of adhesion molecules which share common carbohydrate domains do exist, despite the structural and functional diversity of these glycoproteins^7,8,9. These include the Ca²⁺-independent neural adhesion molecules: N-CAM, myelin associated glycoprotein (MAG)¹⁰ and L1. L1 is involved in neuron-neuron adhesion⁶, neurite fasciculation¹¹, outgrowth of neurites¹², cerebellar granule cell migration¹³, neurite outgrowth on Schwann cells¹⁴ and interactions among epithelial cells of intestinal crypts¹⁵. We show here that in addition to sharing carbohydrate epitopes with N-CAM and MAG, L1 is also a member of the immunoglobulin superfamily. It contains six C2 domains and also shares three type III domains with the extracellular matrix adhesion molecule fibronectin.